Large-scale Stressors Research Articles

Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the world's largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the world's great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.

Comparative application of indices of biotic integrity based on periphyton, macroinvertebrates, and fish to southern Rocky Mountain streams

Abstract To assess the relative sensitivity of assessments using community metrics for macroinvertebrates, periphyton, and fish assemblages, we compared the results of three parallel assessments using these assemblages at 86 stream reaches sampled in 1994 and 1995 by the Regional Environmental Monitoring and Assessment Program (R-EMAP) in the mineralized zone or historical mining region of the Southern Rockies Ecoregion in Colorado. We contrasted assessments using community metrics for each taxa group selected to be diagnostic of the two large-scale stressor gradients identified in this ecoregion: discharges from historical hardrock metal mines and agriculture, particularly pasturing of livestock. While principal components analysis (PCA) extracted axes from the metrics for all three assemblages correlated with increased metal concentrations, the axes differed in their sensitivity to different environmental gradients. Two axes extracted from the fish metrics were correlated with dissolved metals, suspended solids, and sediment embeddedness or with sediment metals. Two axes extracted from the macroinvertebrate metrics partially separated these two stressor gradients, while the single correlated axis extracted from the periphyton metrics did not. The second macroinvertebrate PCA axis was correlated with an environmental gradient correlated both with agricultural effects and with stream size, as were the second and third periphyton PCA axes. The third fish PCA axis was correlated with stream size and slope, but was not sensitive to agricultural effects. Fish, macroinvertebrates, and periphyton differ in their sensitivity to different stressors, and combining metrics for these assemblages into a mixed assemblage index of biotic integrity may increase the utility of the multimetric approach to diagnose environmental stressors at impaired reaches.

El Niño induced local extinction of coral reef bryozoan species from Northern Bahia, Brazil

The 1997–1998 El-Niño Southern Oscillation was the most severe on record and dramatically impacted corals worldwide. However, the effect of this event on the associated community of reef organisms has received much less attention. The composition of the bryozoan assemblage from the coral reefs of Northern Bahia, Brazil were monitored annually from 1995 to 2000, allowing the investigation of the effects of this large-scale stressor on an important, diverse, yet understudied component of the coral reef system. Bryozoan samples (35 replicates/reef) were collected during April/May from four shallow bank reefs (10–40 m depth) located a few kilometres off the coast, together with measurements of the associated environmental parameters. Currently 157 species have been recorded from the study area, but significant reductions in density and diversity were apparent between pre- and post El-Niño Southern Oscillation (ENSO) years, multivariate analysis denoting significant changes in assemblage composition. A total of 61 species were unrecorded following the 1997–1998 ENSO event (22 species from 1997; 25 further species from 1998 and 14 more from 1999). These included several species endemic to Brazil, suggesting that the 1997–1998 ENSO has had a marked influence on the reef bryozoan community, resulting in the local extinction of several species. Bryozoan mortalities were probably initiated by elevated temperatures, but continued disappearance of species for 2 years after ENSO suggests other indirect factors are also influential. These results demonstrate that ENSO events can have severe long-term impacts on the biodiversity of coral reefs, with important conservation consequences.