When looking for a specific marine plant or animal one must be familiar with its habitat. Organisms are not uniformly distributed throughout the marine environment. They are often located in distinct bands or zones along the shore. Physical factors such as wave action, temperature, salinity, and oxygen concentration will influence this zonation. It will also vary from place to place. For example, a rocky shoreline may exhibit clearly defined zones characterized by bands of green algae, barnacles, and rockweed. However, it’s a different situation on a sandy beach where the substrate may shift frequently due to wave activity. Most of the species living there are burrowing deep in the sediments to avoid being dislodged.
The majority of species are part of the benthic zone. This includes all those that live on or in the bottom or substrate of the ocean. For the coastline this would include the marine plants that need sun for photosynthesis from the shallow water seaweeds to the subtidal eelgrass beds. Most of the animal phyla are represented here as well.
The benthic zone can also be divided into those animals that live on the surface of the substrate (epifauna) to the burrowing species (infauna). Some are found in the dynamic intertidal zone which is the area between high and low tide. Not only does this substrate shift with the waves and tides, but animals here have evolved strategies to survive periodic exposure to the air.
Animals of the benthic environment have also evolved different symbiotic relationships. The carapace of a spider crab (Libinia emarginata) may be covered with barnacles, anemones, and sponges. These hitchhikers are moved to areas where there may be food available while giving the spider crab added protection as camouflage. This process in which all the species benefit is called mutualism. On the other hand some mollusks may harbor small, harmless worms in their shells. The relationship may benefit the hidden worm, but doesn’t help or harm the host. This is called commensalism. However, if the worm obtains nutrition from its live host, thus weakening or harming it, then it’s an example of parasitism.
One of the most interesting residents of the infauna is the attractive plumed worm (Diopatra cuprea). This polychaete worm lives in a tube that is often covered by bits of shell and sediments glued there by the animals’ mucous. Broken tubes can be found along the shore where this animal lives. Infauna worms are also found in the deep parts of the ocean benthic environment where they feed on organic debris that drifts down from the surface. This is a world largely unexplored but may consist of many unnamed species. It’s quite possible that these dark and deep sections of the ocean may contain a high diversity and biomass.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.