Changes in Seston Quality and Quantity Associated With Amphibian Declines in Central American Streams

Larval amphibians are important in neotropical streams because their feeding, egestion, and excretion can influence the quality and quantity of food resources available to other consumers.  As part of the Tropical Amphibian Declines in Streams (TADS) project, we have been assessing the ecological consequences of ongoing, catastrophic declines of stream-breeding amphibians in the Panamanian uplands.  For this study, we compared organic seston quantity and quality in 2 headwater stream reaches before, during, and following a massive amphibian decline (El Cope) and in 2 streams that had declined >10 years ago (Fortuna).  Organic seston C/N was consistently higher in Fortuna streams (mean=10.6±0.6) compared to El Cope, and increased from 8.9(±0.3) to 10.5(±0.7) in El Cope streams following the loss of tadpoles. Concentrations of organic seston also decreased from 2.4mg L-1 pre-decline to 1.5mg L-1 post-decline at El Cope sites. However, annual habitat-weighted benthic organic matter standing stocks at both El Cope and Fortuna also decreased during this period, suggesting that other factors such as discharge patterns were responsible.  Our results indicate that tadpoles, and thus their ongoing extirpations in these systems, influence the quality of seston available for other consumers, but it is difficult to assess whether they affect seston quantity.