Elevated temperature alters swimming behavior in Caribbean king crab larvae

Ocean warming is rapidly altering marine ecosystems and is negatively affecting marine invertebrates, especially during their earlier life stages which often exhibit narrower physiological tolerances than adult conspecifics. The Caribbean king crab (Maguimithrax spinosissimus) is a species of interest for coral reef restoration in the Florida Keys and throughout the Caribbean due to its herbivorous grazing which can reduce macroalgae cover on patch reefs. However, the effects of thermal stress on king crab larval physiology and swimming behavior remain unknown. This study determined the effects of thermal stress on survival, metabolic performance, and geotactic vertical swimming behavior in both of the larval stages of M. spinosissimus under two temperature treatments: ​​28 °C (control) and 32 °C (elevated). Exposure to elevated temperature significantly reduced larval survival, with larvae in 32 °C being nearly three times more likely to die than cohorts in the control. In contrast, oxygen consumption did not differ between temperature treatments or larval stages, however larvae in the elevated treatment were observed to be more lethargic (alive with tail movement but no longer swimming) than larvae in the control. Elevated temperature also resulted in a reversal in the geotactic vertical swimming response. First stage larvae significantly swam downward at a faster rate than individuals in the control. In the absence of acclimatization, these results suggest that outplanted king crab populations may experience a reduction in larval supply and a reduced dispersal potential which could limit connectivity among local reef habitats after outplanting. This research has implications for coral reef restoration programs interested in stocking king crabs onto reefs as those efforts will rely on successful recruitment to sustain outplanted populations of M. spinosissimus.