MEPS 340:17-27 (2007)  -  doi:10.3354/meps340017

Subtle and negligible effects of rainfall on estuarine infauna: evidence from three years of event-driven sampling

Richard B. Ford1,*, Marti J. Anderson2, Shane Kelly3

1Leigh Marine Laboratory, University of Auckland, Private Bag 92019, Auckland, New Zealand
2Department of Statistics, University of Auckland, Private Bag 92019, Auckland, New Zealand
3Auckland Regional Council, Private Bag 92012, Auckland, New Zealand

ABSTRACT: Events of heavy rainfall can impact benthic fauna in estuaries. The occurrence of heavy rainfall is predicted to increase in many places due to climatic warming. It is therefore important to know the likely impact of events of heavy rainfall, both now and in the future, particularly as the discharge of some contaminants, such as sediments from large-scale urban developments, is correlated with such events. We tested for evidence of any impacts of rainfall on the structure of assemblages over a period of 3 yr, using event-driven sampling of macrofaunal soft-sediment communities across 5 estuaries in the Auckland region of New Zealand. Changes in assemblage structure that were correlated with gradients in rainfall were detected at only 2 of 50 sites sampled. These site-specific impacts were detected in only one estuary and did not coincide with the largest amount of rainfall measured in the region over that period. Impacts were characterised by a short-term increase in the number of taxa, which probably resulted from deposition of fauna transported with bedload eroded from upstream sites due to increased flow rates. This contrasts with results from previous studies, which reported catastrophic decreases in biodiversity or abundance with storm events. Our work provides a realistic baseline against which potential future impacts of rainfall associated with land development can be tested. We suggest long-term monitoring studies that incorporate measurements of relevant physical variables, including rainfall, are needed in order to more effectively assess significant changes in naturally temporally variable communities.

KEY WORDS: Soft-sediment communities · Climate change · Environmental impacts · Monitoring · Macrofauna · New Zealand

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