Drivers of euphausiid species abundance and numerical abundance in the Atlantic Ocean |
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Authors: | Tom B Letessier Martin J Cox Andrew S Brierley |
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Institution: | (1) Pelagic Ecology Research Group, Scottish Oceans Institute, University of St Andrews, St Andrews, KY16 8LB, UK |
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Abstract: | Mid-ocean ridges are common features of the world’s oceans but there is a lack of understanding as to how their presence affects
overlying pelagic biota. The Mid-Atlantic Ridge (MAR) is a dominant feature of the Atlantic Ocean. Here, we examined data
on euphausiid distribution and abundance arising from several international research programmes and from the continuous plankton
recorder. We used a generalized additive model (GAM) framework to explore spatial patterns of variability in euphausiid distribution
on, and at either side of, the MAR from 60°N to 55°S in conjunction with variability in a suite of biological, physical and
environmental parameters. Euphausiid species abundance peaked in mid-latitudes and was significantly higher on the ridge than
in adjacent waters, but the ridge did not influence numerical abundance significantly. Sea surface temperature (SST) was the
most important single factor influencing both euphausiid numerical abundance and species abundance. Increases in sea surface
height variance, a proxy for mixing, increased the numerical abundance of euphausiids. GAM predictions of variability in species
abundance as a function of SST and depth of the mixed layer were consistent with present theories, which suggest that pelagic
niche availability is related to the thermal structure of the near surface water: more deeply-mixed water contained higher
euphausiid biodiversity. In addition to exposing present distributional patterns, the GAM framework enables responses to potential
future and past environmental variability including temperature change to be explored. |
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