The plankton and the benthos: origins and early history of an evolving relationship

Abstract

Modern marine plankton communities include a broad diversity of metazoans that are suspension-feeding or micropredatory as adults. Many benthic marine species have larval stages that reside, and often feed, in the plankton for brief to very long periods of time, and most marine benthic communities include large numbers of suspension-feeders. This has not always been the case. Cambrian benthic communities included relatively few suspension-feeders. Similarly, there were few metazoan clades represented in the plankton, either as adult suspension-feeders or as larvae. Review of the fossil record suggests that the diversification of the plankton and suspension-feeding marine animals began in the Late Cambrian and continued into the Ordovician. These changes were accompanied by, and probably influenced, concurrent major changes in the marine realm, including an increase in tiering within benthic communities, the replacement of the Cambrian fauna by the Paleozoic fauna, and a general taxonomic diversification. The ultimate cause of these changes 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.

Rocks and clocks: calibrating the Tree of Life using fossils and molecules

“…8the plankton: acritarchs that had survived for eons became extinct and the rate of plankton evolution increased by an order of magnitude, and all of this in close temporal concordance with the clock estimate for the origin of eumetazoans based on distance (but not likelihood) methods [48]. The later origin of planktonic larval stages among a diverse and polyphyletic grouping of eumetazoan phyla, long hypothesized as a life-history strategy to evade predation [50], also coincides with a dramatic rise in the diversity of epifaunal suspension feeders [49].…”

Understanding the Great Ordovician Biodiversification Event (GOBE): Influences of paleogeography, paleoclimate, or paleoecology

“…), which probably served as food for the many predators swimming freely in the water column. This "plankton revolution" fits with the development of abovesubstrate tiering (Ausich and Bottjer, 1982) and the view that the increased food supply in the water column was responsible for the rise of suspension feeders (Signor and Vermeij, 1994). Rigby (1997) noted that planktic groups mostly developed from the benthos; groups of animals with planktic larvae were able to become planktic adults by paedomorphosis.…”

“…Planktonic feeding larvae developed after the Late Cambrian, possibly as an escape strategy from increasing predation pressure due to the appearance of benthic suspension feeders (Signor and Vermeij, 1994). Nützel et al (2006) found the first direct evidence for planktotrophy in gastropods at the Cambrian-Ordovician transition.…”

Origins of the other metazoan body plans: the evolution of larval forms

“…An estimate of the timing for evolution of planktonic larvae of approximately 500 Myr ago is emerging, which if correct puts the origin of these second body plans 100 Myr later than the divergence of the basal bilaterian benthic adult. Signor & Vermeij (1994) noted that the Cambrian fossil record showed relatively few benthic suspension feeders or planktonic forms. They suggested that the evolution of planktonic feeding larvae took place in the Late Cambrian to Early Ordovician, driven by an expansion of plankton and sanctuary from predation-a point reinforced by Peterson (2005).…”