Zooplankton distribution patterns at two seamounts in the subtropical and tropical NE Atlantic

Abstract

Spatial distribution patterns of zooplankton biomass in relation to local and large-scale hydrographical and biological driving forces were studied at Amp ere and Senghor, two shallow seamounts in the subtropical and tropical NE Atlantic, respectively. The study includes a first assessment of the taxonomic composition and an estimation of the respiratory carbon demand of the zooplankton community. Zooplankton was sampled during three cruises at the seamount and open ocean reference sites in May and October 2009 and in December 2010. Zooplankton standing stocks and the corresponding respiratory carbon demand were about six times higher at Senghor than at Amp ere, with mean stocks of 24.7 and 4.6 gÁm À2 , respectively, in the upper 1000 m. Mean respiratory carbon demand in the epipelagic zone was calculated as 61.4 mgÁCÁm À2 Áday À1 for Senghor and 9.6 mgÁCÁm À2 Áday À1 for Amp ere. At neither site were differences between seamount and open ocean sites significant. However, horizontal surveys across Amp ere Seamount show clear differences between day and night distributions and a reduced biomass above the summit. Across Senghor, zooplankton biomass increased from the SW to the NE flank, with the highest concentrations in the subsurface layer of the chlorophyll maximum and just above a strong oxycline. The zooplankton community at Amp ere Seamount reflects the oligotrophic character of the NE Atlantic subtropical gyre, whereas the nutrient-rich waters of the cyclonic tropical gyre at Senghor support a higher biomass. This difference in the zooplankton biomass between the two seamounts can be attributed to the large-scale hydrographical features governing the productivity regimes rather than to regional seamount effects.

Near-bottom zooplankton over three seamounts in the east Canary Islands: Influence of environmental variables on distribution and composition.

“…In the eastern Canary Islands, with some exceptions (e.g., zooplankton associated with both AAIW and MW), near-bottom zooplankton composition changed as a function of which of the different water mass was impinging on the seamounts investigated. Such changes depending on water masses have been reported in previous studies comparing water-column zooplankton adjacent to northeast Atlantic seamounts (Denda and Christiansen, 2013), and affect benthopelagic communities of crustaceans, as also observed at Galicia Bank , with particular fauna associated with water masses of quite different origins (e.g.,…”

Persistent Enhancement of Micronekton Backscatter at the Summits of Seamounts in the Azores

“…Denda and Christiansen (2014) found no significant differences in zooplankton biomass at Ampère and Senghor seamounts (summits of 55 and 90 m, respectively) relative to open-waters. Reduced zooplankton biomass was found above the summits of Sedlo (750 m) and Seine (170 m) seamounts compared to the slope and far-field sites (Martin and Christiansen, 2009).…”

“…For instance, bottom trapping will only be effective for seamounts shallower than the daylight depth of micronekton organisms (Genin, 2004;Martin and Christiansen, 2009;Denda and Christiansen, 2014). Moreover, because different organisms migrate to different daylight depths, the deeper the seamount summit, the fewer the species retained and the lower the biomass (Genin and Dower, 2007).…”

The fish fauna of Ampère Seamount (NE Atlantic) and the adjacent abyssal plain

“…The studies aimed at an advanced understanding of the seamount ecology, in comparison with other seamounts in the NE Atlantic and the Eastern Mediterranean, and addressed, for example, the relationships between flow field and plankton distribution, fluxes of organic matter, the trophic structure and the biodiversity of benthic and pelagic seamount communities. First results show that the oligotrophic nature of the sea area around Ampère is reflected in low zooplankton standing stocks, with no indications of an enhanced biomass at the seamount as compared to the surrounding ocean (Denda and Christiansen 2013). The major aim of the fish studies conducted on the P384 cruise of R.V.…”