Effects
of temperature and body size on the physiological energetics of the stalked sea
squirt Styela clava
Chang-Keun
Kang, Young-Jae Lee, Eunah Han, Hyun-Je Park, Sung-Gyu Yun, Won Chan Lee
An
assessment of the patterns of thermal acclimation of physiological processes of
the stalked sea squirt Styela clava
is needed to further understand growth patterns associated with large seasonal
fluctuations in ambient temperature. The effects of different exposure
temperatures on physiological processes of S.
clava were measured at 5, 10, 15, 20, and 25 ¡ÆC. The impact of temperature
on energy balance at a whole organism level was then assessed by scope for
growth (SFG) and net growth efficiency (K2) measures. Physiological rates of S. clava were well correlated with its
dry tissue weight (DW). Positive allometry with DW indicated that all physiological
rates investigated were generally higher in the larger individuals regardless
of temperature. Some allometric equations (e.g., feces production rate vs. DW and
respiration rate vs. DW) exhibited identical estimates of exponents, enabling
accurate comparisons of the rates across temperatures. In contrast, disparities
across temperatures of the values for the weight exponent were detected in
other allometric quations, revealing that thermal effects on these rates have
different degrees for large and small individuals. The SFG value in S. clava of different sizes was similar
at lower temperatures (5–10 ¡ÆC), peaking at 15 ¡ÆC. The SFG was positive with a
relatively constant K2 in this temperature range. This positive energy balance
reflects the reduction in metabolic costs at lower temperatures. In contrast,
increased metabolic costs at higher temperatures (20–25 ¡ÆC) resulted in lowered
SFG and K2 values, ndicating that the feeding rate did not increase as greatly
in compensation for the increased metabolic costs at higher temperatures. The
lowered absorption at 25 ¡ÆC (compared with 20 ¡ÆC) resulted in negative SFG and
K2 values. Finally, our results confirm that the absence of compensatory
adjustment to warmer conditions leads to energetic disruption at a whole
organism level at such temperatures.
Journal of Experimental Marine Biology and Ecology 462 (2015) 105–112