AN ECOLOGICAL STUDY OF THE RED

ALGA AHNFELTIA CONCINNA

RHODOPHYTA, GIGARTINALES!

A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE

UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

IN BOTANICAL SCIENCES

AUGUST 1977

By

William Henry Ma@ruder

Thesis Committee:

Maxwell.S. Doty, ChairmanK. Alison Kay

Dieter Mueller-Dombois

We certify that we have read this thesis and that in our

opinion it is satisfactory in scope and quality as a thesis for

the degree of Master of Science in Botanical Sciences.

THESIS COMMITTEE

Ql

TABLE OF CONTENTS

Page

AB S TRACT ~ ~ ~ ~ ~ s ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ V

LIST OF FIGURES ~ ~ ~ I v] j

LIST OF PLATES viii~ ~~ ~ ~ ~

INTRODUCTION

A. Identification of the problem

B. Rocky coastline terminology

~ ~~ ~ ~~ ~ ~

~ ~~ ~ ~

C. Environmental factors affecting littoral algae ~ 3

1. Tides 4~ ~ ~

2, Waves ~ 5~ ~ ~ ~ ~ ~ ~

3. Slope 7' ~ ~ ~ ~

4. Water motion ~ 8~ ~ ~

5. Substratum 10~ ~ ~ ~~ ~ ~ ~ ~

6. Atmospheric f actor s 10~ ~ ~ ~ ~ ~

7.. Salinity ~ ~ ~ ~

8. Graz ing ~ ~~ ~ ~

9. Competition 12~ ~

D. Study Area 13~ ~~ ~

15ED Statement of hypotheses

MATERIALS AND METHODS

RESULTS

~ ~ ~

17~ ~~ ~~ ~ ~ ~

1, Kalele-Leilewi Point . . . . . . . . . . . . - . . . . 19

2. Leilewi Point-Hilo breakwater . . . . . . . - . . . . 19

3. Coconut Island Hilo! 20

A. General descriptions of the study sites ........ ~ - 19

iv

Page

B. Location of the Ahnfeltia concinna band . . . . . . . . . . 21

C. Substratum coverage ~ ~ i ~ ~ 23~ ~ ~ ~ ~ ~ ~ ~ ~ ~

D. Frond length ~ ~ ~ ~ ~ ~ 92 23~ ~ ~ ~ ~ ~ ~

E. Salinity ~ ~ ~ ~ ~ a 24~ ~ ~ ~ ~ ~ ~ ~ ~

F. Grazing 24~ ~

26

H. Population structure 26~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~

~ ~ ~

~ 30~ ~ ~

31

~ 33

~ 33

35~ ~ ~ ~ ~

F. A quantitative exposure index 36~ ~ ~ ~

38~ ~ ~ ~ ~

FIGURES ~ I 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 40

P LATES ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 60

LITERATURE CITED,............. ~... - . ~ ~ ~ ~ ~ 7 6

G. Substratum........... ~ ~ ~

I. Factors influencing the upper break

J. Factors influencing the lower break

DISCUSSION

A. The location of the Ahnfeltia concinna band

B. The degree of cover of the substratum

C. The length of the fronds

D. The upper limit of the band

E. The lower limit of the band

SUMMARY ~ ~ ~ ~ ~ a ~ ~ ~ ~ ~ ~

27

28

ABSTRACT

In the Hawaiian Islands, Ahnfeltia concinna is a perennial

macroscopic seaweed found only on basalt coastlines where it often

forms a dense band high in the littoral zone. The location and

factors affecting the coverage of the substratum by the gametophyte

band were measured at three sites with different exposures to waves

and swells along the northeast coast of the island Hawaii. At wave

and swell exposed sites, the vertical distance of the band above

tidal datum was greater on high angle shores than on low angle shores.

At wave and swell sheltered sites, the vertical distance of the band

above tidal datum was equal on shores of all angles. A closed popula-

tion occurred only in areas where water flowed through the fronds.

This occurred on both high and low angle shores at sheltered sites

but only on. low angle shores at exposed sites. Neither grazing nor

water salinity affected the coverage of the substratum by the frond'

The lengths of the fronds were measured at the three sites. The

longest fronds occurred at the most wave and swell exposed site and

the shortest fronds occurred at the most wave and swell sheltered site.

At each site, the fronds on low angle shores were longer than the

fronds on high angle shores. At exposed sites, the longest fronds

occurred at the lower edge of the band while at sheltered sites the

fronds at the lower edge of the band were shorter than the fronds in

the middle of the band due to grazing.

Observations on the causal factors of the vertical limits of the

band were made. The upper limit of the band is determined by desiccation.

vj

Fronds at the upper edge of the band are killed when very small waves

and swells, neap tides, and no cloud cover occur simultaneously. The

causal factor of the lower limit of the band is not obvious, but

competition for surface area with other algae and grazing may be

important.

vii

LIST 07 FIGURES

Pigure Page

Map of the study area 40

2. 42

3. 44

4,46

485.

6.50

56'

56

~ ~ ~ ~ ~ ~ ~ ~ 58

58

Waves and swells arriving in Hawaii

Location of the band at the Kalele-Leilewi Point site

Location of the band at the Leilewi Point-Hilo

breakwater site

Location of the band at the Coconut Island site

Comparison of the locations of the bands at thethree sites

7. Mean percents of the substratum covered by thefronds at the three sites

8. Mean frond lengths on low angle shores

9. Mean frond lengths on high angle shores

10. Salinities and population densities

11. Mean frond lengths and percents of the substratumcovered by the holdfasts at Kalele

12. Mean frond diameters at Kalele

13. Wet and dry weights, and percent dry/wetweights at Kalele

52

54

54

LIST OF PLATES

PagePlate

Summer swell striking the coast near Kalele 60~ ~

2. ~ ~ ~ 60Coconut Island at low tide

A dense population on a law angle shore near Kalele ~ ~ ~ e 623.

A sparse population an a high angle shore alongthe Kalele-Leleiwi Point site

4.

s ~ ~ ~ ~ o 62

A dense population on a low angle shore at.Coconut Island

5.

64

6. A dense population on a high angle shore atCoconut .Island 64~ ~

66

66

68

~ 68

~ 70

12. Dead fionds killed by desiccation along theLeilewi Point-Hilo breakwater site 70

13. Dead fronds killed by desiccation at theCoconut Island site 72

14. Dead fronds killed by desiccation on a highshore along the Kalele-Leilewi Point site

angle~ ~ ~ 72

15. Dead frond tips killed by desiccation alongKalele-Leilewi. Point site

the

74

7. Thalli growing on a glass slide at Kalele

8. A one meter wide transect cleared of fronds at Kalele

9. The largest stand observed during the study

10. The tetrasporophyte of Ahnfeltia concinna

11 ' Close-up of the tetrasporophyte of Ahnfeltia concinna

INTRODUCTION

A. Identification of the roblem

The presence of zones of organisms is Stephensen and Stephensen,

1972! of universal occurrence on coastlines throughout the world. In

Hawaii, Ahnfeltia concinna J. Agardh is Doty, 1967! commonly the

highest growing perennial macroscopic seaweed on basalt coastlines,

where it often forms a dense band. Its life history i,s Nagruder,

1977! triphasic with conspicuous erect dieoceous gametophytes and

crustose tetrasporophytes. The gametophyte thalli consist of multi-

axial fronds that grow from well developed crustose holdfasts. The

fronds can vary from 0.5 cm to 60 cm long. The carposporophyte grows

parasitically on the female gametophyte. In this study, Ahnfeltia

concinna will refer only to the gametophyte stage unless otherwise

specified.

Uery little is known about Ahnfeltia concinna. The polysaccaride

it produces is Doty and Santos, 1973; Santos and Doty, 1975! a

carrageenan with potential commercial value. The upper and lower

limits of its distribution along the shore are Doty, 1967! often very

well defined, its standing crop is greatest at the lower edge of its

band and least at the upper edge, and it can take several years to

appear on newly formed coastlines. The factors that influence its

distribution and abundance are not known. This study was conducted

to identify these factors.

