SOURCES OF FOOD

Possibly the most important limiting factor in deep-sea ecology is food availability. All production in the deep sea, except at hydrothermal vents (see Chapter 15), is fuelled, either directly or indirectly, by the import of organic matter to the bottom, the major part consisting of ‘new’ production sinking from the process of carbon production by photosynthesis in the euphotic zone. This dependency on organic import make it an allochthonous, rather than autochthonous (such as the hydrothermal vents), system. Rowe & Staresinic (1979) and Rowe (1981) have outlined the pathways by which the various forms of organic matter, as a food source, enter the deep sea (Fig. 11.1). Particulate Organic Matter (POM) includes both large food-falls, consisting of animal carcases along with terrigenous and coastal plant debris, as well as fine particulate organic matter mostly from planktonic animals, including faecal pellets and moults, and phy-toplankton. In addition, sediments, particularly those in reducing conditions, have been found to contain a relatively large fraction of Dissolved Organic Matter (DOM). This, it has been argued, also constitutes a significant food source for some biota.

LARGE FOOD-FALLS: ANIMAL CARCASES

These include the bodies of large vertebrates such as marine mammals and fish, and large invertebrates such as squid. In an early review of the characteristics of the deep-sea environment, Bruun (1957) suggested the importance of the sinking of whale and shark remains as a food source, although no direct observations were available at that date.