Abstract
Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems with high species diversity, and in some cases, are densely populated by benthic organisms, such corals, gorgonians, and sponges. In this study, we describe the oceanographic conditions over seamounts and other underwater features in the path of the Mediterranean Outflow Water (MOW), where populations of benthic suspensions feeders have been observed. Using CTD, LADPC and biochemical measurements carried out in the Ormonde and Formigas seamounts and the Gazul mud volcano (Northeast Atlantic), we show that Taylor caps were not observed in any of the sampled features. However, we point out that the relatively high values of the Brunt–Väisälä frequency in the MOW halocline, in conjunction with the slope of the seamount flanks, set up conditions for the breakout of internal waves and amplification of the currents. This may enhance the vertical mixing, resuspending the organic material deposited on the seafloor and, therefore, increasing the food availability for the communities dominated by benthic suspension feeders. Thus, we hypothesize that internal waves could be improving the conditions for benthic suspension feeders to grow on the slope of seamounts.
Highlights
According to the Staudigel et al (2010) definition, seamounts are any geographically isolated topographic feature taller than 100 m
White and Dorschel (2010) proposed that a stable stratification could help the growth of Cold-water corals (CWC) on regions of enhanced energy near the sea bottom. It is in this region of maximum energy, in the interface associated to the presence of the Mediterranean Outflow Water (MOW) (500–1,000 m), where we have found the higher abundance of benthic suspension feeders in the Formigas seamount (Figure 14), invertebrates such as poriferans and cnidarians
We have demonstrated that there is a strong relation between the NACW–MOW interface, associated with the activity of internal waves, and the abundance of benthic suspension feeders
Summary
According to the Staudigel et al (2010) definition, seamounts are any geographically isolated topographic feature taller than 100 m. Seamounts play an important role in the generation, breakdown, and even trapping of eddies (Royer, 1978; Roden, 1986; Bashmachnikov et al, 2009; Sokolovskiy et al, 2013) These oceanographic processes induced by the topography may provoke the enhancement of the primary production and retention of plankton (Xavier and van Soest, 2007; Denda et al, 2016), turning seamounts into ecosystems with high biomass, biodiversity and sometimes with a considerable level of endemism (Boehlert and Genin, 1987; Beckmann and Mohn, 2002; O’Hara, 2007; Pitcher et al, 2007; Clark et al, 2010; Miller and Gunasekera, 2017), which offer good conditions for the settlement of benthic suspension feeders like corals and sponges (Koslow et al, 2001; Xavier and van Soest, 2007; O’Hara et al, 2008). Cold-water corals (CWC) have been described along the path of the Mediterranean Outflow Water (MOW) in several locations: at the Gazul mud volcano (Rueda et al, 2016), the Galicia Bank (e.g., Duineveld et al, 2004; Serrano et al, 2017), and the Porcupine Seabight (De Mol et al, 2002), among others
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