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.

The ocean has absorbed ~one third of the excess atmospheric carbon dioxide (CO[sub.2]) released since the Industrial Revolution. When the ocean absorbs excess CO[sub.2], a series of chemical reactions occur that result in a reduction in seawater pH, a process called ocean acidification. The excess atmospheric CO[sub.2] is also resulting in warmer seawater temperatures. These stressors pose a threat to marine organisms, especially during earlier life stages (i.e., larvae). The larvae of species like the Florida stone crab (Menippe mercenaria) are free swimming, allowing a population to disperse and recruit into new habitats. After release, stone crab larvae undergo vertical swimming excursions in response to abiotic stimuli (gravity, light, pressure) allowing them to control their depth. Typically, newly hatched larvae respond to abiotic cues that would promote a shallower depth distribution, where surface currents can transport them offshore to complete development. As larvae develop offshore, they become less sensitive to certain abiotic stimuli, which promotes a deeper depth distribution that may expose them to variable current speeds, thus influencing the direction of advection (horizontal movement). Environmental stressors like ocean acidification and elevated seawater temperatures may also impact the larvae's natural response to these abiotic stimuli throughout ontogeny (development). Changes in their natural swimming behavior due to climate stressors could, therefore, influence the transport and dispersal of the species. This guided-inquiry lesson challenges introductory marine biology and oceanography students to determine how future ocean pH and temperature projections could impact the swimming behavior of Florida stone crab larvae. Keywords: Crusteacean, Ocean Acidification, Larvae, Stone Crab

This guided, inquiry-based, hands-on lesson uses data from a local monitoring station in Tampa Bay, Florida, to guide students toward understanding how coastal acidification may impact the reproductive success of the Florida stone crab, an important regional fishery. The objectives of the lesson are for students to: (1) determine how pH varies between different habitats, (2) determine how pH can affect the reproductive success of an important commercial fishery, the Florida stone crab, and (3) evaluate whether exposure to variable seawater pH results in greater reproductive success in stone crabs relative to individuals that are not exposed to pH variability.

This guided, inquiry-based, hands-on lesson uses data from a local monitoring station in Tampa Bay, Florida, to guide students toward understanding how coastal acidification may impact the reproductive success of the Florida stone crab, an important regional fishery. The objectives of the lesson are for students to: (1) determine how pH varies between different habitats, (2) determine how pH can affect the reproductive success of an important commercial fishery, the Florida stone crab, and (3) evaluate whether exposure to variable seawater pH results in greater reproductive success in stone crabs relative to individuals that are not exposed to pH variability.

Anthropogenic inputs, like organic-based runoff, can cause extremes in seawater pH within many coastal habitats. Coastal habitats can also experience diurnal variability in seawater pH due to naturally occurring phenomena such as seasonal changes in precipitation and/or daily respiration and photosynthetic processes. Marine organisms that experience diurnal variability in pH may be better acclimatized to tolerate future extremes in seawater acidification that are forecast for future oceans. The Florida stone crab is a commercially important species in south Florida valued at $25 million (USD) annually. Previous research has shown that stone crab hatching success and larval survival can be reduced by ~30% under end-of-century pH scenarios. Here, we tested if stone crabs from pH variable habitats within Tampa Bay may be better acclimatized to tolerate future extremes in seawater pH. We placed ovigerous stone crabs into either sandy habitats with less variable pH or seagrass habitats with more variable pH to determine if embryo development time and hatching success improved under end-of-century pH scenarios. Ovigerous stone crabs were allowed to undergo embryogenesis in both sandy and seagrass habitats and extrude a new egg mass before being brought back to the Florida Southern College experimental ocean acidification system. Ovigerous crabs were then held in either the control (pH = 8.0) or lower pH (pH = 7.7) treatment for the clrirati on of their embryo development. All stone crabs were then monitored for embryo development time and hatching success. Crabs conditioned in the seagrass site but then placed into the low pH treatment experienced a hatching success of 76%. This was 48% higher than reported in previously published studies suggesting that the diurnal variability experienced in local seagrass habitats may serve as a potential refugia habitat for the stone crab fishery as coastal habitats continue to acidify.

Coastal habitats can sometimes experience more frequent and severe extremes in seawater pH due to nutrient discharge after storm events. The adults of coastal marine species are often able to tolerate changes in environmental conditions like seawater pH, however, their earlier and sometimes more sensitive life-stages (embryos and larvae) are still developing the physiological mechanisms needed to acclimate to those changes. The stone crab, Menippe mercenaria, is an important coastal species throughout south Florida valued at ~$25 million per year. We determined the effects of reduced seawater pH on the stone crab's embryonic development and hatching success. Ovigerous crabs were maintained in a laboratory setting that mimicked present-day and future seawater pH conditions throughout the duration of their embryonic development. The rate of embryonic development was significantly slower (i.e., time to hatching delayed by ~24%) in crabs that were exposed to reduced seawater pH, however, there was no effect on the size of the developing embryos (i.e., embryonic volume ). Stone crab larvae that successfully hatched were not morphologically different between treatments, although the overall hatching success was reduced by 28% in lower pH seawater. The hatching success was also more variable in the acidic treatment indicating that some broods may be more tolerant to changes in seawater acidity. Variable hatching success under extreme seawater pH suggests that stone crab embryos may have the capacity to acclimatize to future seawater pH conditions.

Many marine species have been shown to be threatened by both ocean acidification and ocean warming which are reducing survival, altering behavior, and posing limits on physiology, especially during earlier life stages. The commercially important Florida stone crab, Menippe mercenaria, is one species that is affected by reduced seawater pH and elevated seawater temperatures. In this study, we determined the impacts of reduced pH and elevated temperature on the distribution of the stone crab larvae along the West Florida Shelf. To understand the dispersion of the larvae, we coupled the multi-scale ocean model SLIM with a larval dispersal model. We then conducted a connectivity study and evaluated the impacts of climate stressors by looking at four different scenarios which included models that represented the dispersion of stone crab larvae under: 1) present day conditions as modelled by SLIM for the temperature and NEMO-PISCES for the pH, 2) SSP1-2.6 scenario (-0.037 reduction in pH and +0.5 degrees C compared to present-day conditions), 3) SSP2-4.5 scenario(-0.15 reduction in pH and +1.5 degrees C) and 4) SSP5-8.5 scenario (-0.375 reduction in pH and +3.5 degrees C). Our results show a clear impact of these climate change stressors on larval dispersal and on the subsequent stone crab distribution. Our results indicate that future climate change could result in stone crabs moving north or into deeper waters. We also observed an increase in the number of larvae settling in deeper waters (defined as the non-fishing zone in this study with depths exceeding 30 m) that are not typically part of the commercial fishing zone. The distance travelled by larvae, however, is likely to decrease, resulting in an increase of self-recruitment and decrease of the size of the sub-populations. A shift of the spawning period, to earlier in the spring, is also likely to occur. Our results suggest that habitats in the non-fishing zone cannot serve as a significant source of larvae for the habitats in the fishing zone (defined as water depth< 30 m) since there is very little exchange (< 5% of all exchanges) between the two zones. These results indicate that the stone crab populations in Florida may be susceptible to community fragmentation and that the management of the fishery should consider the potential impacts of future climate change scenarios.