Ocean Habitats and their Biota

13-1 Biology of the Continental Shelf The waters of the neritic zone are fertile and support a rich community of organisms. The plankton are floaters and weak swimmers which are helplessly transported by ocean currents. Nekton have the ability to swim against currents and actively search for a more hospitable environment. Many fish display schooling, another form of patchiness.

13-1 Biology of the Continental Shelf Because the water column is shallow in the sublittoral zone, physical factors regulate the number, type and distribution of benthic organisms. Bottom energy is a function of wave energy and tidal currents and these vary inversely with depth. The sea floor can be divided into two areas based upon the energy of the environment: High energy environments and Low energy environments. Bottom energy affects organisms by: moving sediment about and creating an unstable substrate, controlling sediment size. Bottom sediment strongly influences the feeding mode of benthic communities.

Biology of the Continental Shelf 13-1 Biology of the Continental Shelf The two major benthic communities based upon substrate are: Hard-bottom community and Soft-bottom community

13-2 Biology of the Open Ocean and the Deep Sea The open ocean is the largest habitat on Earth, but life is sparse because of low nutrient concentration and great depth. In the open ocean, diversity is high but the number of individual per species is low. The only seaweed in the open ocean sea is sargassum gulfweed. The major phytoplankton are diatoms, dinoflagellates and coccolithophores and the major zooplankton are foraminifera and radiolaria. Diatoms dominate the shallow coasts, but decrease in abundance seaward. Top predators are mackerel, squid, jellyfish, tuna, porpoise, shark and man.

Biology of the Open Ocean and the Deep Sea 13-2 Biology of the Open Ocean and the Deep Sea In the dysphotic zone, seasonal heating is minimal and conditions tend to be uniform most of the year. The aphotic zone is an area of permanent darkness and cold.

13-2 Biology of the Open Ocean and the Deep Sea The biomass on the sea floor tends to decrease with depth faster than it does with distance from shore. The benthic food chains largely depend upon food from the surface which reaches the bottom. Characteristics of the benthic organisms include: year-round reproduction, smaller broods, slow growth, and longer life. Diversity of the benthos is greater than expected because the high predation rate prevents any group from dominating through competitive exclusion (when one group out-competes most others and drives them to extinction).

Biology of the Open Ocean and the Deep Sea 13-2 Biology of the Open Ocean and the Deep Sea Four traits common to all abyssal depths are: perpetual darkness., low temperature, high hydrostatic pressure, and sparse food supply. Rate of bacterial decay is greatly reduced under high hydrostatic pressure. This means that organic material that settles onto the sea floor remains for a long time before it decays and is thus more likely to be consumed.