A guide for planners and managers - IUCN

20 MARINE AND COASTAL
PROTECTED AREAS
FIGURE I-6.
Diverse habitats encourage diverse species; Yanbu Reef, Red Sea.
Also, certain species, such as predatory or nonterritorial fishes, may have large
area requirements, especially if they are poor at dispersing among separated habitats,
and may be absent in smaller habitat areas. For example, in the Chagos Archipelago
(West-Central Indian Ocean) specific corals were found only on reefs larger than a
certain minimum size (Salm, 1995).
1.4 Preserving Genetic Diversity
Wild genetic resources are lost either through the extinction of a species or through
the extinction of individual populations of that species (genetic impoverishment). The
first process is final and irreversible. The second is a matter of degree and is to some
extent reversible (FAO/UNEP, 1981). In the sea, where endemism (the restricted
distribution of a species to a relatively small geographic area) is low compared to that
on land, the problem is less one of species extinction than of genetic impoverishment.
No significant or detectable increase in extinction rates of fish species has been
observed in the ocean, but overfishing, pollution, and habitat destruction have
extinguished populations (Norse, 1993). Organisms occupying diminishing habitats
will likely never again reach their present levels of genetic diversity.
Human activities diminish genetic variation and encourage the extinction of
species in a number of ways:
Pollution and other environmental changes that stress a population, causing
differential mortality, extinction, or both.
Fishing pressure, which can favor some genotypes over others.
Photo by John Clark.