....); .

..Tbis paper not to be cited vithout prior rererence to the author.

International Couneil for theExploration or the Sea

C.M.1979/L:29Biologieal Oeeanography Cttee

EFFECT 0., OXYGER DEFICIENCY ON BENTHICMACROFAUBA IN. FJORDS

RUTGER ROSEl'fBERG

Institute of Marine Research, 8-453 00 Lysekil, Sveden

Running headline: OXYGEH DEFICIENCY .AHD BENTHOS

... ABSl'P..ACT

EFFECT OF OXYGSn DEFICIEUCY OU m;l~THIC I.!ACROFAtnlA

In FJORDS

Rutger Rosenberg

Institute of Marine Research

Lysekil, Sweden

Eenthic fauna1 reactions to oxygen deficiency in ten fjords,

and estuaries in northern Europe are reviewed. Choosen areas exhi-

bit both pennanent and temporary oxygen deficiency due to

organic enrichment and/or eeomorphological conditions. number of

species, abundance, biomass,and faunal composition are given in r€-

lation to oxygen concentration. Results show that the measured

faunal parameters do not change gradually with oxygen concentration,

but abruptly at approximately 2 mg 02/1itre. Benthic faunal reactions

to o)~gen deficiency susgest the followinc croupin&:

1. Ron-tolerant species; most species

2. Tolerant species; mainly molluscs

3. Transitory opportunists; pioneer polychaete colonists appearinz

when conditions improve

4. Transi tory emigrants; .mobile species

The missing macrofaunal biomass in some waters around Scandinavia is

roughly estimated and it is concluded that oxygen depletion due to

geomorphological characteristics of water bodies wipes out significantly

more animals than similar effects caused by organic pollution.

e"

•

1.

INTRODUCTION

In this eentury of eontinously increasing impoverishment of the eeo­

system at many plaees in the sea oxygen depletion io one of the most

easily realisiable, because of its obvious and sometimes visible effects.

Oxygen depletion is eommonly reportedfrom fjords, where stagn~tion

oceurs in the basin inside the sill. The reduetion in oxygen coneentra­

tion 1s eommonly promoted by organie enriehment (Fig. 1). Oxygen dep­

letion begins at the bottom surfaee and afteets the benthie organisms.

In eonnection with oxygen reduction in the water the redox potential

discontinuity in the sediment rises. The benthie fauna in ~he sediments

i8 reacting to this by emerging and less spaee 1s left tor 11ving. This

indueed stress situation will sueeessively kill most of the speeies,

leaving those adapted to redueed oxygen eonditions aslast survivors.

The layer of anoxie ?~ter occurring just above the bottom extends in

some eases only a few eentimetres upwards. Naturally, such a situation

is ditfieult to reeord by traditional sampling"methods. This implies

that oxygen depletion could be a mueh n.ore frequent phenomenon at about

the sediment surfaee than reported. Should stagnation eontinue at the

bottom the anoxie extension will probably inerease in thiekness and" be

stratified by a vertieal temperature and/or salinity gradient.

Anoxie eonditions in marine environments eould be either (1) more or

less temporary where maeroorganisms never establish, or (2) oecurring

periodieally at irregular or rather regular intervals interrupted by

periods of faunal recolonization and establishment. The envelopment of

the anoxia eoula be influeneed by organie enrichment.

2.

In the ~ollowins I will give examples of the effects of oxy~en depletion

on benthic macrofaunal .structure and quantity. Firstly, in staGnant basins

where oxygen deficiency is not mainly a consequence of pollution, and se-

condly, where stagnation in combination with organ1c enricbment have re-species

sulted in oxygendepletion. The succeesion of benthicAalong increaeing

or decreasing enviro~ental gradiente has recently been described and

discussed (Pearson and Rosenberg 1978) and 1S not repeated here.~

II

L

3•.

STAGNATION AHn OXYGEN.DEFICIENCY

Tbe Eytjord, Sweden

The Byfjord is situated on the Swedish west eoast. At the entranee of

the fjord io a sill at 12 m, whieh almost completely prevents exchange

of water'below the bnlocline at 12 to 15 m. The sal1n1tyabove the

haloeline is 22 to 30 ~o. The 1nn~r basin 1s, apart fram temporar.y wa­

ter renewals, anoxie below an osc1llat1ng depth level of 14 to 20 m

(Fig. 2). The. B,yfjord reeeives treated waste water from a population

of 45 000, but th~ anoxia is due to the geomorphologieal eparacteris­

tice of tbe fjord. The anoxie conditions below the halocline atructure

the ecosystem in the fjord: eopepods and pelagie fiah have low abun-

dances compared to other areaa and a large quantity of the energy re-

sources are utilized by epifaunal animals, mainly the blue musale

Mztilus edulis and thc cionid Cions intestinalia (Rosenberg ~ ale 1971).