Rock coastline terminolo

The literature on rocky shore ecology abounds with different

terminologies and schemes of classification, and there is no general

agreement on which terms to use or an their definitions. Most recent

studies have used a scheme which divides the shore into three main

zones using Feldmann, 1937; Stephensen and Stephensen, 1949, 1972;

Lewis, 1961, 1964! the word littoral with various prefixes, although

other schemes have Ricketts and Calvin, 1939; du Rietz, 1940; den

Hartog, 1968! also been used. These three main zones have been. variously

divided into subzones, fringes, horizons, bands, belts, and girdles by

different authors. The precise limits of the zones and their divisions,

and the criteria used to characterize them have Stephensen and

Stephensen, 1949; Womersley and Edmonds, 1952; Chapman and Trevarthy,

1953; Lewis, l961! varied greatly from author to author and even fram

one author's publication to the next. In many publications the terms

have been used without clear definitions.

The coastline has Sjostedt, 1928; Stephensen and Stephensen,

1949; den Hartog, 1968! usually been approached as a boundary of the

ocean. Therefore a reference point in relation to sea level is of

value Despite the many different terminologies, most researchers

recognize a distinctive break somewhere around the 0.0 tide levels

Another distinctive break is usually recognized at about the upper

limit of the tides or the reach of the waves. This break -is usually a

dividing line between marine algae or sessile filter feeding animals

and nan-marine blue-green algae. The exact height of this break in

relation to tide levels varies Lewis, 1964! greatly from coast to coast

depending on wave exposure and other factors. This break has been given

the approximately equivalent names "physiological high water line"

Kylin, 1918! and "litus line" Sjostedt, 1928!. Recent analytical

studies have Russel, 1972, 1973! supported the idea of the "litus

line" as a sharp floristic discontinuity.

For this study, the following terminology and definitions will

be used.

SUBLITTORAL � -- The zone of algal growth below the 0.0 tide level.

LITTORAL � � � � The zone of algal growth between the 0.0 tidelevel and the "litus line."

SUPRALITTORAL � The zone of algal growth above the "litus line."

BAND The area occupied by a dominant species or groupof species.

BREAK � � � � � The upper and lower limits of a band.

C. Environmental factors affectin littoral or anisms

The occurrence of several sharply defined vertical bands of

different species in a relatively small area has attracted many people

to the study of rocky coastlines. Despite the enormous amount of pub-

lished literature, the causal factor or factors which produce the

sharp breaks between bands is still largely a matter of speculation.

The organisms living on a rocky coastline are subject to a great many

environmental factors. Classically, ecological studies conducted on

coastline organisms have produced very detailed descriptions of the

vertical distributions of the different species. These studies have

been based mainly on observations of a limited section of coastline

for short periods of time under conditions where the effects of a

single. factor are very difficult to separate from other factors.

Nevertheless, the observed limits of the distribution of a species or

group of species are Southward, 1958; Lewis, 1964; Gurganova, 1966;

Stephensen and Stephensen, 1972! usually explained in terms of one or

two causal factors which are influenced by many modifying factors.

The two factors that have received the most discussion as the

causal factors in the production of a littoral zone are the tides

and wind generated waves. It is usually accepted Stephensen and

Stephensen, 1949, 1972; Doty, 1957; Southward, 1958! that only a sub-

littoral zone and supralittoral zone would occur at the edge of a body

of water in which tides and waves we' re absent. Most authors Doty,

1957; Lewis, 1964; Hedgepeth, 1968!,recognize the tides as the causal

factor in the production of the littoral zone, but wind generated

waves have Stephensen and Stephensen, 1972! also been advocated.

Experimental data are largely lacking, but since the littoral zone is

characterized by the up and down movement of the ocean surface, the

tides alone, the waves alone, or the tides and waves together could

Southward, 1958; Mokyeysky, 1960! probably produce a littoral zone.

1. Tides

Host authors recognize a clear relation between the tide and

zonation, with the essential feature being the alternation of periods

of emersion and submersion. The fluctuations of the surface of the

ocean caused by the tides do not produce Colman, 1933! a uniform

gradient of time of emersion and submersion but instead, there are

Doty, 1946! sharp changes at certain "critical" tide levels. These

tide levels have Doty, 1946; Evans, 1947a, 1947b; Gurjanova, 1966!

been found to closely coincide with the vertical breaks between bands

in some locations. Others Elmhirst, 1934; Moore and Sproston, 1940;

David, 1943! have tried to relate the bands to the rapid or slow rate

of tidal rise and fall.

The widening of bands in areas of increasing tidal range has

Johnson and York, 1915! long been observed and has been reported by

many authors. The widening of bands while maintaining the same vertical

height of the breaks along coastlines of low angle has Doty, 1957!

been cited as evidence for the critical importance of tide levels. A

small change in the level of breaks between bands has been attributed

Orton, 1929; Lewis, 1964! to different times of high and low tides

causing one area to receive more sunlight and therefore increased

desiccation. The type of tidal curve diurnal, semi-diurnal, mixed!

may also affect Southward, 1958! the pattern of zonation.

2 ~ Waves

In many areas, the breaks between bands do not closely correspond

Stephensen and Stephensen, 1972! to the "critical" levels based on

tidal range alone. Many authors Borgensen, 1908; Johnson and Skutch,

1928; Coleman, 1933; Ercegovic, 1934; Broekhuysen, 1940; Stephensen,

1944; Lewis, 1953, 1964; Burrows and others, 1954; Conway, 1954;

Mokyevsky, 1960; Kingsbury, 1962; Gurjanova, 1968! have observed the

elevation and widening of bands in the littoral zone that occurs on

wave exposed coastlines. There are exceptions however'. The upper break

of the Laainaria ~di itata band tends to be Evans, 19d7b; Southward,

1993! a. little higher in sheltered areas and Focus ~s irelis can South-

ward and Orton, 1954! form a wider band in sheltered areas than in

exposed areas. Bands usually remain in the same positions relative to

1943! exchange positions in exposed and sheltered locations.

In wave exposed areas, the upper bands of the littoral zone

usually show a greater increase Stephensen, 1944; Lewis, 1953, 1964,

1968! in the width of the band than do the lower bands. The breaks

between bands can move Borgensen, 1908; Kylin, 1918; Gislen, 1930;

den Hartog, l959! up and down at one location during seasons with

larger and smaller waves'

The importance of wave exposure in the horizontal distribution of

littoral organisms has Stephensen, 1944; Southward, 1963; Lewis, 1953,

1961, 1964; Burrows and others, 1954; Ballantine, 1961; Dayton, 1971!

been often observed. Most species seem to have Lewis, 1968! an expo-

sure preference although a few species are ubiquitous. There are

Southward and Orton, 1954; Ballantine, 1961! species which grow best

in wave sheltered locations and others which grow best in wave exposed

locations. The reasons for this are still speculative but physical

damage, dislodgement, spore dispersal, water movement, salinity, light,

oxygen content of the water, and competition have Lewis, 1964! been

suggested as possible causal factors'

The practical measurement of wave exposure has been a very diffi-

cult task and there is no satisfactory method for quantifying it.

Sub!ective measurements have been used by many authors. The frequency

and velocity of local winds has Moore, 1935; Southward, 1953; South-

w«d and Orton, 1954! also been used to assess'exposure. Guiler �950!

proposed a formula incorporating the depth and characteristics of the

surrounding ocean, the local wind force, the distance the wind blew

over the water, and a subjective exposure value. Southward. �953!

measured the height of the wave swash above predicted tide levels.

