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 Niño–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.

Biotic resistance to invasion along an estuarine gradient

“…High spiny lobster density on transects in the front of Mission Bay, coupled with few observations of round rays and crabs, suggest that spiny lobsters play a large role in restricting Asian mussels to the back of the bay. Although the ability of lobsters to consume other invasive species is unknown, our results suggest that further reductions in lobster abundance and size due to overfishing (Dayton et al 1998) may render estuarine communities more susceptible to invasion by non-native species, particularly if other native predators are unable to compensate.…”

The dynamics of Kelp Forests in the Northeast Pacific Ocean and the relationship with environmental drivers

“…Canopy kelp species are foundation species that provide an important natural feature in temperate oceans globally. Their primary productivity is unsurpassed (Mann, 1973), and their tissues enhance productivity in situ and in adjacent ecosystems (Dayton, Tegner, Edwards, & Riser, 1998;Krumhansl & Scheibling, 2012;Hansell, 2013). Kelp provide habitat and food for a myriad of invertebrates and fishes (Bodkin, 1986;Duggins, Simenstad, & Estes, 1989;Teagle, Hawkins, Moore, & Smale, 2017); their biogenic structure means that any changes in their abundance will have cascading effects (Sunday et al, 2016).…”

Acute effects of removing large fish from a near-pristine coral reef

“…Sinclair and Norton-Griffiths 1995; Terborgh et al 2001). Following this model in the oceans has been problematic because densities of large marine animals were greatly reduced in many accessible ocean ecosystems prior to the onset of most modern marine ecological research (Dayton et al 1998; Lotze et al 2006). Much of the literature on the ecological role of “large” marine animals has been generated in ecosystems already depleted of their large fauna (Jackson 1997).…”