Temperature adaptation in the early ontogenesis of decapod crustaceans in the Humboldt Current under ENSO impact

The Humboldt Current System is a highly productive ecosystem supportingone of the worlds largest fisheries. The oceanographic characteristics with yearroundupwelling, low seasonality, and comparably low latitudinal changes allowwide distributional ranges of species. One of these species is the hairy crab Cancersetosus (Molina 1782) with a distributional range from 2°13S to 46°00S, whichcorresponds to a temperature range from ~10 to ~20 °C. The relatively temperaturestable habitat is subjected to the El Niño Southern Oscillation, which might lead todrastic temperature changes of up to 10 °C. Temperature is one of the mostimportant determining factors of species distribution. The early ontogeny ofbrachyurans was detected to be the bottleneck for survival, as the early life stagesare especially sensitive to temperature changes. The pelagic phase presents thedispersal stage of the life cycle and influences biology, ecology, evolution andrecruitment of a species. This study analyzed the influence of temperature changeson different levels of biological organisation at different simulated habitattemperatures ranging from 12 °C (LN temperature) to 24 °C (EN temperature).Results of this thesis show that C. setosus Zoeal instars react highly sensitive totemperature changes which is reflected in the whole organism function as well as inlower levels of organism complexity.Survival rates of larvae reared at different temperatures define a very limitedwindow of tolerated temperatures and the duration of larval instars variesdependent on the temperature. Those features seem to vary dependent on thelatitude, showing thermal adaptation of larvae. The elemental composition of larvaerevealed that the larval metabolism is very sensitive to temperature changes andthe composition of larvae varies even within the small range of toleratedtemperatures. Elemental analyses furthermore revealed that the temperature withmaximum growth rates of C. setosus larvae varies with larval instar, probably beingacclimated especially to the path of larval dispersal of larvae from the Antofagastabay. Additionally thermal sensitivity seems to increase with instar. High temperaturesensitivity was also found in larval morphometric traits. The temperatureencountered during embryonic and larval development as well as the latitudinalorigin of larvae influenced the morphometric parameters. Generally larger larvaeare produced at cold temperatures. This phenotypic plasticity might be a key to thespecies success to cover a wide distributional range and to survive highly variablehabitat conditions.The oxygen consumption rates show, that cold acclimated larvae displaythermal plasticity (high Q10 values) being able to compensate for elevatedtemperatures. Routine metabolic rates of warm acclimated animals were found tofunction at its upper limits and had only very limited capacities to adjust themetabolism to further increased temperatures. The properties of the metabolic keyenzyme citrate synthase (CS) revealed a certain level of acclimation in cold andwarm acclimated animals, but CS was found to be a possible key for thermallimitation of C. setosus larvae at elevated temperatures.Due to the highly temperature sensitive metabolism, larval survival duringEN/LN events does not seem likely, although acclimation mechanisms could beidentified within this study. Further studies on phenotypic and physiologicalplasticity and acclimation processes of different populations within the distributionalrange would provide further knowledge about mechanisms that allow such a widegeographical species distribution. It would be crucial to reveal if temperatureconditioning of larvae might take place during embryonic development or if it isgenetically defined, which would also have implications for larval recruitment. Themaintenance of the northern stock that frequently is encountered by the fluctuationsof ENSO seems to be dependent on the survival of adult specimen or arecolonization after strong catastrophic EN events. Further investigation of larvaldispersal modes, recruitment and recolonization would be of great use whendetermining optimal spacing and size of potential protected areas