THE PLANKTON AND THE BENTHOS - ORIGINS AND EARLY HISTORY OF AN EVOLVING RELATIONSHIP

Modern marine plankton communities include a broad diversity of metazo ans that are suspension-feeding or micropredatory as adults. Many bent hic marine species have larval stages that reside, and often feed, in the plankton for brief to very long periods of time, and most marine b enthic communities include large numbers of suspension-feeders. This h as not always been the case. Cambrian benthic communities included rel atively few suspension-feeders. Similarly, there were few metazoan cla des represented in the plankton, either as adult suspension-feeders or as larvae. Review of the fossil record suggests that the diversificat ion of the plankton and suspension-feeding marine animals began in the Late Cambrian and continued into the Ordovician. These changes were a ccompanied by, and probably influenced, concurrent major changes in th e marine realm, including an increase in tiering within benthic commun ities, the replacement of the Cambrian fauna by the Paleozoic fauna, a nd a general taxonomic diversification. The ultimate cause of these ch anges is uncertain, but it appears likely that the plankton was and is a refuge from predation and bioturbation for adults and larvae alike. The expansion in plankton biomass thus provided increased ecological opportunities for suspension-feeders in the plankton and benthos.