Lithoselatium tantichodoki, a new species of intertidal crab (Crustacea:Brachyura: Sesarmidae) from southern Thailand

A new species of intertidal sesarmid crab, Lithoselatium tantichodoki new species, is described from the Gulf of Thailand. The species is superficially similar to L. kusu Schubart, Liu & Ng, 2009, from Singapore and Malaysia, but differs in the proportions of the ambulatory legs and the structure of the male first gonopod.

The influence of habitat on metabolic and digestive parameters in an intertidal crab from a SW Atlantic coastal lagoon

The hepatopancreas of decapod crustaceans is an organ which can act as indicator for digestive and metabolic parameters under different physiological and / or environmental conditions. However, biochemical studies on digestive and metabolic parameters of the hepatopancreas of euryhaline burrowing crabs such as Neohelice granulata from habitats with different diet compositions are still scarce. In the wild, adult males of N. granulata from Mar Chiquita Coastal Lagoon (Argentina) in mudflat habitat have diets with higher lipid and protein content than crabs from the saltmarsh, suggesting that diets could be an important factor influencing hepatopancreas activities. We tested this hypothesis here by exposing adult male crabs to a similar experimental diet and comparing hepatopancreas parameters for lipid components and protein metabolism between males from these two habitat types at different times (up to three months). At month 3, we noticed a decrease of the triglyceride concentration and lipase activity and an increase of protein concentration in crabs from the mudflat. In contrast, triglycerides and protein concentration did not change in crabs from the saltmarsh, while lipase activity decreased and levamisole insensitive AP increased at month 3. The results indicate that digestive and metabolic parameters in the hepatopancreas of crabs from habitats varying in diet content remain different, even if crabs are subsequently fed by a similar experimental diet. This suggests that specific intrinsic regulations of these hepatopancreas parameters could operate differently in each habitat and could not be changed by recent diet conditions.

Field-based body temperatures reveal behavioral thermoregulation strategies of the Atlantic marsh fiddler crab Minuca pugnax

Behavioral thermoregulation is an important defense against the negative impacts of climate change for ectotherms. In this study we examined the use of burrows by a common intertidal crab, Minuca pugnax, to control body temperature. To understand how body temperatures respond to changes in the surface temperature and explore how efficiently crabs exploit the cooling potential of burrows to thermoregulate, we measured body, surface, and burrow temperatures during low tide on Sapelo Island, GA in March, May, August, and September of 2019. We found that an increase in 1°C in the surface temperature led to a 0.70-0.71°C increase in body temperature for females and an increase in 0.75-0.77°C in body temperature for males. Body temperatures of small females were 0.3°C warmer than large females for the same surface temperature. Female crabs used burrows more efficiently for thermoregulation compared to the males. Specifically, an increase of 1°C in the cooling capacity (the difference between the burrow temperature and the surface temperature) led to an increase of 0.42-0.50°C for females and 0.34-0.35°C for males in the thermoregulation capacity (the difference between body temperature and surface temperature). The body temperature that crabs began to use burrows to thermoregulate was estimated to be around 24°C, which is far below the critical body temperatures that could lead to death. Many crabs experience body temperatures of 24°C early in the reproductive season, several months before the hottest days of the year. Because the use of burrows involves fitness trade-offs, these results suggest that warming temperatures could begin to impact crabs far earlier in the year than expected.

Periodic invasions during El Niño events by the predatory lined shore crab (Pachygrapsus crassipes): forecasted effects of its establishment on direct-developing indigenous prey species (Littorina spp.)

