The effects of elevated temperature on oxygen consumption, swimming direction, and survival of Caribbean king crab larvae

Since the 1970s, Florida’s coral reefs have significantly declined due to bleaching, disease, and hurricanes, leading to increased macroalgae dominance in some locations. Herbivory helps maintain coral-dominated ecosystems by limiting macroalgal growth and opening space for new coral recruits. The Caribbean king crab (Maguimithrax spinosissimus) is an effective native algal grazer of chemically defended macroalgae, making it a promising candidate for reef restoration. However, their ability to tolerate stressful environmental conditions, such as warmer sea surface temperatures, remains unknown. This study examined how warming influences larval survival, metabolic performance, and geotactic swimming behavior in M. spinosissimus under two temperature treatments: ​​28°C and 32°C. Elevated temperature significantly reduced larval survival but did not impact oxygen consumption. Larvae exposed to elevated temperature swam upward less often in the first zoeal stage and exhibited faster swimming speeds than those in the control treatment. Our results suggest that ocean warming may affect larval performance by increasing mortality and reversing larval geotactic swimming behavior. 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. This research has implications for coral reef restoration programs interested in outplanting king crabs onto reefs as those efforts will rely on successful recruitment to sustain M. spinosissimus outplanted populations.