Document: BRU-3-93-3

Links between rocky intertidal communities and nearshore oceanic conditions in upwelling vs. non-upwelling ecosystems in New Zealand.

MENGE, B.A.* ^1,2, J.LUBCHENCO ^1,2, T.FREIDENBURG ^1,2, M.BRACKEN ^1,2, M.FOLEY ^1,2, G.HUDSON ^1,2, C.KRENZ ^1,2, H.LESLIE ^1,2 and R.RUSSELL ^1,2

Oregon State University, Corvallis, OR 97331 USA ¹
University of Canterbury, Christchurch, New Zealand ²

Abstract:
We tested the hypothesis that variation in bottom-up effects strongly influences community dynamics by comparing rocky intertidal ommunities at a range of sites around the South Island of New Zealand. We predicted that micro- and macroalgal productivity and recruitment of sessile invertebrates (mussels and barnacles) would be higher at upwelling sites and lower at non-upwelling sites. As the eastward-flowing Tasman Current approaches the central portion of the west coast of New Zealand, it splits into the northward-flowing Westland Current and the southward-flowing Southland Current. The Southland Current wraps around the southern end of the island and flows northward along the east coast. The northern and central portions of the west coast experience intermittent coastal upwelling driven by the Westland Current; the southern portion of the west coast and the east coast lack upwelling. The abundances of ecologically-important mussels, barnacles and sea stars, (all characterized by planktonic larval dispersal), varied differentially among sites. Mussels were abundant at central and northern sites on both coasts but were less robust on the east coast (light shells, less tissue). Barnacles were abundant at all sites except the southern east coast. Sea star predators were abundant on the west coast and rare on the east coast. At the upwelling sites, phytoplankton concentration and benthic algal biomass accumulation were greater than at all four non-upwelling sites. Recruitment of barnacles and mussels, and barnacle growth rates were greatest at upwelling sites, least at east coast non-upwelling sites and intermediate at the southern west coast non-upwelling site. Predation rates on transplanted mussels were low on the east coast (nonupwelling) sites and high at the west coast (two upwelling and one non-upwelling) sites. Rocky intertidal community dynamics thus reflected both upwelling-related processes (recruitment, growth rates, condition of mussels) and current-related processes (recruitment, population density, predation rate).

Keywords: top-down, bottom-up, benthic-pelagic coupling, New Zealand, rocky intertidal, community ecology, recruitment, upwelling, predation

This abstract is being presented at: 4:00 PM in session:
Oral Session #47: Zooplankton Ecology.