Rocky shore ecology Flashcards
What is the rocky shore
The interface between sea and land, its a Benthic environment with large particle size (rocks rather than sand)
Area between high and low water (littoral zone) Subdivisions include supralittoral, eulittoral and sublittoral
The term intertidal is misleading as not all rocky shores experience tides and other gradients other than tides define patterns (like waves)
Why is rocky shore important
Its important due to its species diversity
The resources available and morphology of the
habitat support a high number of species in close proximity
Its perfect for studying the relationship between habitat complexity and species diversity
What did charles darwin notice about barnicles
how barnacles live in close
proximity, this lead to the thought of possible existence of interspecies competition.
The removal of Balanus favoured growth of
Chthamalus
* Previous studies conducted in labs. One of the first to test an ecological model in the wild
What are the gradients of the rocky shore
Wet/dryness, Wave action, Particle size and salinity
Wet/dryness
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 upperlimits such as: Movement, Shell morphology, Metabolic rates (slower in tolerant spp.).
Biological pressures influence lower limits such as, Predation and Competition
Wave action
- Wave action is determined by fetch and wind →
drives period, height and swell - Steep cliffs with deep water = maximum impact
- Shallow coasts with kelp beds = minimum impact
- Preventing displacement by waves: Timing, Positioning (scale dependent), Burrowing, Attachment (e.g. byssal threads, cementing)
Particle size and salinity
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
Zonation in the rocky shore
Organisms are grouped by shared conditions such
as:
* Niche partitioning
* Physical and biological forces e.g. Chthamalus
barnacles
* Upper limit desiccation tolerance
* Lower limit competition
However, much variation and many exceptions
* Focus on environmental gradients as drivers of
species distribution rather than zonation
What is a functional group
A functional group is a set of species, or collection of organisms, that share alike characteristics within a community
What are the different functional groups in the rocky shore
Primary producers, Grazers, suspension feeders, predators
Primary producers
Algae, lichens and cyanobacteria
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)
Grazers - Sweepers
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
Grazers - Rakers
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
Grazers - Diggers and abraders
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
Grazers - Biters and cutters
Biters & cutters: fish & majid crabs
* Herbivorous fish – scrape algae from rocks
(e.g. blenny). Some feed on large algae but
mostly in tropics.
* Majid crabs – chelids cut through algae (e.g.
spider crabs)
* Nudibranchs – some are rakers, others
puncture algal cell walls
Suspension feeders - Individuals
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). Sub-
phlylum Tunicates are found Australia, S.
Africa & S. America
Suspension feeders - Colonial
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
Predators - Borers and drillers
Borers and drillers: Whelks
* Prominent on rocky shores
globally. E.g. Nucella and Thais
spp.
* Proboscis effective
* Bore into shells or push
between shell plates
* Once through the shell, radula
rasps upon soft tissues
Predators - Crushers and crackers
Crushers & crackers: (non-grapsid) crabs (Omnivorous)
Portunidae (swimming crabs)
* Fast-moving & aggressive with sharp chelae.
E.g. Carcinus maenas & Necora puber
Cancridae (edible crabs) and Xanthidae (stone crabs;
W. Atlantic only).
* Large, slow moving
Predators - External digesters
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
Predators - Browsers and partial predators
Browsers & partial predators: Nudibranch molluscs
* Feed on sessile prey: Bryozoans, sponges, colonial
ascidians, hydroids & soft corals
* Huge diversity of body forms (>2,300 spp.)
* Aposematic colouration
* Nudibranch radula apparently effective at removal
* Radula shape linked with prey type
Predators - Mobile vertebrates
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
Predators - Sit and wait
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
