Abstract: Migratory freshwater shrimps represent important links between the headwaters and estuaries of many tropical rivers. These species exhibit amphidromous life cycles in which larvae are released from females in upper reaches of rivers; first stage (i.e., newly hatched) larvae drift passively to coastal environments where they develop and metamorphose into postlarvae that subsequently migrate back upstream to adult (freshwater) habitat. In 1996, we conducted short-term estuarine sampling to determine if developing (post-first stage) freshwater shrimp larvae were present in the estuaries of two river (Espiritu Santo and Mameyes) that drain the Luquillo Experimental Forest (LEF) in northeastern Puerto Rico. We also used traps to examine the upstream migration of post-larval freshwater shrimps and its relationship to river discharge in the same two rivers. We found post-first stage larval shrimps in both estuaries, although they were present at low densities relative to other planktonic organisms (e.g., calanoid copepods). Most larval shrimps (79-98% on each sampling date) were in the smallest size class (<1 mm carapace length; i.e., first stage). Although these data do not preclude the possibility of fully marine development of freshwater shrimp larvae, the presence of several larval stages in the two estuaries suggests that at least a proportion of larvae (and species) develop to post-larval stage in estuarine habitats. Several large peaks in upstream post-larval migration were recorded, particularly in the Mameyes during the latter half of the study period. Most peaks in migration appeared to be associated with recent (previous 1-4 d) increase in discharge. Our results indicate that the timing and magnitude of upstream post-larval migration from larval habitat may be partly controlled by peak discharges, as observed in other diadromous species (Drinkwater & Frank 1994).
Benstead, J. P., J. G. March, and C. M. Pringle. 2000. Estuarine stages and upstream migration of freshwater shrimps in two tropical rivers, Puerto Rico. Biotropica 32: 545-547.
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