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Components of benthic communities

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.

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Components of benthic communities

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  1. 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

  2. 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?

  3. Functional groups: examples of sediment stabilizers and bioturbators

  4. Parallel infaunal communities in North Temperate oceans: Ecological convergence

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

  6. Why not have more competitive exclusion? • More niches than we thought? • Vertical sorting hypothesis

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

  8. 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

  9. 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

  10. Effects of trawling on bottom structure Fished Unfished Kaiser & Spencer. 1996. Journal of Ecology 65: 348-358

  11. Changes in community diversity with trawling

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

  13. Benthic processes: deep ocean systems

  14. Benthic processes: coastal, subtidal systems

  15. Benthic processes: vegetated, subtidal systems

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