Coevolutionary arms races between shelled gastropods and their predators are more escalated near the equator. Therefore, temperate gastropods are predicted to be maladapted to highly specialized tropical shell-crushing crabs. The northern geographical limit of the lined shore crab (Pachygrapsus crassipes J.W. Randall, 1840) does not usually overlap with the southern limit of the Sitka periwinkle (Littorina sitkana Philippi, 1846), which lacks a pelagic larval stage. Large El Niño events increased the winter abundance and poleward transport of P. crassipes larvae from California (USA) in the Davidson Current. Temporary intertidal crab populations that included females with eggs were observed 1–4 years later, >1000 km north of its usual geographical range. Laboratory experiments showed that L. sitkana did not have a size refuge from adult P. crassipes. Moreover, consumption rates of adult L. sitkana by P. crassipes were 10-fold higher than those published for indigenous purple shore crabs (Hemigrapsus nudus (Dana, 1851)) with similar claw sizes. Additionally, the upper intertidal limit of invading P. crassipes was higher than that of H. nudus. Consequently, the invasion of P. crassipes reduced the width of L. sitkana‘s spatial refuge from predation. The permanent presence of this subtropical predator could reduce the intertidal distribution of this temperate gastropod, thereby causing contraction of its southern range limit.

Different ontogenetic trajectories of body colour, pattern and crypsis in two sympatric intertidal crab species

Animals frequently exhibit great variation in appearance, especially in heterogeneous habitats where individuals can be concealed differentially against backgrounds. Although background matching is a common anti-predator strategy, gaps exist in our understanding of within- and among-species variation. Specifically, the drivers of changes in appearance associated with habitat use and occurring through ontogeny are poorly understood. Using image analysis, we tested how individual appearance and camouflage in two intertidal crab species, the mud crab Panopeus americanus and the mottled crab Pachygrapsus transversus, relate to ontogeny and habitat use. We predicted that both species would change appearance with ontogeny, but that resident mud crabs would exhibit higher background similarity than generalist mottled crabs. Both species showed ontogenetic changes; the mud crabs became darker, whereas mottled crabs became more green. Small mud crabs were highly variable in colour and pattern, probably stemming from the use of camouflage in heterogeneous habitats during the most vulnerable life stage. Being habitat specialists, mud crabs were better concealed against all backgrounds than mottled crabs. Mottled crabs are motile and generalist, occupying macroalgae-covered rocks when adults, which explains why they are greener and why matches to specific habitats are less valuable. Differential habitat use in crabs can be associated with different coloration and camouflage strategies to avoid predation.

Field-based body temperatures reveal behavioral thermoregulation strategies of the Atlantic marsh fiddler crab Minuca pugnax

Behavioral thermoregulation is an important defense against the negative impacts of climate change for ectotherms. In this study we examined the use of burrows by a common intertidal crab, Minuca pugnax, to control body temperature. To understand how body temperatures respond to changes in the surface temperature and explore how efficiently crabs exploit the cooling potential of burrows to thermoregulate, we measured body, surface, and burrow temperature data during low tide on Sapelo Island, GA in March, May, August, and September of 2019. We found that an increase in 1°C in the surface temperature led to a 0.70-0.71°C increase in body temperature for females and an increase in 0.75-0.77°C in body temperature for males. Body temperatures of small females were 0.3°C warmer than large females for the same surface temperature. Female crabs used burrows more efficiently for thermoregulation compared to the males. Specifically, an increase of 1°C in the cooling capacity (the difference between the burrow temperature and the surface temperature) led to an increase of 0.42-0.50°C for females and 0.34-0.35°C for males in the thermoregulation capacity (the difference between body temperature and surface temperature). The body temperature that crabs began to use burrows to thermoregulate was estimated to be around 24°C, which is far below the critical body temperatures that could lead to death. Many crabs experience body temperatures of 24°C early in the reproductive season, several months before the hottest days of the year. Because the use of burrows involves fitness trade-offs, these results suggest that warming temperatures could begin to impact crabs far earlier in the year than expected.

Does physiological tolerance to acute hypoxia and salinity change explain ecological niche in two intertidal crab species?

Lay summary In response to acute salinity change or hypoxia, Hemigrapsus crenulatus exhibited better maintenance of osmoregulatory and cardiovascular function than Hemigrapsus sexdentatus. The greater physiological resilience of H. crenulatus is consistent with its habitation of an ecological niche that promotes greater exposure to environmental stressors than that of H. sexdentatus.