Saturday, July 01, 2006

Ecology and Values: Harm (and recovery?) in estuaries

A report in the latest Science on human-caused habitat loss:
Lotze, H.K. et al. Depletion, degradation, and recovery potential of estuaries and coastal seas. Vol. 312 (23 June 2006): 1806-1809.

This study of species distributions for ancient and recent sites of human settlement on estuaries and coastal seas compares historical baselines (recovered from paleontological and ecological records) with post-settlement conditions. It finds that human-caused overexploitation and habitat loss explains about 95% of observed declines in species richness. The sites were picked from various continents (mostly Europe and N. America), including the Chesapeake Bay, Galveston Bay, and the north Adriatic. Patterns of decline in each system were similar, commonly destroying over 65% of seagrass and accelerating the rate of species invasions by exotics. Systems with the longest history of intense human impacts were the most degraded.

This sounds like overwhelmingly BAD NEWS. Human settlement on coastlines is associated with severe declines in diversity and productivity.

Two points about how these results are reported:

1. The rhetoric of bad news is always accompanied by a promise for recovery. Maybe things aren't as bad as they seem: "It's important to rescue the frog." In fact, a graph in the report depicts very moderate improvement scenarios over the next century even in the best of situations and the text indicates, "Despite some extinctions, most species and functional groups persist, albeit in greatly reduced numbers. Thus the potential for recovery remains."
In spite of such restrained language, the news report in Science portrays the results far more optimistically, saying that the study indicates "that well-targeted management can reverse destructive trends" (1713). Mainstream news reports consistently conclude with this positive message.

2. This study in historical ecology provides detailed evidence of the type and degree of declines in relative abundance and species richness. It does not actually provide evidence of whether or how the situation can be improved. In this, the conclusions exceed the available evidence. Work on historical baselines is essential for establishing the magnitude of the problem, but it is far from being integrated with management.

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