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Marine Ecology Progress Series

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MEPS 479:47-62 (2013)  -  DOI:

Wind chop and ship wakes determine hydrodynamic stresses on larvae settling on different microhabitats in fouling communities

M. A. R. Koehl1,*, J. P. Crimaldi2, D. E. Dombroski2

1Department of Integrative Biology, University of California, 3060 VLSB, Berkeley, California 94720-3140, USA
2Department of Civil, Environmental and Architectural Engineering, University of Colorado, 428 UCB, Boulder, Colorado 80309-0428, USA

ABSTRACT: Fouling communities living on hard surfaces in harbors are model systems for studying larval recruitment and ecological succession. Although they live in protected harbors, fouling communities are exposed to waves due to wind chop and ship wakes. We studied how superimposing waves onto unidirectional currents affects hydrodynamic stresses experienced by larvae settling into different microhabitats within rugose fouling communities. We exposed fouled plates in a flume to turbulent water currents and waves mimicking those measured across fouling communities in Pearl Harbor, Hawaii, USA, and used laser-Doppler velocimetry to measure water velocities on the scale of larvae (500 µm from surfaces) at specific positions within each community chosen to represent a wide range of microhabitat types. These data were used to determine instantaneous hydrodynamic stresses encountered by larvae and to calculate larval settlement probabilities. Local topography was more important than successional stage in determining hydrodynamic stresses on the scale of larvae. Increasing current velocity reduced settlement probabilities, with the largest effects on a flat unfouled surface and on microhabitats on the tops of fouling organisms. Wind chop and ship wakes reduced the probability of larval settlement at all current speeds and in all microhabitats, with the most pronounced effects on sites atop fouling organisms. Episodic peak stresses can be orders of magnitude higher than mean stresses, so using instantaneous stresses to calculate settlement probability yields a lower value than is predicted using mean stress. The factor by which the use of mean stress over-estimates settlement probability depends on both microhabitat and flow conditions.

KEY WORDS: Larval settlement · Biofouling · Reynolds stress · Turbulence · Waves · Microhabitat · Boundary layer

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Cite this article as: Koehl MAR, Crimaldi JP, Dombroski DE (2013) Wind chop and ship wakes determine hydrodynamic stresses on larvae settling on different microhabitats in fouling communities. Mar Ecol Prog Ser 479:47-62.

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