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

BE Scott, J Sharples, ON Ross, J Wang, GJ Pierce, CJ Camphuysen
2010 Marine Ecology Progress Series  
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 fisheating seabirds and marine
more » ... mmals, we determined which habitat characteristics were consistently important across species. A static habitat variable, tidal stratification, log 10 (h/U 3 ) (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 (CHL max ) and (2) high variance in bottom topography, with different species preferring to forage in different locations within these habitats. Patchiness of CHL max 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 subsurface 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 Resale or republication not permitted without written consent of the publisher Editorial responsibility: Hans Heinrich Janssen,
doi:10.3354/meps08552 fatcat:cn5ldhuw5zfy7ideixvj2b336i