The presence or absence of certain species has Fischer-Piette, 1932;

Ballantine, 1961! been used as a biological exposure scale. Lewis

�964! proposed the vertical width of the band of the lichen Verrucaria

in the supralittoral zone as a measure of exposure, and Gurj anova

�968! compared exposure by using the vertical height of bands above

tidal datum. Jones and Demetroptus �968! compared exposure by

measuring the maximum drag produced by the waves. Barrales and Lobban

�975! determined exposure by measuring the angle open to the ocean

at a 50 mile radius from the shore.

The distribution of several littoral algae and animals has

Dellow, 1950; Southward, 1953; Vomersley and Edmonds, 1958; Stephen-

sen and Stephensen,,1961; Jorde and Kladestad, 1963; Lewis, 1964;

Jorde, 1966; den Hartog, 1972; Dayton, 1975! been related to the slope

of the coastline. Hormosira was found Dellow, 1950! to grow only on

low angle shores, and was replaced by Corallina on steep shores. In

exposed areas, Laeinaria ~di itata grows Southward, 1933! only on

shores with an angle of less than 50 degrees, but in sheltered areas

n it grows on both horizontal and vertical shores. Fucus distichus, Fucus~s iralis, and pelvitia canaliculate are Jorde, 1966! abundant on low

angle shores, but are absent on steep shores.

The causal factors producing these distributions .have not been

identified but the quality of water motion and differences in the

amount of sunlight have Southward, 1953; Lewis, 1964; den Hartog,

1972! been suggested. Lewis �964! stated that algal spores would

"certainly" settle easier on low angle shores. Hopkins �935! found

that Ostrea larvae settled in much greater numbers on horizontal

surfaces than on vertical surfaces. Southward �953! observed that waves

break differently on shores of different slope. He divided breaking

waves into three parts: wash, splash, and spray. The proportions of

each depended on the slope of the shore and the nature of its surface.

Irregular high angle slopes greater than 50 degrees! usually had very

little wash but lots of splash spray, while low angle shores less than

50 degrees! were mostly wash and very little splash and spray. Den

Hartog �972! noted that on vertical surfaces the vegetation is beaten

by the waves while on horizontal surfaces it is washed. Also, steep

surfaces tend Southward, 1953; Lewis, 1964! to drain more rapidly

than low angle surfaces.

A change in the vertical level of breaks between bands has

Jorde, 1966! been observed in relation to the slope of the shore. In

exposed areas, the breaks were higher on steep shores than they were

on low angle shores, and the width of the bands was greater on low angle

shores than on high angle shores. However, it has also been reported

Nordgaard, 1905; Gurjanova, 1966! that the slope of the shore does not

affect the vertical height of the bands, but only the vertical width,

4. Water motion

Water motion is Riedl, 1972! a very important factor in marine

habitats that can Schwenke, 1971! af feet both the growth and

morphology of marine algae. Waves are Lewis, 1964! usually the most

important factor in producing water motion in the littoral zone,

although currents can be important in some locations. The water

motion in breaking waves produces Carstens, 1968! two types of force,

pressure and friction sometimes termed shear!. The effects of wave

induced pressure on littoral algae has not been investigated. Fric-

tion forces are of two types, skin friction and form drag. Skin

friction determines Ruttner, 1926; Carstens, 1968! the boundary

layer of still water around an object. Increased water motion, which

reduces the boundary layer, enhances Witford and Schumacher, 1964!

mineral uptake, increases Whitford, 1960! metabolism, and generally

leads to increased growth. Field methods presumably measuring skin

friction are Nuus, 1968; Doty, 1971! available, but can not be

applied to wave exposed locations in the littoral zone.

Form drag is the main force responsible for the dislodgement of

littoral algae. Burrows and others �954! believed the limited amount

of algal vegetation found on some steep shores was due to removal by

large storm waves. Walker and Richardson �955! reported a SO percent

loss in biomass of Laminaria following large winter storm. waves,

SeveraL authors Hattow, 1938; Williams and Blomquist, 1947; Lawson,

19S4! have reported that algal species growing in wave exposed locations

tend to be shorter and thicker than when growing in wave sheltered

locations.

10

5. Substratum

Most authors have found that the substratum generally has little

influence on benthic organisms other than providing a suitable place

for attachment. Surface texture and rock composition has Stephensen,

1942; Southward, 1953! only minor influence on most benthic organisms.

However, minor variations in the abundance of barnacles has Moore

and Kitching, 1939! been associated with surface texture. Southward

�951! found that chalk substratum was unsuitable for some organisms

and den Hartog �972! noted that limestone was unsuitable for Rissoella.

A slight elevation of bands in the littoral and supralittoral zones

has been related den Hartog, 1972! to a porous limestone substratum

which holds water and does not dry out as quickly as non-porous sub-

stratum. In general, the substratum exerts a presence or absence

affect on benthic organisms.

6. Atmos heric factors

Marked differences in the elevation of bands and the species

present occur Lewis, 1964; Stephensen and Stephensen, 1972! between

shaded and sunny locations. Burrows and others �954! believed that

cloud cover during the summer prevented desiccation of littoral

organisms during low tide and low wave conditions. Rain can be

expected Lewis, 1964! to affect the rate of desiccation and the ability

to tolerate salinity changes. Sunlight can raise Lewis, 1964! the

temperature of the rock and organisms above the surrounding air tempera-

ture. Strong onshore winds will carry splash and spray further Lewis,

1964! up the shore and could be expected to raise the leveI of bands in

11

the upper littoral and supralittoral zones but winds will also increase

Broekhuysen, 1940; Stephensen and Stephensen, 1972! the rate of

desiccation, which could lower the bands.

7.

Variations in salinity have been, proposed den Hartog, 1968! as a

critical factor in the littoral and supralittoral zones. .The tolerance

of marine algae to various salinities has been frequently studied, and

attempts have been made Hoffman, 1929! to classify them' in relation

to their tolerance. Littoral and supralittoral algae are Legendre,

1921; Ogata and Matsue, 1965; Kjeldsen, 1972! usually able to tolerate

a wide range of salinities, Salinity can Feldmann, 1951! be responsible

for the horizontal li'mits of some species. Variations in salinity have

Jorde and Klavestak, 1963! little effect on the vertical distribution

of littoral algae except in very calm areas a sudden lowering of the

upper limits of some algae occurs where a surface layer of nearly

fresh water is present.

8.

Grazing by herbivorous gastropods can greatly affect littoral

algae. Limpets can Jones, 1948; Lodge, 1948; Burrows and Lodge, 1950;

Southward, 1953, 1956! limit the horizontal distribution of many

fucoid algae. When the limpets were Lodge, 1948! removed, dense growths

of algae developed' The general absence of fucoids from wave exposed

areas may Southward, 1958! be the result of grazing by limpets. In

other areas, herbivorous gastropods have Dayton, 1975! little effect

on littoral algae.

12

The importance of urchins in removing and preventing the establish-

ment of algae in the sublittoral and littoral zones has Kitching and

Ebling, 1961; Jones and Kain, 1967; Paine and Vadas, 1970! been

determined experimentally in many areas. Dayton �975! found only

crustose coralline algae present low in the littoral zone when a large

population of urchins was present.

Grazing by fish can Hiatt and Strasburg, 1960; Randall, 1961;

Bakus, 1972; van den Hock and others, 1975! prevent the development

of large algae in the sublittoral zone. The turbulent water usually

found in the littoral zone reduces van den Hock and others, 1975!

grazing, but during calm periods some grazing may occurs

9.

Most littoral and supralittoral studies have considered zonation

only in terms of physical factors, but the importance of competition

has Gause and Wit, 1935; Southward, 1958; Lewis, 1964; Connell, 1972;

Chapman, 1973! also been proposed. Competition can Chapman, 1973!

explain sharp boundaries over smooth gradients of physical factors.

It is usually accepted Connell, 1972; Chapman, 1973! that physical

factors set the limits of a band in harsh environments such as the

upper limits of the littoral and supralittoral zones. There is, how-

ever, no evidence that the lower limits of bands are determined by

intolerance to physical factors. There are Gail, 1918; Fisher, 1929!

physiological lower limits for some littoral algae, but these are

lower than their observed limits on the shore.

