In recent years biodiversity is receiving considerable attention in both the scientific literature and the press. Humankind is now aware that the loss of biological richness is a pressing problem. This new vision is based on the realization that human activities have significantly increased the rate of extinction of species.
Although nearly a million and a half species have been described, we have no clear idea of the total number of species that may actually exist on our planet. This gap in our knowledge is particularly severe in the case of microorganisms but applies to all groups of living beings.
The planet's biodiversity is a repository of the gene sequences used by life to colonize a particular habitat at a given moment in time. Though the abundance of many of those genes may be low at any point in evolution, they nonetheless make up a gene pool available for use.
Any significant decrease in that gene pool constitutes a potential threat of unknown proportions to our quality of life and perhaps to the survival of the human species. The reason for this is that there is evidence of a link between diversity and production, stability, and the ability of ecosystems to absorb anthropogenic impacts and recover to their natural state. Another reason is that biodiversity is a storehouse of information for substances that have therapeutic properties or are simply useful to our species.
In a global context, marine biodiversity has certain special characteristics. The oceans appear to contain greater animal diversity at the phylum level but lower diversity at the species level than do terrestrial systems. In the case of microorganisms, the existence of cryptospecies differentiable solely by molecular methods and the existence of bacterial clones entirely unknown to conventional bacteriology have been demonstrated. As a result, it is not surprising that a large numbers of unknown species are being discovered on the seabed at great depth. All these findings suggest that marine biodiversity has received insufficient attention and that there are large numbers of as yet undescribed organisms.
The inclusion of quantitative aspects of population dynamics is necessary to any understanding of the functioning of marine ecosystems. For larger organisms, models for estimating abundance and predicting changes in population levels in response to both natural conditions and exploitation by humans need to be improved. For smaller organisms, methods of measuring biomass and determining activity levels need to be developed. An example of the importance of this type of quantitative study is the recent discovery that prochlorophytes, a group of prokaryotic organisms unknown just ten years ago, are responsible for a substantial proportion of phytoplankton biomass and primary production.
Community make-up and dynamics in ocean ecosystems are closely linked to the presence and variability of physical features of the habitat. Marine primary production is based on sunlight, which furnishes energy for photosynthesis. But there are also other forms of energy that may interact with organisms. The movement of water masses, for instance, are of basic importance in selecting the dominant forms of primary producers and accordingly in determining the routes for energy transfer from primary and secondary production through the food web.
The recent concern about community composition and dynamics has resulted in numerous international programmes and meetings intended to promote studies in this area. For example, Systematic Agenda 2000 on biodiversity promoted by the U.S. NSF and a variety of scientific bodies and the Diversitas programme sponsored by IUBS, SCOPE, UNESCO, and other international bodies, culminating in the U.N. Conference on the environment and development held in Rio de Janeiro in 1992. Population dynamics are of great importance in the Global Ocean Ecosystem Dynamics (GLOBEC) programme sponsored by SCOR and other bodies, aimed at explaining the effects of physical processes on predator-prey interactions, population dynamics, and their links to oceanic ecosystems in the context of a global system of climate and anthropogenic change.
To define the sources and sinks of the major substances present in the ocean and to quantify the processes regulating element cycles, it is necessary to have an understanding of the physico-chemical variability of water masses and their interfaces, the biological activity of marine organisms, the geology of sinking particulate matter and the interactions among all these factors. The interest of enhancing our knowledge of oceanic biogeochemical cycles by bringing together experts in different fields and countries has resulted in the launching of major international programmes like JGOFS.
The particular features of the biogeochemical carbon cycle in a given area will affect the equilibrium of CO2 with respect to the atmosphere and will determine the values of parameters such as the sinking rate of carbonates to the seabed, the rate of decomposition of pollutants or the production of exploited species. Coastal regions are particularly relevant from the standpoint of human activities. On the other hand, the size of the pelagic zone makes it of primary importance for many processes. The magnitude of primary production and its consequences for the environment are related to whether new or recycled production predominates. In the planktonic ecosystem, carbon may circulate mainly via the microbial food web or through the classical pathway; the amount of primary production reaching the sediment will depend upon the balance between the two pathways. In turn, secondary producers may affect both the growth and biomass accumulation by primary producers. The different components and processes integrated in the biogeochemical cycles present close links at many different scales. For example, recent research has linked the sulfur cycle to a climate control loop via sulfur-containing compounds synthesized by certain species of phytoplankton as solutes for osmotic regulation. For all these reasons an understanding of the mechanisms governing the rates and circulation patterns of biogenic elements is basic to making any prediction of the future behaviour of the marine environment and hence to establishing a scientific groundwork for proper management of that environment.