Effects of food supplies and water temperature on growth rates of two species of freshwater tropical shrimps

Growth rates of individual freshwater shrimp of the species Atya lanipes and Xiphocaris elongata were measured in a second‐order stream in the Luquillo Experimental Forest in Puerto Rico over 10 years (1997–2007). Shrimp living at lower altitudes in warmer water and wider stream channels with more algal and detrital foods were predicted to grow and reproduce more rapidly. Shrimp were marked and recaptured periodically in pools located at three altitudes to determine whether temperature affected growth rates among individual A. lanipes and X. elongata. Mean annual water temperatures ranged from 20 to 24 °C with the uppermost pool being cooler than the lower pools. Mean annual growth rates for Atya and Xiphocaris were 0.27 and 0.1 mm carapace length, respectively, for all three populations. Differences in growth were partially influenced by how each species obtains its food. Atya is a filter feeder and scraper and has continuous access to suspended organic particles and biofilms. The slower growth rate for Xiphocaris elongata is most likely a result of the wider range in quality and accessibility of food resources. Differences in pool morphology and depths probably affected differences in food availability. Increased leaf litter retention in the deeper upper and lower pools probably increased shrimp growth rates, while washout of leaf litter from the relatively shallow, elongate mid‐altitude pool decreased Atya lanipes growth rates. These long‐lived, slow‐growing shrimp species transform a wide range of organic materials into their biomass. Because of the slow growth rates of these detritivores shrimp, tropical storms, hurricanes, droughts or other disturbances could have persistent, long‐term impacts on detrital processing and on the populations of their predators.