13

D.

The present study was primarily conducted along the northeast

coast of the island of Hawaii from Coconut Island Hilo! to Kalele

Figure 1!. Observations of Ahnfeltia concinna populations were also

made elsewhere around the island and. on the islands of Kauai, Oahu,

and Maui. The tropical climate of the entire study area is Fullerton,

1972! nearly the same, and can Moberly and Chamberlin, 1964! be

roughly divided into two seasons, summer and winter. Summer is approx-

imately from May through October and winter is approximately from

November through April. The study area is on the windward side of the

island, subjected Armstrong, 1973! to the northeasterly trade winds

which are present 90 percent of the time in the summer and 60 percent

of the time in the winter. The trade winds blow onshore at similar

angles along the entire study area, varying Patzert, 1969! from 30

to 60 degrees from north. The mean trade wind velocity varies

Armstrong, 1973! from 12 km per hour at Coconut. Island to 19 km per

hour at Kalele. During the winter, westerly winds known as Kana storms

are present approximately 10 to 15 percent of the time, but the year

to year variation of these winds is great. Some winters may have no

Kona storms while others may have several.

Rainfall occurs Fullerton, 1972! principally from showers within

the ascending moist trade winds. The study area is Fullerton, 1972!

entirely within the same rainfall zone, 312 to 375 cm per year. Average

rainfall in the winter is 207 cm and average rainfall in the summer is

137 cm at Hilo. Rainfall can be very heavy at times, with as much as

10 to 15 cm falling in one hour. Rainfall data indicate that the solar

insolation should be nearly the same throughout the study area. Tem-

peratures are Fullerton, 1972! similar all along the windward coast,

with a mean temperature of 23 C and an average seasonal variation in

mean temperature of only 2.9o C.

The substrate throughout the study area is NacDonald, 1949!

prehistoric pahoehoe olivine basalt lava that flowed from Mauna Loa.

The tidal range is Armstrong, 1973! small throughout the Hawaiian

Islands, with spring tides never exceeding 1 m. The tides are of the

mixed type with two high and two low tides per day. Tidal datum �.0!

is mean lower low water. On the island of Hawaii, the maximum variation

in high tides among the six tide recording stations is Armstrong, 1973!

0 ' 12 m and the maximum variation in low tides is only 0.03 m. The

maximum time difference of high tides is 70 minutes and the maximum

time difference of low tides is 54 minutes.

The wind generated waves reaching the Hawaiian Islands can Kelly,

1973! be divided into two types: short period waves generated by local

winds, usually with periods of less than 10 seconds; and long period

waves generated distant from the islands, usually with periods of

greater than 10 seconds. The short period waves are Moberley and

Chamberlain, 1964; Kelly, 1973! usually produced by the northeast trade

winds and they approach the islands from the northeast Figure 2!.

Long period waves are Kelly, 1973! referred to as swells. Ocean

swells can Bigelow and Edmonson, 1947! travel long distances without

significant reduction in size. Swells reaching the Hawaiian Islands

Moberley and Chamberlain, 1964! be generated anywhere in the Pacific

ocean and even in the South Indian Ocean. There is Moberley and

15

Chamberlain, 1964; Kelly, 1965, 1973; Walker, 1971, 1974! a very pro-

nounced seasonal variation in swell direction Figure 2!. There are

two main directions from which swells approach the islands: northwest

in the winter from North Pacific storms, and south in the summer from

South Pacific and South Indian Ocean storms. Kona storms can produce

southerly waves in the winter. Strong trade wind's during the winter

can sometimes produce large northeast waves with periods greater than

10 seconds.

At any given time, waves and swells with different heights,

lengths, periods, and velocities can Moberley and Chamberlain, 1964!

be arriving in the Hawaiian Islands from several different generating

areas' Their interactions result in very complex and poorly understood

patterns of surf along the coastlines of the different islands' Large

swells can Barber and Trucker, 1962! refract and diffract, producing

high surf in areas not greatly open to the ocean. Where the different

wave and swell directions that reach the Hawaiian Islands will produce

surf is' poorly known except for general observations by Wright, 1971!

surfers. In some areas, a variation in approach direction of only 10

to 15 degrees can Kelly, 1965! result in completely calm conditions or

gigantic surf. The wave and swell directions which will cause surf

along the study area are not known.

ED Statement of H otheses

Following preliminary observations made at the study area and

an analysis of the pertinent literature, the following hypotheses

related to the distribution and abundance of Ahnfeltia concinna seemed

worth testing.

16

1. The type of water motion determines the distribution and

abundance of the Ahnfeltia concinna population.

2. Grazing determines the distribution and abundance of the

Ahnfeltia concinna population.

3. Salinity determines the distribution and abundance of the

Ahnfeltia concinna population.

4. The size of the fronds is determined by the amount of water

motion.

5. The upper limit of the Ahnfeltia concinna band is determined

by desiccation,

6. The lower limit of the Ahnfeltia concinna band is determined

by biological factors.

MATERIALS AND NETHODS

Observations at the study area Figure 1! were made approximately

monthly from June 1974 through October 1976. From May 1976 through

October 1976, observations were made at least weekly. Data were

collected at three sites along the study area coastline: from Kalele

to Leilewi Point, from Leilewi Point to the Hilo breakwater, and at

Coconut Island Hilo!.

Measurements were made on transects running through the littoral

zone. At the Coconut Island site transects 0.5 m wide were measured

every 2 m, at the Leilewi Point-Hilo breakwater site transects 1 m

wide were measured every 3 m along low angle shores and every 5 m

along high angle shores, and at the Kalele-Leilewi Point site trans-

ects 1 m wide were measured every 5 m along low angle shores and

approximately every 50 m along high angle shores.

Data were recorded only where the slope of the coastline was

fairly constant throughout 'the littoral zone, where the waves and

swells approached the shore at an angle of less than 30 degrees, and

where all except unusually large waves and swells broke directly on

the shore. The data recorded at each transect were the number of

bands and their dominant species, the distance of the upper and lower

breaks of the Ahnfeltia concinna band from tidal datum, the slope of

the shore, the salinity of the water, the height of the fronds at the

lower and upper breaks and at one fourth, one half, and three fourths

of the width of the band from the lower break, and the percent of the

substratum covered by the fronds in the lower three fourths of the band.

18

Measurements were made in the following ways. The distances of

the upper and lower breaks from tidal datum were measured in two ways.

Where possible, measurements were made with a 5 m bamboo pole marked

in 12 cm increments. Where this was not possible, an optical tape

measure Ranging Inc. N100! was used. Measurements were made only on

calm days when reliable estimates of tidal datum could be made. The

times of low tide were obtained from the Dillingham Corporation tide

calendars. The time of low tide and the range of the tide was assumed

to be equal to the predicted values for Hilo at all sites. The slopes

of the shore were measured with a protractor mounted on a small

carpenters level. The salinities were measured with a temperature

compensated refractometer American Optical Co. Model 10402!. Water

samples were collected directly where possible, or with a small plastic

cup on the end. of the bamboo pole. The heights of the fronds were

measured with a meter stick where possible or estimated with the bamboo

pole. The percent of the substratum covered by the fzonds was estimated

at 100, 80, 60, 40, 20, or less than 5 percent. The holdfast areas

were measured with a meter stick after removing the fronds with a

serrated knife. The diameters of the fronds were measured with vernier

calipers.

19

RESULTS

A. General descri tions of the stud sites

1. Kalele-Leilewi Point

There are usually three bands in the littoral zone along this

coastline. The lowest band is usually dominated by the red alga

datum. The dominant species in the middle band are the red alga

Porolithon onkodes and the urchin Colobocentrotus atratus. The limpets

Cellana sandwicensis and Cellana exarata are also present in this band.

The dominant species in the upper band is usually Ahnfeltia concinna.

