The effects of bioturbation by stingrays at Ningaloo Reef, Western Australia
O'Shea, O., Meekan, M. and van Keulen, M. (2011) The effects of bioturbation by stingrays at Ningaloo Reef, Western Australia. In: 48th Annual Conference of the Australian Marine Science Association, 3 - 7 July, Fremantle, Western Australia.
Stingrays are an important part of the biomass of the fishes in shallow, coastal ecosystems, particularly in inter-reefal areas. In these habitats they are thought to be keystone species, responsible for modifying physical and biological habitats through their foraging and predation. However, there have been few attempts to quantify the effects of these animals on benthic environments. Here, we examine the effects of bioturbation by rays on sand flats of the lagoon of Ningaloo Reef WA. At Mangrove Bay we surveyed 15, 10x10 m quadrats during August 2009, September 2010 and February 2011. We recorded all pits that could be identified as due to ray feeding. Of these, 98 were selected randomly to be measured (length, breadth, depth) on a daily basis for a week. Over the 21 day period, a total of 2.01 cubic m of sediment was excavated by ray pits equating to a wet weight of 1,411.3 kg and 2.42% of the total area sampled. Based on these figures, up to 42% of the soft sediments in our study area would be reworked by stingray feeding to an average depth of 5.16 cm over a year. Within the 15 quadrats, new pits were formed at a rate of 0.41/day and then maintained a clear shape for an average of 1.57 days, after which time they could no longer be measured. All evidence of the pit was lost after an average of 3.3 d. In addition to the turnover of sediment and removal of prey, pits created sheltered habitats for a range of organisms, including larval fish, crabs and gastropods. The role of stingrays is compared with that of other organisms that are seen as important ecosystem engineers in soft-sediment environments such as dugongs, crabs and callianasiid shrimps.
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|Murdoch Affiliation:||School of Biological Sciences and Biotechnology|
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