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.

Summary of day 4

1. Large-scale patterns of marine biodiversity

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

The close relationship between species richness and effort implies that, with the current rate of description, robust large scale patterns would require considerable effort.

Availability of suitable habitat is an important control on biodiversity, which may confound other existing patterns. This suggests that it ought to be, therefore, simpler to find large scale patterns in the distribution of planktonic organisms.

2. The role of rare species

Are rare species only rare at some spatial or temporal scales but ready to become abundant as the environment changes?. May a currently rare species be a potential key-species in the future?

3. Ecosystem engineers and key-species

What are the ecosystem engineers and key-species?

The concept of keystone species is identical with intermediate disturbance. these concepts are probably important to understand species roles, but cannot be used to decide priorities in conservation. Advice to manage biodiversity may be premature before we have solid scientific evidence to base our advice upon.

A link between species richness and stability link has been assumed for decades, but there is no robust evidence, and it is yet to be demonstrated. This should be one of the main questions to address experimentally (comparative analyses are much to confounded with other co-variates to be useful as a test of the concept).

Engineer species modify habitat conditions and, therefore, possibly the pool of species to be encountered therein. These effects may be either positive or negative, but it is clear that such species (e.g. mangroves, seagrasses, kelps, some corals, etc.) hold a prominent position on the biotic control of biodiveristy, and their loss or appearance may lead to important – albeit still poorly understood - changes. They should be particular targets for management once these interactions are understood

Do engineer species really have such a prominent position, or is this merely an artefact of the restricted scales we study? Obviously they often sustain a high species density. But often they take a small area only on a regional (a few 100 km) scale. Therefore, in many species the majority of individuals may be scattered in the surroundings and the 'hot spot' of species richness may not be very important for regional population endurance. So, what happens if an ecosystem engineer is removed? Is there any lasting effect on the other species, or is it readily replaced by formerly rare (possibly outcompeted) species within a few decades (what would appear as a sudden change on an evolutionary time scale). Finally, if the environment changes dramatically, wouldn't conservation of an established engineer prevent natural succession?

What about human engineers? or Do artificial structures enhance coastal biodiversity? The public rarely has a "direct view" of marine species richness, except for habitats such as coral reefs and shallow rocky reefs. As a consequence there is a tendency by coastal managers to "enhance the quality" of coastal habitats by using artificial structures. Artificial structures are also claimed to contribute to habitat conservation and restoration. This human activity often acts at large spatial scales on a very short temporal scale. Moreover, if little is known about species engineers, often acting at a very slow rate, even less is known about question such as: "What are the effects of artificial structures on coastal ecosystems?" "How do they affect biodiversity?" Deployment of artificial substrata on coastal sandy bottoms obviously increases the number of species in the area and makes it more "economically valuable". However, alterations of ecosystem functioning (e.g. trophic webs, energy fluxes etc.) and of the abiotic features (e.g. hydrodynamic regimes, sedimentation rates etc.) need a careful assessment before planning creation of artificial rocky island.

4. Rate of recovery following disturbance

The decline of biodiversity following disturbances caused by physical disruption, pollution, over-fishing and introduction of exotic species differ in their mechanisms, and so will the possible recovery, taking into account differing spatial and temporal scales. There is an urgent need to establish the "point of no return" for those disturbances in different communities - when is the change too extensive for a turnaround.

5. Comparison with freshwater and terrestrial ecosystems

Freshwater habitats are clearly more ephemeral (except deep lakes as Baikal etc.) than marine habitats, so isolation processes and species turnover in freshwater biogeographic regions may be expected to be enhanced compared to the marine.

6. Non-equilibrium conditions

The larger the spatial scale, the more we may expect diversity to be a reflection of the steady-state conditions. So, what is the spatial scale of a 'particular marine community' (respectively, the spatial scale we should use in a study on diversity)? As an example, does the North Sea represent a single community (as fishery biologists might argue) or does it contain dozens (macrobenthos) or even hundreds (meiobenthos) of communities?

Carlos M. Duarte
Profesor de Investigacion CSIC / Research Professor Spanish Research Council