The distinctive features of marine biodiversity

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The origin of live

Life originated in the sea and is therefore much older than life on land. As a consequence the diversity at higher taxonomic levels is much greater in the sea, where there are fourteen endemic (unique) animal phyla in comparison to only one endemic phylum on land. There is also a remarkable diversity of life-history strategies in marine organisms. The sum total of genetic resources in the sea is therefore expected to be much more diverse than on land.[1]

Environmental stability

The physical environment of the seas and land is totally different. Marine organisms live in water; terrestrial organisms live in air. Environmental change in the sea has a much lower frequency than on land, both in time and in space.[1]

Open system

Marine systems are more open than terrestrial ones and dispersal of species may occur over much broader ranges. Although most species in the ocean are benthic and live attached to or buried in a substratum, in coastal seas a very large proportion have larvae that remain floating in the water for a period of days to months. These high dispersal capacities are often associated with very high fecundities and this has important consequences for their genetic structure and their evolution.[1]

Primary production by small organisms

The main marine primary producers are very small and often mobile (phytoplankton), whereas on land primary producers are large and static (plants). The standing stock of grazers in the sea is higher than that of primary producers; the opposite is true on land. Ocean productivity is on average far lower than land productivity. In the largest part of the ocean, beneath the thin surface layers, no photosynthesis occurs at all.[1]

Large carnivores

High-level carnivores often play key roles in structuring marine biodiversity, but are exploited heavily, with unquantified but cascading effects on biodiversity and ecosystem functions. This does not occur on land, where the ecosystems are dominated by large herbivores and increasingly by humans, who monopolise about 40% of the total world primary production.[1]

High exploitation

A greater variety of species at a higher trophic level is exploited in the seas than on the land: man exploits over 400 species as food resources from the marine environment, whereas on land only tens of species are harvested for commercial use. Exploitation of marine biodiversity is also far less managed than on land and amounts to the strategy that hunter-gatherers abandoned on land over 10,000 years ago, yet exploitation technology is becoming so advanced that many marine species are threatened with extinction. Insufficient consideration has been given to the unexpected and unpredictable long-term effects that such primitive food-gathering practices engender.[1]

Vulnerability to pollution

All pollution (of air, land and freshwater) ultimately enters the sea. Marine biodiversity is thus most exposed to and critically influences the fate of pollutants in the world. Yet marine species are probably least resistant to pollutants. The spread of pollutants in marine food chains, and therefore the quality of marine food, is uncontrollable by man.[1][2]

Further reading

Marbef booklet Marine Biodiversity Ecosystem Functioning