Sliding Baselines, Ghosts, and Reduced Expectations in Kelp Forest Communities

Abstract

The detection of trends in ecosystems depends upon (1) a good description of the foundation or benchmark against which changes are measured and (2) a distinction between natural and anthropogenic changes. Patterns and mechanisms observed over 25 years in a large kelp forest suggest that definition of a meaningful benchmark is impossible, because many of the large animals have been gone for years to decades, and kelps are sensitive to large-scale, low-frequency El Niñ o-Southern Oscillation events and longer term regime shifts. A shift in the oceanographic climate has significantly reduced the average size and carrying capacity of the dominant plant. The animals that have been functionally removed from the community include sea otters, black sea bass, yellowtail, white sea bass, and abalones. Other species are still present, but fisheries have had huge effects on the abundances, size-frequencies, and/or spatial distributions of sheephead, kelp bass, rays, flatfish, rock fish, spiny lobsters, and red sea urchins. Now even sea cucumbers, crabs, and small snails are subject to unregulated fishing. The plants continue to exist without a hint of the effects of the loss of so much animal biomass. Furthermore, most of the megafauna have been removed with very little documentation or historical understanding of what the natural community was like. Thus, our ability to separate anthropogenic impacts from the ''natural'' dynamics of the system is severely compromised. We discuss the importance of both an ecosystem focus on productivity and careful monitoring of as many populations as possible. In addition, we show that this community is not tightly integrated with mutual dependencies; hence, many species can be removed without much affecting the rest of the ecosystem.

Forecasting the limits of resilience: integrating empirical research with theory

“…Broadening the concept of resilience into social-ecological systems emphasizes the importance of defining the ecological and social context Folke et al 2004;Carpenter et al 2005). Unfortunately, perspectives on values, states and trends are easily biased by shifting baselines that plague ecological comparisons when information on ecosystem history is limited (Dayton 1989;Dayton et al 1998;Duarte et al 2009). …”

What was natural in the coastal oceans?

“…In both cases, the interval studied is much less than the generation times of most common coral species and the intervals between some kinds of major disturbances in coral reef environments (13). Several kelp forests and rocky intertidal communities have been surveyed for about 25 years over scales of several hectares, so that the data approximate or exceed generation times of most important species, but not the periodicity of major climatic cycles (5,6). Ecological data for oyster reefs, seagrass meadows, level bottoms, and virtually all other marine communities have similar limitations (14)(15)(16)(17)(18).…”

“…Transformations of benthos are subtler and known only to a few specialists. I also focus on ecological extinction because the magnitude of ecological changes is not generally understood (1,2,5,9), and documentation of actual extinctions of marine species is just beginning (21). More importantly, too great a focus on species detracts attention from the transformation and loss of habitats and collapse of natural ecosystems that drive the processes of extinction.…”

“…Thus, the filter of individual experience has two components. Changes caused by humans are the signal and natural variability constitutes the noise that obscures the human footprint (4)(5)(6). An important example of the potential magnitude of natural change comes from annually layered sediments of the Santa Barbara Basin (7).…”

“…Conventional ecological data are clearly inadequate to measure the ecological impacts of fishing or any other long-term human disturbance (4,5,9). Most observational records are much too short, too poorly replicated, and too uncontrolled to encompass even a single cycle of natural environmental variation.…”