What is marine biodiversity?
In its most simple form, biodiversity is 'Life on Earth'. It refers to a variety of life forms including plants, animals and microorganisms, the genes that they contain and the ecosystems that they form. de Fontaubert et al (1996) defines biodiversity more specifically as 'the variability among living organisms from all sources including terrestrial, marine and other aquatic inter alia ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.' Indeed, as this definition illustrates, biodiversity is composed of three main categories: (1) genetic diversity, (2) species diversity and (3) ecosystem diversity. These different components portray how biodiversity encompasses a number of different scales ranging from the gene to the ecosystem.
Genetic diversity is the variation in the amount of genetic information within and among individuals of a population, a species, an assemblage, or a community. It is reflected by the level of similarity or differences in the genetic makeup of individuals, populations and species. These similarities and differences may evolve as a result of many different processes: e.g. chromosomal and/or sequence mutation, and physical or behavioural isolation of populations. Although genetic diversity is not always obvious, it is extremely important as it is a requisite for evolutionary adaptation to a changing environment. Therefore, genetic diversity can be thought of as insurance, which allows adaptation to changing environmental conditions.
To understand many ecological and evolutionary processes, one must understand something of the genetic diversity of the species, population, or individual of interest. Further, it is desirable to understand the mechanisms for creating and maintaining the observed patterns of diversity. Thus, studies of genetic diversity have the potential to provide insight in many fields including conservation biology, population and community ecology, and evolutionary biology.
Species diversity is the variation in the number and frequency of species in a biological assemblage or community. Species diversity is the most commonly used synonym for biodiversity, where species richness (number of species in a given habitat) is the main index used for its measurement. The working estimate of the total number of species on earth is 12.5 million, however, the total number that could exist ranges from 5-100 million. Grassle and Maciolek (1992) suggest that there may be 10 million undescribed species in the deep sea alone!
In both marine and terrestrial realms, diversity of the smaller organisms is much less established than the larger organisms. For example, in the ocean, there is a plethora of information on whales, dolphins, porpoises and fish while only recently are scientist understanding the extreme diversity present in microorganisms such as bacteria and phytoplankton (i.e. the plants of the sea).
It is the origin and extinction of species that are the main components which determine biological diversity. However, the contribution of species to the overall diversity is not equal. Organisms that differ widely from each other will have a higher contribution to the overall diversity as compared to species that are more similar to each other. This illustrates that species richness may not be the best estimate for species diversity and it may be essential to use a different index in the future.
An ecosystem consists of all living and non-living things in an area. Ecosystems include a unique combination of animals, plants, microorganism and physical characteristics that define the location. Ecosystem diversity is the variation in the collection of assemblages, communities, and habitats within a region. Currently, there is no universal classification or unique definition of ecosystems at a global scale, however, this area of research is evolving quickly. Inherent in ecosystem diversity are both biotic (living) and abiotic (non-living) components, which differs from both genetic and species diversity.
There are a number of habitats that continue to be discovered at an alarming rate and there may be more ecosystems of this nature waiting to be revealed. In the ocean, hydrothermal vents were discovered less than 25 years ago! They are known to be extremely unique habitats with many endemic species (Grassle, 1986; Tunnicliffe, 1991). Furthermore, whale carcasses have been discovered to be a unique microhabitat (Smith et al, 1989) and they many also be connecting points between hydrothermal vent communities allowing these organisms transverse vents.
It should be noted that in some of the literature, ecosystems and habitats are considered as separate phenomena. Gray (1997) amalgamates community and ecosystem diversity, arguing that one cannot separate the community and ecosystem. He concludes that 'no ecological system, whether individual, population or community, can be studied in isolation from the environment in which it exists'. In this report, habitat diversity considers habitats as physical areas and the biotic components they contain and thus, habitat diversity is actually more useful than ecosystem diversity.
Other types of diversity
It is evident from the above discussion that biodiversity encompasses many levels including genes, species, ecosystems and habitats. Although these are the main components of biodiversity, there are two other kinds of biological diversity that have been suggested. They include (1) higher taxonomic diversity and (2) functional diversity (Norse, 1993).
Phyletic or taxonomic diversity involves the variation and variability of the working body plans (phyla) of organisms. An example of a phylum includes Arthropoda of which the class Insecta is part. Phyletic diversity can result in a higher diversity of phyla without requiring a high diversity of species. For example, in the marine environment there are 32 out of the 33 animal phyla present (Norse, 1993) and this is considered a high phyletic or taxonomic diversity.
Functional diversity is a grouping of species on the basis of how similar their functions are. For example, in the ocean, all organisms that deposit feed may be amalgamated into one functional group just like all filter feeders would compose another group based on that particular function. This can also extend to reproduction methods or biochemical diversity.
de Fontaubert, C. A., Downes, D.R. & Agardy, T.S. 1996. Biodiversity in the seas: Implementing the convention on biological diversity in marine and coastal habitats. IUCN Environmental Policy and Law Paper No. 32. A Marine Conservation and Development Report. 82 pp.
Grassle, J.F. 1986. The ecology of deep-sea hydrothermal vent communities. Adv. Mar. Biol. 23: 301-362.
Grassle, J.F. & Maciolek, N.J. 1992. Deep-sea species richness: regional and local diversity estimates from quantitative bottom samples. Amer. Nat. 139: 313-341.
Gray, J.S. 1997. Marine biodiversity: patterns, treats and conservation needs. GESAMP reports and studies No. 62. 24 pp.
Norse, E.A. 1993. Global marine biological diversity: A strategy for building conservation into decision making. Island Press, Washington D.C.383 pp.
Smith, C.R., Kukert, H., Wheatcroft, R.A., Jumars, P.A. & Deming, J.W. 1989. Vent fauna on whale remains. Nature. 341: 27-28.
Tunnicliffe, V. 1991. The biology of hydrothermal vents: ecology and evolution. Oceanogr. Mar. Biol. Ann. Rev. 29: 319-407.