Cellana exarata is sometimes present in the lower part of this band

and nerit Nerita picea is sometimes present in the upper part. The

dominant species in the supralittoral zone is the blue-green alga

Brach trichia ~up~i. Nerita picea is found in the lower part of this

cone and the littorine Littorina pintado is found in the upper part.

This section of coastline is exposed to very large waves and

swells Plate 1! and calm conditions are rarely present. Observation

shows that all trade wind waves and almost all southern swells, but

i'd

waves and swells approaching the island from about 335 to 215 degrees

from north will strike this coastline Figure 2!.

2. Leilqwi Point-Hilo breakwater

The pattern of bands in the littoral zone along this site is

similar to the Kalele-Leilewi Point site, but the bands are all at

only a few northwest swells will produce surf here. This indicates thac

20

extends only slightly above tidal datum. The middle band is dominated

by Porolithon onkodes and Colobocentortus atratus and the upper band is

dominated by Ahnfeltia concinna. h ~uo ri is the dominant

species in the supralittoral zone. Cellana sandwicensis, Cellana

enarata, Merits ~ines, and tittering pintado have the same distribution

as at the Kalele-Leilewi Point site.

Waves and swells are not present at this site as often as the

Kalele-Leilewi Point site. All trade wind waves and a few northwest

swells, but no southern swells, will produce surf here, This indicates

that waves and swells approaching the island from about 335 to 130

degrees from north will strike this coastline Figure 2!. When waves

and swells approach from these directions, they produce slightly lower

surf than at the Kalele-Leilewi Point site.

3. Coconut Island Hilo!

The pattern of bands in the littoral zone at this site is similar

to that of the other two study sites, but several species are absent,

not form a distinctive band. The middle band is usually a mixture of

Brachidontes cerebristriatus, but may be nearly devoid of macroscopic

organisms in some places. The upper band is dominated by Ahnfeltia

concinna and the supralittoral zone is dominated by ~u0$<X e

In many places the middle band is not very distinct and the upper break

21

concinna band overlap. The nerit Theodosus ~ne lectus and Cellana

exarata are found in the lover part of the Ahnfeltia concinna band.

Cellana sandwicensis, Nerita preen, tittering pintado, and Colobocen-

trotus atratus are not present.

This site is sheltered Plate 2! from large trade wind waves and

ocean swells by the Hilo breakwater. However, strong trade winds will

generate small waves inside the breakwater and large swells can dif-

fract around the breakwater, but are greatly reduced in size. Swells

that diffract around the breakwater and strike this site come from the

same direction as the swells that strike the Leilewi Point-Hilo break-

water site, 335 to 130 degrees from north Figure 2!.

B. Location of the Ahnfeltia concinna band

Ahnfeltia concinna forms a more or less continuous band along the

entire study area. The band can be extremely dense or very sparse,

but it is rarely absent. The locations of the upper and lower breaks

of the band above tidal datu~ are presented in relation to the slope

of the coastline in Figure 3 for the Kalele-Leilewi Point site, in

Figure 4 for the Leilewi Point-Hilo breakwater site, and in Figure 5

for the Coconut Island site. At the Kalele-Leilewi Point and Leilewi

Point-Hilo breakwater sites, the vertical distance of the breaks of

the band above tidal datum varies with the slope of the shore ~ The

breaks are highest on vertical shores and lowest on low angle shores.

At the Coconut Island site, the locations of the breaks do not vary

with the slope of the shore, but remain at the same vertical distance

above tidal datum.

22

The three sites are compared in Figure 6. The widest and highest

band was at the most exposed site, Kalele-Leilewi Point, and the

narrowest and lowest band was at the most sheltered site, Coconut

Island. At the two more exposed sites, the band is above the limit

of the tidal fluctuations although on low angle shores the lower

breaks can be slightly below maximum high water level �.95 m at

Hilo!. On high angle shores at these two sites, the band was usually

above the run up of the waves and swells and was only reached by splash

and spray, even at high tide. On low angle shores, ho~ever, the band

was usually below the run-up level of the waves and swells. at high

tide. At the Coconut Island site, more than one half the band is below

mean higher high water level �.7 m at Hilo!. At the two more exposed

sites, the upper breaks of the band are raised further than the lower

breaks in relation to the break levels at Coconut Island.

Obviously the breaks of the band at the two exposed sites can not

directly correspond to tidal levels. However, the band was still

affected by the rise and fall of the tides. On 24 out of 37 days when

Kalele was visited, the waves did not reach the lower break of the band

at 0,0 tide but did so as the tide began to rise. On the other days,

the waves reached the band even at 0 ~ 0 tide.

At three locations along the Kalele-Leilewi Point site and at one

location at the Leilewi Point-Hilo breakwater site, the upper and lower

breaks of the band were marked in June 1974, and no change in their

location occurred at any time during the study.

23

C. Substratum covera e

The percent of the substratum covered by the fronds varied con-

siderably with the slope of the shore at the Kalele-Leilewi Point and

Leilewi Point-Hilo breakwater sites but not at the Coconut Island site

Figure 7!. At the Kalele-Leilewi Point and Leilewi Point-Hilo

breakwater sites, dense growths occurred only on low angle shores

Plates 3 and 4! while at the Coconut Island site, dense growths

occurred on shores of all angles Plates 5 and 6!. At the Kalele-

Leilewi Point site there were a few places where a dense band covered

75 to 100 percent of the substratum on vertical shores' These were

shallow narrow channels perpendicular to the approach of the waves

which were filled with water by each wave and then slowly drained.

D.

The lengths of the fronds at the three study sites are presented

in Figure 8 for low angle shores and in Figure 9 for high angle shores.

The longest fronds occurred at the Kalele-Leilewi Point site and the

shortest occurred at Coconut Island. The longest fronds occurred on

low angle shores at each study site, even at the Coconut Island site

where the percent cover was equal on shores of all angles. At the

Kalele-Leilewi Point and Leilewi Point-Hilo breakwater sites, the

longest fronds occurred at the lower edge of the band, while at

Coconut Island, the longest fronds occurred in the middle of the band.

At protected locations along the Kalele-Leilewi Point and Leilewi Point-

Hilo breakwater sites, the longest fronds also occurred in the middle

the band. The shortest fronds occurred at the upper edge of the

break at all study sites. The fronds were not removed or damaged by

24

large waves or swells at any time during this study. The largest

swells observed were approximately 5 m high during December 1974 and

the tsunami of November 31,'1975, both of which left detritus lines as

far as 15 m inland of the Ahnfeltia concinna band on low angle shores.

E.

Ahnfeltia concinna can tolerate a wide range of salinities. The

salinity of the ocean water measured at the study sites varied con-

siderably, from 18.6 to 36 parts per thousand, largely due to sub-

surface freshwater springs. Most measurements were between 32 and 36

parts per thousand �22 out of 158! with but few lower values. Popula-

tions with 80 to 100 percent cover occurred at both the lowest and

highest salinities and there is not a significant statistical dif-

ference between percent cover and salinity Figure 10!.

In protected areas along the Leilewi Point-Hilo breakwater site,

there were several areas where large amounts of freshwater entered the

ocean. In these areas, Ahnfeltia concinna was usually the last seaweed

present along the salinity gradient. At low tide, it was present in

salinities as low as 3.9 parts per thousand. Heavy rains caused no

mortality, even when 5 to 6 cm fell in one hour at low tide.

On sunny days at low tide, the surfaces of the fronds often dried

out, leaving a pile of salt crystals at the branch tips.

F.

At Kalele, Cellana exarata and Nertta picea were removed from a 1 m

square area of high angle shore with a sparse population of Ahnfeltia

concinna for 18 months. No new thalli developed during this time. At

25

the same time, glass slides were anchored in a dense population on a

nearby low angle shore. Crustose holdfasts developed on these slides

within 4 months, and /eeet fronds 10 cm high were present after 9

months Plate 7!.

Colobocentrotus atratus was removed from a 2 square meter area

just below the Ahnfeltia concinna band on a low angle shore at Kalele.

