ABSTRACT
The total surface area of living organisms in marine environments is really enormous. It appears to be comparable with, or even exceed, the area of non-living hard substrates on the shelf. This seems quite probable if one takes into account not only the population of benthos, including the hard-substrate communities (see Section 1.1), but also plankton and nekton. Many “living” surfaces are populated by certain organisms. The extent of epibiosis becomes evident from the following example. Out of 2254 pairwise interactions between species of multicellular algae, invertebrates, and ascidians inhabiting underwater rocks in New England (U.S.), 59% represent active interactions and are the result of the overgrowing of one organism by others (Sebens, 1985b). Competition for space is especially severe on natural substrates in coastal areas and on the shelf.
