top-down and bottom-up regulation of new zealand rocky intertidal communities
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Ecological Monographs, 69(3), 1999, pp. 297330q 1999 by the Ecological Society of America
TOP-DOWN AND BOTTOM-UP REGULATION OF NEW ZEALAND ROCKYINTERTIDAL COMMUNITIES
BRUCE A. MENGE,1 BRYON A. DALEY,2 JANE LUBCHENCO, ERIC SANFORD, ELIZABETH DAHLHOFF,3PATRICIA M. HALPIN, GREGORY HUDSON, AND JENNIFER L. BURNAFORD
Department of Zoology, University of Canterbury, Christchurch, New Zealand,and Department of Zoology, Oregon State University, Corvallis, Oregon 97331-2914 USA
Abstract. Studies on the west coast of North America suggest that nearshore ocean-ographic conditions can have important effects on rocky intertidal community structureand dynamics. Specifically, upwelling-dependent processes in coastal waters can affectboth top-down and bottom-up processes on adjacent rocky shores. As a first step intesting the prediction that similar linkages occur elsewhere, we investigated the effectsand rates of predation, grazing, and recruitment on rocky intertidal community dynamicsat upwelling and non-upwelling sites on the South Island of New Zealand. Comparative-experimental studies were done at each of two sites on both the east and west coastsof the South Island. We quantified benthic community structure, maximal wave force,nearshore sea-surface temperature, air temperature at low tide, nutrient concentrations,survival of mussels, rates and effects of predation, rates and effects of limpet grazing,recruitment of mussels and barnacles, and RNA:DNA ratios (a growth index) of mussels.
Overall, zonation patterns were similar on the upper shore on both coasts: barnacles(Chamaesipho columna) dominated the high zone, and mussels (Mytilus galloprovincialis)the middle zone. In the low zone, however, community structure differed markedly betweencoasts. East-coast low-zone communities were dominated by mussels with a moderatecanopy of kelp, primarily Durvillea spp., while mussels were largely absent from west-coast low zones. Food webs were similar on the different coasts and included predaceouswhelks, sea stars, oystercatchers, and herbivorous limpets. Field experiments showed thatonly sea stars and limpets had strong effects at west-coast sites, and only limpets had strongeffects at east-coast sites. The sea star Stichaster australis, previously identified as a key-stone species on the west coast of the North Island, was common and important on thewest coast of the South Island but was absent from the east coast.
Physical conditions (wave forces, low-tide air temperature) were comparable on thetwo coasts, suggesting that other factors caused the differences in low-zone communitystructure. Experiments and observations indicated that predation, grazing, prey recruit-ment, and mussel growth were greater on the west than on the east coast. While somebetween-coast contrasts in community dynamics could emanate from differences in spe-cies composition (e.g., the absence of S. australis from the east coast), the higher west-coast rates of most of the ecological processes studied suggest that between-coast dif-ferences may also depend on other factors. Among the alternatives, a difference in near-shore oceanographic conditions on the opposite coasts of the South Island seems mostlikely. Prior oceanographic research, and our onshore measurements of sea-surface tem-perature and nutrients indicate that summer upwelling may be relatively frequent on thewest coast and rare on the east coast. While detailed oceanographic studies synchronizedwith benthic studies in nearshore coastal environments are needed to evaluate this hy-pothesis, present evidence is consistent with the view that rocky intertidal communitystructure and dynamics vary with large-scale oceanographic conditions in nearshore coast-al environments around New Zealand.
Key words: barnacles; benthicpelagic coupling; grazing impact; mussels; nearshore ecosystemdynamics; predation; recruitment; RNA:DNA; rocky intertidal community regulation; rocky intertidaloceanography; scale-dependent variability; sea stars.
Manuscript received 23 December 1997; revised 9 September 1998; accepted 25 September 1998; final version received23 October 1998
1 E-mail: email@example.com Present address: Section of Ecology and Systematics, Cornell University, Ithaca, New York 14850 USA.3 Present address: Department of Biology, Santa Clara University, Santa Clara, California 95053 USA.
298 BRUCE A. MENGE ET AL. Ecological MonographsVol. 69, No. 3
Rocky intertidal communities have been productivesystems for developing both empirical understandingand conceptual models of community patterns (e.g.,Paine 1966, 1974, Dayton 1971, Connell 1975, Mengeand Sutherland 1976, 1987, Bertness and Callaway1994). These and many other studies provide insightinto community dynamics that incorporate strong directand indirect effects of biotic interactions and environ-mental stresses (Menge and Olson 1990). Despite theseinsights, comparisons among intertidal sites within aregion usually reveal that much variation among com-munities remains unexplained by these factors, sug-gesting that additional processes need to be taken intoaccount (e.g., Menge 1992). Among the possibilitiesare factors dependent on larger scale, oceanographi-cally driven processes such as recruitment and pro-ductivity.