A dense growth of the green alga Ulva fasciata developed in 3 weeks.

Colobocentrotus atratus gradually returned to the area after 6 months.

Ahnfeltia concinna did not develop in the area during this time, but

Ulva fasciata after 3 months.

At Coconut Island, the Ahnfeltia concinna fronds in the lower part

of the band were grazed by Theodoxus ~na lectue and probably by Cellana

exarata also. Freshly grazed surfaces were easily observed on the

fronds, and pseudoparenchymatous algal material characteristic of

Ahnfeltia concinna was present in the guts of Theoduxus ~ne lectue.

The grazing organisms present at both the other study sites were never

observed on the fronds in wave and swell exposed areas, nor was there

any evidence of grazing scars. In wave 'and swell protected areas at

these sites, however, Theodoxus n~a lectue was present on the fronds

and grazing scars were observed.

It may also be possible that fish graze on the fronds during high

tide in protected areas, but this was not observed. Several local

fishermen said that schools of nenue ~Khosus cinerascens! grazed on

Ahnfeltia concinna fronds and it was possible to tell the size of the

nenue and if they were still in the area by the scars at the tips of the

branches.

26

G. Substratum

Ahnfeltia concinna populations were never observed growing on any

substratum except hard basalt rock anywhere in the Hawaiian Islands.

They never grew on limestone or volcanic tuff, even though dense

populations on basalt extended right up to the edge of these rock

types.

H. Po ulation structure

The largest population of Ahnfeltia concinna at any location

visited in the Hawaiian Islands occurred on a low angle shore near

Kalele. The population structure was measured in this area where the

lower three -fourths of the band covered 100 percent of the substrate.

The lengths of the fronds in this area were longer Figure 11! than

the averages for this coastline Figure 8!, but followed the same

pattern of longest fronds at the lower edge of the band and 'shortest

at the upper edge. The diameter of the fronds varied within the popula-

tion Figure 12!. The smallest diameter fronds were at the lower edge

of the band and the largest were at the upper edge, The diameter

of the male fronds was larger than the diameter of the female fronds.

The standing crop also varied from the lower break to the upper break

Figure 13!. The wet weight was approximately equal at the lower edge

and in the middle of the band, but was lower at the upper edge. The

greatest dry weight standing crop was at the middle of the band

followed by the lower edge and then the upper edge. The percent dry

weight/wet weight was greatest at the upper edge and least at the lower

edge of the band.

27

The 100 percent cover was maintained throughout the lower three

fourths of the band in areas of different frond length by variations

in the surface area covered by the holdfasts of individual thalli

Figure ll and Plate 8!. At the lower edge of the band the holdfast

area was least, and at the upper edge of the band it was greatest.

The shape of the holdfasts also varied in the band Plate 8!. At the

lower edge of the band they are approximately circular and distinct

fram one another. In the middle of the band they are long and thin and

form rows oriented parallel to the waves, At the upper edge of the

band, they are irregular.

The most extensive growth in this area occurred in a bowl which

was slightly higher at the seaward edge. The waves filled Plate 9!

the bowl with water, which then drained slowly.

The crustose tetrasporophyte of Ahnfeltia concinna was identified

in this area. It usually grew in shallow tide pools Plate 10!

landward of the gametophyte band and can be distinguished from other

red crustose algae by the unpigmented spots produced by the release

of the tetrasporangia from sori Plate 11!.

I. Factors influencin the u er break

During neap tides in the first week in June 1976, there were

four days in a row at the study sites with no clouds, very light

winds,' no waves, and only a very small southern swell. At the Coconut

Island and Leilewi Point-Hilo breakwater sites, dieback of fronds to

the holdfast occurred in the upper one third to one fourth of the band

Plates 12 and 13!. At the very upper limit of the band, the outer

28

part of the holdfasts also died, but the center remained alive. The

dead fronds were very persistent, remaining for 10 to 20 days before

disintegrating. At the Kalele-Leilewi Point site, where very small

southern swells were striking, there was also some dieback. On high

angle shores, fronds were killed downwards to the holdfast in the

upper one fourth of the band Plate 14!, but on low angle shores, only

the very tips of the fronds in isolated locations were killed Plate

15!. Small new fronds growing from the holdfasts were present within

four weeks at all such affected areas.

From July 28 to August 2, 1976, there were several days during

neap tides with no clouds, light winds, no waves, but very large

southern swells. The fronds in the upper parts of the band at the

Coconut Island and Leilewi Point-Hilo breakwater sites were killed,

but there was no dieback at the Kalele-Leilewi Point site. Dieback

of fronds was not observed at any other time during the two year study.

J. Factors influencin the lower break

No changes in the lower limits of the Ahnfeltia concinna band or

destruction of fronds at the lower edge were observed at any of the

sites at any time during the study. However, entire thalli would

sometimes be moved into the lower Porolithon onkodes band along the

Kalele-Leilewi Point site when large blocks of basalt were shifted

during periods when the swells were very large. The fronds that were

present when the blocks were moved grew to resemble the long thin

fronds found at the lower limit of the band. These thalli persisted

from 4 to 15 months, but eventually all of them disappeared.

29

Colobocentrotus atratus removed some of the fronds by graring at their

base, but the complete disappearance of the thalli was observed when

the crustose holdfasts of Ahnfeltia concinna were overgrown by Porolithon

onkodes. The break between the Porolithon onkodes and Ahnfeltia

concinna bands appears to be very sharp if- the erect fronds are

present. When the fronds are removed, however, the break is Plate

8! not distinctive and there is considerable overlap.

30

DISCUSSION

A. The location of the Ahnfeltia concinna band

Ahnfeltia concinna has a somewhat unusual distribution Figure

6! for a littoral alga because it forms 'a band on both high and low

angle shores in both wave and swell sheltered and extremely wave and

swell exposed areas. The Coconut Island site is an area where the

waves are very small when compared to the tidal range, and the Kalele-

Leilewi Point site is an area where the waves and swell are very large

when compared to the tidal range. Environmental conditions suitable

for the growth of Ahnfeltia concinna are produced in both the presence

and absence of large waves and swells. This indicates that differ-

ences in the size of the waves and swells and how they break on the

shore do not determine the presence or absence of the band, but only

its size, location, and coverage of the substratum.

Although the breaks of the band do not closely correspond to a

tide level, this does not necessarily mean that a sharp change in the

time of emersion and submersion due to tidal fluctuations can not occur.

Even at the most exposed site the band is usually subjected to emersion

and submersion by the changing tides. The ecologically equivalent

levels of emersion and submersion are at different vertical levels at

sheltered and exposed locations. It is possible that the tidal fluctua-

tions create the necessary environment for the alga even though the

vertical breaks of the band do not directly correspond to tidal levels.

If it is the amount of wetting or desiccation that determines the

location of the band, a change in vertical elevation of the band on

31

shores of different angles would occur at exposed locations and no

change in vertical elevation would occur on shores of different angles

at sheltered locations' At very sheltered sites, the amount of

wetting or desiccation depends only on the rise and fall of the tides,

and the vertical elevations reached by the water are the same on shores

of all angles. At very exposed sites, the elevation reached by the

water varies with the slope of the shore. Wave run up and splash will

have a larger vertical than horizontal component on high angle shores,

while on low angle shores the horizontal component will be larger

than the vertical.

B. The de ree of cover of the substratum

The occurrence of a closed band of Ahnfeltia concinna on high and

low angle shores of sheltered coastlines, but only on low angle shores

of wave exposed coastlines Figure 7! can be correlated with the type

of water motion. A closed band forms only in areas where water flows

through the fronds and then drains slowly. At the exposed Kalele-

Leilewi Point and Leilewi Point-Hilo breakwater sites, in areas where

the approach of the waves and swells is approximately parallel to the

coastline, this type of water motion occurs only on low angle shores

where the Ahnfeltia concinna band is usually below the wave and swell

run-up at high tide ~ The same type of water motion also occurs on

vertical surfaces in shallow narrow channels perpendicular to the

approach of the waves. On high angle shores at the two exposed sites

where the band is usually below the limit of wave and swell run-up at

high tide, the water motion is mostly splash and a closed population

32

does not occur. At the sheltered Coconut Island site where most of

the Ahnfeltia concinna band is below mean higher high water, the tidal

fluctuations also produce an alternate flowing water at high tide and

emersion at low tide. When the tide is in, the small waves cause

water to flow fhrough the submerged fronds.

