2. Benthic systems: Unvegetated Sediments
                                                                                         
Associations, Diversity, Disturbance

3. 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)

4. 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

5. 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

6. 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

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

8. Spatial variability in distribution of polychaetes

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

10. Topography of a typical continental shelf
                                                              

11. 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)

12. 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

13. 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?