166
The Biology of Sea Turtles, Vol. II
Sea turtles are at particular risk from the stresses presented by degraded tropical
coastal marine environments. Indeed, the high public awareness of sea turtles is such
that they can serve as effective sentinels of tropical coastal marine ecosystem health
(Aguirre and Lutz, in press).
6.3 STRESSORS
This review selects some of the most critical identified natural and anthropogenic
stressors of sea turtle physiology, while omitting some (oil, nesting, capture stress)
that have been previously reviewed (see Lutz and Musick, 1997).
6.3.1 T EMPERATURE
Both high and low temperatures are known to negatively impact sea turtle physiology,
affecting feeding behavior, acid–base and ion balance, and stress hormone levels.
6.3.1.1 Hypothermia
Temperature has a marked effect on the feeding rates of sea turtles. At 20 ∞ C Kemp’s
ridley turtles decreased food consumption to 50% of control levels (at 26°C), and a
similar reduction in food intake was found in green turtles at 15°C (Moon et al.,
1997). Below 15 ∞ C both species ceased feeding. Interestingly, Moon et al. (1997)
found that green and Kemp’s ridley turtles’ swimming behavior differed as temperatures decreased. When temperatures dropped below 20°C green turtles reduced
swimming activity, but at these temperatures the ridleys became very agitated. Below
15°C both species became semidormant, hardly moving and only coming to the
surface at intervals of up to 3 h to breathe. Field evidence supports these findings.
During cold temperatures in winter, loggerhead turtles in Tunisian waters reduce
overall activity even though they continue to forage (Laurent and Lescure, 1994).
Temperature also profoundly influences the physiology of sea turtles. In ridleys
and greens, both venous blood partial pressure of oxygen (pO 2 ) and partial pressure
of carbon dioxide (pCO 2 ) decreased with temperature (Moon et al., 1997), whereas
venous blood pH increased. Similar temperature-dependent changes in blood pH,
pCO 2 , and pO 2 have been widely found in other reptiles, including loggerhead sea
turtles (Lutz et al., 1989). Temperature-related adjustments of blood pH in the
loggerhead appeared to be managed at both the lung and tissue (ion exchange) levels
(Lutz et al., 1989). In both wild (Lutz and Dunbar-Cooper, 1987) and captive (Lutz
et al., 1989) loggerheads, plasma potassium increased with temperature, which may
be related to cellular-mediated adjustments in blood pH. Excessively low temperatures can also interfere with physiological functioning. For example, there was an
abrupt failure in pH homeostasis and a sharp increase in blood lactate at temperatures
below 15°C in the loggerhead (Lutz et al., 1989). At 10°C the loggerheads were
lethargic and “floated” (Lutz, personal observation). Such positive buoyancy is
probably due to cessation of intestinal mobility and the collection of ferment gases
and is commonly observed in cold stunning.
1123 book.book Page 166 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
Sea turtles are at particular risk from the stresses presented by degraded tropical
coastal marine environments. Indeed, the high public awareness of sea turtles is such
that they can serve as effective sentinels of tropical coastal marine ecosystem health
(Aguirre and Lutz, in press).
6.3 STRESSORS
This review selects some of the most critical identified natural and anthropogenic
stressors of sea turtle physiology, while omitting some (oil, nesting, capture stress)
that have been previously reviewed (see Lutz and Musick, 1997).
6.3.1 T EMPERATURE
Both high and low temperatures are known to negatively impact sea turtle physiology,
affecting feeding behavior, acid–base and ion balance, and stress hormone levels.
6.3.1.1 Hypothermia
Temperature has a marked effect on the feeding rates of sea turtles. At 20 ∞ C Kemp’s
ridley turtles decreased food consumption to 50% of control levels (at 26°C), and a
similar reduction in food intake was found in green turtles at 15°C (Moon et al.,
1997). Below 15 ∞ C both species ceased feeding. Interestingly, Moon et al. (1997)
found that green and Kemp’s ridley turtles’ swimming behavior differed as temperatures decreased. When temperatures dropped below 20°C green turtles reduced
swimming activity, but at these temperatures the ridleys became very agitated. Below
15°C both species became semidormant, hardly moving and only coming to the
surface at intervals of up to 3 h to breathe. Field evidence supports these findings.
During cold temperatures in winter, loggerhead turtles in Tunisian waters reduce
overall activity even though they continue to forage (Laurent and Lescure, 1994).
Temperature also profoundly influences the physiology of sea turtles. In ridleys
and greens, both venous blood partial pressure of oxygen (pO 2 ) and partial pressure
of carbon dioxide (pCO 2 ) decreased with temperature (Moon et al., 1997), whereas
venous blood pH increased. Similar temperature-dependent changes in blood pH,
pCO 2 , and pO 2 have been widely found in other reptiles, including loggerhead sea
turtles (Lutz et al., 1989). Temperature-related adjustments of blood pH in the
loggerhead appeared to be managed at both the lung and tissue (ion exchange) levels
(Lutz et al., 1989). In both wild (Lutz and Dunbar-Cooper, 1987) and captive (Lutz
et al., 1989) loggerheads, plasma potassium increased with temperature, which may
be related to cellular-mediated adjustments in blood pH. Excessively low temperatures can also interfere with physiological functioning. For example, there was an
abrupt failure in pH homeostasis and a sharp increase in blood lactate at temperatures
below 15°C in the loggerhead (Lutz et al., 1989). At 10°C the loggerheads were
lethargic and “floated” (Lutz, personal observation). Such positive buoyancy is
probably due to cessation of intestinal mobility and the collection of ferment gases
and is commonly observed in cold stunning.
1123 book.book Page 166 Monday, November 11, 2002 11:11 AM