Larval salinity tolerance of the South American salt-marsh crab, Neohelice (Chasmagnathus) granulata: physiological constraints to estuarine retention, export and reimmigration

Abstract

The semiterrestrial crab Neohelice (=Chasmag-nathus) granulata (Dana 1851) is a predominant species in brackish salt marshes, mangroves and estuaries. Its larvae are exported towards coastal marine waters. In order to estimate the limits of salinity tolerance constraining larval retention in estuarine habitats, we exposed in laboratory experiments freshly hatched zoeae to six diVerent salinities (5-32‰). At 5‰, the larvae survived for a maximum of 2 weeks, reaching only exceptionally the second zoeal stage, while 38% survived to the megalopa stage at 10‰. Shortest development and negligible mortality occurred at all higher salt concentrations. These observations show that the larvae of N. granulata can tolerate a retention in the mesohaline reaches of estuaries, with a lower limit of ca. 10-15‰. Maximum survival at 25‰ suggests that polyhaline conditions rather than an export to oceanic waters are optimal for successful larval development of this species. In another experiment, we tested the capability of the last zoeal stage (IV) for reimmigration from coastal marine into brackish waters. Stepwise reductions of salinity during this stage allowed for moulting to the megalopa at 4-10‰. Although survival was at these conditions reduced and development delayed, these results suggest that already the zoea-IV stage is able to initiate the reimmigration into estuaries. After further salinity reduction, megalopae survived in this experiment for up to >3 weeks in freshwater, without moulting to juvenile crabs. In a similar experiment starting from the megalopa stage, successful metamorphosis occurred at 4-10‰, and juvenile growth continued in freshwater. Although these juvenile crabs showed signiWcantly enhanced mortality and smaller carapace width compared to a seawater control, our results show that the late larval and early juvenile stages of N. granulata are well adapted for successful recruitment in brackish and even limnetic habitats.

Growth, tolerance to low ­salinity, and osmoregulation in decapod crustacean larvae

“…osmoregulation is a 'waste of energy' or a 'luxury' that is negatively selected by physically stable marine environments. This also may explain the ontogenetic pattern of osmoregulation in the crab Neohelice granulata (Charmantier et al 2002): the first zoeal stage, which is released in estuarine and sometimes even oligohaline waters, is a hyper-osmoregulator in dilute media, but this capacity is lost in the subsequent stages, which presumably develop outside the estuaries and may not need to hyper-regulate (Anger et al 2008a). The capacity to hyper-osmoregulate is later recovered in the last larval stage, the megalopa, which re-invades estuarine habitats to recruit to the adult populations (Luppi et al 2002).…”

“…In other exporting species, however, the larvae are directly released in brackish or freshwater, where the adults live, and are subsequently transported by surface currents towards lower estuarine or coastal marine waters with higher and less variable salinities (e.g. Armases roberti: Anger et al 2006, Torres et al 2006; Neohelice granulata: Anger et al 2008a). In both cases, the late larval or early juvenile stages begin to actively reimmigrate into estuarine habitats (see e.g.…”

Cumulative effects of low salinity on larval growth and biochemical composition in an estuarine crab, Neohelice granulata

“…This barrier should therefore select for larval export towards the sea (Anger et al 1994, Giménez 2003. However, retention of the larvae in lower estuarine waters with moderately reduced salinities, for instance in the Bay of Sanborombón on the southern shore of the Rio de la Plata estuary (Argentina), is certainly possible, especially after gradual acclimation to slowly decreasing salinities (Anger et al 2008). On the other hand, there are also coastal marine populations of Neohelice granulata, which are not normally exposed to reduced salinities (Bas et al 2005(Bas et al , 2007.…”

The crab Neohelice (=Chasmagnathus) granulata: an emergent animal model from emergent countries

“…The following are examples of such projects: embryonic, larval and adult structural, biochemical and physiological adaptations to reduced or changing salinities; developmental plasticity and carry-over effects (e.g., effects of the salinity or nutrition experienced at one developmental stage on the following stages, see a review by Giménez 2006); strategies of larval export; cues for settlement; post-settlement patterns and processes in estuarine habitats; the effects of season, diet, anoxia and osmotic stress on carbohydrate and lipid metabolism; and the effects of pollutants, particularly heavy metals and pesticides on different phases of the life cycle (see Bianchini et al 2008;Pellegrino et al 2008;Anger et al 2008 and the references herein).…”