rocky shores Flashcards
what is a rocky shore?
- The interface between sea and land, with large particle size (rocks rather than sand)
what are the subdivisons of the rocky shores called? and what do they mean?
Subdivisions include supralittoral, eulittoral and sublittoral
- Supralittoral: above the high-tide mark and is usually not under water
- Eulittoral: breaking waves to a depth of 5 to 10 metres (16 to 33 feet) below the low-tide
- Sublittoral: beyond the low-tide mark and is often used to refer to substrata of the continental shelf, which reaches depths of between 150 and 300 metres.
what are the importance of the rocky shores?
- Species diversity
- Habitat complexity and species diversity
- Interspecific competition
what is Interspecific competition
between individuals of different species
what is the wetness/dryness of the rocky shore determined by/like?
- Defined by distance from the low tide position
- All rocky shore species are marine so unable to survive indefinitely out of water
- Tolerance to desiccation influences upper limits- movement, shell morphology, metabolic rates
- Biological pressures influence lower limits- predation, competition
what is the wave action of the rocky shore like?
- Defined by distance from the low tide position
- All rocky shore species are marine so unable to survive indefinitely out of water
- Tolerance to desiccation influences upper limits- movement, shell morphology, metabolic rates
- Biological pressures influence lower limits- predation, competition
what is the Particle size and salinity like at the rocky shore?
- Particle size- Varies greatly due to wave action and substrate (deposition vs erosion), Species diversity is highest for median levels of disturbance
- Salinity- Most marked in estuaries and rock pools, Some hypersaline due to evaporative loss, Others have low salinity levels due to rainfall/ runoff
what are the functional groups of species on the rocky shores?
- Primary producers
- Suspension feeders
- Grazers
- Predators
what are the species in the primary producers?
Algae, lichens and cyanobacteria
Algae, lichens and cyanobacteria facts
- Microalgae -Biofilms: cyanobacteria, macro-algae spores and diatoms
- Simple algae (filamentous and foliose) -Short-lived with few defences from grazers
- Complex algae (canopy forming)-Red, green and brown, Some protection from grazing
- Encrusting algae- Calcifying (CaCO3 )
what species are apart of suspension feeders
- Individuals: Barnacles, mussels and solitary ascidians
- Colonial: Polychaetes, bryozoans, sponges and ascidians
Individuals: Barnacles, mussels and solitary ascidians
- Barnacles – strainers. Much variation in size (e.g. Megabalanus). Global
- Mussels – siphonal. Mytilus & modiolus are global.
- Large solitary ascidians (sea squirts). Subphlylum Tunicates are found Australia, S. Africa & S. America
Colonial: Polychaetes, bryozoans, sponges and ascidians
- Polychaetes – Sabellaria forms large structural mats
- Bryozoans (Phylum) – Colonies can be encrusting or foliate
- Sponges – body consists of flagellated cells which can draw in water
- Ascidians – colonies join but avoid non-kin
Grazers species
- Sweepers: Topshells and nerites
- Rakers: winkles, isopods, amphipods & grapsid crabs
- Diggers & abraders: limpets, chitons and urchins
- Biters & cutters: fish & majid crabs
Sweepers: Topshells and nerites
- Trochidae – small primitive gastropods, wideglobal distribution. High diversity in tropics
- Neritidae – tropical, can excavate rock
- Rows of many small, blunt teeth to sweep up dislodged biofilm and detritus
Rakers: winkles, isopods, amphipods & grapsid crabs
- Littorinidae – Littorina obtusata on algae and Littorina littorea on rocks
- Mega-grazing isopods and amphipods – density up to 10,000 m-2
- Grapsid crabs - herbivorous crabs more common in the tropics
- Sharp teeth to dig into a bite off macroalgae
Diggers & abraders: limpets, chitons and urchins
- Prosobranch limpets (gills & no lungs) e.g. Patellids. Worldwide.
- Pulmonate limpets (lungs & secondary gills). Tropical
- Chitons (Polylacophora). Global but more common in warm waters
- Urchins (Echinoderms). Graze using Aristotle’s lantern
- Hardened teeth dig into rock surface
Biters & cutters: fish & majid crabs
- Majid crabs – chelids cut through algae (e.g. spider crabs)
- Nudibranchs – some are rakers, others puncture algal cell walls
Predators species
- Borers and drillers: Whelks
- Crushers & crackers: (non-grapsid) crabs (Omnivorous)
- External digesters: Starfish
- Browsers & partial predators: Nudibranch molluscs
- mobile vertebrates: Fish & birds
- Sit & wait: Anemones & hydroids
Borers and drillers: Whelks
- Prominent on rocky shores globally.
- Proboscis effective - Bore into shells or push between shell plates, once through the shell, radula rasps upon soft tissues
Crushers & crackers: (non-grapsid) crabs (Omnivorous)
- Portunidae (swimming crabs)- Fast-moving & aggressive with sharp chelae.
- Cancridae (edible crabs) and Xanthidae (stone crabs; W. Atlantic only), Large, slow moving
External digesters: Starfish
- Found submerged in water
- Tube feet to allow rapid (relatively) movement
- Feed on bivalves, sea urchins, snails, barnacles and carrion
- Everts stomach through mouth to engulf prey
- Potential as keystone consumers i.e. could trigger a trophic cascade if removed
Browsers & partial predators: Nudibranch molluscs
- Feed on sessile prey: Bryozoans, sponges, colonial ascidians, hydroids & soft corals
- Huge diversity of body forms (>2,300 spp.)
- Nudibranch radula apparently effective at removal
Mobile vertebrates: Fish & birds
- Fish at high tides, birds at low tides
- Highly active, not constrained by predator/ prey limitation
- Fish- Wide range of taxa inc. blennies & gobies, Clingfish on limpets
- Birds-Charadriiformes (waders & gulls), Passerines in supralittoral – some terrestrial
Sit & wait: Anemones & hydroids
- Sedentary Cnidarians - Global
- Sting prey with nematocysts
- Hydroids -Colonial, forming delicate cup-shaped polyps, cannot withstand desiccation
- Anemones- Gelatinous, Mainly feed on zooplankton but able to immobilize larger animals
