Thermal tolerance of the nektonic puerulus stage of spiny lobsters and implications of ocean warming

Abstract

Recent recruitment declines in important spiny lobster fisheries worldwide have triggered conjecture about negative impacts of anthropogenically induced environmental change on their long-lived planktonic larval life stages. Puerulus larvae are the critical transitional stage between pelagic larval development and coastal juvenile recruitment and may be particularly sensitive to environmental change due to immature cardiorespiratory capacity and exceptional energy demands associated with shoreward migration. We measured Sagmariasus verreauxi pueruli energy metabolism and defined their thermal tolerance, which are considered against published coastal recruitment data and spatially explicit ocean warming scenarios. The upper threshold of the thermal optimum window (upper pejus temperature range) was defined by the temperature optimum for aerobic scope. Within the upper pejus temperature range, pueruli had diminished aerobic capacity for physiological performance and used more of their finite lipid reserves to support an amplified metabolism. Sea surface temperatures at the northern extent of their natural range already reach the upper pejus range, and monitoring settlement data from the wild indicted that fewer puerulus successfully recruit during hot seasons in this area. Our study provides some evidence that physiological thermal tolerance constraints are already limiting postlarval recruitment. Predicted increases in water temperatures for their rapidly warming habitat will amplify the thermal challenge experienced by pueruli and may result in large shifts in lobster distribution and significant re-shuffling of species assemblages, creating challenges for sustainable natural resource management.

Cardiorespiratory ontogeny and response to environmental hypoxia of larval spiny lobster, Sagmariasus verreauxi

“…However, it is noted that the regression slope of Ṁo 2 in hypoxia was slightly elevated for instar 16 phyllosoma compared to instar 9 phyllosoma and puerulus suggesting that this stage has the least respiratory control supporting the hypothesis of the study that late-phyllosoma would be most prone to oxygen limitation (Fitzgibbon et al, 2014b). This hypothesis is also supported by culture studies which show that the optimum temperature for late-stage phyllosoma growth and development (21°C) is reduced by 2°C compared to the early-and mid-stages and thermal optima for pueruli aerobic scope (15-27°C) far exceeds growth optima of all the phyllosoma stages (Fitzgibbon and Battaglene, 2012b;Fitzgibbon et al, 2014b). Further ontogenetic analysis of the physiological capacity is required to explain the apparent reduced thermal tolerance of late-stage phyllosoma and to confirm if it presents a thermally sensitive bottleneck in the lobster life cycle.…”

“…However, gobies naturally experience severe nocturnal hypoxia among the branches of coral colonies and are known to be among the most hypoxia tolerant of coral reef fishes (Sørensen et al, 2014). Little is known about the anaerobic capacity of phyllosoma but Fitzgibbon et al (2014b) showed that pueruli have significant anaerobic capacity most likely from within the tail white muscle fibres.…”

“…The Ṁo 2 of individual larvae were measured within an automated multi-chamber intermittent flow-through respirometer system similar to that described by Fitzgibbon et al (2014b) with four micro respiration chambers instead of two (CH10650, www.loligosystems.com). From each measurement trial, two chambers were stocked with larvae and the other two chambers were used as simultaneous measures of background respiration, which was subtracted from stocked chambers to determine the Ṁo 2 of the larvae.…”

“…Respiration chambers were 8 ml in volume for instar 9 phyllosoma and 19 ml for instar 16 phyllosoma and pueruli. Respiratory system configuration and dissolved oxygen measurement were as described by Fitzgibbon et al (2014b). Larvae Ṁo 2 were calculated as the mean of the three recordings at each Po 2 for 5 individual larvae at each development stage (n = 5).…”

“…Furthermore, spiny lobster larvae have low mass-specific metabolism compared to other larval decopod crustaceans and there is some evidence that temperature-dependent oxygen limitation is impacting post-larvae recruitment and distribution (Fitzgibbon et al, 2014a,b;Ikeda et al, 2011;Jensen et al, 2012). The ontogeny of cardiac function and respiratory control ability in hypoxia of larval spiny lobsters has never been examined and thus our understanding of physiological oxygen constraints are still lacking, particularly for the late phyllosoma stages, which are suggested to be most sensitive to environmental change due to their large size and immature cardiorespiratory anatomy (Fitzgibbon et al, 2014b).…”