Philip M. Gravinese

Over the last half century, Florida’s Coral Reef has significantly declined due to bleaching, disease, and hurricanes, leading to increased macroalgae dominance of some reefs. Herbivory helps maintain coral-dominated ecosystems by limiting or mediating macroalgal growth. The Caribbean king crab (
Maguimithrax spinosissimus
) is an effective native grazer of chemically defended macroalgae, making it a promising candidate for reef restoration given its potential to increase grazing intensity and facilitate improved survival, growth, and recruitment of restored and natural corals via a reduction in coral-algal interactions. However, the influence of chemical cues on mortality and development of
M. spinosissimus
is unclear. This study examined the effect of four seawater chemical cues on early life history development: (a) control, (b) algae (
Dictyota
spp.), (c) conspecific, and (d) predator (
Panulirus guttatus
). Results indicate higher molting rates in control and conspecific treatments, while predator and algae cues increased mortality and reduced molting. Our results suggest that
Dictyota
spp. macroalgae and predator chemical cues can hinder larval survival (
Dictyota
: 8.8% survival;
P. guttatus
: 7.3% survival; Control: 34.7% survival; Conspecific: 28% survival), highlighting the need to take predator density and algal community composition into account when planning for successful Caribbean king crab stocking efforts (e.g., potential effects on appropriate stocking size, density, and frequency).

Coastal acidification is being exacerbated by terrestrial organic inputs, especially after high precipitation events. Florida’s rainy season coincides with stone crab (Menippe mercenaria) reproduction, and pH extremes could limit future harvests by reducing reproductive output. Populations that experience pH variability can serve as “natural laboratories” for estimating the tolerance of a species to coastal acidification. Here, we conducted a series of experiments to determine if ovigerous stone crabs conditioned in more variable pH habitats (seagrass) would result in faster embryonic development, greater hatching success, and higher larval survival relative to crabs conditioned in habitats with lower pH variability (sandy habitats). After field conditioning, crabs were transported to the laboratory and randomly acclimated to either a control pH (pH = ~ 7.90) or a reduced pH condition (pH = ~ 7.60) until larval release. The rate of embryo development was slower in the laboratory reduced pH treatment, however, there were no observable field condition effects on embryo development rate. Crabs conditioned in the more pH variable seagrass habitat did have greater hatching success and higher larval survival than crabs in less pH variable sandy habitats; however, larval survival was low across all treatments. These results suggest that the pH variability experienced in seagrass habitats during brooding may serve as a mechanism for stone crabs to acclimatize to extremes in seawater pH.

The Florida stone crab occupies habitats that can experience a range of salinities throughout the year, yet nothing is known about their salt balance physiology. We acclimated stone crabs for a week to conditions that mimic the range of salinities they experience in coastal habitats to determine their ability to regulate or conform their hemolymph osmolality and chloride ion concentration. At a salinity of 35 ppt or higher, the hemolymph osmolality mirrored the treatment seawater indicating that crabs were osmoconforming. Stone crabs physiologically shifted to being osmoregulators in the lowest salinities (20 and 25 ppt). Similarly, crabs switched from being chloride ion conformers at higher salinity to chloride ion regulators at salinities of 20 and 25 ppt. The ability of stone crabs to physiologically shift from being conformers to regulators is important for predicting how the species may respond to future changes in salinity associated with freshwater runoff or hypersaline events that are triggered by marine heat waves.