Tbe distribution of macrofauna was lim1ted to depths above 17 m 1n 1911

(Rosenberg 1977). The benthie commun1tiea were composed by rather short­

lived spee1es and displnyed great sensonal fluetuations. Among the moat

consp1cuous spec1es we~e Corbula (= Aloidis) ßibba and Nephtye hombergi,

whieh charactcrized two different eommun1tes separated by. eimilarity

analysis. The bottom area without maerofauna in 1971 eomprised an area

of 3.41 km2 (Rosenberg ~~. 1971). The mean biomass in coastal areas

-2bel~w 15 m along the Swedish west eoast has been estimatcd to 146g m

(Rosenberg and Möller 1919). Thus, thc anoxie bottoms could have accom-. .modated approximately 500 tonnes wet weight of macrobenthic animals, 1f

oxygen concentrat1ons were sufficientto support a permanent fauna.

••

~.'

.The oxygen concentration in the fjord decreaaed abruptly with increasine

depth ovar a few metors range. As an example a situation preva1l1ng for

a few days. in Octobcr 1971 is presented in ~ig. 2. Then, 4 mg 1-1 of

oxygen was recorded at 10 m, whereas the concentration bad dropped to

zero nt 14 m. A few dayo later thc zero-level was faund at 17 m. Tbio

sharp decline in oxygen concentration in thc fjord creates a s1m1larly. .

sharp declinc in number of species, abundanoe and biomass. At an oxygen

-1·concentration.of approximately 2 mg 1 ,which at that time was found

at 11 m, the divers1ty waa maintained fairly high (Shannon - Wiener ~=

In conneot1on witb water renewals in the B,yfjord oxygen concentrations

of below 1 mg 1-1 bave been observed to r1se towarda the surface over

a few days duration, but without any notablc effect on the macrobenthos.

Speoies repeatcdly recorded.at depths with oxygen deficency were the

polyohae~cs Po1ydoru c11iata, Ophiodromus f1exuosus; the molluscs

•

Corbula gibba, Nassu reticulata; and

Lough Ine, Ireland

. Phoronis mU11eri •

L

In Lough Ine anoxia deve10ps nnnually as a consequencc o~ topography

favouring tempcrature etratification, which norma11y begins in lJarch

and increase until earlTSummer. In 1970 the sharp discontinu1ty of

temperature in the summer at a deptb of 20 to 30 m resulted in oxygen .

depletion in~he hypolimnion to a level of around 5 peroent saturation.

Tbe salin1ty in the watercolumn was stable, between 34.4 to 34.9 ~o.

Faunal succcesion during thc dcoxygenation procesa 1s descr1bedby

Kitchins ~!!. (1976). In JUly only a few infauna1 species were still

present: Pseudopo1ydora pu1chra, Corbu1a ßibba, Sca1ibreSEß inflatum

L

•

5.

and a few others. B.Y m1d-AuguatC. gibba was tbe only spec1es recorded

bclow 40 m and the diotribution of P. Eulchra was limited to 25 m leve~ •.

Thc progressive elimination of P. Eulchra trom below and upwards in

1970 1s illustrated in Fig. 3. Later in winter or spring tbe species io

reestab11shed in tbe loch aga1n.

The Limfjord rangeo over an area of 1 500 km2 and approx1mately 330 km2

. (2~) of the bottom arca is 1nfluenced by annual oxygen depletion 1n. . .late summer resulting in maDS mortality of benthie anima~ Reeoloniza-

tion Beems to take place largely within a year. The bentbie fauna in

tbe Limfjord has been invest1gated by Jörgensen (in press). When d1ving

dur1nginereas1ng oxygen depletion at·tbe bottom he observed mot1onless

but still alive polychaetes lay1ng on the anoxie mud (Nereis diversi­

color, N. vivens, Pect1nar1a koren1, Heteromastus tiliformis).Molluscs

(t41a arenaria, Cardium edule, Abrs alba) reacted at tbe Dame time by

·stretehing their siphons up into the water. ~ith eontinued oxygen dep-

letion for anotber week tbe polyehaetes died. Now, the molluBes began

to creep out of the sediment and lay on the sediment surface. Yl! bent

their siphons upwards and could stretch them 20-30 em a~~ve .the bottom.

