Rocky Shores

Phyla in rocky intertidal shores:

• Mollusca
• Atrthropoda
• Chordata
• Echinodermata
• Cnidaria
• Porifera

Macrofauna - over 1mm size

Meifauna - under 1mm size, caught in 45um mesh:

• Ostracods
• Amphipods
• Gastropods
• Forams
• Diatoms

Macroalgae - seaweeds

• Rhodophyta (red)
• Chlorophyta (green)
• Phaeophyta (brown - fucoids, kelps)

Species-specific zones between upper and lower shore formed

Great biomass of macroalgae but not important in direct energy supply. Most degraded to detritus and exported into food chain.

Survival from grazers - escape into crevices, tolerance (fast growth), deterrence (defences)

Kelp forests - subtropical and temperate regions

Benthic microalgae - prevalent on wave-swept shores.

Phytoplankton imported with tide - food for suspension feeders

Limpets and periwinkles - intertidal regions

Sea urchins - subtidal

Dominant grazers - molluscs

Limpet's radula teeth with hardest biomaterial on Earth

All feed on biofilms and seaweed fronds

Sponges, mussels, barnacles (dominant), tube worms, sea squirts

Sessile and situate where water movement will supply them with plankton and detritus in suspension

Dogwelks (drills holes in shells), shore crabs (pincers), starfish (evert stomach), oystercatchers (beak cracks shells) and humans

Important in structuring communities - control lines of grazers on shore

Dogwhelk radula feeding dates back to early - fossils found with circular holes in them

Distributed vertically according to physiologically coping with changes. May increase by few metres (sheltered) to 30m (exposed)

Ballantine Scale - describes changes in distribution of dominant sessile animals/seaweed in relation to tidal height and wave exposure.

Moderately exposed shores - distinct vertical zones, characterised by indicator organisms

Patterns on vertical zonation causes:

• Larval settlement/recruitment and adult preference
  • Unlimited recruitment and limited space = lower limits set by dominant competitor
  • Zonation breaks down with low recruitment - no space competition
• Physiological tolerance
  • Stress increased closer to land
  • Emersion = heat and dessication stress (buffered by canopies and crevices)
  • Topography and aspect - affect heat and light
  • Behaviours and adaptions - moving into crevices, dense groups, mushrooming, inhabiting rock pools, hiding under canopies
• Biological interactions - competition, predation, growth
  • Recruitment supply influences zonation boundaries (supply-side ecology)

Upper limits = physical factors

Lower limits = biological factors

Exceptions - limpet distribution set by predation (upper) and compeition for space (lower)

• Direct developing (30% benthic invertebrates) - juveniles hatch and crawl away e.g. dogwhelks
  • Predictable food source
  • No water column predators
  • Entire life cycle in one area
  • Sutible habitat once hatched
  • Large mother energetic cost - protection, eggs
  • Few eggs produced
  • Poor dispesal - exchanging genes problem
  • Benthic predators e.g. crabs
• Lecithotrophic - larvae planktonic using yolk-sac as nourishment e.g. limpets
  
  • Own food supply
  • Less plankton time - less predation
  • Close to habitat
  • Fewer produced
  • Lower dispersal distances

• Planktotrophic (70% benthic invertebrates) - larvae free-swimming and feeding
  • Large numbers produced (scattergun approach)
  • Stay in water column long time - increase dispersal distances
  • Unpredictable food source
  • Long exposure to predators
  • Last development needs to be time with good habitat - likely to miss the mark

Larvae settlement not random - chemical and physical cues

Theories on bi-phasic life history (larvae and adult)

• Larvae - different food sources, reduces competition between stages
• Disperse long distances - colonise new areas and increase gene flow
• Break parasitic life cycles
• Plagic larvae have no benthic predators

Competition important when resources limit. Primary limiting resource - space

3 competition types:

• Exploitative - harvest limiting food resources
• Pre-emptive - competition recruits and dominates space
• Interference - physical contest resources

Large size and rapid growth = competitive dominance

Adults can outcompete juveniles

Sexual dimorphism competition - larger sex dominant

Dominant grazers - limpets, marks on rocks from radula

Female limpets territorial and defend 'garden' (home range) - knock off competitors

Owl limpets - graze proportionally more area if larger (home range scaling) - more likely to be harvested for food though. Therefore male will take old range and become female + other species e.g. microalgae and barnacles colonise. = lots of small territories

Home range scaling - larger and organism is larger its home range as more food needed

Complex rocky shore communities with direct and indirect species interactions

Predators mediate interactions between competitors - otherwise competitive exclusion. Hierachies can develop Structure of communities is a complex of:

• Recruitment success (supply-side ecology)
• Resources
• Growth rates and body size
• Competitive ability
• Biodiversity
• Predatory effects
• Disturbance

Biogeography - study of geographic distribution of species

Range limit - geographical boundary beyond species does not occur

Species range limits affected by life history, pop genetics, abundance distribution, habitat avilability, oceanographic/atmospheric factors

British Isles - transition zone between 2 communitu types - warm southern species and boreal cold northern species

South Africa, Benguela -upwelling affects primary production, biomass, offshore flow, diversity. West coast = high productivity, East coast = low

• Climate change - alters biogeorgaphy, warm species move north in UK
• Ocean acidification
• Harvesting
  • Size-selective harvesting - affects home ranges
  • Easy to catch and constant food source]Human beginnings shown in shellfish fossil size range
  • Influence human brain development - DHA amino acid
• Trampling
• Pollution
• Atrificial substrates e.g. rip rap, gryones
  • Biodiversity similar to natural
  • Increases habitat availability
  • Reduces habitat gaps - increases geographic ranges
  • Connects populations = gene flow
  • Invasive species use as stepping stones