whole-jensen-thesis.pdf (1.5 MB)
Physiological responses to different environmental and culture conditions during ontogeny of the spiny lobster, Sagmariasus verreauxi
thesisposted on 2023-05-26, 00:02 authored by Jensen, MA
Very little is known about the metabolic and biochemical physiology of spiny lobsters as they develop. An improved understanding of the physiological responses of spiny lobsters to different environmental and culture conditions during ontogeny is essential for gaining a better understanding of environmental influences on wild populations and for their successful propagation. This study addresses important gaps in our knowledge by examining stage-specific changes in metabolic rates, ammonia-N excretion rates, thermal tolerance thresholds, and whole body and haemolymph biochemistry of larval and juvenile Sagmariasus (Jasus) verreauxi in order to observe these physiological parameters through ontogeny. Automated intermittent flowthrough respirometry was used to measure the aerobic metabolism of larval and juvenile lobsters accurately. Whole body biochemical analysis was used to examine energy storage and utilisation of phyllosoma. Haemolymph biochemistry was used to determine the thermal tolerance thresholds of juvenile lobsters. The effect of temperature change on the final instar (instar 17) was examined to assess whether it could serve as a cue for metamorphosis and it was found that temperature affected routine metabolic rate (`R_r`), but did not alter instar duration, and therefore is not a cue for metamorphosis. Fewer phyllosoma, however, completed metamorphosis and progressed to the puerulus stage at sub-optimal warm temperatures compared to cooler temperature. The effect of culture density was examined from hatch to pueruli. High culture density reduced growth (dry mass) and development (moult increment) of phyllosoma. There was a shift in metabolism via energy storage and utilisation of instar 17 phyllosoma in preparation for the morphological changes associated with metamorphosis. There was also an accumulation of lipid reserves during larval development that fuelled metamorphosis and the non-feeding puerulus stage. The aerobic scope of juvenile lobsters was determined through chasing lobsters by hand until the lobster was exhausted and did not respond to further stimuli along with the effects of handling, anaesthesia, and activity on the oxygen consumption rate (`¬¿œÄvÑO_2`) and ammonia-N excretion rate. Handling caused a relatively minor increase in `¬¿œÄvÑO_2` and anaesthetics reduced activity of lobsters, but did not reduce `¬¿œÄvÑO_2` or recovery periods from force feeding or handling. S. verreauxi juveniles have a narrow aerobic scope. Increased `¬¿œÄvÑO_2` from anaesthesia and activity uses a large proportion of energy within the metabolic scope that could otherwise be utilised for other physiological functions. Thermal tolerance thresholds were examined in different sized juvenile lobsters. Sudden changes in haemolymph `O_2` concentrations with water temperature indicated large lobsters have a higher optimum water temperature than small lobsters. Maximum attainable rates of standard metabolism indicated the upper critical temperature (`T_c`) for juvenile S. verreauxi, characterised by the onset of anaerobic metabolism. Juveniles utilised lipid as an energy substrate at optimal temperatures, but shifted towards protein catabolism at temperatures above their thermal tolerance range. This research revealed the long larval phase of S. verreauxi is essential for accumulating lipid reserves to fuel later larval stages and provided a more complete picture of the environmental and culture requirements of spiny lobsters during ontogeny, particularly for the rarely studied late phyllosoma stages. It also established that induced stress uses a large proportion of the aerobic scope in juvenile lobsters, which limits their ability to perform aerobically and deal with additional physiological challenges. The thermal tolerance of S. verreauxi juveniles identified the potential to expand their geographic distribution, which may have a large impact on benthic community structures and dynamics through competition for resources with existing lobster populations and other animals within the ecosystem. This may also impact local economies, particularly valuable local southern rock lobster fisheries.
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