Cardium,~ and Corbula gibba lied scattered on the mud surface and

could perhaps survive for another week.

The Balt1c See.

Tbe Balt1e Sea is like an enormous fjord1c estuary, beavily diluted in

its northern parts with a calinity of aröund 3 %0. The aalinity 15

sueo~ssively increas1ng to approximateiy 15 %. in the·soutbern parts.

Renewal of tbe bottom water oeeurs tbrough irregular1nflowa trom tbe

L

•

6.

west (Kattegat). Absence or inflow or bottom water results in stagnation

and oxygen depletion in the deeper basins. The extension of tbe anoxie

bottoms increases with retardation of water renewals and the processes

have been described by Fonse1ius (1969). Bottoms complete1y devoid of

macrozoobenthos or with on1y few animals showed its maximal extension

in 1975 during this century. According to Zmudzinski (1977) these bot­

tom deserts bad an extension of 84 000 km2, of which 7 000 km2 were 10­

eated to theBornho1m bas1n (F1g.' 4). At the end of 1975 a large inflow

of bottom water oecurred and all the anoxie water was renewed •

Tbe vertieal extension of the maero- and meiofauna in tbe western eent-

ral Baltie (oee Fig. 4 point A) has.been reported by Elmgren (1975, 197~) •

. He ;divided~', tbe ~aunal distribution into tbree zones (see Fig. 5).

1. An upper zone do~~ to 50 m witb higb oxygen eontent and rieb fauna.

'2. An intermedinte zone with dcereasing oxygen eoncentrationswitb in-

crea&±ng deptK. In this zone the macrofauna d1sappeard gradually,

and at its lowerborder on1y the mobile polyehaete Harmothoe sarsi

wasfoundalong with abundant nematodes •. .

;. A lower zone with little or no oxygen virtual1y devoid of macrofauna

and extremely impoverisbed me10fauna cons1sting of a few thou-

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•

2sand nematoden per m •

The b10mass decreased ~rom normally above 100 g m-2 1n the upper zone

to less thnn 1 Sm-2 in the intermediate zone nnd 0.01 g m-2 in the .

lower zone.

A joint sampling programme ineludingseveral countr1es and covering~ "

most of thc Ealtic was eonducted in 1974 (Elmgren ~ a1., in press).

Tbe results sho~ed that in the northern parts, in tbe ~othnian Bay,

the meiofauna1 biamass was bigber than that of tbe macrofauna. Tbis

was in agreement witb Ger1acb'e (1971) idcae tbat meiofauna io quanti­

tatively more important relative tö macrofauna in brackish "~ter .than

in marine areas. Similar1y, tbc bio~ass ratio between macro- nnd meio-

. ~auna was extreme1y low.(2.2:1) in tbe oxygen ntressed ~yfjord (Rosen­

berg ~~., 1977). Along a depth transect in the Baltic the macrofauna

domi~ated in'~he ~reviously described upper zone, whereas theimpor­

tance of tbe meiofauna1 biomass successive1y increaaed by deptb and,aominated below 60 m (Elmgren, 1979). Thua, there aeems to be a gene­

ral tendency for meiofauna to increase its relativeimportance in re-

1ation to macro~auna.along cnvironment~i ctreos sradients.

8.

Thc Borholo Essin in thc soutbern part of tbe Baltie, witb a mixicu~

deptb exeeedinc 100 m, is also per10dieally anoxie in its deeper parts

below about

animale bas

80 m (Pig. 4, point B). Tbe trans1tory return of~..

been described b'y;\1Jeppäkoski (1969, 1971, 1975).

bentbie

Based on

bis data a diagramatie presentation oftbe ehanges of number of speeies

end abundance in relation to tbe oxygen oscillatio~has been construc-

ted (Fig. 6). It 1s elear from tbe diagram that the improved oxygen

•conditions in 1969 vms immediately followed by repopulation of previously

defaunated bottoms. Tbe eolonists were Atlantie-borcal and cosmopoli-

tan species of tbe opportunistic type. They ware replacing tbe Arctic

relicts inhabitinG.tbose bottoms before the severe stagnat;on in tbe

1950's. Thereby, the previous dominance of suspension feeders was

s~itched to predo~intly deposit-swallo~ing species. The do=inants b~lo~

75 m in 1970 wcre the polychaetes Scoloplos a~iger, Harmothoa sarsi,

Trochochaeta. multis.·etosa and Heteromastus filiformis. Leppäkoski cO:lclu-

ded that Scoloplos armiger utilizes tbe accumulated nutritives after

prolonged stagnation and that it io one of thc most tolerant specics to

low oxygen concentrationsin tbc south~rn Baltic.

