Sediment-induced turbidity impairs foraging performance and prey choice of planktivorous coral reef fishes

Johansen, J.L., and Jones, G.P. (2013) Sediment-induced turbidity impairs foraging performance and prey choice of planktivorous coral reef fishes. Ecological Applications, 23 (6). pp. 1504-1517.

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Sedimentation is a substantial threat to aquatic ecosystems and a primary cause of habitat degradation on near-shore coral reefs. Although numerous studies have demonstrated major impacts of sedimentation and turbidity on corals, virtually nothing is known of the sensitivity of reef fishes. Planktivorous fishes are an important trophic group that funnels pelagic energy sources into reef ecosystems. These fishes are visual predators whose foraging is likely to be impaired by turbidity, but the threshold for such effects and their magnitude are unknown. This study examined the effect of sediment-induced turbidity on foraging in four species of planktivorous damselfishes (Pomacentridae) of the Great Barrier Reef, including inshore and offshore species that potentially differ in tolerance for turbidity. An experimental flow tunnel was used to quantify their ability to catch mobile and immobile planktonic prey under different levels of turbidity and velocity in the range encountered on natural and disturbed reefs. Turbidity of just 4 NTU (nephelometric turbidity units) reduced average attack success by up to 56%, with higher effect sizes for species with offshore distributions. Only the inshore species (Neopomacentrus bankieri), which frequently encounters this turbidity on coastal reefs, could maintain high prey capture success. At elevated turbidity similar to that found on disturbed reefs (8 NTU), attack success was reduced in all species examined by up to 69%. These reductions in attack success led to a 21–24% decrease in foraging rates for all mid to outer-shelf species, in spite of increasing attack rates at high turbidity. Although effects of turbidity varied among species, it always depended heavily on prey mobility and ambient velocity. Attack success was up to 14 times lower on mobile prey, leaving species relatively incapable of foraging on anything but immobile prey at high turbidity. Effects of turbidity were particularly prominent at higher velocities, as attack success was overall 20-fold lower and foraging rates 3.3-fold lower at flow velocities ≥30 cm/s relative to ≤10 cm/s. Given that many planktivorous reef fishes predominantly occupy exposed, high-flow habitats, these results provide a reasonable explanation for the lack of planktivores on inshore coral reefs and warn that the performance of visual predators could be impaired at turbidity levels of only 4 NTU.

Item ID: 29777
Item Type: Article (Research - C1)
ISSN: 1939-5582
Keywords: abundance, cross-shelf distribution, disturbance, flow velocity, habitat use, prey mobility, resilience, runoff, sediment loading, swimming, visual range and acuity, water quality
Funders: Lizard Island Doctoral Research Fellowship, ARC Centre of Excellence for Coral Reef Studies, James Cook University (JCU)
Date Deposited: 09 Oct 2013 05:27
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060202 Community Ecology (excl Invasive Species Ecology) @ 50%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
96 ENVIRONMENT > 9699 Other Environment > 969902 Marine Oceanic Processes (excl. Climate Related) @ 30%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960310 Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) @ 20%
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