Variation in scope for growth: a test of food limitation among intertidal mussels |
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Authors: | Jeremy G Helson Jonathan P A Gardner |
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Institution: | (1) Island Bay Marine Laboratory and Centre for Marine Environmental & Economic Research, School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand;(2) Present address: Deepwater and National Issues, Ministry of Fisheries, PO Box 1020, Wellington, New Zealand |
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Abstract: | Wellington Harbour supports large populations of the mussels Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus that are almost entirely absent from nearby coastal locations in Cook Strait. We calculated scope for growth (SFG) using
ambient Cook Strait water over a broad temporal scale and a broad range of seston conditions to determine if negative SFG
explains this phenomenon. Although all three mussel species had positive mean SFG values, variation in SFG was high and negative
values often occurred: A. maoriana 19.1 J g−1 h−1, 43% of mussels showed negative SFG; M. galloprovincialis 1.26, 52% negative SFG; P. canaliculus 45.6, 27% negative SFG. Negative SFG was most often due to negative absorption efficiency caused by metabolic faecal loss
that is characteristic of mussels feeding in environments with low seston quality. From our ecophysiology data we constructed
a model to estimate SFG based on physiological responses to the narrow range of seston conditions typical of Cook Strait (Model
One), and a model to estimate SFG based on physiological responses of mussels to the broad range of seston conditions typical
of Wellington Harbour and Cook Strait (Model Two). We used seston data collected over an 18-month period from sites in Wellington
Harbour and Cook Strait to derive 159 estimates of species-specific mussel SFG from both models. Both models produced higher
estimates of SFG for mussels in the Harbour compared with those at Cook Strait sites. This was consistent with elevated particulate
concentrations in the Harbour than at Cook Strait sites, and in agreement with previous studies. For Cook Strait mussels,
both models produced negative estimates of net energy balance for long periods of time (several months), whereas for Harbour
mussels negative SFG estimates were generally short in duration. We conclude that our short-term laboratory-based determinations
of SFG and our long-term bioenergetics modelling estimates do not conclusively support the hypothesis of food limitation for
three coexisting taxa of mussels in the intertidal region of Cook Strait, New Zealand.
Handling editor: P. Viaroli |
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Keywords: | Aulacomya maoriana Bioenergetics modelling Bottom-up regulation Intertidal community structure Mussels Mytilus galloprovincialis Perna canaliculus New Zealand Scope for growth |
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