Speculatively, tbe bio~ass wiped out in the äeep basin could be rour,hly

estimated. Tnken tbe mean bio~ass (net wt) recoröed at six station~

below 80 m in 1951-1952 from Lcppäkoski (1969: Tab. 3) approximately

20 g m-2 is obtained. Tb . i f i th B b 1o area m1DS ng macro auna n e orn 0 =basin in 1975 \7aD 7 000 km2 (Fie. 4) and thia augGcsts a lost bio=ass

of 140 000 tonnes. If tbe same 20g in app11ed to tbc whole desort area

in Fig. 4, wbicb'is double thc size.o~ Denmark, onc would arriv~ at

L

a ~igure o~ elose to 1.7 million to~nes of macrofaunal biomass missing

because of the anoxie conditions.

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•

Kiel Bay, eituated in tbe eoutb-weetern Baltie (Fig. 4,. point C), is re-

latively rieh in marine epceicD eompared to tbe reet of the Baltie. Thc

renDon is the comparatively higher salinity, 13-20 %D' nnd inflow of

benthie larvae from theKattcgat in tbe north. An impoveriabed fauna i8

found in the deoper ehannelo below 20 m of Kiel Bay, where oxygen deple-

tion oeeurs annunlly in late summer. Faunal eomposition of these ,ebannels

have bean described by Arntz (1977), snd Arntz and Erunswig (1976, in

press). AhAbra alba eommunity dominates bottoI:ls below 15 m wbere oxygen

ie sufficient. The mean biomaee of this cOI:lmunity wae 93 g wet wt m-2 in

1968. The b10mace decreaeed abruptly at bottOI:lO affected by periodic oxy­

gen depletion (Fig.·7), where the biomaee 1s a few grams onl~. Periodio

dominants here were tbe polyehaetee Capitella eapitata, Harmotboe sarsi,

Scoloplos armiger und Pectinaria koreni alang with thc priapulid

Halierzptus spinulosus, and when conditiono ware periodically improved

tbe mobile eumacean Diaetylis rathkei. Also other speeies showed a con­

siderable recruitment in the spring following these eataetrophies and sub-

sequent recovery of the sediments during thc winter. ~he few speeies which

permanently seem to have withstnnded thc oxyg~n depletion were old speei-

mens of tbe bivalves Astarte elliptieu, lila truneata und Cyprina islandica.

Similarly, in LUbeek Bay cast of Kiel Bay the last survivors in a region

of low oxygen eoneentration were c. islandiea, Harmothoe spp., H. spinu­

losus and D. rathkei (Sehultz 1968).

Arntz (1977), in hio report of reeolonization experiments, elearly dc-

monstrated the extremely rapid recolonization by Capitella capitata as

L

10.

ORGAllIC ElmICIDJEllT Alm OXYGEN ~EF:(EnCY

Organic enrichment in combination with poor water exchange is known to

cause oxygen depletion in fjords and estuaries. The far most reports

concerning such effects on benthic fauna1 communities are from enrich-

ment by sewage and pulp mill effluents. Tbe weIl documented effecta of

the pulp mill in the Saltkällefjord in Sweden was estimated to reduce

the macrobenthic biomass in an 1.5 km2 area by about 60 tonnes. Simi­

~arly~ a pulp eill effluent in the Gulf of Bothnia (northern Baltic)

1 "km2 6wiped out al macrofauna in an 1 area, also esttmated to 0 tonnes

tt of missing biomaso (Rosenberg 1976). Subsequent to pollution abatement.and improved oxygen conditions in the Saltkällefjord the first colon1zers

were Capitelln capitata and Scolelepis fuliginoa (Rosenberg 1972).

