- Temperature Fluctuates
- Shallowness mean greater impact from waves
- Turbulence prevents stratification
- Nutrients high, from estuaries & rivers
- Salinity sometimes diluted by fresh water
- Sediments primarily lithogenous, large inputs from rivers
- Murkier water so light penetrates less deeply
The Ecosystem of the Subtidal
Soft-Bottom Communities (Unvegetated)
General Characteristics
- Dominant substrate type
- Primarily infauna, some epifauna, almost no sessile
Species Richness
- Greater than intertidal soft bottom communities
- Abiotic factors milder:
- Desiccation not a problem
- Temperature & salinity more stable
Distribution on Organisms
- Particle size affects distribution on infauna especially
- Partitioning by depth in sediment
- Organisms can dig deeper in sand than mud (more water flow in sand)
- Sediment types patchy, so organismal distribution also patchy
- Some larvae sample the substrate before metamorphosing
- Some larvae detect and settle near adults
- Many marine ecologists use the lottery hypothesis to explain community structure
Productivity
- Productivity minimal, by diatoms & other micro algae
- Communities mostly detrital based
Deposit Feeders
- polychaete worms: Collection by tentacles or ingestion of sediment
- Sand dollars: Use mucus to carry food to mouth
- Bent-nosed clam: Collects sediment with siphon
- Brittle stars: Collect detritus with tube feet
- Peanut worms, sea cucumbers, ghost shrimp
- Tend to exclude suspension feeders (loosen sediment too much)
Suspension (Filter) Feeders
- Clams: Draw water through siphon
- Polychaete worms & amphipods
- Brittle stars: Raise arms and trap particles with tube feet
- Sea pens: Traps particle from water
Scavengers & Predators
- Shrimp & other large crustaceans (scavengers)
- Whelks & moon snails: feed on bivalves
- Sea stars & Crabs can be either predators or scavengers
- Rays & skates
- Flounder, halibut & sole
Rocky Bottom Communities
General Points
- Least common type of subtidal community
- Submerged extension of rocky seashore or outcrops
- Often called reefs
- Hard substrate may include calcium carbonate producing organisms
- Rich epifauna, poor infauna
The Producers
- Seaweeds are the most conspicuous component of community
- Stiff competition for attachment sites
- Amount of light determines distribution of seaweed to a large extent
- Seaweeds of greater depths have more chlorophyll
Grazers
- Slow moving invertebrates: sea urchins, limpets, chitons, abalone
- Defenses of algae
- Unpalatability
- Quick regrowth
- Calcification
- Crabs, lobsters & fish are carnivores and eat many grazers
