Benthic systems: Unvegetated Sediments                                                                                           Associations, Diversity, Disturbance

Deep Sea Benthic diversity In & on sediments Dominated by “macrofauna” Defined by size (> 300 μm) Include polychaetes, molluscs, crustaceans, echinoderms Estimated to include between 500,000 and 10,000,000 species Program to inventory under way (CeDAMar or “Census of Diversity of Marine Life” – abyssal plains)

Ecological importance of benthic macrofauna Nutrient cycling at ecosystem level Food resource for commercially important species Pollutant metabolism Dispersion & burial Energy cycling Influence sediment structure & turnover

Why so many species of macrofauna? Why would we expect low diversity? Apparently low variety of habitats so apparently low number of different niches Low rate of input for new energy/nutrients “Competitive exclusion principle” predicts low diversity

What ecological mechanisms would explain high diversity? H1: Niches are defined by more dimensions than sediment type Location within sediments (e.g., vary in O2) Other organisms create “biotic” variation H2: Competition is not a major factor Predator influence Disturbance influence H3: Local diversity may be low but regional diversity can be high This is multiplied by a very large area of habitat

Sediment variation – “Bioturbation” Variable sediment surface from biological activity: 1100 m Box Core from 1900 m

Spatial variability in distribution of polychaetes

Continental Shelves: overview 7.4% of ocean surface Average 78 km wide, 135 m deep Most above water during ice ages (18k bp)

Topography of a typical continental shelf                                                               

Characteristics of the habitat High productivity along continents Higher turbulence than in deep ocean More variable salinity and temperature Light penetration usually is reduced (often to 10 to 20 m)

Components “Infauna” classified by size Major taxonomic groups Bacteria & protozoa Macro- and meiofauna Major taxonomic groups Polychaetes, crustacea Echinoderms, molluscs In similar habitats, community composition suggests convergence in form

Major questions What are the major components of communities in unvegetated sediments? What is the relationship between taxonomic classification and ecological function? (“Functional equivalents”) How can disturbance promote diversity? What are the consequences of bottom-dredging fishing techniques?