These two spccies were also among the dominants on the heavily enriched

bottomo outside a pulp mill discharge point in Loch Eil, Scotland

(Pearson, 1975).The Idefjord, Swedcn-NorwayAnother example of the deterioration by pulp millo wastes in fjords is

from the Idefjord on the border between Sweden and Norway. Tbe wbole

water column inside tbe two main sills io anoxic most of the year due

• to the pulp mill and sewngc discharges from Halden (Fig. 8). In 1967-68

Dybern (1972) found a otrong reduct10n in number of macr~benthic spe­

eies from ~he mouth of the fjord and invmrds. At about point A in FiC. 8

he recorded 130 specieo, at point B 80, and at point C 35' ·species.

Inside point C no macrofauna was found on the bottoms(shaded aren in the.figure).The numbers given in Fig. 8 are from arecent report by Afzelius

(1979) and comprise thc ycars 1974-1978. ThuB, thc.situation has been

similar over the-last ten years. However, in 1925 a rich fauna (24 species)

was found by Agassiz-trawling close to the island west of Halden (Jäger­

skj~ld, 1971), indica~1ng the poss1b111~y offauna1 recovery ~o11ow1ng the

po11u~1an aba~emcn~ which ~ll be introduQcd this year. The shares ware

L

11.

investigated at 10 localities and Afzelius reported no anfmale on the io­

calities closeet to Halden. However, further away in tbe inner branch litto.

ral animals were present again, indieat1ng ox1c cond1t1ons in the surface

water.

Also tbe Oslofjord bas changed due to pollution during tbe last century.

In reporte of investigations performed a hundred years ago neith~r pol­

lution, decaying sediments, nor azoie areaa were mentioned aecord1ng to

Beye;'(196S). He listed three faunal groups, wb1ch were abundant in his

epibenthic samples on polluted bottoms; Spionidae, Hes10nidae and l1udi­

branohia. Among thc spionidea Polydora oiliata seems to have been tbe

dominant.

DISCUSSION

Oxygen depletion is a widespread phenomenon in stagnant marine basins.

It ooeurs naturally and in combination with organio enr1chment, which

aots as an aooellerator towards depletion. De-oxygenation of the bottom

water affeots the'interstitial water and results in an emerging redox-

.. cline concentrating the infauna at the top sediment layer. This prooess

1s accellerated by temperature, and periodic annual oxygen depletion is

L

12.

known to oeeur predominantly in late summer on the nQrthern bemisphere

(Pearson and Rosenberg, 1978). The examplea given above of effects of oxy­

gen depletion on benthic animals in fjords and estuaries are all from nor-

thern Europe. It is evident, however, that aa a consequence of. anoxia vast

areas are missing macrosoopio animals_and, thereby, enormous potentials

for fiab food production.

In several of the examplcs vertical oxygen concentratiob gradients ware

prevailing. However, the benthic communities are. not responding to this

4t gradual change in oxygcn concentration ~th a gradual decrease in rich­

ness and diversity. Rather, tbe notable deterioration of the communities'

. -1seems to begin rather abruptly at a concentration of ap~roximately 2 mg 1

?f oxygen as indicated by .the generalized SAB-diagram in Fig. 9. Below

that coneentration only a few species seems to be able to survive prolonged

periods and no species are directly favoured by increased abundance during

such conditions. Indirectly. however, opportunists are favoured in that

they take advantage wbcn oonditions improve. Tbey are the first colonists

and utilize tbe aceumulated food until thcy are outeompeted by seeond inva-

ders.

Based on the results presented in this review it seems reasonable to do. ~el~tio~~~

the following generalized categorization of macrobentbic species ln,··their

tolerance to low oxygen concentrations in nature:

13.

1. non-tolerant spccies

Species unconnected with oxygen depletion, i.e. most species.

2. Tolerant species

Species survivins periodic oxygen depletion. Species belonging to

this group are mainly mollusca (~Astarte, Corbula, Mla, Cyprina).

~imil~ reaults have been reported based on laboratory experiments,

.~ Theede 1973).

• 3. ,TransitOry opportunista

Species colonizing the bottoms as soan as oxygen conditions improve.

These species tolerate, even as larvae end juveniles, organically

enriched sediments with low redox-potentials. Species belonging to

this group are mainly polychaetes (~ Capitella, Polydora, Pseudo­

Eolldora, Scolelepis).

4. Transitory emigrants

Mobile species inhabiting the vicinity of the oxygen depleted bottoms.

•When cond1tions improve for shorter or longer periods they emigrate

into the area. Representative species are crrant polychaetes (Har­

mothoe, 0Ehiodromus) and cumaceans (Diastylis).

