Tropical saltmarshes cannot be considered refuge for juvenile of fiddler crabs

Abstract

A habitat may be considered a refuge of countless disturbances, such as refuge against predation, herbivory, physiological stress, competition, but most studies evaluate refuge against predation. In the estuarine environment, refuges may be found in several habitats, such as saltmarshes. Few studies have focused on tropical saltmarshes and nothing is known about its role as refuge for fauna in this region. Here, we tested the hypothesis that tropical saltmarshes serve as refuge against (i) variations in temperature of superficial sediments and (ii) predation for megalopa and juvenile of fiddler crabs. Measurements (temperature and abundance of megalopa and juveniles along the vegetation density gradient) and manipulative experiments (field predation experiment) were used to test the hypothesis. Data from the mensurative experiment indicate that abundance of megalopa is explained by temperature and vegetation density, while abundance of juveniles is explained only by vegetation density, suggesting that only megalopa benefit from milder temperatures that occur in the saltmarshes. Future studies may elucidate the mechanisms behind this pattern. Data from the manipulative experiment indicate that predation is similar in the saltmarshes and nearby non vegetated areas, thus, tropical marshes can not be considered as predation refuges for juveniles of fiddler crabs. In the present study, hermits were attracted to the closed cages of the non-vegetated area of the experiment. These organisms are found both in and out of saltmarshes and may act as potential predators, but this has yet to be tested. Although not offering refuge against predation, the presence of marshes seems to play a role in the recruitment of juvenile fiddler crabs. The abundances of megalopas are affected by temperature and this aspect should be studied more deeply. In addition, future studies should consider the evaluation of the role of hydrodynamics in the settlement and the availability of food in plants of tropical saltmarshes.