MEPS 408:207-226 (2010)  -  doi:10.3354/meps08552

Sub-surface hotspots in shallow seas: fine-scale limited locations of top predator foraging habitat indicated by tidal mixing and sub-surface chlorophyll

B. E. Scott1,*, J. Sharples2, O. N. Ross3, J. Wang1, G. J. Pierce1,4, C. J. Camphuysen5

1School of Biological Sciences, Institute of Biological and Environmental Sciences University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK
2Proudman Oceanographic Laboratory, Joseph Proudman Building, 6 Brownlow Street, University of Liverpool, Liverpool, L3 5DA, UK
3Mediterranean Centre for Marine and Environmental Research, (CMIMA, CSIC), Marine Technology Unit (UTM), Pg. Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain
4Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, PO Box 1552, 36200 Vigo, España
5Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands

ABSTRACT: The foraging habitats of 7 species of marine apex predators were observed simultaneously in a shallow sea, with continuous measurements taken of the detailed bio-physical water column characteristics to determine habitat preferences. We found the occurrence of small-scale ‘hotspots’, where 50% of all animals were actively foraging in less than 5% of the 1000 km of transects surveyed. By investigating a contrasting range of foraging strategies across a variety of fish-eating seabirds and marine mammals, we determined which habitat characteristics were consistently important across species. A static habitat variable, tidal stratification, log10(h/U3) (h = water depth, U = tidal current amplitude), was found to be the best indicator of the probability of presence and abundance of individual species. All 7 mobile top-predators preferentially foraged within habitats with small-scale (2 to 10 km) patches having (1) high concentrations of chlorophyll in the sub-surface chlorophyll maximum (CHLmax) and (2) high variance in bottom topography, with different species preferring to forage in different locations within these habitats. Patchiness of CHLmax was not associated with the locations of strong horizontal temperature gradients (fronts) or high surface chlorophyll values, but instead may be related to areas of high sub-surface primary production due to locally increased vertical mixing. These small-scale areas represent a newly identified class of spatially important location that may play a critical role within the trophic coupling of shallow seas. Such sub-surface hotspots may represent the limited locations where the majority of predator-prey interactions occur, despite making up only a small percentage of the marine environment.

KEY WORDS: Biological hotspots · Foraging habitats · Marine top predators · Predator-prey interactions · Shallow sea · Sub-surface chlorophyll maximum · Tidal mixing · Topography

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Cite this article as: Scott BE, Sharples J, Ross ON, Wang J, Pierce GJ, Camphuysen CJ (2010) Sub-surface hotspots in shallow seas: fine-scale limited locations of top predator foraging habitat indicated by tidal mixing and sub-surface chlorophyll. Mar Ecol Prog Ser 408:207-226

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