Differential effects of water loss and temperature increase on the physiology of fiddler crabs from distinct habitats

Abstract

Temperature is one of the main environmental constraints to organism distribution, affecting physiology and survival. Organisms that inhabit the intertidal zone are exposed to temperature variation and, with climate change, they should face different conditions which include higher temperatures, leading to higher rates of water loss through evaporation and then fitness reduction or mortality. Here we tested the effects of desiccation and increased temperature in two fiddler crabs species that occupy distinct habitats in regard to vegetation cover and position on the intertidal zone and thus may respond differently to these stressors. Leptuca thayeri, which is restricted to the mid-tide zone and vegetated areas, had higher desiccation and mortality rates than Minuca rapax, a generalist species, when exposed to desiccation for 120 min. Also, compared to M. rapax, L. thayeri had a more permeable carapace. Temperature elevation of 10 °C and 20 °C for 72 h caused no mortality in either species. However, there were changes in hemolymph osmolality and muscle hydration in both species. Leptuca thayeri osmolality was low in the intermediate temperature, suggesting that at this temperature this species has a better salt secretion capability. Minuca rapax, however, had an increase in hemolymph osmolality at the highest temperatures with no LDH increase, which indicates that osmotic control in this species is more sensitive to temperature increase. Our results show that L. thayeri suffers more from desiccation, due to a more permeable carapace. However, because of this higher permeability L. thayeri is capable of lowering its temperature more than M. rapax. As temperature elevation produces great physiological changes in M. rapax, a reduced ability to keep a low temperature can be an issue for this species if temperature increases. However, higher water loss to keep body temperature low may decrease L. thayeri survivability in the same scenario.

Point-of-care testing for measuring haemolymph glucose in invertebrates is not a valid method

“…Table 1 shows the mean levels of glucose in the haemolymph of some freshwater and marine crustaceans and molluscs. Fiddler crab glucose levels are usually around 30 mg/dL, depending on physiological status and species (Matsumasa and Murai, 2005; Matsumasa et al , 2013; Principe et al , 2018), more than three times lower than human levels. Other species of crabs have similar levels of glucose, like the ghost crab Ocypode quadrata (Vinagre et al , 2007) and the swimming crab Portunus trituberculatus (Lu et al , 2015).…”

“…These results can be aggregated to laboratory experiments and enhance the prediction of environmental change effects. As fiddler crab and mussel species are expected to be harmed by climate change (Smith et al , 2006; Levinton et al ., 2015; Principe et al ., 2018), such improvement in predictions can subsidize conservation efforts for those groups. Aquaculture professionals can also benefit from the use of POC devices for evaluating glucose of invertebrates during transport and in farms as these data can inform them about animal stress and welfare (e.g.…”

“…As other fiddler crabs, they play a crucial role in the cycling of nutrients in the mangrove, acting as ecosystem engineers (Kristensen and Alongi, 2006; Kristensen et al , 2008). Because of their importance, they have been used in studies in ecology (Cuellar-Gempeler and Munguia, 2013; De Grande et al , 2018b; De Grande et al , 2018c), animal behaviour (Gusmao-Junior et al , 2012; De Grande et al , 2018a) and physiology (Thurman et al , 2010; Principe et al , 2018). Perna perna are a common mussel on east Atlantic rocky shores, forming large patches in the intertidal region (Marques et al , 1991; Hicks et al , 2001; Henriques and Casarini, 2009).…”

“…The control group was exposed to a temperature of 25°C, and crabs in the high temperature treatment were exposed to 35°C. This temperature can be easily reached in the areas where L. thayeri occur and was used in a previous study with this species (Principe et al , 2018). Flasks were placed into a water bath with the corresponding temperature for each treatment, and organisms were exposed for 24 hours to the experimental conditions.…”

Survival strategies on a semi-arid island: submersion and desiccation tolerances of fiddler crabs from the Galapagos Archipelago

“…Many minimize the effects of desiccation, for example, by inhabiting burrows as a refuge (Powers and Cole, 1976), albeit with fewer opportunities to forage and reproduce (Allen and Levinton, 2014). Desiccation and submersion tolerance varies among fiddler crabs and is an indicative of their resistance to aerial exposure during low tide (Thurman, 1998;Levinton et al, 2015;Principe et al, 2018). Large scale landscape changes, such as mangrove deforestation or altered ocean levels, may cause physiological changes resulting from submersion and desiccation challenge that affect ecological distribution patterns (Araújo et al, 2007, Wilson et al, 2005 and survival.…”