Larval mortality during export to the sea in the fiddler crab Uca minax
Dense populations of the fiddler crab Uca minax (Le Conte 1855) are common along tidally influenced freshwater rivers and streams >50 km from the sea. Adults do not migrate from inland sites to release larvae, but instead release them directly into an environment where the zoeae cannot survive. Laboratory salinity tolerance experiments were used to determine how long larvae from the inland-most population of U. minax along the Pee Dee River, South Carolina, USA can survive zero salinity compared to larvae from a brackish water population (salinity 5) near the mouth of Winyah Bay in the same estuary. Larvae from the brackish water population were also exposed to a salinity of 5 and their survival tracked. These experiments were conducted from May to August 2004 and 2005. To determine if inland larvae suffered significant mortality in transit due to salinity stress, current profiles were measured in the field and used to model the time taken by a larva using ebb-tide transport to travel to permissive salinities. The laboratory tolerance experiments showed that larvae from the inland freshwater population had LT50’s of 4–5 days at 0 salinity, which were significantly longer than those of the brackish water zoeae (2–3 days). Zoeae from the brackish water population survived for at least one larval molt at a salinity of 5 with LT 50’s of ∼12 days. Estimated travel times to reach permissive salinities from the inland-most population based on current profiles were 3–5 days for larvae using night-time only ebb-tide transport and 1.5–2.5 days for those using ebb-tide transport both day and night. Previously published field data indicate that U. minax larvae do use both day- and night-time ebb-tide transport, and are found in high densities in the water column during the day. These results lead to the conclusion that U. minax stage I zoeae do not undergo significant salinity-induced mortality during their 50+ km trip to the sea.
KeywordsTidal Cycle Acoustic Doppler Current Profiler Zoeal Stage Discharge Velocity Freshwater Population
We thank the staff at the Baruch Marine field Laboratory, especially Paul Kenny, for valuable assistance with field logistics. We also thank the West’s for allowing us to establish a field site at the Bates Hill Plantation. The Geoprocessing laboratory at Mount Holyoke College assisted us with our field site map. We thank Alan Kohn and two anonymous reviewers for valuable comments and suggestions on drafts of this work. This work was supported by the National Science foundation (NSF IBN-0237484) and the Office of Naval Research (N00014-02-1-0972). This is manuscript no. 1455 for the Baruch Marine Field Laboratory.
- Anger K (2003) Salinity as a key parameter in the larval biology of decapod crustaceans. Invertebr Reprod Dev 43:29–45Google Scholar
- Christy JH, Stancyk SE (1982) Timing of larval production and flux of invertebrate larvae in a well-mixed estuary. In: Kennedy VS (ed) Estuarine comparisons. Academic, New York, pp 489–503Google Scholar
- Crane J (1975) Fiddler crabs of the world. Princeton University Press, PrincetonGoogle Scholar
- Crisp DJ (1974) Factors influencing the settlement of marine invertebrate larvae. In: Grant PT, Mackie AM (eds) Chemoreceptors in marine organisms, Academic, London, pp 177–277Google Scholar
- Crisp DJ (1976) Settlement responses in marine organisms. In: Newell RC (ed) Adaptation to environment: essays on the physiology of marine animals. Butterworths, London, pp 83–124Google Scholar
- DeCoursey PJ (ed) (1979) Egg-hatching rhythms in three species of fiddler crabs. Pergamon Press, New YorkGoogle Scholar
- DeCoursey PJ (ed) (1983) Biological timing. Academic, New YorkGoogle Scholar
- De Wilde PAWJ (1973) On the ecology of Coenobita clypeatus in Curacao with reference to reproduction, water economy, and osmoregulation in terrestrial hermit crabs. Stud Fauna Curacao 44:1–138Google Scholar
- Finney DJ (1947) Probit analysis. Cambridge University Press, CambridgeGoogle Scholar
- Forward RBJ (1987) Larval release rhythms of decapod crustaceans: an overview. Bull Mar Sci 41:165–176Google Scholar
- Le Conte J (1855) On a new species of Gelasimus. Proc Acad Nat Sci Philad 7:402–403Google Scholar
- Young CM, Chia FS (1987) Abundance and distribution of pelagic larvae as influenced by predation, behavior and hydrographic factors. In: Giese C, Pearse JS, Pearse VB (eds) Reproduction of marine invertebrates. Blackwell Scientific and The Boxwood Press, Palo Alto and Pacific Grove, pp 385–463Google Scholar