164
The Biology of Sea Turtles, Vol. II
that bedevil an exact scientific definition. In biology, the term embraces psychology
to biomechanics, and it is only in the latter that it is used in the precise and
quantitative terms of Hooke’s law, where stress (the deforming force) is proportional
to strain (the deformation). For the rest there is no agreement about whether stress
refers to external or internal factors, what it consists of, or how it can be measured.
Nevertheless, the fact that the concept is still widely used in biology, from the
molecular to ecosystem level, indicates its utility and its necessity (Bonga, 1997).
Perhaps the term should be used only in combination with the causal factor (i.e.,
crowding stress, temperature stress), with the concept that there is an (identified)
tolerance range for the external factor within which the individual or community
copes by means of adaptive responses, but that outside this range there is a quantitative or qualitative break in the (described) response.
The adaptive function of the stress response is to accommodate changes in the
environment (stressors) by adjustments in behavior and/or changes in physiology. However, an excessive exposure to the stressor, in either intensity or duration, will result in
dysfunctional debilitating responses. Environmental conditions to which an animal
cannot adapt lead to both transient and relatively long-term physiological changes. Such
changes often contribute to the development of disease, especially if the organism is
exposed at the same time to potentially pathogenic stimuli. Various stressors, however,
do not all produce the same outcomes; effects will depend on the quality, quantity, and
duration of the stressor; the temporal relationship between the exposure to a stressor
and the introduction of pathogenic stimuli; environmental conditions; and a variety of
host factors (age, species, gender, etc.) (Ader and Cohen, 1993).
This chapter presents an overview of the relationship between sea turtles and
some of the more important stressful aspects of their environment. Because stress
is such a broad topic, many aspects of stress have been treated in previous chapters
and elsewhere in this volume (see Lutcavage et al., 1997; George, 1997; Epperly,
Chapter 13; and Herbst and Jacobson, Chapter 15, this volume). This chapter reviews
a few environmental stressors of particular significance to sea turtles: temperature,
chemical pollutants (organic and inorganic) and habitat degradation, and the sea
turtle’s physiological and potential genetic responses are discussed. Distinct environmental stressors affect the terrestrial nest and hatchlings, and are discussed
separately from the other (oceanic) life stages .
6.2 WHY SEA TURTLES ARE AT SPECIAL RISK
Sea turtles naturally encounter a wide variety of stressors, both natural and anthropogenic, including environmental factors (salinity, pollution, temperature), physiological
factors (hypoxia, acid–base imbalance, nutritional status), physical factors (trauma),
and biological factors (toxic blooms, parasite burden, disease). Although they are
physically robust and able to accommodate severe physical damage, sea turtles appear
to be surprisingly susceptible to biological and chemical insults (Lutcavage and Lutz,
1997). For example, in the green sea turtle even a short exposure to crude oil shuts
down the salt gland, produces dysplasia of the epidermal epithelium, and destroys the
cellular organization of the skin layers, thus opening routes for infection (Lutcavage
et al., 1995). The effects of many stressors, however, are likely to be less obvious, as
in the (unknown) long-term effects of toxin exposure and bioaccumulation.
1123 book.book Page 164 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
that bedevil an exact scientific definition. In biology, the term embraces psychology
to biomechanics, and it is only in the latter that it is used in the precise and
quantitative terms of Hooke’s law, where stress (the deforming force) is proportional
to strain (the deformation). For the rest there is no agreement about whether stress
refers to external or internal factors, what it consists of, or how it can be measured.
Nevertheless, the fact that the concept is still widely used in biology, from the
molecular to ecosystem level, indicates its utility and its necessity (Bonga, 1997).
Perhaps the term should be used only in combination with the causal factor (i.e.,
crowding stress, temperature stress), with the concept that there is an (identified)
tolerance range for the external factor within which the individual or community
copes by means of adaptive responses, but that outside this range there is a quantitative or qualitative break in the (described) response.
The adaptive function of the stress response is to accommodate changes in the
environment (stressors) by adjustments in behavior and/or changes in physiology. However, an excessive exposure to the stressor, in either intensity or duration, will result in
dysfunctional debilitating responses. Environmental conditions to which an animal
cannot adapt lead to both transient and relatively long-term physiological changes. Such
changes often contribute to the development of disease, especially if the organism is
exposed at the same time to potentially pathogenic stimuli. Various stressors, however,
do not all produce the same outcomes; effects will depend on the quality, quantity, and
duration of the stressor; the temporal relationship between the exposure to a stressor
and the introduction of pathogenic stimuli; environmental conditions; and a variety of
host factors (age, species, gender, etc.) (Ader and Cohen, 1993).
This chapter presents an overview of the relationship between sea turtles and
some of the more important stressful aspects of their environment. Because stress
is such a broad topic, many aspects of stress have been treated in previous chapters
and elsewhere in this volume (see Lutcavage et al., 1997; George, 1997; Epperly,
Chapter 13; and Herbst and Jacobson, Chapter 15, this volume). This chapter reviews
a few environmental stressors of particular significance to sea turtles: temperature,
chemical pollutants (organic and inorganic) and habitat degradation, and the sea
turtle’s physiological and potential genetic responses are discussed. Distinct environmental stressors affect the terrestrial nest and hatchlings, and are discussed
separately from the other (oceanic) life stages .
6.2 WHY SEA TURTLES ARE AT SPECIAL RISK
Sea turtles naturally encounter a wide variety of stressors, both natural and anthropogenic, including environmental factors (salinity, pollution, temperature), physiological
factors (hypoxia, acid–base imbalance, nutritional status), physical factors (trauma),
and biological factors (toxic blooms, parasite burden, disease). Although they are
physically robust and able to accommodate severe physical damage, sea turtles appear
to be surprisingly susceptible to biological and chemical insults (Lutcavage and Lutz,
1997). For example, in the green sea turtle even a short exposure to crude oil shuts
down the salt gland, produces dysplasia of the epidermal epithelium, and destroys the
cellular organization of the skin layers, thus opening routes for infection (Lutcavage
et al., 1995). The effects of many stressors, however, are likely to be less obvious, as
in the (unknown) long-term effects of toxin exposure and bioaccumulation.
1123 book.book Page 164 Monday, November 11, 2002 11:11 AM