A guide for planners and managers - IUCN

22 MARINE AND COASTAL
PROTECTED AREAS
FIGURE I-7.
Whales breed in several protected lagoons in Baja California, Mexico.
maintained. It is this diversity that enables recruitment of larvae best suited to the new
conditions in decimated areas, and it is recruitment that begins community restoration.
Genetic material determines how much species can adapt to changes in their
environment. In several organisms, including some fish species, individuals having
the most genetic variation (and hence greater tolerance of environmental changes)
have been shown to have better survival rates or higher relative growth rates
(FAO/UNEP, 1981). New genetic variation arises in a population from either the
spontaneous mutation of a gene or the immigration of genetically different individuals
from a different population of the same species. For example, there are pale or
smoky varieties of the tiger cowrie (Cypraea tigris) and dark ones. These varieties are
the expressions of different genotypes, i.e., combinations of genes. Alternative forms
of a particular gene (called alleles) cause variation among individual organisms, for
example, in the background colour of shell. The number and relative abundance of
alternative forms of a gene in a population is a measure of genetic variation (called
heterozygosity). The total amount of genetic variation in all populations of a species
is a measure of its genetic diversity. Finally, genetic diversity is a measure of a
population’s ability to adapt to environmental change or stress, and thus of its ability
to survive (FAO/UNEP, 1981).
Genetic differences may explain the differential susceptibilities of corals of the
same species to elevated seawater temperatures at various locations. While unable
to save a population in one location, these differences could confer resilience to
climate change in a species over all its range. Although the mechanism is not clear,
an example of susceptibility to climate change is provided by the corals along the
Photo by John Clark.