The absence of dense populations on high angle shores Figure 7!

is not a result of drag preventing the spores from attaching and

developing, since the alga is present in these areas, and since even

the largest waves observed over a two year period failed to damage

thalli at any site. If the areas with flowing water reduce the

boundary layer surrounding the fronds morethan splash and spray, this

could also influence the density of the thalli, but since a closed

band grows on vertical shores in sheltered areas where the total amount

of water motion is low compared to the total water motion on shores of

any slope at the more exposed sites, the total amount of water motion

is probably less important than the, type of water motion. The greater

amount of sunlight striking low angle shores could have an influence,

but would not explain the occurrence of dense populations on vertical

surfaces in narrow channels.

Although the density of the population was not affected Figure

10! by the salinity of the water, the ability of Ahnfeltia concinna to

tolerate a wide range of salinities may influence the presence or

absence of the band along some coastlines. In areas with high rainfall

or large amounts of freshwater entering the ocean from springs of

rivers, Ahnfeltia concinna may be at a competitive advantage.

33

C. The len th of the fronds

The occurrence of longer fronds at the lower edge of the band,

except where grazing occurs, and the occurrence of the longest fronds

at the most exposed site indicates that the quantity of water motion

influences the size of the fronds. The more water motion present,

the greater the length of the fronds. The increase in frond length

could be a result of either an increase in frequency or intensity of

water motion or both. If there is an optimum water motion value beyond

which frond growth is reduced, it was not reached at the study sites.

However, the reduction in dry weight of the standing crop at Kalele

Figure 13! indicates that the optimum water motion value for growth

may have been exceeded there.

More sunlight is received by low angle shores and this could also

be important. But since the longest fronds occur at the lower edge of

the band where water more frequently covers the fronds and reduces

sunlight, water motion would seem to be the more important factor,

The small diameter of the fronds at the lower edge may be a

response to differences in the frequency of desiccation. Pronds at

the upper edge of the band are exposed to greater desiccation, and a

larger diameter frond has less surface area for evaporative water loss

in relation to the volume of the frond.

D. The u er limit of the band

The upper limit of the Ahnfeltia concinna band is not determined

by a single factor or by the average of several factors but by 'an

extreme value resulting when several factors occur simultaneously to

34

produce maximum desiccation, The limitation of the band at its upper

break by the physical factor of desiccation indicates that the "litus

line" or "physiological high water line" along this coastline does not

provide an average level of the influence of the tides and waves, but

a minimum value.

When the tidal and atmospheric factors which produce maximum

desiccation are present, they occur along the entire study area coast-

line. The other factor, however, the waves and swells, can vary

considerably at the different study sties. The frequency of the waves

and swells below a certain size is the factor that determines the

upper limit of the Ahnfeltia concinna band along this coastline. No

dieback occurred unless waves and swells were virtually absent. During

the winter months, the frequency of the waves and swells reaching the

Kalele-Leilewi Point and Leilewi Point-Hilo breakwater sites is

approximately the same, but during the summer months, the frequency at

the Kalele-Leilewi Point site is much greater. This corresponds with

the greater dieback of the fronds at the Leilewi Point-Hilo breakwater

site in the summer. The frequency of waves .and swells may be asI

important in determining the width of the band as the size of the waves

and swell. At the study area, the site with the largest population of

Ahnfeltia concinna was the Kalele-Leilewi site, where the waves and

swells were most frequent.

The frequency of waves and swells below a certain size may also

be important in determining the presence or absence of Ahnfeltia concinna

on a coastline. Since it takes several months to colonize new surfaces,

36

and fish would not be able to graze at these locations since even at

high tide most of the thalli are out of the water when calm conditions

occur .

F. A uantitative ex osure index

The greatest problem in determining the exposure of a coastline

is the lack of a simple method to obtain a quantitative value. Sub-

jective measurements are undesirable since they rely on personal

experience. The exposed area according to one author's experience can

be the sheltered area of another' s. Neither the frequency nor velocity

of local winds gives a reliable value for exposure since swells striking

a coastline can originate thousands of kilometers away. Using the

angle open to the ocean at a 50 mile radius from the shore ignores the

differences in swell direction and the ability of large swells to

refract and diffract. Direct measurement of waves and swells for a

short period of time will not give reliable values since wave and

swell size can vary greatly from season to season, day to day, and

even from hour to hour. Continuous measurement at more than a few

locations is impractical for most studies. The use of indicator

species may be possible in some areas, but this circular reasoning

ignores other possibly important factors in the distribution of an alga.

In the area of this study, indicator species would not be of much value

since the species present are similar in areas of very different expo-

sure. Measuring the width of the band of a single species provides a

quantitative value, but the species may not be present on many coastlines.

Measuring a band in the supralittoral zone would be more an indication

37

of the wind and spray than of exposure. Areas with strong offshore

winds may be very exposed to ocean swells, but would have a very small

supralittoral zone, The measurement of maximum drag could give very

erroneous values since one area may have the same maximum wave size

but the frequency of large waves and swells may be greatly different.

The algae may be more influenced by the occurrence of low wave and

swell conditions than by high conditions.

Measuring the distance of the upper limit of the littoral zone

above a given tide level alone can not provide a good estimate of the

exposure along a coastline unless the. slope of the shore is also

considered. However, by measuring the horizontal and vertical distance

af the upper limit of the littoral zone above a tide level along

different coastlines Figures 3, 4, 5, and 6!, it appears possible to

quantitatively compare their exposure. The distance calculated from

the best fitting curve of the upper limit of the littoral zone, accepted

here as the upper break of the Ahnfeltia concinna band, above a tide

level on a shore of 90 degrees slope, can be used as an exposure index.

An upper littoral limit occurring at mean high water �.55 m at the

study area! would be defined as 0 exposure. Using this index, the

Coconut Island site would have an expoure of 0.22, the Leilewi Point-

Hilo breakwater site would have an exposure of 1.65, and the Kalele-

Leilewi Point site would have an exposure of 4.11..It would be passible

to obtain an approximate value from a single measurement by interpolating

it in relation to Figure 6. Close comparisons using this index could only

be made between areas with similar tidal fluctuations. This index could

be used anywhere in the Hawaiian Islands, since the variation in tidal

range is very small.

38

SUMMARY

l. Ahnfeltia concinna forms a band on basalt rocks on both high and

low angle shores in both wave and swell sheltered and extremely wave

and swell exposed locations.

2. On wave and swell exposed coastlines, the vertical distance of

the band above tidal datum is greater on high angle shores than on

low angle shores.

3. On wave and swell sheltered coastlines, the vertical distance of

the band above tidal datum is the same on high and low angle shores.

4. The band is subjected to submersion and emersion by tidal

fluctuation at both wave and swell sheltered and wave and swell exposed

locations.

5. A closed population occurs only in areas where water flows through

the thalli.

6. Grazing does not affect the coverage of the substratum by the

fronds.

7. Ahnfeltia concinna can tolerate a wide range of salinities, but

this does not affect the coverage of the substratum by the fronds.

8. The longest fronds occur at the most wave and swel1 exposed site

and shortest fronds occur at the most wave and swell sheltered site.

9. At each study site, the fronds on low angle shores are longer than

the fronds on high angle shores.

10. In wave and swell exposed locations, the length of the fronds is

greatest at the lower edge of the band and least at the upper edge of

the band.

