(i.e., are endothermic), the body temperatures of estuarine
invertebrates and plants are driven by the exchange of heat
with the ambient environment – they are ectothermic –
and can vary substantially over the course of a day, season,
and year.
Heat exchange and body temperature
Intertidal organisms in estuaries are subject to diel tidal fluctuations, and so their body temperatures at low tide aerial
exposure can significantly differ than that during submergence (Jost and Helmuth, 2007). The dominant driver
of heat input in these systems is solar radiation, so that the
temperature of an animal’s or a plant’s body is generally
much warmer than the temperature of the surrounding air
during the day; at night, as heat is lost through infrared
radiation, organisms can be several degrees cooler than
the air. The amount of shading can have a large influence
as can the amount of wind (convection). Thus, for example,
snails at the top of a marsh canopy can have temperatures
different from animals near the substrate (Iacarella and
Helmuth, 2011). Solar heating can also increase the temperature of shallow waters so that continually submerged estuarine organisms can in some cases experience large
fluctuations in temperature.
The behavioral and morphological characteristics of an
organism dictate the rate of heat transfer between the surrounding environment and the organism, and the size,
shape, mass, and color of an organism can affect body
temperature. Thus, two organisms exposed to identical
environmental conditions can display very different body
temperatures from one another, even when neither is making any appreciable metabolic heat (Figure 1). The behavior of an organism can also affect rates of heating and
cooling. Organisms such as algae and sea stars with wet
surfaces lose considerable amounts of heat via the evaporation of water, although this water loss potentially comes
at the cost of desiccation (Iacarella and Helmuth, 2011).
As above, the movement of organisms into shaded crevices, on the shaded sides of rocks, or depth in the sediment
can lead to temperature differences over the scale of centimeters that exceed those observed over thousands of kilometers of latitude (Denny et al., 2011).
Direct and indirect effects of body
temperature on estuarine organisms
Organism temperature has numerous effects on physiological processes in estuarine organisms (Somero, 2011),
including functioning of critical enzymes and other
cellular functions, changes in metabolic rate, and increases
in metabolic oxygen demand (Pörtner, 2010). For an
excellent overview of physiological impacts of temperature on marine organisms, see Somero (2011). The thermal
biology of estuarine organisms also indirectly affects species through interactions such as competition and predation (Russell et al., 2012). Wethey (1984) showed that
the competitive ability of barnacles is affected by their
temperatures and that the zonation of two barnacle species
could be explained by their differential physiological sensitivity to body temperature. Sanford (2002) demonstrated
that rates of predation by the keystone sea star Pisaster
were elevated at increased water temperature, and conversely, Pincebourde et al. (2008) reported decreases in
predation rate by up to 40 % during elevated temperatures
at low tide in air.
Monitoring temperature
In water, the temperature of a marine organism approximates that of the surrounding water, although in some
Thermal Biology, Figure 1 Photographic image of the intertidal community (left) demonstrates species vertical zonation and substrate
heterogeneity, with concurrent infrared (IR) thermal image (right) of the same site during low tide. The IR image demonstrates the
large variability in temperatures (15–37
C) observed in this small section of shore, which may in part drive small-scale distribution and
zonation patterns. Photograph courtesy of N. Colvard and B. Helmuth, FLIR E60 Infrared Camera.
662
THERMAL BIOLOGY
invertebrates and plants are driven by the exchange of heat
with the ambient environment – they are ectothermic –
and can vary substantially over the course of a day, season,
and year.
Heat exchange and body temperature
Intertidal organisms in estuaries are subject to diel tidal fluctuations, and so their body temperatures at low tide aerial
exposure can significantly differ than that during submergence (Jost and Helmuth, 2007). The dominant driver
of heat input in these systems is solar radiation, so that the
temperature of an animal’s or a plant’s body is generally
much warmer than the temperature of the surrounding air
during the day; at night, as heat is lost through infrared
radiation, organisms can be several degrees cooler than
the air. The amount of shading can have a large influence
as can the amount of wind (convection). Thus, for example,
snails at the top of a marsh canopy can have temperatures
different from animals near the substrate (Iacarella and
Helmuth, 2011). Solar heating can also increase the temperature of shallow waters so that continually submerged estuarine organisms can in some cases experience large
fluctuations in temperature.
The behavioral and morphological characteristics of an
organism dictate the rate of heat transfer between the surrounding environment and the organism, and the size,
shape, mass, and color of an organism can affect body
temperature. Thus, two organisms exposed to identical
environmental conditions can display very different body
temperatures from one another, even when neither is making any appreciable metabolic heat (Figure 1). The behavior of an organism can also affect rates of heating and
cooling. Organisms such as algae and sea stars with wet
surfaces lose considerable amounts of heat via the evaporation of water, although this water loss potentially comes
at the cost of desiccation (Iacarella and Helmuth, 2011).
As above, the movement of organisms into shaded crevices, on the shaded sides of rocks, or depth in the sediment
can lead to temperature differences over the scale of centimeters that exceed those observed over thousands of kilometers of latitude (Denny et al., 2011).
Direct and indirect effects of body
temperature on estuarine organisms
Organism temperature has numerous effects on physiological processes in estuarine organisms (Somero, 2011),
including functioning of critical enzymes and other
cellular functions, changes in metabolic rate, and increases
in metabolic oxygen demand (Pörtner, 2010). For an
excellent overview of physiological impacts of temperature on marine organisms, see Somero (2011). The thermal
biology of estuarine organisms also indirectly affects species through interactions such as competition and predation (Russell et al., 2012). Wethey (1984) showed that
the competitive ability of barnacles is affected by their
temperatures and that the zonation of two barnacle species
could be explained by their differential physiological sensitivity to body temperature. Sanford (2002) demonstrated
that rates of predation by the keystone sea star Pisaster
were elevated at increased water temperature, and conversely, Pincebourde et al. (2008) reported decreases in
predation rate by up to 40 % during elevated temperatures
at low tide in air.
Monitoring temperature
In water, the temperature of a marine organism approximates that of the surrounding water, although in some
Thermal Biology, Figure 1 Photographic image of the intertidal community (left) demonstrates species vertical zonation and substrate
heterogeneity, with concurrent infrared (IR) thermal image (right) of the same site during low tide. The IR image demonstrates the
large variability in temperatures (15–37
C) observed in this small section of shore, which may in part drive small-scale distribution and
zonation patterns. Photograph courtesy of N. Colvard and B. Helmuth, FLIR E60 Infrared Camera.
662
THERMAL BIOLOGY