Phanerozoic development of tiering in soft substrata suspension-feeding communities

Abstract

Tiering is the vertical distribution of organisms within the benthic boundary layer. Primary tierers are suspension-feeding organisms with a body or burrow that intersects the seafloor. Secondary tierers are suspension-feeders that maintain positions above or below the sediment-water interface as either epizoans on primary tierers and plants or by living in the burrows of primary tierers. Different primary tierers from soft substrata, nonreef, shallow subtidal shelf and epicontinental sea settings have had different tiering histories, resulting largely from contrasting constructional and phylogenetic constraints. Primary colonial tierers generally occupied lower epifaunal tiers during the Paleozoic and Mesozoic, but since the Cretaceous they have been dominant in the highest tier (+ 20 to +50 cm). Primary echinoderm tierers have been almost exclusively epifaunal, and from the Paleozoic through the Jurassic they were present throughout the epifaunal tiered structure. Although primary bivalve tierers have been both epifaunal and infaunal, they have occupied only lower epifaunal tiers, whereas they have adapted to all levels of the infaunal tiering structure, particularly from the late Paleozoic through the Recent. Brachiopods have lived primarily in tiers directly above or below the water-sediment interface and have not contributed significantly to tiering complexity.Of the numerous physical and biotic processes and constraints that affect shallow marine benthos, a few have contributed more significantly to changes in tiering patterns. Trends for increasing body size could have accounted for most of the development of tiering complexity up to +50 cm and down to –12 cm. Development of tiering above +50 cm could have been due to processes which would have yielded greater feeding capability, such as competitive interactions for a place from which to feed or adaptations to velocity gradients in the hydrodynamic boundary layer. The most significant process for development of infauanl tiering below –12 cm appears to have been as an adaptive response for predator avoidance.Unlike infaunal tiering, which never declined after it developed, epifaunal tiering has undergone a general reduction twice. Reduction in epifaunal tiering at the end of the Paleozoic appears to have been the result of the mass extinction at this time, whereas long-term biotic processes seem to have been more important for the tiering decline at the end of the Mesozoic. Tiering structure through the Phanerozoic was thus produced through interactions of a number of physical and biotic factors, tempered by constructional and phylogenetic constraints of each primary tierer group.

Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

“…Only corals profited from a higher level while the other groups such as polychaetes and bryozoans exploited lower levels. Additionally, in many instances, the encrusting organisms in our assemblages did not exceed a tier of even 5 cm, while during Cretaceous higher tiers clearly existed (Bottjer and Ausich 1986).…”

Diversity and palaeoecology of Early Devonian invertebrate associations in the Tafilalt (Anti-Atlas, Morocco)

“…Vertical tiering is defined by the vertical distribution of animals in or on the sediment as well as in the water column and includes the categories pelagic, erect, surficial, semi-infaunal, shallow infaunal und deep infaunal (Ausich & Bottjer 1982, Bottjer & Ausich 1986, Bush et al 2007.…”

Climate Change and Invasibility of the Antarctic Benthos

“…Durophagous predators originated onshore, largely eliminating epifaunal, suspension-feeding populations from soft-substratum habitats ( Jablonski & Bottjer 1991, Sepkoski 1991. From the Jurassic onward, epifaunal suspension feeders on soft substrata were replaced by infaunal and more mobile epifaunal suspension feeders, giving onshore soft-substratum communities their modern, bivalve-dominated ecology (Aberhan et al 2006, Bottjer & Ausich 1986, Stanley 1977. As a broad generalization, predation is lower and community structure is archaic in offshore, deep-water habitats compared to nearshore, shallow-water habitats.…”