39

11. In wave and swell sheltered locations, the length of the fronds

is greatest in the middle of the band and is shorter at the upper and

lower edges of the band. The shorter length of the fronds at the

lower edge of the band is due to grazing.

12. The upper limit of the band is determined by desiccation. Fronds

in the upper part of the band are killed by desiccation when very

small waves and swells, neap tides, and no cloud cover occur simul-

taneously.

13. The causal factor of the lower limit of the band is not obvious,

but competition with other algae for surface area and grazing may be

important.

14. The crustose tetrasporophyte of Ahnfeltia concinna grows in tide

pools above the gametophyte band.

Figure 1. Nay of the study area.

41

FIGURE

KAUAI

OAHUNI IHAU MOLOK AIAUI

LAN

KAHOOLAWE

Frequencies, directions, and seasons of waves and swells

arriving in the Hawaiian Islands calculated from data

in Noberley and Chamberlain, 1964!. Only frequencies

greater than 5 percent are shown.

43EP

NCo

GURE 2

Op

E

OJ

SSWELLS~

o 10 second periods!

N

c" S e

WAVES[ 610 second periods J

~ tH>O~ srree Nov Apl~ NIO ~

May � Oct

44

Figure 3. The location of the Ahnfeltia concinna band in relationto the slope of the shore at the Kalele-Leilewi Point

site. The curve fitted to the upper break data is an2=exponential curve, a=4.74, b=-0.125, r =0.94. The curve

fitted to the lower break data is an exponential curve,

a=2.13, b=-0.093, r =0 ~ 46.2

LllO

CO

O

Pz

0 N IZO X

Q7 LO CV

pg WALVQ 30ll WORE 3ONVLSIO 1VOI J.83A

46

Figure 4. The location of the Ahnfeltia concinna band in relation

to the slope of the shore at the Leilewi Point-Hilo break-

water site. The curve fitted the upper break data is an

2exponential curve, a=2.56, b=-0.153, r =0.69. The curve

fitted to the lower break data is an exponential curve,

a=1.41, b=-0.151, r =0.53.2

47 DO

UJOI-

LLj

O z

h

CI

z

0 NCC

0 X

gg AAJ.VO 30ll WO83 33NVJ.SJO lVO/J.B3A

48

Figure 5. The location of the Ahnfeltia concinna band in relation to

the slope of the shore at the Coconut Island site. The

line fitted to the upper break data is a linear regression,

a =0.86, a -0.006, r =0.01. The line fitted to the lover2=0

break data is a linear regression, a =0.43, a1=-0.003,

r =0.01.2=

allV

0!

O

I-z

0 NIZ

0 Z

O LhO

Wn J.VO 3OI J. WOUR 3ONVI.SIQ 1 VOI J.83A

50

7igure 6. The locations of the Ahnfeltia concinna bands in relationto the slope of the shore at the thr'ee study sites.

W An>Va 3aij. AOS8 33NV>Sia aVOi<83a

52

Figure 7. Mean percents of the substratum covered by the fronds in

the lower three fourths of the band at the three study

sites. ~ = Kalele-Leilewi Point, F value 54.4 with 3

and 70 degrees of freedom. 0 = Leilewi Point-Hilo

breakwater, F value 37.9 with 3 and 39 degrees of freedom.

V Coconut Island, F value 0.13 with 3 and 33 degrees of

freedom.

53

10

60

50

! 40

30Ci

X 20

10

71-9010-30 3f-50 51-70ANGLE OF THE SHORE degrees

Figure 8. Mean fred lengths through the band at the three study sites

0on shores with a slope of 50 or less. 0 = Kalele-Leilewi

Point, F value 16.4 with 4 and 160 degrees of freedom.

0 = Leilewi Point-Hilo breakwater, F value 15.8 with 4

and 95 degrees of freedom. V = Coconut Island, F value

4.0 with 4 and 55 degrees of freedom.

Figure 9. Mean frond lengths through the band at the three study sites

on shores with a slope of more than 50 . 0 = Kalele-Leilewi

Point, F value 8.2 with 2 and 60 degrees of freedom.

0 = Leilewi Point-Hilo breakwater, F value 36.7 with 2

and 48 degrees of freedom. V = Coconut Island, F value

2.01 with 2 and 12 degrees of freedom.

55

%20

O X�Z

o10Z 0K

.1/4 1/2 3/4distance from lower break

total width of t e band

10

O ZI-�Z

0Z

0 CC

1/2distance from lower break

total width of the band

Figure 10. Mean salinities in relation to the p ercent of thesubstratum covered by the fzonds in the lower threefourths of .the band. Data is from all study sites.7 value 2.74 with 2 and 155 degrees of freedom. Thisis not significant at the 0.05 percent level.

Figure 11. Mean ron eng sf d 1 th and percents of the substratum covered

wa leby the holdfasts through a dense population on a low angshore near Kalele. 0 = mean frond length, P value 13.4with 4 and 35 degrees of freedom. 0 = percent holdfastarea, 7 ~alue 46.9 wi.th 2 and 18 degrees of freedom.

57

3

30

80-100-60

60

50

3

O0

0 0O

Z~ 20

0x 100

32

I-

Z

31

FROND COVER

1/4 1/2 3/4distance from lower break

total width of the band

l-

20 QICI

0 0Z

58

Figure 12. Mean frond diameters measured 1 cm from the tip for male

and female thalli through a dense population on a low

angle shore near Kale'.e. ~ = male fronds, P value 57.6

with 2 and 117 degrees of freedom. 0 = female fronds,

F value 67.7 with 2 and 129 degrees of freedom.

Figure 13. Wet weights, dry weights, and percent dry/wet weights

through a dense population on a low angle shore near

Kalele. L = wet weight, F value 29.4 with 2 and 21

degrees of freedom. V = dry weight, F value 4.6 with 2

and 21 degrees of freedom. Cl = percent dry/wet weight,

F value 20.5 with 2 and 21 degrees of freedom.

59

50

40

E

X� 4

~ i.o

X

O

o05Z0

0 i/2distance from lower break

total width of the band

1/2distance from lower break

total width of the band

30 pZ

20~I-

i0 ~a

60

PLATES

Summer swell striking the coast near Kalele, June 18,

1976. The upper edge of the Ahnfeltia concinna band

is just visible.

Plate l.

Plate 2. Coconut Island at low tide, August 1976. The dark band

is Ahnfeltia concinna.

61

.I

~OPS'-C

62

Plate 3. A dense population of Ahnfeltia concinna on a low angle

shore at Kalele, October 1976.

Plate 4. A sparse population of Ahnfeltia concinna on a high angle

shore along the Kalele-Leilewi Point site, November 1976.

63

Plate 5. A dense population of Ahnfeltia concinna on a low angle

64

Plate 6.

shore at Coconut Island, November 1976.

A dense population of Ahnfeltia concinna on a high angle

shore at Coconut Island, November 1976.

65

66

Ahnfeltia concinna thalli which grew on a smooth glassPlate 7 ~

slide anchored in a dense band at Kalele, January 1976 '

Plate 8. A one meter wide transect through the lower part of the

Ahnf el tis conc irma band near Kale le with the 'erect f rond s,

removed, October 1976.

67

68

The largest stand of Ahnfeltia concinna observed duringPlate 9.

the study.

Plate 10. The yellow-brown alga growing on the boulder in this

tidepool is the tetrasporophyte of Ahnfeltia concinna.

69

70

Plate 11. The tetrasporophyte of Ahnfeltia concinna showing the

light spots where sari of tetrasporangia have been

released,

Plate 12. Dead fronds in the upper one third of the band at a

protected area along the Leilewi Point-Hilo breakwater

site which were killed by desiccation, June 1976.

1'

7l

72

Plate 13. Dead fronds in the upper one fourth of the band at the

Coconut Island site which were killed by desiccation,

June 1976.

73

74

Plate 15. Fronds with dead tips on a low angle shore along the

Kalele-Leilewi Point site which were killed by

desiccation, June 1976.

l

,lq

S

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