Most benthic marine organisms have planktonicstages, many with potentially long-range dispersal. Asa result, successive generations of shore-based popu-lations are often completely independent from one an-other (review in Caley et al. ). Moreover, manymarine species depend on oceanographic influences forfood or nutrients and transport of propagules to appro-priate adult habitat (e.g., Ebert and Russell 1988, Gros-berg and Levitan 1992, Menge 1992). Oceanographicconditions vary over far larger scales than those usuallystudied by benthic marine ecologists, and are typicallypoorly known in nearshore waters (010 km from theshore). As a result, understanding the coupling betweenbenthic and nearby pelagic environments has proceed-ed slowly.
As marine ecology and oceanography have matured,however, and with advances in technology and meth-odology, attention has focused more on nearshorecoastal environments (e.g., Roughgarden et al. 1988,Menge 1992, Witman et al. 1993, Wing et al. 1995a,b, Robles et al. 1995, Menge et al. 1996, 1997a, b,Robles 1997, Connolly and Roughgarden 1998). Forexample, recent studies along the Oregon coast suggestthat among-site variation in rocky intertidal communitystructure at intermediate, or meso-scales (i.e., 10sto 100s of kilometers) may be driven by consistentamong-site differences in nearshore oceanographicprocesses (Menge 1992, Menge et al. 1994, 1996,1997a, b). Inverse between-site differences in relativeabundance of sessile invertebrates and macrophytes ap-pear to vary with upwelling intensity, currents, andphytoplankton concentration. Specifically, high abun-dances of sessile invertebrates occurred on rockyshores adjacent to a region characterized by gyres andeddies that may both concentrate zooplankton and phy-toplankton and transport them to shore during upwell-ing relaxations. High phytoplankton abundance sup-ported increased growth of filter feeders, potentiallyreducing macrophyte abundance through competition
for space. High sessile invertebrate abundance also at-tracted high concentrations of predators, leading tohigh rates of predation. The oceanographic processesthat appeared to drive these patterns were consistentin space, and were associated with features of coastalmorphology and shelf bathymetry that influenced near-shore currents and circulation (Menge et al. 1997a).
Generality of benthicpelagic linksThe Oregon (USA) studies cited above suggest that
pelagic and benthic ecosystems are coupled via thelinkage: plankton-concentrating gyres phytoplank-ton and invertebrate larvae filter-feeding inverte-brates predators. Because these postulated connec-tions between oceanographic conditions and intertidalcommunity structure have implications for how near-shore ecosystems will respond to large-scale environ-mental perturbations, the issue of the generality of suchlinkages is important. Is the Oregon example unique,or are similar nearshoreonshore couplings seen onother coasts? To begin evaluating the generality ofthese results, we initiated a comparative-experimentalstudy of rocky intertidal community dynamics in NewZealand. Our approach focused on comparisons andexperiments aimed at quantifying processes that eitherdirectly or indirectly reflected certain top-down,bottom-up, and larval transport processes (see,e.g., Menge 1992, Robles et al. 1995, Menge et al.1997a, b, Robles 1997). Studies were done at pairedrocky shore sites on opposite coasts (east vs. west) ofthe South Island of New Zealand.
Here, top-down refers to effects of predation andgrazing on invertebrates and algae. Bottom-up pro-cesses refer to factors that affect the abundance ofplants and, through them, possibly higher trophic lev-els. Here we broaden this definition of bottom-upto accommodate the unique role of particle-feeding ses-sile invertebrates such as mussels and barnacles inrocky intertidal communities (e.g., Menge 1995). Theseorganisms are heterotrophs (dependent on plankton orparticulate material), but they are also basal species(like macrophytes, live attached to the rock surface andcompete for space; Pimm 1982). Also like marineplants, sessile animals obtain their raw materials forgrowth and reproduction from seawater. Hence, factorssuch as phytoplankton and detritus that influencegrowth of filter feeders are bottom-up effects. Forthis reason we consider nutrients, plant-derived detri-tus, and primary productionwhether of macrophytesor phytoplanktonto be bottom-up factors.
Recruitment of sessile organisms might also be con-sidered a bottom-up process, because it p