Physiological and Genetic Responses to Environmental Stress
173
some PCBs could cause a reversal of gonadal sex in freshwater turtles ( Trachemys
scripta ), which, like sea turtles, have temperature-dependent sex determination. In
some areas, sex-reversal in turtles is so prevalent that it can be utilized as a marker
of environmental contamination.
The exposure of sea turtle eggs to such pollutants could be significant, because
there is evidence that females offload contaminants to their eggs (Mckenzie et al.,
1999). In one study, eggs sampled from 20 nests in northwest Florida had detectable
amounts of polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyldichloroethane (DDD, a DDT metabolite), and PCBs (Alam and Brim, 2000). However,
the effects of these compounds on sea turtles are not known. A direct application
of DDE, another estrogen-like compound, to green turtle eggs did not alter normal
sex ratios, incubation times, hatchling success or size, or number of deformities
(Podreka et al., 1998).
6.3.3 E UTROPHICATION AND A LGAL B LOOMS
Eutrophication caused by excess nutrient pollution in coastal waters, particularly of
nitrogen derived from sewage and agricultural fertilizers, affects sea turtles both
directly and indirectly (Magnien et al., 1992; Burkholder, 1998). In particular, there
is a growing link between harmful algal blooms (HABs) and eutrophication. Cyanobacteria blooms in Moreton Bay, Australia, for example, have been increasing in
recent years in both size and severity, resulting in loss of seagrass beds, decreased
fish catches, and increased levels of ammonia and toxins, including tumor promoters
and immunosuppressants (Osborne et al., 2001). HABs thus may have many direct
(toxic) and indirect harmful impacts on sea turtles and other marine fauna; in
Moreton Bay, the cyanobacteria blooms affect green turtles by decreasing feeding
directly (as well as indirectly through the loss of seagrasses) and through the ingestion of toxins (Arthur et al., 2002). A strong association has also been noted between
the prevalence of a variety of diseases and coastal pollution in multiple taxonomic
groups, such that the occurrence of the diseases derived from pathogens or algalderived biotoxins often serve as indicators of declining ecological integrity in coastal
areas (Epstein et al., 1998). Groups adversely affected by eutrophication-related
diseases include humans, birds, marine mammals and turtles, fish, invertebrates, and
seagrass beds (Epstein et al., 1998).
The most prevalent tropical–semitropical algal blooms are the so-called red tides
(which may be any color or even be invisible), which are due primarily to dinoflagellate
blooms and can lead to morbidity and mortality in many species. Immediate effects
occur through aerosolized transport, and the sea turtle’s mode of respiration (rapid
inhalation to fill the lungs before a dive) puts the sea turtle at special risk here. Longterm effects may occur through the consumption of prey and toxin bioaccumulation.
Long-term exposure to biotoxins may exert more subtle, sublethal effects such
as impaired feeding, physiological dysfunction, impaired immune function, and
reduced growth and reproduction. Long-term effects often emerge as an increased
susceptibility to disease (immunosuppression) and in the development of neoplasia
(Epstein et al., 1998). Deaths are often attributed to viral factors as the immediate
cause of mortality, whereas viral expression and host immunity have been affected
1123 book.book Page 173 Monday, November 11, 2002 11:11 AM
173
some PCBs could cause a reversal of gonadal sex in freshwater turtles ( Trachemys
scripta ), which, like sea turtles, have temperature-dependent sex determination. In
some areas, sex-reversal in turtles is so prevalent that it can be utilized as a marker
of environmental contamination.
The exposure of sea turtle eggs to such pollutants could be significant, because
there is evidence that females offload contaminants to their eggs (Mckenzie et al.,
1999). In one study, eggs sampled from 20 nests in northwest Florida had detectable
amounts of polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyldichloroethane (DDD, a DDT metabolite), and PCBs (Alam and Brim, 2000). However,
the effects of these compounds on sea turtles are not known. A direct application
of DDE, another estrogen-like compound, to green turtle eggs did not alter normal
sex ratios, incubation times, hatchling success or size, or number of deformities
(Podreka et al., 1998).
6.3.3 E UTROPHICATION AND A LGAL B LOOMS
Eutrophication caused by excess nutrient pollution in coastal waters, particularly of
nitrogen derived from sewage and agricultural fertilizers, affects sea turtles both
directly and indirectly (Magnien et al., 1992; Burkholder, 1998). In particular, there
is a growing link between harmful algal blooms (HABs) and eutrophication. Cyanobacteria blooms in Moreton Bay, Australia, for example, have been increasing in
recent years in both size and severity, resulting in loss of seagrass beds, decreased
fish catches, and increased levels of ammonia and toxins, including tumor promoters
and immunosuppressants (Osborne et al., 2001). HABs thus may have many direct
(toxic) and indirect harmful impacts on sea turtles and other marine fauna; in
Moreton Bay, the cyanobacteria blooms affect green turtles by decreasing feeding
directly (as well as indirectly through the loss of seagrasses) and through the ingestion of toxins (Arthur et al., 2002). A strong association has also been noted between
the prevalence of a variety of diseases and coastal pollution in multiple taxonomic
groups, such that the occurrence of the diseases derived from pathogens or algalderived biotoxins often serve as indicators of declining ecological integrity in coastal
areas (Epstein et al., 1998). Groups adversely affected by eutrophication-related
diseases include humans, birds, marine mammals and turtles, fish, invertebrates, and
seagrass beds (Epstein et al., 1998).
The most prevalent tropical–semitropical algal blooms are the so-called red tides
(which may be any color or even be invisible), which are due primarily to dinoflagellate
blooms and can lead to morbidity and mortality in many species. Immediate effects
occur through aerosolized transport, and the sea turtle’s mode of respiration (rapid
inhalation to fill the lungs before a dive) puts the sea turtle at special risk here. Longterm effects may occur through the consumption of prey and toxin bioaccumulation.
Long-term exposure to biotoxins may exert more subtle, sublethal effects such
as impaired feeding, physiological dysfunction, impaired immune function, and
reduced growth and reproduction. Long-term effects often emerge as an increased
susceptibility to disease (immunosuppression) and in the development of neoplasia
(Epstein et al., 1998). Deaths are often attributed to viral factors as the immediate
cause of mortality, whereas viral expression and host immunity have been affected
1123 book.book Page 173 Monday, November 11, 2002 11:11 AM