Results from experiments and investigations on the kelp crab Taliepus dentatus

Studies of thermal tolerance in marine ectotherms are key in understanding climate effects on ecosystems; however, tolerance of their larval stages has rarely been analyzed. Larval stages are expected to be particularly sensitive. Thermal stress may affect their potential for dispersal and zoogeographical distribution. A mismatch between oxygen demand and the limited capacity of oxygen supply to tissues has been hypothesized to be the first mechanism restricting survival at thermal extremes. Therefore, thermal tolerance of stage zoea I larvae was examined in two populations of the Chilean kelp crab Taliepus dentatus, which are separated by latitude and the thermal regime. We measured temperature-dependent activity, oxygen consumption, cardiac performance, body mass and the carbon (C) and nitrogen (N) composition in order to: (1) examine thermal effects from organismal to cellular levels, and (2) compare the thermal tolerance of larvae from two environmental temperature regimes. We found that larval performance is affected at thermal extremes indicated by decreases in activity, mainly in maxilliped beat rates, followed by decreases in oxygen consumption rates. Cardiac stroke volume was almost temperature-independent. Through changes in heart rate, cardiac output supported oxygen demand within the thermal window whereas at low and high temperature extremes heart rate declined. The comparison between southern and central populations suggests the adaptation of southern larvae to a colder temperature regime, with higher cardiac outputs due to increased cardiac stroke volumes, larger body sizes but similar body composition as indicated by similar C:N ratios. This limited but clear differentiation of thermal windows between populations allows the species to widen its biogeographical range.

Investigations on the Chilean kelp crab Taliepus dentatus

Physiological responses of larval stages can differ from those of the adults, affecting key ecological processes. Therefore, developing a mechanistic understanding of larval responses to environmental conditions is essential vis-à-vis climate change. We studied the thermal tolerance windows, defined by lower and upper pejus (Tp) and critical temperatures (Tc), of zoea I, II, and megalopa stages of the Chilean kelp crab Taliepus dentatus. Tp limits determine the temperature range where aerobic scope is maximal and functioning of the organism is unrestrained and were estimated from direct observations of larval activity. Tc limits define the transition from aerobic to anaerobic metabolism, and were estimated from the relationship between standard metabolic rate and temperature. Zoea I showed the broadest, Zoea II an intermediate, and megalopae the narrowest tolerance window (Tp). Optimum performance in megalopae was limited to Tp between 11 and 15°C, while their Tc ranged between 7 and 19°C. Although Tc may be seldom encountered by larvae, the narrower Tp temperatures can frequently expose larvae to unfavorable conditions that can drastically constrain their performance. Temperatures beyond the Tp range of megalopae have been observed in most spring and summer months in central Chile, and can have important consequences for larval swimming performance and impair their ability to avoid predators or settle successfully. Besides the well-documented effects of temperature on development time, variability in field temperatures beyond Tp can affect performance of particular larval stages, which could drive large-scale variability in recruitment and population dynamics of T. dentatus and possibly other invertebrate species.