It has rep~atedly been argued that opportunistic species, mainly capi­

tellides and spionidea, are exceptionally tolerant to low'oxygen con-

centrations. However, in all cases presented here, opportunists are pio-,

neers on deserted bottoms at the very moment orJgen cocentration goes

up again. (See also Hiscock & Hoare 1975; Uatling 1975.) Such is their

adaptation, and they are not particularly tolerant to oxygen depletion,

aso shown in experiments by~ Henriksson (1969).

14.

It is impossible with our present knowledge to evaluate the ecological

eonsequenceo of the vast areas missing maerofauna due to oxygen deficiency.

The production of demersal fio~ood is lacking in these anoxie areas, but

oxic vmters in the vieinity could have been stimulated to inereased pro­

duetion,~ anoxie leads to increased release of phosphorus whieh might

increase primary produetion and atthe end more fooq is produced·for the

benthic animals. Thus, oxygcn deplction could have both negative and

positive effects if the total production of larger regions are considcred.

The direet effeets on the benthic macrofauna in anoxie areas ean be esti-

mated snd comparcd 'by ealeulating the missing biomass, i.e."the macro­

benthie biomass that probably would have been preocnt i~ the'area was

permanently o7.ic. Thc results given in Tab. 1 are to some extent bascd

on rough approximations and should not be used by administrators to make

economical calculations, but are rather put forward to stimulate eoo10-

gists to future studies about the eeological consequences of such vast

defaunated areas. References to the ealculations of most of the figures

are givenin the previous sections. The missing biomass in thc Limfjord

at the time of most serious oxygen depletion in autumn could be approxi-• mately 71 g -2m ,which was presented as a mean va1ue in shal10w wators

above the ha10cline ~or adjacent coastal arens in Sweden (Rosenberg and

llöller 1979). The area without mncrofauna in thc Idefjord··(Fig. 8) has

been deflned to depths below 10 m snd calcu1ated from a sea-chart, 1.e.

it is an underestination. The mean value of missing macrofaunal biomaos

in the Idefjord io taken from the mean presented beloTI the ha1oc1ine in

adjaeent waters (Rosenberg and Möller 1979). It is evident, based on the

figures in the table, that oxygen depletion creates enormous defaunated

bottoms in Scandinavia and that the most extensive effects are due to

natural reasons,~ geomorphological ch~raeteristics of the \yater bo­

dies leading to stagnation, and that only.a minority is caused by orga-

nic pollution.

REFEREUCES

AfzeliUs, L. 1979: Nasjonalt program for ov~rväkning av vannressurser.

Utvikling os status i Iddefjordens biologie Norsk insti­

tutt for vannrorsknin~, rapport 0-75038, 50 pp.

Arntz, W. E. 1971: Biomasse und Production des Makrobenthos in den

tieferen Teilen der Kieler Bucht ~ Jahr 1968. Kieler

Meeresforsch. 27;36-72.

Arntz, W. E. und n: Brunowig. 1976. Studios on structure and dynamics

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(SF~ 95-Kiel). In: Prece~dings of the 10th E~ropean SYm­

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soone & E. Jaspers, Universa Press, Wetteren, Belgium,

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Arntz, ·W. E. and D. Drunswlg: Zonation of macrobenthos in the

Kiel Bay channel system and its implications for demeroal

fioh. Pr. morsk. Inst. ryb. Gdyni (in press).

Beyer, F. 1968: Zooplankton, zoobenthos, und bottom sediments as rela­

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Elmgren, R. 1975: Denthic mciofauna as indicator of oxygen conditions

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11 1979: Structure and dynamics of Baltic benthos communities,

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(in press).

Elmgren, R., R. Rosenberg, A. B. Andersin, S. Evans, P. Kangas,

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macro- and meiofauna in tbc Gulf.of ~othnia (NorthernBaltic). Pr. mor~k. "tnst. iyb. Gdyni,(in press).

16.

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Jörgensen, ~. B: Seasonal oxygen deplet10n in the b~ttom vmters

of a Danish fjord and ita effect on the benthic community.

Oikos (in press).

Kitching, J. A., F. J. Ebl1ng, J. C. Gamble, R. Hoare. A. A. Q. R.McLeod and T. A. Norton. 1976: The ecology of Lough Ine.

XIX. Seesonal cbanges in tbe western trough. J. Anim.

Ecol. 45;731-157.

