POST-HURRICANE HUGO INCREASES IN ATYID SHRIMP ABUNDANCES IN A PUERTO-RICAN MONTANE STREAM

We report the first data on changes in tropical scream biora resulting from a major hurricane. Beginning in January 1989, we trapped freshwater shrimp, Atya lanipes, along 1200 m of a montane stream in the Luquillo Experimental Forest, Puerto Rico. Prior to Hurricane Hugo, shrimp densities were greater in the headwaters than at mid- and low elevation. In October 1989, one month after the hurricane, shrimp densities were reduced on average by 50 percent in the headwaters (apparently from washout) and increased by 80 percent at mid-elevation. From December 1989 to May 1990 overall shrimp densities increased rapidly to the highest abundances ever recorded. These densities most likely resulted from increased numbers of shrimp that migrated upstream from riverine pools; and, from increased availability of unusually abundant food resources (decomposing leaves and algae) that increased recruitment of these generalized consumers. Benthic communities in forested, headwater streams are likely to be resilient after intermediate levels of disturbance, because rapid debris-dam formation increases retention of food resources and reduces washout of invertebrate consumers. However, storms generating greater stream flow and/or less wind than Hurricane Hugo could cause extensive, longer-lasting decreases of benthic-dwelling shrimp because of greater washout of both consumers and food supplies.