m@rble ELectronic conference on MARine Biodiversity in Europe

summaries theme 1

Summaries of theme 1, as they are posted here, are compiled by the session's chairman, Carlos Duarte.

main issues in marine biodiversity research

Summary of day 1

There was sizeable activity in the discussion forum, including lively interchanges over most of the questions originally posed. The text below summarises the contents of the opinions issued by topic.

1. Large-scale patterns of marine biodiversity

What are the large-scale patterns of marine biodiversity in Europe?

The elucidation of large-scale patterns of marine biodiversity was found to be a very ambitious objective, challenging the efforts possible even with large resources available. Pragmatic decisions must, therefore be adopted, including:

• Adequate representation of sampling scales, including very large scales as to unravel patterns derived from evolutionary processes from those reflecting shorter-term processes, such as disturbance. The appropriate grain or scale of efforts to elucidate large-scale patterns must be determined, and this may differ across taxa.
• The search for patterns on global marine biodiversity will be challenged by an uneven capacity to elucidate species membership across taxa. In addition, estimates of biodiversity, as species richness, are dependent on effort. Approaches that reflect taxonomic breadth or relatedness of species, seem to be better for broad-scale geographical comparisons than absolute estimates of species richness. In addition, synthetic descriptions of community structure, such as use of replicated photographs at standard depths to examine species and cover may be adequate for comparative purposes.
• The goals of efforts to establish large-scale patterns in marine biodiversity must be operational, which is not the case for attempts to describe synoptic large-scale patterns for all of marine biodiversity. Provided a pragmatic decision must be adopted to select a group of organisms that is amenable to this question, how should be this selection driven? From previous knowledge of the organisms or from any objective trait that renders these organisms more important (e.g. functional properties, status - endanger, etc.).
• Testing a priori ideas about drivers of large-scale patterns. Another possibility to explore may be to formulate hypotheses on what the drivers of large-scale patterns may be (e.g. the existence of biogeographic boundaries, strong, permanent water fronts as barriers for dispersal, etc.) and test them for a range of organismal groups. This approach will be complementary to a strictly explorative one.

2. Biogeochemical cycling and ecosystem functioning

What is the function of biodiversity in biogeochemical cycling and ecosystem functioning?

The evaluation of the relationship between biodiversity and ecosystem function and biogeochemical cycling has proved cumbersome. What communities would be most convenient as subjects to test this notion? (planktonic communities, where synthetic communities can be easily constructed from cultured organisms, may be ideal for "species addition" experiments, whereas benthic communities, may be most convenient for "species removal" experiments).

Meiobenthic assemblages in sediments may be good candidates to test the relationship between biodiversity and ecosystem functioning, since natural assemblages are much easier to maintain in replicated manipulative microcosm experiments in the laboratory than planktonic or macrobenthic assemblages.

3. Taxonomical and functional biodiversity

What are the links between taxonomical and functional biodiversity?

The biodiversity is very interesting not only itself. It is very interesting both as natural phenomenon influencing on the activity of ecosystem and a consequence of ecosystem function simultaneously. The assessment of the link between biodiversity and stability is a difficult one, and need be challenge using perturbation experiments.

4. Species redundancy

Is there species redundancy? If so, what is its role?

• Species redundancy is an old topic in plankton ecology (i.e. the plankton paradox), which was resolved by invoking non-equilibrium conditions to account for the co-existence of species with similar resource requirements. While the presence of "functionally-redundant" species can be explained, the question as to how much biodiversity can be lost before any effects on ecosystem functions is detected is still unresolved, both for marine ecology as well as terrestrial ecosystems, where the experimental demonstration of a link between species diversity and ecosystem functions has proved elusive.
• The issue of "functional redundancy" in animals that feed on particles (as opposed to phytoplankton that absorb nutrients in solution) is problematic. Just because there are several deposit-feeders present in a community does not mean that they are competing for resources or that there is functional redundancy. Most smaller species, at least, are very selective about what they eat.
• Functional redundancy cannot be readily tested. The concept of functional redundancy implies a nearly-perfect functional match in all relevant functions. This is impossible to test, since it can be always argued that there may be important functions that were missed by any one test.

5. Life cycles

What is the importance of life cycles in the evaluation of biodiversity?

• What is the relative importance of the dispersal (e.g. planktonic larval stages) vs. adult stages in determining the large-scale biodiversity patterns of sessile organisms?
• Strathmann, among others, has argued that the significance of a planktonic larval phase is a migration for feeding and safety and, although dispersal is an inevitable by-product, it is not selection for dispersal that maintains a planktonic stage in the life histories. There is no evidence that benthic assemblages dominated by species with planktonic larval stages are any more or less diverse than those with direct development.
• What is the contribution of settling diversity to community diversity?, to what extent does the diversity of settlers - from largely planktonic stages - may influence the diversity of the steady-state community (are resource or competitive interactions stronger than contingency events involved in settling?)?. There may also be a feed-back between the diversity of the community and that of settlers.
• supply side ecology is based on individual organisms that disperse through larvae only, whereas sessile organisms are clonal and they disperse in other ways, besides larvae. Among the other ways there are not only rafting adults, there are also asexual propagules that can be specialised or also simple, but viable, fragments. clonals lose pieces, and they travel in the water column and on the bottom. specialised asexual propagules are known for algae, sponges, ascidians, hydroids, bryozoans, namely for all sessile organisms with a clonal habit. fragments are usually considered as detritus, but they can settle with no problem.

6. Comparison with freshwater and terrestrial ecosystems

What are the differences between marine, freshwater and terrestrial ecosystems?

• Are large-scale patterns in marine biodiversity driven by similar gradients (elevation-depth, latitude) than those of land and freshwater biota?

7. Rate of recovery following disturbance

What are the rates of biodiversity recovery following disturbance?

• Patterns of recovery in macrobenthic communities are well established. In contrast, at local scales, rates of recovery seem to be much more variable and depend on e.g. hydrography, season, extent and nature of disturbance. Are we able to predict rates of recovery?
• Establishing rates of biodiversity recovery is a key goal. There may be sufficient data as to conduct a meta-analysis for some particular taxa, however, it is difficult to standardise the disturbances as to render the recovery rates comparable.
• The research questions to formulate on this key topic must include the question, what role does biodiversity has in setting recovery rates?
• Examination of case studies suggests that there may be no general answer to these questions.