Leppäkoski,

«

«

E. 1969: Transitory return of the benthic fauna of thetafter)

Bornholm Basin~ (extermination by oxygen.insufficiency.

Cah. Biol. mare 10;163-172.

1911: Benthic recolonization of the Bornholm bas1n

(Southern Baltic) in 1969-71. Thalassia jugosl. 7,171-179.

1975: Macrobenthic fauna'as indicator of oceanization in

the south~rn-Baltic. Merentutkimuslait. julk. Skr. No.

239,280-288.

Pearson, T. -H. 1975: The bcnthic eoology of Loch Linnhe and Looh Eil,

-s sea-loch sy~tem on the·.w~st coast of Scotland.IV. Changes

in the fauna attributable to organic enricbment. J. eXR.

mare Biol. Ecol. 20;1-41.

17.

Pearson, T. H. and R. Rosenberg. 1978: Maorobenthic succession in rela­

tion to organic enrichment and pollution of thc marine en­

vironment. Occanogr. Mar. Biol. Ann. Rev. 16.229-311 •.

Rosenberg, R. 1972: Benthio faunal recovery in Swedish fjord following

the closure of a sulphite pulp mille Oikos 23.92-108.

•

"

"

1976: The relation of treatmen~ and ecological effects in

brackish water regions. rure Appl. Chem. 45,199-203.

1917: Benth10 macrofaunal dynam1cs, produot1on, and dis­

persion in an oxygen - deficient estuary of west Sweden•

J. exp. mare Biol. Eool. 26,107-133.

Rosenberg,' R., I. Olaoon and E. ölundh•. 1971: Energy flow model of an

oxygen - defioient estuary on the Swedish west ooast. Mar.

Biol. 42~99-107.

Rosenberg, R. and P. Möller. 1979: Salinity stratified benthio maoro-

faunal oommunities and long-term monitoring along the west

coast of Sweden. J. eXE. mare Biol. Bcol. 37, 175-203.

Schultz, S. ·1968: Rüokgang des Benthos in der LUbecker Bucht. Monats­

beriohte Deutschen Akad. Wisse Berl., 10,748-154.

Theede, H. 1973: Comparative studies on the influence of oxygen defi­

ciency and hydrogen sulphide on marine bottom invertebra­

tes. Neth. J. Sea Res. 7/244-252.

Watling, L. 1975: Analyois of structural variations in a shallow estua-.rine deposit-feeding community. J. exp. mare Biol. Eool.

~.,.·215-3'3.

Zmudzinski, L. 1917: Thc Baltic deserts. Ann. Biol. 32;50-51.

Table 1. Approximative estimation of missing macrofaunal

biomass (wet wt) in same anoxie waters in Scandinavia.

For references see text.

AREA MEAN :BiOMASS :BIOMASS YEAR

in km2 -2 MISSINGgm tonnes

:Byfjord 3.41 146 498 1971-74

Saltkälle~jDrd 1.5 60 1968

Nätra,fjärd 1.0 60 1969-72

e :Baltie 84000 20 1680000 1975

L1mfjord 330 71 23430 1973-78,periodically

Idefjord 13.9 146 2029 1967-78

•

LEGDIDS

Fie. 2.

Fig. 3.

Fig. 4.

Simplified diae:rwn showing the effects of oreanic input to

the marine environment in relation to water .renewal (rrom

Pearson and Rosenberg 1918).

Number of speeies (S, per 0.5 m2 ), abundance (A, per m2 ) and

~~.omass (B, per m2

) in relation to deereasing oxygen con­

centrations (mg/I) by increasing depth in October 1971 in

the Byfjord, Sweden. Oxygen concentration was at a minimum at

that tire (see Rosenberg 1971). (Hydrobia spp. exc1uded at

station 8.)

Distributio~ and abundance of Pseudopolydora Eulchra in. relation

to depth and oxygen saturation from July to September 1970 in

LouCh Ine, Ireland. Open circ1e indieates that no~. pu1ehra was

found. (Hodified after Kitching ~&. 1976.)

Extension of the bottom deserts (shaded areal in the Ba1tic in

1915 according to Zmudzinski (1971). The desert area in tbe

central Baltie was 17 000 km2

and in the Bornholm basin 1 000 kr.2

•

Examp1es of benthic faunal conposition given in the text are from

western eentral Baltic (A), the Bornholm basin (B), and the Kiel

Bay (e).

