Rocky Shores Flashcards
Ideal habitat for study
Higher taxonomic diversity
Easy access for ecological study
Global habitat type
One of the oldest habitat types
Many groups well represented in Natural History Museums.
Good study system to assess human impacts
Macrofauna/flora
What we can see with the naked eye.
228 animal species and 155 algae species.
>1mm
Meiofauna
<1mm, as many as 1 million animas per metre squared.
Ostracods, amphipods, gastropods, forams.
Especially diverse in turf forming algae
Primary producers
Diatoms:
- Microalgae
-First things to colonize a rocky habitat
Filamentous algae
Foliose algae
Macrophytes
Leathery macrophytes
Articulated calcareous algae
Crustose coralline algae
Sea weeds
Grouped by their colour.
- Chlorophyta, green.
- Rhodophyta, red.
- Phaeophyta, brown.
Grazers
Limpets, periwinkles, urchins, top shells.
Filter feeders
Barnacles, sponges, sea squirts, mussels.
Wave impacted areas of rocky shores.
Predators
Shore crab, sea star, birds, dogwhelks.
Predation pressure can affect the distribution and abundance of organisms on the rocky shore, top down impacts.
Predation pressure can also affect the morphology of their prey, predator induced defenses.
Phenotypic response or evolutionary change.
Zonation classification scheme
High intertidal, lichens, periwinkles, barnacles, isopods.
Mid intertidal, barnacles, limpets, mussels
Low intertidal, sea stars, kelp, macroalgae.
Littoral zone across all 3
Exposed and sheltered shores
Exposed, a lot of filter feeders, lots of water movement and water action.
Sheltered, lots of algae and grazers.
Zonation causes
Larval settlements/recruitment and adult preference
Physiological tolerance to environment variables
Biological interactions:
- Interspecific competition.
- Predation
Influence of recruitment supply on zonation
Higher recruitment = high larval development.
Higher competition for space, lower limits are set by presence of a dominant competitor.
Low recruitment, the distinct zonation breaks down since space is not limiting and competition for space doesn’t occur.
Physiological tolerance to emersion
Low tide causes desiccation and heat stress problems.
Upper distribution of organisms broadly reflects their thermal limit.
Distribution can be modified by moving into crevices, rock pools, SA:V, limiting water loss, living in dense groups.
Rock temperatures under canopies
Seaweed canopies and rock crevices help buffer organisms from both heat and desiccation stress associated with tidal emersion.
Distributions can extend up shore in the presence of seaweeds.
Biological interactions
Predator-prey
When the predatory sea star was removed, the mussels and stalked barnacles moved down shore.
Vertical distribution of rocky intertidal species
Rocky intertidal species are distributed vertically, according to their capability to cope physiologically with changes in physical factors and response to biological interactions.
Larval ecology
70% of benthic invertebrates have planktonic larvae.
Settlement of larvae is not a random process, chemical and physical cues.
Types of larvae
Direct developing:
- Juveniles hatch from eggs and “crawl away”
Lecithotrophic:
- Larvae are planktonic using a yolk-sac for nourishment
Planktotrophic
- Larvae are free-swimming and feeding.
Direct developers
Dogwhelks.
Advantages:
- Predictable food source.
- No water column predators.
- Suitable habitat ready when hatched.
Disadvantages:
- Large reproductive cost for mothers.
- Few eggs.
- Poor dispersal.
- Benthic predators.
Lecithotrophic
Limpets
Advantages:
- Own food supply.
- Less time for predation.
- close to suitable habitat.
Disadvantages:
- Fewer larvae produced.
- Lower dispersal distances.
Planktotrophic:
Barnacles
Advantages:
- Large numbers are produced.
- Capable of staying in the water column for a long time, increasing dispersal distances.
Disadvantages:
- Unpredictable food sources
- Long exposure to predators.
- Last development stage needs to be timed when suitable habitat is found for settlement.
Why have a pelagic larval phase
Larvae decreases competition between life stages
Disperse long distances, colonization of new regions.
Long pelagic phases can break parasite life cycles.
Pelagic larvae do not have benthic predators.
Interactions with other species
Giant Kelp:
- Just offshore rocky coasts.
- Kelp forest slow current speeds.
- Helps larvae of rocky shore species to stay close to suitable habitat.
Mussel beds:
- Juveniles live within mussels and then move to bare rock as they grow into adults.
Role of competition
Important when resources are limiting.
Types:
- Exploitative: ability to harvest limiting food resources.
- Pre-emptive: competitor recruits to and dominates space.
- Interference: competitors physically contest resources.
Large size and rapid growth translate into competitive dominance in many organisms.
Competition can occur with species or between them.
Role of grazers
Limpet can defend a territory.
Physically push mussels off.
Hume range scaling
Large limpet needs a larger territory.
Less grazing space means a shift in space occupancy.
Less area available for limpet to grow and feed, harder to increase home range size.
Role of predators
Role of dogwhelks where seaweed fucus was removed.
Control, nucella ate many barnacles and mussels.
No nucella, mussels dominated.
No nucella and mussels, fucus resettled.
Oystercatcher birds not common in dog walking areas, in sheltered areas eat lots of limpets.
Indirect effects of predation
Starfish play important role in maintained species diversity and community structure through indirect and direct effects.
Community interactions:
Recruitment success
Resources
Growth rates and body size/shape
Competitive ability
Biodiversity
Predatory effects
Disturbance
Biogeographic range limits
Affected by life history, population, genetics, abundance distribution, spatial availability of habitat, atmospheric factors or a combination.
Biogeography of S Africa rocky shores
West coast:
- extensive kelp beds, v high production.
- many sea birds.
- kelps, brown and green algae, limpets, littorinids.
East coast:
- Subtropical community.
- low production
- greater diversity.
- Corals, coralline algae, barnacles, tube worms, oysters, whelks.
Habitat Gaps
Sand beach between rocky shores can create a gap in range limits.
Larvae can’t make it across the sand to new rocky area.
Climate change
Warmest sea-surface temperatures recorded in history.
Many southern warm species are moving North
Artificial rocky substrates
Biodiversity is like natural substrate.
Seawalls, jetties, groynes, piers, riprap.
Artifical coastal habitat can
Increase overall size of geographic rangers.
Increase genetic connectivity between populations.
be used as stepping stones for the spread of invasive species or range expansion of native species.
Harvesting
Size-selective
Major food source for 125000+ years
