Components of benthic communities  “Infauna” classified by size 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?

Functional groups: examples of sediment stabilizers and bioturbators

Parallel infaunal communities in North Temperate oceans: Ecological convergence

Apparent paradox: high diversity, low habitat heterogeneity  “Competitive” exclusion is observed  Deposit feeders exclude suspension feeders (really “amensalism”)  Competition for space is documented

Why not have more competitive exclusion?  More niches than we thought? Vertical sorting hypothesis

More niches?, continued  Biotic facilitation  Mutualism  Commensalism (e.g., inquilines in tubes)

Can disturbance facilitate diversity?  Sources of disturbance  Biotic disturbance Burrowing, sediment processing predation (exclosure experiments)  Water turbulence, wave action  Human disturbance Beam trawls – designed to scrape sediments a few centimeters below surface Otter trawls, etc. along surface Consider differences in scale

Effects of local and mid-scale disturbance  Very patchy distributions Leading to high species turnover in space  Lower density than required for competitive exclusion Superior competitor is reduced before inferior competitors disappear Recolonization patterns add to diversity because larval settlement depends on timing

Effects of trawling on bottom structure FishedUnfished Kaiser & Spencer Journal of Ecology 65:

Changes in community diversity with trawling

Why does disturbance from trawling reduce diversity?  Direct effects on habitat  Scale of disturbance Disrupt biotic interactions Reduce potential for recolonization

Benthic processes: deep ocean systems

Benthic processes: coastal, subtidal systems

Benthic processes: vegetated, subtidal systems