New Zealand Journal of Marine and Freshwater Research abstracts

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Macroinvertebrate diet in intertidal seagrass and sandflat communities: a study using C, N, and S stable isotopes

Daniel Leduc¹
P. Keith Probert¹
Russell D. Frew²
Catriona L. Hurd³

¹ Department of Marine Science
² Department of Chemistry
³ Department of Botany
 University of Otago
 P.O. Box 56
 Dunedin, New Zealand
 email: ledda951@student.otago.ac.nz

Abstract Most seagrass community food-web studies using stable isotopes have been carried out in subtidal habitats during one sampling event. We used C, N, and S stable isotopes to characterise the diet of the dominant macroinvertebrates found in intertidal Zostera capricorni and sandflat communities of southern New Zealand in late summer and winter. The range of d13C and d34S values for Z. capricorni was wide (>5‰), which highlights the importance of accounting for spatial and temporal variability in primary producer isotopic signatures. The range of d15N values for Z. capricorni was comparatively small (<1‰). Mixing models based on d13C and d15N signatures suggested that Z. capricorni was a potentially important contributor (24–99%) to the diet of most consumers sampled at the seagrass site, whereas microphytobenthos dominated the diet of the same consumers at the sandflat site. The main exception was the bivalve Austrovenus stutchburyi, which had a diet consisting mostly (up to 85%) of Ulva and Polysiphonia spp. at both sites. S isotopes proved to be of limited use owing to the difficulty of sampling microphytobenthos and to potential non-dietary sources of 34S-depleted sulfur to consumers. Mixing models also suggested that Z. capricorni contributed more to the diet of deposit feeders in August (late winter) than in March (late summer).

Keywords intertidal; food web; Zostera capricorni; Austrovenus stutchburyi; macroinvertebrates; detrital pathway; New Zealand; temporal variation

New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40: 615–629
0028–8330/06/4004–0615     © The Royal Society of New Zealand 2006
M06042; Online publication date 15 November 2006. Received 12 July 2006; accepted 13 September 2006

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