Fibrocapsa japonica (Raphidophyceae) occurrence and ecological features within the phytoplankton assemblage of a cyclonic eddy, offshore the Eastern Alboran Sea.

Abstract

The Raphidophycean Fibrocapsa japonica Toriumi & Takano was detected for the first time offshore in the Eastern Alboran Sea (Western Mediterranean) in October 2006. Its distribution appeared very localised and atypical, as it was abundant only in the open waters of a cyclonic eddy. Microscope counts of the natural phytoplankton assemblages revealed that F. japonica was dominant in the microplankton, together with Dinophyceae, within and below the cyclonic nutrient-rich dome (25 - 30 m). Bacillariophyceae were the primary microplanktonic fraction in only a few samples. Moderately high abundances of F. japonica (maximum of 60 cells ml-1), with preliminary cysts and many cells aggregated in mucous nets, indicated a senescent phase. We also suggest a Mediterranean origin for this species. This was confirmed by molecular identification and by a water temperature of 15 °C, which could have favoured pre-cyst formation. Finally, we hypothesise that F. japonica, which is generally a coastal species, could have a coastal origin. Since F. japonica was confined to the cyclonic waters, which typically derive from coastal waters, it was collected at a depth of 40-60 m at the coastal sites and it is generally a coastal species, we hypothesise that it could have a coastal origin and it was entrapped by the cyclonic eddy, which could have carried offshore this harmful species.

Spatio-temporal variability of a chlorophyll-a based biomass index and influence of coastal sources of enrichment in the Algerian Basin

“…On a large scale, the variability of Chl-a concentration in the AB is known to be driven by the inflow of nutrient-rich Atlantic waters that enter the Alboran Sea through the Gibraltar strait (Taupier-Letage and Millot, 1988) and progress eastwards along the AB. The same conclusions have also been drawn more recently by several authors (Fani et al, 2014;Huertas et al, 2012;Lazzari et al, 2012;Pasqueron de Fommervault et al, 2015). Consequently, the eastward propagating eddies modulate the circulation of water masses beyond the continental shelf (Pessini et al, 2020), generating intense vertical mixing (Millot et al, 1990).…”

“…It generally follows the continental slope and generates small eddies of 10-100 km diameter, lasting a few weeks or months. Periodically, this current forms a growing meander of 50-100 km; it can detach to form an anticyclonic eddy of 100-200 km diameter that encompasses the entire thickness of the Med water (El-Geziry and Bryden, 2010;Fani et al, 2014;Millot, 1989). Some oceanic eddies persist for up to three years, circulating in the AB in a cyclonic circuit (Millot and Taupier-Letage, 2005).…”

“…AB is characterised by two contrasting seasons (Fig. 7a): an early 3.5-month high-biomass season It is well known that winter and spring blooms in the region are almost exclusively driven by the nutrient input following autumn and winter vertical mixing (Fani et al, 2014;Huertas et al, 2012;Lazzari et al, 2012;Millot et al, 1990;Pasqueron de Fommervault et al, 2015), as reflected by our biomass index (Fig. 8d).…”

Assessment of three algorithms for the operational estimation of [CHL] from MODIS data in the Western Mediterranean Sea

“…Increased phytoplankton levels may also occur in coastal areas, especially near large river mouths, due to the nutrients available in the water. In addition to this, harmful algal blooms have been detected in many coastal areas, producing problems for human health and activities [Penna et al, 2007]; these blooms have been also observed in offshore mesoscale eddies, representing a 'seed bank' for further dispersion and spreading of the harmful species [Fani et al, 2014]. The red box in Figure 1 delimits a subarea which is currently considered to correspond to that of the MOMAR project, although the study area of respective Project was actually slightly smaller and centered on the Ligurian Sea.…”