PARENT SESSION
Oral Session #9: Trophic structure and community interactions. Presiding: B. Menge.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.
Cross-scale linkages between bottom-up factors and interaction strength in rocky intertidal communities.
Menge, Bruce1,4, Blanchette, Carol2,4, Freidenburg, Tess1,4, Gaines, Steven2,4, Lubchenco, Jane1,4, Lohse, David3,4, Raimondi, Peter3,4, 1 4 2 3
ABSTRACT- Evidence has accumulated suggesting that rocky intertidal communities vary with nearshore oceanographic conditions. Effects of consumers tend to be stronger, or weaker, at sites with higher, or lower rates of "supply" (nutrients, particulates, phytoplankton, recruitment of prey), respectively. From north to south the nearshore oceanography of the California current undergoes macroscale shifts, with transitions from weak, intermittent to strong, persistent upwelling at Cape Blanco and from upwelling to downwelling at Point Conception. Within each region there are also mesoscale discontinuities. In 1999 and 2000, we evaluated the relation between bottom-up and top-down effects at both macro- and mesoscales. Similarly-designed studies were done at 14 sites along the coasts of Oregon, central California and southern California. We quantified recruitment, prey growth rates, chlorophyll-a concentrations, predation rates, and mussel and predator abundance. Mussel recruitment, chlorophyll-a, and mussel abundance were higher north than south of Cape Blanco. Mussel growth, predator abundance, and predation rates varied more on mesoscales than macroscales. Multiple regression indicated that per population predation rates varied with mussel recruitment and predator density, while per capita predation rates varied with mussel growth and predator density. These results thus suggest that predation regimes and mussel performance both vary primarily on mesoscales while supply factors vary primarily at macroscales, implying that biophysical coupling, and its community impact, varies differentially across spatial scales.
KEY WORDS: cross-scale linkages, bottom-up/top-down, rocky intertidal, California current