Abstract
The vertical and horizontal distributions of Euphausiacea in the northern Gulf of Mexico, including the location of the Deepwater Horizon oil spill, were analyzed from 340 trawl samples collected between April-June 2011. This study is the first comprehensive survey of euphausiid distributions from depths deeper than 1000 m in the Gulf of Mexico and includes stratified sampling from five discrete depth ranges (0-200m, 200-600m, 600-1000m, 1000-1200m, and 1200-1500m), and expands the depth ranges of 30 species. In addition, this study demonstrates significantly higher abundance and biomass of the euphausiid assemblage from slope vs. offshore stations, while the offshore assemblage was significantly more diverse. There is also some evidence for seasonality in reproduction amongst the seven species that had gravid females. Lastly, these data represent the first quantification of the euphausiid assemblage in the region heavily impacted by the Deepwater Horizon event, and as there are no pre-spill data, may serve as an impacted baseline against which to monitor changes in the euphausiid assemblage in the years following exposure to Deepwater Horizon oil and dispersants in the water column.
Highlights
Euphausiids are pelagic crustaceans that range in size from mesozooplankton (0.2 μm to 2 mm), macrozooplankton (2–20 mm), and actively swimming micronekton (20–200 mm) (Omori and Ikeda, 1984; Sutton, 2013)
Sixteen species of euphausiids made up 99% of the euphausiid abundance, with the most abundant species being the combined species group N. atlantica/N. microps, in both slope and offshore stations
The only previous study in this region was by Kinsey and Hopkins (1994), conducted at their Standard Station, which overlapped with Station SE-5 in the current study
Summary
Euphausiids are pelagic crustaceans that range in size from mesozooplankton (0.2 μm to 2 mm), macrozooplankton (2–20 mm), and actively swimming micronekton (20–200 mm) (Omori and Ikeda, 1984; Sutton, 2013). Euphausiacea are important because most of them undergo diel vertical migrations, in which they remain in deeper waters during the day to avoid visual predators, and ascend 100 s of meters into shallower waters at sunset to feed under the cover of darkness (reviewed in Cohen and Forward, 2009) This behavior means that are they potential prey for a variety of different organisms at multiple. When Burghart et al (2007) collected samples of Decapoda, Lophogastrida and Mysida from depths greater than 1000 m in the eastern GOM, they found that the bathypelagic zone was dominated by different species than those that dominated in the mesopelagic zone. The Burghart et al study emphasized the need to extend these studies to the Euphausiacea, one of the dominant groups of crustaceans in the GOM (Kinsey and Hopkins, 1994; Burdett et al, 2017)
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