Rocky Shores

Phyla in rocky intertidal shore:

• Mollusca
• Arthropoda
• Chordata
• Echinodermata
• Cnidaria
• Porifera

Macrofauna/flora - animals/algae over 1mm

Meiofauna - animals/algae under 1mm size

• Ostracods
• Amphipods
• Gastropods
• Forams
• Diatoms

Macroalgae - seaweeds and divided into Rhodophyta (red), Chlorophyta (green) and Phaeophyta (brown)

Form species-specific zones between upper and lower shore - giant biomass

Not that important for direct energy supply - most biomass is degraded to detritus and exported to detrital food chain

Seaweeds - 3 methods to survive from grazers

• Escape into inaccessible crevices
• Tolerance
• Deterrence - structural (calcareous elements) and chemical defences

Kelp forests - subpolar regions and 20C summer isotherms except for upwelling in subtropical 

Benthic microalgae prevalent on wave-swept shores

Phytoplankton imported with tides - provides food for suspension feeders

Intertidal regions - limpets and periwinkles

Subtidal - sea urchins

Dominant grazers are molluscs

Limpets' radula teeth = hardest biomaterial on Earth

Grazers feed on biofilms and seaweed fronds

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

Most sessile

Situate themselves where water movement supplies with plankton and detritus in suspension

Dogwhelks - radular drills circular holes in shells

Shore crabs - pincers crack open shells

Starfish - evert stomachs

Oystercatchers - thick beaks crack shells

Humans

Important role in structuring communities - starfish control barnacle lines on shores

Dogwhelk radular feeding - fossils found with circular holes in

Species distributed vertically according to capability to cope physiologically w/ changes to biotic/abiotic interactions

Vertical extent of shore - increase from few metres (sheltered) to 30m (extremely exposed)

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

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

Patterns or vertical zonation caused by:

• Larval settlement/adult preference
  • Unlimited recruitment/limited space = lower limits set by dominant competitor presence
  • Zonation breaks down w/ low recruitment - no space competition
• Physiological tolerance to variables
  • Stress increased closer organism is to land
  • Emersion = heat and desiccation stress - bufffered by seaweed canopies and crevices
  • Topography and aspect - affect heat/light levels

• • Behaviours/morphological adaptations - modify distributions
    • Moving into crevices
    • Mushrooming
    • Inhabiting rock pools
    • Hiding under algal canopies
  • High water (spring tides) = higher upper limits for species
• Biological interactions - interspecific competition, predation and growth
  • Supply-side ecology - recruit supply influence zonation patterhsn

Upper limits of zonation - physical factors 

Lower limits of zonation - biological factors

Exceptions - limpet distribution set by predation on upper and competition for space on lower

Direct developing - juveniles hatch from eggs and crawl away - dogwhelks

• Positives
  • Predictable food source
  • No water column predators
  • Entire life cycle in 1 area
  • Suitable habitat when hatched

• Negatives
  • Large energetic cost for mothers
  • Few eggs produced
  • Poor dispersal - limited gene exchange
  • Benthic predators

Leithotrophic - larvae planktonic using yolk-sac as nourishment e.g. limpets

• Positives
  • Own food supply
  • Less time as plankton = less time for predation
  • Close to suitable habitat

• Negatives
  • Fewer larvae produced
  • Lower dispersal distances

Planktotrphic - larvae free-swimming and feeding

• Positives
  • Large number produced (scattergun approach)
  • Stay in water column for long time - high dispersal distances from parents

• Negatives
  • Unpredictable food source
  • Long exposure to predators
  • Last development stage timed when suitable habitat found for settlement - high probability of missing mark

70% bethic invertebrates - planktonic larvae

Larval settlement not random - chemical and physical cues

Theories on bi-phasic life history (larval and adult) evolved:

• Different food sources - reducing competition
• Pelagic larvae disperse long distances - colonisation of new regions = increase gene flow
• Break parasitic life cycles
• Pelagic larvae - no benthic predators

Competition important where resources limit

Primary limiting resource - space

3 types of competition:

• Exploitative - ability to harvest limiting food resources
• Pre-emptive - compeititor recruits and dominantes space
• Interference - compeitior physically contests resources

Large size/rapid growth = competitive dominance

Adults can somtimes outcompete juveniles or different sexes (sexual dimorphism)

Dominant grazers = limpets - shown by marks on rocks by radula

Only female territorial - defend their 'garden', knocking competitiors off their home range

Owl limpets - important Californian grazer

• Larger owl limpets = grazer large areas than smaller individuals = home range scaling
• Larger limpets more likely to be harvested for food = amount of grazing space reduced
• Females eaten first - bigger = male take over old home range and become female
• Other species will colonise - limpets may not regain large territories 
• = Many small territories

Home range scaling - the larger an organism the larger its' home range is because of more food it needs to eat

Rocky shore communities are complex - direct and indirect species interaction effects

Predators can mediate interactions between competitors - otherwise competitive exclusion occurs

= Hierarchy of compeitive and predatory relationships develop

Structure of communities is complex of:

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

Biogeography - study of geographical distribution of fauna and flora

Range limit - geographical boundary beyond which a species doesn't occur

Species range limits affected by life history, population genetics, abundance distribution, spatial availability of habitats, oceanographic/atmospheric factors

Habitat gaps - caused by short dispersal period for larvae

British Isles - transition zone between 2 community types - warm southern species and boreal cold north species

Souther Africa - Benguela upwelling affects primary production, biomass, offshore flow and diversity - West coast has high productivity and East coast has low

Affect rocky shores:

• Climate change - marine and atmospheric changes - alters biogeography (southern warm species moving north)
• Ocean acidification
• Harvesting - size-selective harvesting catches bigger ones first
  • Easy to catch and constant food source
  • Evidence of human beginnings shown in shellfish fossil size range - potentially influenced human brain development
• Trampling
• Pollution
• Artificial substrates e.g. rip rap, groynes
  • Biodiversity similar to natural
  • Increases habitat availability
  • Reduces habitat gaps - increases geographic ranges
  • Connects populations = gene flow
  • Invasive species can use as stepping stones