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?

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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 Shore Rocky 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 Shore The 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 Shore Species 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 fronds reduce water loss by trapping water in the downward facing channels Ingrained black lichen

The Middle Shore The 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 0.69  m Shore crabs, anemones, flat periwinkles, limpets and mussels are some of the animals found inhabiting the middle shore

Pairs of air bladders keeping the fronds afloat for maximum photosynthesis

The Lower Shore Environmental 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 the commonest species of the lower shore

The Laminaria Zone The Laminaria Zone is occupied by species that are rarely uncovered by the tide but are subjected to 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 a large 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 growth These giant algae are intolerant of desiccation and possess flexible stipes that attach firmly to the ocean bottom with 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 cannot tolerate 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 microscopic algae 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 Diversity The 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 pattern of brown seaweeds on the sheltered rocky shore Organisms inhabiting the upper shore are subjected to fluctuating environmental conditions and the drying effects of the air during the tidal cycle