Fig. 5. Oxygen concentration (ml/l), number of taxa and biomass

wt), a11 on x-ans, in relation to depth in the western

Baltic in 1912. (Hodi:fied after E1mgren 1975.)

(g/m2 , wet

central

Fig. 6.

Fig. 7.

Number of speeies, ~an abundance and oxygen eoncentration durinr,

1967 to 1971 below 80 m in the Bornbo1m basin (southern Baltic).

Tbe diagram is based on data from Ieppäkoski (1969: Tab. 2;

1971: Fig. 2; 1975: Fig. 1).

Abundance of the polychaetes Scoloplos armi ser and eapitella

capi tata in experimntal boxes in relation to oxygen concentration

during 1972 to 1974 at 20 m depth in Kiel Bay (south-west Baltic).

(}.~o~fied after Arntz 1977.)

•

•

Fig. 8.

Fig. 9.

The Idefjord between Sweden and Ilo1'"\o7ay. NWrber of macrobenthic

species and doninants found at the si tes At Band C during 1974

to 1978. No benthic fauna was recorded be1o'W' 2 m inside site C

(shaded area). Number of species quall tati ve1y co11ected at ten

sites along the shores are indicated by the filled circ1es.

FaUl'lal data from Afzelius (1979). Insertedis the extension of

H2S and axygen concentration in August 1968 (fram Dybern 1972).

The discha.rge of pulp mi11 wastes occurred at Halden •

. Generalized diagramatic presentation of macrobenthic SAB-curves

(Speeies-Abundance-Biomass) in relation to approximate oxygen

concentrations (mg!l) •

Fig. 1.

Input

ORGANIC MATTER

Sedimentot ion,11

REDUCED 0 1 : EMERGING EhIN WATER tiN SEDIMENT

Weil. ~ flushed.r--------..,......r-

OXII;>IZED SEDIMENTWITH PLENTIFULFOOD SUPPlY

High Bioturbation

HIGH BIOMASS

HIGH ORGANICeONTENT IN SEDIMENT

BACTERIAlDECOMPOSITION

moderate waferre-, I1 newol

Few .11 niches

POOR MACROfAUNA

Stagnation

ANOXie SEDIMENTAND OVERlAYINGWATER

NO MACROFAUNA

Fig. 2.

2

3

1

20 440

'------+--+--+----4._-+--1 m

1211 8 5

10810

64

.'...•~/ ........../ ..- "-

/' .' '..S • ....•.. •... \

ß b,' •••••••• \

"".\ A

A \\

\\\•~\\.. ----.

.", \. "-. ... ""A~······· ..A ".~-•....... "-.... 0

14 16 DEPTH, m20 13 STATION

o

No.OF SPECIES

I D BIOMASS :::.99N.30

500 10

1500

1000

L

Fig. 3.

o

108

o 1000l-L.J

IND. m2

'" 0cu 20 8....1»

8E ...~.c 301:1.tJ

0

.408 0

0 8AUGUST SEPT.

L

r

•

Fig. 4.·

...

.'

o

E- 50J:

Ii:wo

100

o 5

--- TAXA....... BIOMASS

10

Fig. 5.

,r,,; . ,,"

•

Ind./m2 (_...~

1967 1969 1971

..

. .,

r..

...

Inrm I' Scotoplos

1400I ..\I \

.', \

.... CapiteUae 1200

J \.. ..: \: ,, I

.. •.. .... ..1000

.. :.., .. •I • .... .... •.. ..

I , • •.. •.. •

800• :

/.. •, .. .... .... .... •

/ , .. .... .... .... •/

.. ..600 , • ....:. •..

02my[/.... •

I • ..: ../

• .... •.. .., I ..ltOO

..I 8: \°2I :: 6·I · \..·

200..

e' · '-tI 1,.. 20 0

'72 1973 '74

r -~---.,~ • 1 •

121• •mphi" ·uro filiformls

A .t.daAbra ru ICorbula glbbaGl era alba

yc gracilisSosane1 .. minutaPhooe tOSQChaetozone se

o 2 4 6 km

>'IiJ....l7:l•CD•

L

'.••

o

5A --=-~_------B -- ......... -- ............. .....-........... \", \'. ".\

~\. \.. ,.. \.••.\'. \'. ,\,'. \

'. "'. \.. \". \.,

6 , 2 0

OXYGEN CONCENTRATION

Fig. 9.