THE BENTHOS - LIFE ON THE SEA FLOOR

Benthic life adapts to two basic means of using the environment during some portion of an organisms life-cycle.

Epifauna - Living on the seafloor itself as

Infauna - Living in the sediments as
Burrowers - Clams, polychaete worms and various mobile forms such as crabs that use burrows of other animals.
or
Interstial organisms - Microfauna living within the sediment matrix. These forms are highly dependent on the type of sediment (grain size) and the availability of oxygen in the sediment layers.

FOOD SOURCES
Primary production in the benthos:

Phytoplankton - either filtered from the plankton, fixed to the bottom themselves or as SYMBIOTIC forms in benthic animals such as corals, jellyfish and giant clams.

Macroalgae - Sea grasses, sea weeds such as kelp.

Chemosynthesis - This is the only direct source of fixed carbon below the photic zone. These are typically tied to geological features that provide the necessary chemical fluxes. (These will be covered further later in the course.)

Secondary and Tertiary production:
Grazers using the above.
Detrital feeding - This is very significant in most benthic environments. In near shore waters there is a large use of terrestrial input organic matter. In the deep sea, below the photic zone many organisms make use of the detrital rain that amounts to less than 10% of the surface production because of recycling and uses of the falling particles in the water column.

Some of the most important detrial feeders are DEPOSIT FEEDERS that act like earthworms in the terrestrial environment. These organisms stir the sediment creating what is known as BIOTURBATION.
Filter feeders and grazers on hard substrates - These include various forms that crop algae off rocks and animals such as barnacles ( a sessile crustacean) that filter feed from the plankton.
 

FILLING SPACE:
All life on our planet is either limited by space or resources, or is kept in check by predators or pathogens. If they were not we would be overwhelmed by things. This is especially true in the narrow zone that makes up the benthos. In this way it is the habitat in the ocean that most closely resembles the terrestrial world. Typically environments depend on disturbances that open new benthic habitat. This is then occupied by successive waves of colonizers that compete for space and food. One way that some of the most successful benthic forms like barnacles deal with this competition is by having MEROPLANKTONIC LARVAE that do not compeate with their parents but are DISPERSED by ocean currents. This allows the species to inhabit wide ranges of suitable habitat.