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?
Jan 21, 2016
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