succession what changes occur in the variety of species that occupy an area over time? what are...

Succession

• What changes occur in the variety of species that occupy an area over time?

• What are meant by the terms succession and climax community?

A

B

Plan an investigation to consider the distribution of living

organisms on this shoreline.

• How will you collect your data?

• What abiotic factors will you need to measure?

• How will you do this?

The Rocky ShoreRocky shores are diverse and dynamic ecosystems where the inhabiting communities survive between

two worlds – the sea and the land

The familiar shoreline or littoral region is that area of shore which lies between the high-water mark and the low-water

mark of spring tides

Living organisms in these intertidal regions face continual fluctuating environmental conditions as they are subjected

to cyclic exposure and submergence from tidal activity

The distribution of life on the littoral shore reflects the development of specialised structures and tissues that adapt

the different species to the prevailing conditions

Diversity on The Rocky ShoreThe sheltered rocky shore provides a variety of

habitable environments where the diversity of species and the population of each species can be related to

their positions on the shore

The sheltered rocky shore described here is located on the east coast of North Yorkshire where encrusting barnacles and

mussels and seaweeds dominate the shore

The following discussion describes the findings of a group of students who surveyed the shore and who carried out a number of investigations based upon their observations

The Upper ShoreSpecies occupying the upper shore generally

experience only one to two hours of immersion by the sea, and face problems associated with drying out

(desiccation)Temperature and salinity fluctuate widely on the upper shore,

and the growth and productivity of inhabiting organisms is low

The ingrained black lichen, Verrucaria maura is found covering the bare rock of the upper shore and the brown alga, Pelvetia canaliculata (channel wrack) dominates this area of the shore

The presence of Pelvetia canaliculata is an indicator of the high water mark and this species displays a number of adaptations

for resisting desiccation; these include:

• Rolled fronds for trapping moisture• An oily layer covering the cells• Thick cell walls (mean thickness 1.5 m)

The rolled frondsreduce water lossby trapping waterin the downwardfacing channels

Ingrained black lichen

The Middle ShoreThe species occupying the middle shore are covered

by the tide for 50% of the day and desiccation is a less severe problem than on the upper shore

The dominant algal species on the middle shore of this site was found to be Fucus vesiculosus (bladder wrack).

Fucus vesiculosus is intolerant of desiccation and displays the following features:

• Pairs of air bladders that provide buoyancy and float the fronds towards the light

• Cell wall thickness 0.69m

Shore crabs, anemones, flat periwinkles, limpets and mussels are some of the animals found inhabiting the

middle shore

Pairs of air bladderskeeping the fronds afloat for maximum

photosynthesis

The Lower ShoreEnvironmental conditions on the lower shore are

less harsh and relatively stable as surface populations are never uncovered by the tide for more than a few hours at a time

Species diversity is high on the lower shore and competition for food and space is fierce

Fucus serratus (toothed-wrack) is the dominant brown alga of the lower shore and is intolerant of desiccation

(cell wall thickness 0.45 m)

Red algae are intolerant of desiccation and form dense turfs beneath the carpet of Fucus serratus; these algae are tolerant of shade and possess the additional pigment (phycoerythrin)

for efficient photosynthesis at low light levels

Sponges, anemones, sea slugs, blenny fish and shrimps occupy this zone alongside many other species of animals and algae

This species is intolerant of desiccation and is thecommonest species of the lower shore

The Laminaria ZoneThe Laminaria Zone is occupied by species that are

rarely uncovered by the tide but are subjectedto intense wave action

Environmental conditions in this zone are relatively constant and productivity is high; this is the least harsh area of the rocky shore providing niches for the establishment of alarge diversity of organisms where competition is fierce

The kelps (Laminaria species) are the dominant brown algae of this zone where they form underwater ‘forests’

displaying prolific growthThese giant algae are intolerant of desiccation and possess

flexible stipes that attach firmly to the ocean bottomwith their powerful holdfasts

Starfish, brittle stars, marine worms and sea urchins are found feeding in this zone

Numerous, shade-tolerant species of red algae are found growing among the kelps

These kelps cannottolerate any degree

of desiccation

The limpet (Patella vulgata) is found in all zones of the seashore and uses its powerful muscular foot to create a ‘vacuum’ that clamps this

mollusc to the rocks; the limpet grazes on the microscopicalgae at the surface of rocks

These mussels secrete threads by which they cling to the rocks and to each other; this close packing protects them from

predators such as the dogwhelk

Barnacles are filter feeders that inhabit all zones of the rocky shore and whose feather-like limbs filter suspended material from the sea

water; intra-specific competition and temperature are two of the factors that influence their distribution

The dogwhelk (Nucella lapillus) is a carnivore and feeds on the limpets, mussels and barnacles inhabiting the middle shore.

Dogwhelks are in turn preyed upon by crabs

This shore crab (Carcinus maenas) shelters under sea

lettuce (Ulva lactuca) to avoid environmental

stresses

The sea anemone extends its tentacles to

feed on crustaceans and small fish

Zonation and DiversityThe zonation of both plants and animals observed on this

sheltered shore reflected adaptations to different environmental conditions, with diversity increasing from

the harsh upper shore to the less harsh lower shore

The brown algae displayed a distinctive zonation pattern that related largely to their ability to resist desiccation

and to photosynthesise effectively

Brown algae have developed specialised structures and tissues for reducing desiccation, anchoring themselves to the rocks and ocean bottom, and photosynthesising effectively

Zonation patternof brown seaweeds

on the shelteredrocky shore

Organisms inhabitingthe upper shore are

subjected to fluctuatingenvironmental conditions

and the drying effectsof the air during the

tidal cycle