Biodiversity changes and ecosystem functioning
The most fundamental meaning of biodiversity is probably the concept of species richness, i.e., the number of species which occur at a given site, or within a region or an ecosystem. It's often assumed that ecosystems with a higher diversity can better cope with environmental fluctuations. A large number of species present might increase the resilience of an ecosystem to changes in environmental conditions or to anthropogenic impacts.
More information on the importance of biodiversity can be found here.
Biodiversity at risk
The maintenance of high diversity is often seen as something positive to aim for; and to “halt the loss of biodiversity” has become a major political aim. It is now clear that marine ecosystems are at risk, especially those which receive the most pressure from human activities, mainly estuaries, intertidal shores and coastal waters.
The composition of species within marine communities can change in three main ways:
- species may be lost (extinctions);
- species may be added (invasions or speciation);
- species’ relative abundances can change (rare species become abundant, abundant species become rare).
An overview of all threats towards marine biodiversity can be found here.
Although the number of rare species comprise the majority of the taxa in a biologically diverse region, they only form a minority of the biomass. However, when species are removed or added to a community, the energy flow, predator-prey interactions or food web-related processes may change dramatically. As a consequence, the productivity of the seas is directly affected.
Habitat heterogeneity is another important factor when describing biodiversity. Presently, a gradual transition from very complex to simpler habitats is being observed. MarBEF explored the numerous ways in which habitat loss can affect marine species diversity, and thus community structure.
The loss of habitat structure is generally thought to lead to lower abundance (biomass) of key species and often to a decline in species richness. However, experiments in different coastal areas of Europe, have shown that the removal of key species does not always affect the stability of the ecosystem and that effects depend on where, when and what species are removed. For example, an invading species may replace a resident species which plays an ecologically important role for ecosystem structure and functioning. The ecosystem may continue to function and provide similar services, but not necessarily in the same way as before.
MarBEF also showed that, despite increasing pressure from overfishing, habitat destruction and pollution, species richness appears to be increasing in many coastal and marine European waters. This is due to the establishment of non-indigenous species, especially of warm-water affinity, and to a general northward movement of species due to climate change. The observed increase might also be due to the addition of newly recorded species to already existing species lists which haven’t been amended for a long time, or be related to more intensive research and the discovery and description of rare species.
Anthropogenic activities such as shipping and aquaculture further enhance the spread of species, even across geographic or ecological boundaries. Such shifts in species or changes in regional biodiversity will have consequences on the structure and functioning of ecosystems.
This raises two questions: Can we expect the same response from all European marine ecosystems? And can we predict how this will affect ecosystem functioning? Below, some examples are provided of how biodiversity might change in 4 different regions.
- Predicted biodiversity changes in the Arctic
- Predicted biodiversity changes in the Baltic Sea
- Predicted biodiversity changes in the Mediterranean Sea
- Previous biodiversity changes in the North Sea
- Heip, C., Hummel, H., van Avesaath, P., Appeltans, W., Arvanitidis, C., Aspden, R., Austen, M., Boero, F., Bouma, TJ., Boxshall, G., Buchholz, F., Crowe, T., Delaney, A., Deprez, T., Emblow, C., Feral, JP., Gasol, JM., Gooday, A., Harder, J., Ianora, A., Kraberg, A., Mackenzie, B., Ojaveer, H., Paterson, D., Rumohr, H., Schiedek, D., Sokolowski, A., Somerfield, P., Sousa Pinto, I., Vincx, M., Węsławski, JM., Nash, R. (2009). Marine Biodiversity and Ecosystem Functioning. Printbase, Dublin, Ireland ISSN 2009-2539