benthic invertebrates

FOOD PATHWAYS ASSOCIATED WITH PENAEID SHRIMPS IN A MANGROVE·FRINGED ESTUARY

STONER, A. W. & ZIMMERMAN, R. J. 1988. Food pathways associated with penaeid shrimps in a mangrove-fringed estuary. Fisheries Bulletin 86:543-551.

Abstract: 
High abundance and production of juvenile Penaeus spp. in tropical estuaries has been attributed to high concentrations of mangrove-derived detritus in the nursery habitats. Examination of the diets of Penaeus notialis, P. subtilis, and P. brasiliensis in the mangrove-fringed Laguna Joyuda, Puerto Rico showed that even the smallest juveniles are predators consuming capitellid polychaetes (20-38% of diets) and amphipods (20-76%). Less than 25% of the diets was detritus. Ontogenetic variation in diets was greater than interspecific variation, and there was no evidence for dietary separation among the sympatric species. Seasonal shifts in foods reflected abundance patterns of macrobenthic prey species. Despite the consumption of prey organisms generally classified as detritivorous, stable carbon isotope ratios in the penaeids (-18.1 to -15.0%0), their food items (-18.8 to -17.7°/00), and primary producers indicated that shrimps and the majority of sediment dwellers in Laguna Joyuda obtain most of their carbon from benthic a1gae (-14.4°/00) and not from mangrove detritus (- 25.0 to - 22.9°/00).

INDIRECT UPSTREAM EFFECTS OF DAMS: CONSEQUENCES OF MIGRATORY CONSUMER EXTIRPATION IN PUERTO RICO

GREATHOUSE, EFFIE A.; PRINGLE, CATHERINE M.; MCDOWELL, WILLIAM H.; HOLMQUIST, JEFF G. 2006. INDIRECT UPSTREAM EFFECTS OF DAMS: CONSEQUENCES OF MIGRATORY CONSUMER EXTIRPATION IN PUERTO RICO. Ecological Applications, 16(1), :339-352.

Abstract: 
Large dams degrade the integrity of a wide variety of ecosystems, yet direct downstream effects of dams have received the most attention from ecosystem managers and researchers. We investigated indirect upstream effects of dams resulting from decimation of migratory freshwater shrimp and fish populations in Puerto Rico, USA, in both high- and low-gradient streams. In high-gradient streams above large dams, native shrimps and fishes were extremely rare, whereas similar sites without large dams had high abundances of native consumers. Losses of native fauna above dams dramatically altered their basal food resources and assemblages of invertebrate competitors and prey. Compared to pools in high-gradient streams with no large dams, pool epilithon above dams had nine times more algal biomass, 20 times more fine benthic organic matter (FBOM), 65 times more fine benthic inorganic matter (FBIM), 28 times more carbon, 19 times more nitrogen, and four times more non-decapod invertebrate biomass. High-gradient riffles upstream from large dams had five times more FBIM than did undammed riffles but showed no difference in algal abundance, FBOM, or non-decapod invertebrate biomass. For epilithon of lowgradient streams, differences in basal resources between pools above large dams vs. without large dams were considerably smaller in magnitude than those observed for pools in highgradient sites. These results match previous stream experiments in which the strength of native shrimp and fish effects increased with stream gradient. Our results demonstrate that dams can indirectly affect upstream free-flowing reaches by eliminating strong top-down effects of consumers. Migratory omnivorous shrimps and fishes occur throughout the tropics, and the consequences of their declines upstream from many tropical dams are likely to be similar to those in Puerto Rico. Thus, ecological effects of migratory fauna loss upstream from dams encompass a wider variety of species interactions and biomes than the bottom-up effects (i.e., elimination of salmonid nutrient subsidies) recognized for northern temperate systems.
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