Behavioral thermoregulation of the common brown shrimp (Crangon crangon, L.) throughout the seasonal cycle

Abstract

Ectothermic organisms rely on behavioral thermoregulation to modulate their body temperature and the final thermal preferendum (FTP) paradigm (FTPP) postulates that a given species holds a species-specific FTP. The FTPP, however, has been challenged by a considerable amount of recent findings on vertebrate ectotherms, indicating that the FTP is not as static as originally postulated but can be modulated by various factors. In contrast to vertebrates, evidence from invertebrate ectotherms is far more limited. To test for the validity of the FTPP and to study whether behavioral thermoregulation in a marine invertebrate varies seasonally, thermal preferenda of the common brown shrimp (Crangon crangon, L.) were determined through a 14month period. Thermal preferenda of males and females of different size groups were measured in an annular chamber system (4–25°C) using the gravitational method for thermal preference testing. The results revealed that brown shrimp behaviorally selected a wide range of temperatures and did not show a single or constant thermal preferendum. Thermal preference was modulated following a seasonal pattern suggesting the existence of distinct seasonal preference zones rather than a species-specific preference temperature. Brown shrimp selected low temperatures during winter, however, a difference of 5°C in preferred temperature was observed between a cold and a relatively mild one. Highest thermal preferenda did not coincide with field water temperatures but were observed after field water temperatures exceeded the annual temperature peak. Besides season, body size of brown shrimp significantly affected thermal selection and small individuals selected higher temperatures compared to large ones. A significant interaction of body size and water temperature at which the shrimp were caught was detected. The study further provides evidence that cohort identity as well as female reproductive state may affect thermal preference as well. The results of the study reveal that thermal selection in brown shrimp is complex, not static and that preference temperature can be modulated by various factors, representing the first evidence for a marine invertebrate ectotherm.