I. Background
A. From edge of the continental shelf (<200 m)
to the lowest tides – sublittoral zone
B. Dominated by infauna
1. Macrofauna --
greater than 0.5 mm
2. Meiofauna -- 0.5
to 0.062 mm
3. Microfauna --
less than 0.062 mm
II. Environmental Conditions
A. More variability than epipelagic or deep sea
B. Very productive
C. Important factors
1. Wave action
2. Salinity
3. Temperature - seasonal
changes
4. Light penetration reduced
5. Food supply abundant
-- nutrients; high production of attached plants
6. few large grazing animals
D. Community differences based on type of substrate
1. Regions with soft bottoms
a. Size of grains, chemical composition, percent organic matter of the
sediment are important
b. More infauna than epifauna
2. Rocky areas - less
infauna
than epifauna
E. Four major habitats
1. open vegetated
sedimentary
environments
2. hard substrates with
low-encrusting plants and animals
3. kelp beds and forests
4. seagrass beds
III. Unvegetated sedimentary environments
A. Sampling
1. Grab samplers –
a. quantitative - Petersen grab, Smith-McIntyre grab; Reineck box corer
b.
non-quantitative - bottom trawls
2. SCUBA and Sub or ROV
with video
B. Infaunal associations –
1. Who's there
a. producers
(1) allochthonous (detritus; plankton)
(2) autochthonous -- mostly diatoms on surface
b. Class Polychaeta (Phylum Annelida)
(1) most abundant
(2) burrow, build tubes
(3) some are suspension feeders; some scavengers and predators
c. Crustacea (Phylum Arthropoda) -- mostly on surface
d. Echinoderms
e. Molluscs -- burrowing bivalves; some gastropods at surface
2. Relatively few species
dominate
3. Benthic communities named
for their most dominant members
C. Community Patterns
1. parallel bottom
communities
2. spatial variation
3. temporal variation --
daily, seasonal, annual, longer
4. functional groups of
organisms
a. how they feed
(1) deposit feeders
(2) suspension feeders
(3) scavengers
(4) algal grazers
(5) predators
b. what they do to the sediments
(1) stabilizers -- create structures that bind sediment or slow
the flow of water
(2) destabilizers or bioturbators -- activities cause
sediment
to move, be resuspended,
erode or change; many also oxygenate deeper sediments
c. trophic group
D. Community Structure
1. Abiotic factors
a. Temperature
b. Oxygen
c. Wave action
(1) Sedimentation -- burial
(2) Erosion – exposure
d. examples
(1) California subtidal
(2) Massachusetts -- tube-dwelling amphipods; snails; polychaetes; Severe winter storms
2. Biotic factors
a. Competition
(1) Direct -- contact between organisms or the direct interference
(a) Overgrowth - space
competition; not as common in soft sediments as
in hard
(b) Can be direct aggression
(2) Indirect -- one organism prevents resource use by the other
(a) more common in soft sediments
(b) trophic group amensalism -- exclusion of a trophic group by
another's modification of the environment
i. clamse.g., burrowing deposit feeders abundant where muddy sediments have high organic matter; exclude suspension feeders – fine particles clog filtering apparatus of suspension feeders and bury the suspension feeder larvae
ecosystem engineers - either directly or indirectly control the availability of resources to other organisms by causing changes in the physical state of biotic or abiotic materials and by changing energy flows
facilitation
(c) competitive interference -- exclusion by interference with
normal
activities
b.
Predation
(1) Surface predators
(a) fish, crabs, predatory worms
(b) suspension feeders may eat the larvae of conspecifics
(2) Burrowing predators -- don't disturb sediments
(a) ‘weasel-like predators’ - move down tubes and attack the organisms
-- nemertean worms; some gastropods
(b) Starfish, Pisaster brevispinus can extend its tube feet 20 cm
(3) Digging predators -- excavate holes
(a) Greater effect on the infauna because they disturb the sediment
(b) rays
(4) infaunal predators
(a) nemertine worms and predatory polychaetes
(b) can consume 20-50% of standing stock of prey
(5) Often studied by using cages that exclude predators
c. Recruitment
(1) should theoretically be important in some cases
(a) little mortality
(b) high recruitment rate -- swamp predators
(c) or overall low recruitment with none of the settling species a
competitive
dominant
(2) recruitment of juveniles from motile larvae; of mobile adults
(3) lottery hypothesis
d. Disease and parasitism
E. Vertical Distribution and Competition
1. Infauna is not
distributed
randomly in the sediments
2. Competition for space
may select for commensalisms
F. Community Patterns, Stability and Variability
1. Stable for several years
2. Cyclical oscillations between 'stable states'
3. Mosaic of patches
Zuma beach in CA
sand dollar; sea pansy occupies area inshore of the sand dollar
IV. Rocky Subtidal Communities
A. Who lives there?
1. Low-profile encrusting
species or gregarious forms, kelp forests and coral reefs -- have more
types of algae; more primary production in these areas
2. Motile animals -- sea
urchins, crabs and gastropods
3. Many suspension feeders
a. colonial encrusting species -- sponges, tunicates, bryozoans,
cnidarians
b. single individuals that settle in groups -- bivalve mollusks, sea
urchins…
4. harder to sample
a. dredges that scrape the bottom
b. direct observation and manipulation
B. Abiotic factors
1. rock type (may be
selected
by larvae)
2. substrate angle is
important
(slope) – horizontal vs. vertical
3. disturbance -- waves,
currents; creates free space
4. flow rate -- food,
settlement,
sedimentation
5. light
C. Biotic factors
1. space competition
2. grazing -- sea urchins
are often important grazers
3. mass recruitment
4. mutualism
5. keystone species
(disproportionately important in maintaining community composition) and
top down control
6. disease -- sea urchin
and sponge diseases (e.g., paramoebiasis)
D. Examples
E. Alternate stable states -- existence
in
the same area of different groups of organisms
1. occur when dominant
species
is disturbed
2. get shift to new
community
3. example (in book)
2 islands 4 km apart off of S. Africa; lobsters; mussels; gastropods