Organization of macroalgal assemblages in the Northeast Pacific: the assumption of homogeneity and the illusion of generality

Abstract

Evidence for the geographic generality of the causes of intertidal zonation and the indirect effects of a 'keystone' predator, the sea otter, on subtidal kelp assemblages was examined. Most research on intertidal algal assemblages has been done at a few protected sites where zonation is distinct. Surveys of wave-exposed intertidal sites in central and northern California show that assemblage structure is highly variable. This indicates that our present understanding of assemblage organization, including the effects of mussel-algal interactions, may not be widely applicable. Surveys of kelp forest habitat along the entire coast of California suggest that deforestation by sea urchins is uncommon in the absence of sea otters. These examples indicate that the generality of commonly accepted causes of algal assemblage structure in the Northeast Pacific may be an illusion based on assumptions of environmental homogeneity.

Limited effects of a keystone species:trends of sea otters and kelp forests at the Semichi Islands, Alaska

“…Their influences can vary among systems (Mills et al 1993) and may be contextdependent within a system (Foster 1990, Menge et al 1994, Robles 1997. This study of the effects of sea otters on subtidal communities at the Aleutian Islands is one of the first to present quantitative data suggest---ing that internal variables (density and residence time) may be influencing the effects or mediating the time required to see effects of keystone species (see also Dean et al 2000).…”

“…In fact, the evidence from nature indicates that these roles are highly context dependent (Foster 1990, Menge et al 1994, Dean et al 2000. The ability of a given species to exert a strong influence on a community structure (as either a dominant or a keystone) is dependent upon community composition and can be particularly sensitive to conditions.…”

Evaluation of effective shore level as a method of characterizing intertidal wave exposure regimes

“…Yet attempts to generalize such local zonation schemes to larger regions are frequently unsuccessful (Stephenson and Stephenson 1972). There is often great disparity in zonation patterns among locations or within a location over time (Lawson 1957, Paine 1966, Leigh et al 1987, Foster 1990.…”

Distributional expansion ofCarpophyllum flexuosumonto wave‐exposed reefs in north‐eastern New Zealand

“…1998), and alterations to species ranges (reviewed by Grosholz 1996) may change through time, along with anthropogenic modifications to the physical environment (e.g., Duarte 1995;Dayton et al 1998). Temperate reefs in the southern hemisphere lack the strongylocentrotid sea urchins which dominate the most-studied sites in the northern hemisphere (Chapman & Johnson 1990;Foster 1990), and historically the predatory faunas of the hemispheres may have differed considerably (Estes & Steinberg 1988). There have been reviews of Australian (Underwood & Kennelly 1990), South African (Branch & Griffiths 1988), South American (Santelices 1990), and New Zealand (Schiel 1988(Schiel , 1990) seaweed stands.…”