Abstract
The Cape of Gata region (southeast Spain) allocates the thermo-haline Almeria–Oran front (AOF), which separates two biogeographical zones, with a very irregular bathymetry, consisting of two canyons and seamounts in an area of 100 × 100 km. An interdisciplinary oceanographic sampling strategy allowed us to solve mesoscale processes including current–bathymetry interactions. Subsurface fertilizing processes and elevated chlorophyll a concentrations were found at the front, seamount, and submarine canyons, turning an apparently oligotrophic area into a rich one. According to a horizontal tracking simulation, the deep chlorophyll maximum (DCM) at the front is located above the pycnocline and travels fast offshore, transporting productivity from the fertilization process quickly from the region. The DCM at the seamount, in contrast, develops below the pycnocline and remains for almost three weeks in this area. In spite of the coastal marine protected areas (MPAs), a high surface nitrate concentration plume with its origin in a small coastal area without any protection was detected. Local circulation patterns and bathymetry–current interactions provide elevated productivity in surface water which is vertically connected to deep-sea fauna via the daily vertical migration of zooplankton, suggesting elevated biodiversity on the seamount and canyons of the area studied. Based on these results, and considering the presence of coastal MPAs and a Coastal Area Management Program, future studies on benthic fauna, an enlargement of coastal MPAs, and a transboundary land–deep-sea management program are suggested.
Highlights
The Mediterranean Sea supports many endangered and endemic species, and it is an important hotspot for targeted conservation [1,2]
The weekly composed sea surface temperature (SST) shows the north-western Alboran upwelling area characterized by cold water (Figure 1a)
Fertilizing processes linked to topography–current interactions were described for seamounts [11] and submarine canyons [7,8,9,10], while fertilizing processes at fronts [29,61,62] are related to ageostrophic vertical circulation associated with the frontal structure
Summary
The Mediterranean Sea supports many endangered and endemic species, and it is an important hotspot for targeted conservation [1,2]. Water 2018, 10, 1403 identification, low interest is given to the pelagic ecosystem, the biggest marine ecosystem, which connects all the others and provides the primary production that feeds the whole marine food web. Structures such as fronts [5,6], canyons [7,8,9,10], and seamounts [11] are described as sites of local fertilization due to the hydrodynamic processes that induce mixing of nutrient-rich water into the upper photic zone. Fronts are described as indicators of pelagic diversity [20], channelling nutrients through multiple trophic levels including commercially important fish and marine mammals [21]
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