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Seamounts are considered to be “hotspots” of marine life but, their role in oceans primary productivity is still under discussion. We have studied the microbial community structure and biomass of the epipelagic zone (0–150 m) at two northeast Atlantic seamounts (Seine and Sedlo) and compared those with the surrounding ocean. Results from two cruises to Sedlo and three to Seine are presented. Main results show large temporal and spatial microbial community variability on both seamounts. Both Seine and Sedlo heterotrophic community (abundance and biomass) dominate during winter and summer months, representing 75% (Sedlo, July) to 86% (Seine, November) of the total plankton biomass. In Seine, during springtime the contribution to total plankton biomass is similar (47% autotrophic and 53% heterotrophic). Both seamounts present an autotrophic community structure dominated by small cells (nano and picophytoplankton). It is also during spring that a relatively important contribution (26%) of large cells to total autotrophic biomass is found. In some cases, a “seamount effect” is observed on Seine and Sedlo microbial community structure and biomass. In Seine this is only observed during spring through enhancement of large autotrophic cells at the summit and seamount stations. In Sedlo, and despite the observed low biomasses, some clear peaks of picoplankton at the summit or at stations within the seamount area are also observed during summer. Our results suggest that the dominance of heterotrophs is presumably related to the trapping effect of organic matter by seamounts. Nevertheless, the complex circulation around both seamounts with the presence of different sources of mesoscale variability (e.g. presence of meddies, intrusion of African upwelling water) may have contributed to the different patterns of distribution, abundances and also changes observed in the microbial community.

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<p><strong>Abstract.</strong> The plankton community response to natural fertilization caused by the Saharan dust was studied in the Canary Islands waters during winter–spring 2010. For this, a weekly sampling was carried out to characterize the pico-, nano- and microplankton communities. During this period several dust events were identified from atmospheric suspended matter and metal composition. Temperatures above 19 °C in the mixed layer, high stratification and a very low concentration of chlorophyll <i>a</i>, indicated the absence of the characteristic late winter bloom during this year. However, relatively high primary production rates were measured, probably fuelled by nutrient release from the deposited atmospheric dust. In fact, this winter–spring was one of the most intense dust periods during the last years and Saharan dust events were identified in every month. The effect of the Saharan dust over the plankton community mainly consisted in the enhancement of primary producers, mostly diatoms, and the increase of the mesozooplankton stock, whereas cyanobacteria and autotrophic picoeukaryotes were negatively affected. These results suggest that the Saharan dust deposition would be partly fuelling the primary production in these oligotrophic waters of the northeast Atlantic, and could be especially significant during stratified periods, when the atmospheric dust would be the most important nutrient source.</p>

Canarias es uno de los destinos turísticos principales de Europa. El Archipiélago recibió en 2015 más de 13 millones de turistas y todo ello en un territorio muy limitado (7.4 mil km2 y una población de 2.1 millones). Las dimensiones de estas cifras adquieren relevancia en un contexto donde el 63 % de la superficie de las Islas ha sido declarada Reserva Mundial de la Biosfera. Se estudia aquí pues, el impacto del turismo –así como algunas alternativas en aras de paliar dicho impacto–, en las cinco islas que han sido declaradas en su integridad como tales, partiendo de sus particularidades.

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