Species richness of marine soft sediments

Abstract

Marine soft sediments comprise one of the largest and oldest habitats in the world, yet remarkably little is known about patterns of species richness. Here I present a short review of patterns of species richness and possible factors that influence such patterns. Species richness in general is remarkably high in both shallow coastal areas and the deep sea. However, there are clear differences -the deep-sea has higher number of species for a given number of individuals than the coast. This can be explained by the larger amounts of primary production that reach coastal compared with deep-sea sediments, leading to higher numbers of individuals per unit area. Species density (the number of species per unit area) is also higher in the deep-sea than in coastal areas, but it is not obvious why this is so. Most studies of the broad patterns of species richness have used samples taken at small scales only. The problem with such analyses is that unless a large number of samples are taken, the true underlying pattern (or lack of it) may be wrongly interpreted. Recent studies have analysed species richness at larger scales. In general there seems to be a cline of increasing species richness from the Arctic to the tropics, but this is not the case in the southern hemisphere, where Antarctic species richness is high. However, it is not known whether high species richness in the Antarctic occurs at all spatial scales. To what extent these patterns are determined by evolutionary factors remains to be determined by the application of molecular methods. The available evidence suggests that environmental factors such as productivity, temperature, and sediment grain-size diversity play dominant roles in determining patterns of regional-scale species richness and patterns in species turnover, and it is probably the regional scale that primarily determines local species richness.

Mapping benthic faunal communities in the shallow and deep sediments of Las Perlas Archipelago, Pacific Panama

“…These shell-sand sediments were generally more diverse, with a high abundance of crustaceans and other polychaete families. This supports Gray (2002) who noted that shell-gravel sediments globally have high species richness, probably due to the heterogeneity of the substrate but also because they are geologically old and relatively stable. Our findings also support the suggestion by Gray (2002) that in the tropics most continental shelves are dominated by mud (over 50%) with the other main sediment being carbonate sand.…”

“…Marine soft sediments comprise one of the largest and oldest habitats in the world but these habitats, their communities and patterns of species richness are greatly understudied (Gray, 2002;Zajac, 2008). Survey work is a vital element in defining the composition, distribution and condition of soft sediment habitats and, traditionally, studies that have been conducted to collect quantitative biological data have relied on core or grab samplers with sampling stations that are regularly dispersed over the survey area (Hewitt et al, 2004).…”

“…Survey work is a vital element in defining the composition, distribution and condition of soft sediment habitats and, traditionally, studies that have been conducted to collect quantitative biological data have relied on core or grab samplers with sampling stations that are regularly dispersed over the survey area (Hewitt et al, 2004). Faunal components of marine soft sediments are also more often targeted for monitoring work (compared to pelagic communities) as it is possible to gather many species in one grab, they are relatively sessile and cover a range of feeding and reproduction types so that change detection is easier (Gray, 2002). However, it is widely recognized that more research is required into soft sediments, especially in tropical and sub-tropical areas (Jackson, 1994;National Research Council, 1995;Gray, 2002).…”

“…Faunal components of marine soft sediments are also more often targeted for monitoring work (compared to pelagic communities) as it is possible to gather many species in one grab, they are relatively sessile and cover a range of feeding and reproduction types so that change detection is easier (Gray, 2002). However, it is widely recognized that more research is required into soft sediments, especially in tropical and sub-tropical areas (Jackson, 1994;National Research Council, 1995;Gray, 2002). Previous studies in these areas include both regional and localized studies of, for example, Kingston Harbour in Jamaica (Wade, 1972), Gray's Reef National Marine Sanctuary, Florida (Hyland et al, 2006), the mid-Atlantic (Bergstad and Gebruk, 2008), Singapore, Asia (Lu, 2005), Victoria, Australia (Coleman et al, 1978), southern Californian continental shelf (Bergen et al, 2001), Gulf of Nicoya (Maurer and Vargas, 1984;Vargas, 1987) and Golfo Dulce, Costa Rica (Leon-Morales and Vargas, 1998).…”

“…deposit feeders), there should be a measurable relationship between the two (Etter and Grassle, 1992). Additionally some studies have also found depth to be an influential variable (Etter and Grassle, 1992;Bergen et al, 2001;Hyland et al, 2006) although, as Gray (2002) points out, gradients of sediment properties can also vary with depth.…”