Dana Giffen
Temperate to Tropical: The Trouble with Using Temperate Aquatic Insect
Analysis Methods in Costa Rica
Abstract
Reliable methods to characterize the biological integrity of tropical aquatic systems are important
for conservation and research agendas. Aquatic insects live in streams for extended periods of
time and are good indicators of long-term ecosystem health. However, almost all analysis
methods for families of benthic macroinvertebrates have been developed for temperate streams,
and these appear to have only limited applicability to tropical systems. This baseline study
examined pH, hardness, alkalinity, canopy cover, substrate dynamics, fish populations, and the
composition of aquatic insect populations in three headwater streams-the Jucó, the Grande, and
the Chires-near Mastatal, Costa Rica. Three months prior to this study, the Lower Jucó
experienced a poisoning event, so this ecosystem was compared to the undisturbed Upper Jucó.
Results illustrated the uncertainties of using indexes developed for temperate freshwater systems
to analyze tropical insect data. Seven indexes, primarily used in temperate waters were
analyzed; the family biotic index (FBI), taxa richness, Ephemeroptera-Plecoptera-Trichoperta
index (EPT), Shannon-Wiener diversity index, Simpson’s index, number of endemic taxa, and
one newly created index specific for Costa Rican aquatic insects--the Springer index. It appears
that some of these indexes may not be appropriate to assess tropical streams (Davis et al. 2003
and Deliz Quinones 2005). The indexes examined used variant tolerance values for different
families, leading to inconsistent results based on the index employed. The family-specific
indexes did the poorest job of reliably characterizing the streams, while generic diversity indexes
produced less specific, but uniform results. Simpler indexes that were not family-specific, such
as the Shannon-Wiener diversity index, taxa richness, and number of endemic families were
subject to less uncertainty than results obtained from indexes like the Springer index, FBI, and
EPT that lacked information about prevalent tropical insect families. This paper cautions
researchers to use a variety of indexes to characterize tropical streams until more diagnostic
studies are conducted to compare and modify these indexes.