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Wave disturbance overwhelms top‐down and bottom‐up control of primary production in California kelp forests
Author(s) -
Reed Daniel C.,
Rassweiler Andrew,
Carr Mark H.,
Cavanaugh Kyle C.,
Malone Daniel P.,
Siegel David A.
Publication year - 2011
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/11-0377.1
Subject(s) - kelp , macrocystis pyrifera , kelp forest , disturbance (geology) , environmental science , ecology , primary production , biomass (ecology) , ecological succession , oceanography , ecosystem , biology , geology , paleontology
We took advantage of regional differences in environmental forcing and consumer abundance to examine the relative importance of nutrient availability (bottom‐up), grazing pressure (top‐down), and storm waves (disturbance) in determining the standing biomass and net primary production (NPP) of the giant kelp Macrocystis pyrifera in central and southern California. Using a nine‐year data set collected from 17 sites we show that, despite high densities of sea urchin grazers and prolonged periods of low nutrient availability in southern California, NPP by giant kelp was twice that of central California where nutrient concentrations were consistently high and sea urchins were nearly absent due to predation by sea otters. Waves associated with winter storms were consistently higher in central California, and the loss of kelp biomass to winter wave disturbance was on average twice that of southern California. These observations suggest that the more intense wave disturbance in central California limited NPP by giant kelp under otherwise favorable conditions. Regional patterns of interannual variation in NPP were similar to those of wave disturbance in that year‐to‐year variation in disturbance and NPP were both greater in southern California. Our findings provide strong evidence that regional differences in wave disturbance overwhelmed those of nutrient supply and grazing intensity to determine NPP by giant kelp. The important role of disturbance in controlling NPP revealed by our study is likely not unique to giant kelp forests, as vegetation dynamics in many systems are dominated by post‐disturbance succession with climax communities being relatively uncommon. The effects of disturbance frequency may be easier to detect in giant kelp because it is fast growing and relatively short lived, with cycles of disturbance and recovery occurring on time scales of years. Much longer data sets (decades to centuries) will likely be needed to properly evaluate the role of disturbance relative to other processes in determining patterns of NPP in other systems.