Gotzon Basterretxea

The Transition Zone of the Canary Current Upwelling Region.

Abstract Like all the major upwelling regions, the Canary Current is characterised by intense mesoscale structure in the transition zone between the cool, nutrient-rich waters of the coastal upwelling regime and the warmer, oligotrophic waters of the open ocean. The Canary Island archipelago, which straddles the transition, introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and Trade winds. The combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability. On the basis of historical data and a series of interdisciplinary field studies, the principal features of the region are described. These include a prominent upwelling filament originating near 28°N off the African coast, cyclonic and anti-cyclonic eddies downstream of the archipelago, and warm wake regions protected from the Trade winds by the high volcanic peaks of the islands. The filament is shown to be a recurrent feature, apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone. Its role in the transport and exchange of biogenic material, including fish larvae, is considered. Strong cyclonic eddies, observed throughout the year, drift slowly southwestward from Gran Canaria. One sampled in late summer was characterised by large vertical isopycnal displacements, apparent surface divergence and strong upwelling, producing a fourfold increase in chlorophyll concentrations over background values. Such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen. The lee region of Gran Canaria is shown to be a location of strong pycnocline deformation resulting from Ekman pumping on the wind shear boundaries, which may contribute to the eddy formation process.

The influence of island-generated eddies on chlorophyll distribution: a study of mesoscale variation around Gran Canaria

This study reports hydrographic and biological observations from three cruises where cyclonic and anticyclonic eddies were observed downstream of Gran Canaria island. Based on field data and remote sensing images (AVHRR and CZCS), two mechanisms associated with island- generated eddies, largely responsible for the formation and distribution of chlorophyll around the Canary Islands, are proposed. First, nutrient pumping and vertical uplifting of the deep chlorophyll maximum by cyclonic eddies might represent important sources of primary production in the oligotrophic waters of the Canary region. Second, eddies are responsible for the horizontal transport and distribution of chlorophyll originating near the islands or off the African coast. Water with high chlorophyll content, resulting from island stirring or local upwelling at the flanks of the islands, is incorporated into cyclonic eddies in their development and subsequently transported downstream. On the other hand, anticyclonic eddies can also entrain water rich in chlorophyll when interacting with the offshore boundary of the African coastal upwelling. This chlorophyll will be advected southward as the eddy drifts. The recurrence of cyclonic and anticyclonic eddies, together with the presence of upwelling filaments throughout the year, must have important biological consequences in the formation and transport of organic matter in the Canary region. 0 1997 Elsevier Science Ltd. All rights reserved

Effectiveness of protection of seagrass (Posidonia oceanica) populations in Cabrera National Park (Spain)

Posidonia oceanica, the dominant seagrass species in the Mediterranean, appears to be experiencing widespread loss. Efforts to conserve Posidonia oceanica are increasing, as reflected in the increase in the number of marine protected areas in the Mediterranean. However, the effectiveness of these measures to conserve seagrass meadows is unknown. In this study, the present status of the Posidonia oceanica meadows in the Cabrera National Park (Mediterranean), the only marine national park in Spain, was assessed, and the effectiveness of the conservation measures adopted was tested. This was done by reconstruction of past and present growth, quantification of the demographic status of the established meadows, and quantification of patch formation and growth rates in areas where recolonization is occurring. The meadows extended from 1-43m deep at Santa Maria bay and from 1-33 m at Es Port. Leaf production rate of the stands examined ranged between 6.5 and 7.8 leaves shoot -1 yr -1 , with higher rates in Santa Maria than in Es Port. Vertical rhizomes elongated at rates ranging from 5.39-10.12 mm yr -1 , annual vertical growth in Santa Maria stands being larger than that in the stands developing at Es Port. Horizontal rhizomes elongated slowly (from 2.6-6.1 cm yr -1 ), and branching was sparse (<0.25 branches yr -1 axis -1 ), with maximum elongation and branching rates in areas where patches were actively colonizing. Flowering was a rare event in all the stands (<0.015 flowers shoot -1 yr -1 ). Patch formation and patch growth rates in active colonizing areas were slow, but they increased after implementation of mooring regulations in the Park. Similarly, the leaf production tended to increase, and vertical rhizome growth to decrease, in both bays following the onset of regulation measures. However, the decrease in vertical growth detected was greater at Santa Maria, where access is prohibited to visitors, than at Es Port, where boats are allowed to moor, attached to permanent weights. Shoot mortality rate was generally low (mean 0.10 ± 0.02 In units yr -1 ) but exceeded the recruitment rate (<0.009 and 0.17 In units yr -1 ) in 55% of the meadows examined, indicative of negative net population growth rates. Regulation of mooring activities has improved the status of the P. oceanica meadows at Cabrera National Park. The demographic analysis, however, indicated that while P. oceanica meadows at Santa Maria are in good shape, those at Es Port seem to be compromised. The observed differences in meadow status reflect the large differences in circulation inside the bays (water residence time at Santa Maria = 4 days, water residence time at Es Port = 11 days) and the anthropogenic pressure both bays support.

Sunscreen Products as Emerging Pollutants to Coastal Waters

A growing awareness of the risks associated with skin exposure to ultraviolet (UV) radiation over the past decades has led to increased use of sunscreen cosmetic products leading the introduction of new chemical compounds in the marine environment. Although coastal tourism and recreation are the largest and most rapidly growing activities in the world, the evaluation of sunscreen as source of chemicals to the coastal marine system has not been addressed. Concentrations of chemical UV filters included in the formulation of sunscreens, such as benzophehone 3 (BZ-3), 4-methylbenzylidene camphor (4-MBC), TiO2 and ZnO, are detected in nearshore waters with variable concentrations along the day and mainly concentrated in the surface microlayer (i.e. 53.6–577.5 ng L-1 BZ-3; 51.4–113.4 ng L-1 4-MBC; 6.9–37.6 µg L-1 Ti; 1.0–3.3 µg L-1 Zn). The presence of these compounds in seawater suggests relevant effects on phytoplankton. Indeed, we provide evidences of the negative effect of sunblocks on the growth of the commonly found marine diatom Chaetoceros gracilis (mean EC50 = 125±71 mg L-1). Dissolution of sunscreens in seawater also releases inorganic nutrients (N, P and Si forms) that can fuel algal growth. In particular, PO4 3− is released by these products in notable amounts (up to 17 µmol PO4 3− g−1). We conservatively estimate an increase of up to 100% background PO4 3− concentrations (0.12 µmol L-1 over a background level of 0.06 µmol L-1) in nearshore waters during low water renewal conditions in a populated beach in Majorca island. Our results show that sunscreen products are a significant source of organic and inorganic chemicals that reach the sea with potential ecological consequences on the coastal marine ecosystem.

Copper aerosols inhibit phytoplankton growth in the Mediterranean Sea

Aerosol deposition plays an important role in climate and biogeochemical cycles by supplying nutrients to the open ocean, in turn stimulating ocean productivity and carbon sequestration. Aerosol particles also contain elements such as copper (Cu) that are essential in trace amounts for phytoplankton physiology but that can be toxic at high concentrations. Although the toxicity of Cu associated with aerosols has been demonstrated in bioassay experiments, extrapolation of these laboratory results to natural conditions is not straightforward. This study provides observational evidence of the negative effect of aerosols containing high Cu concentrations on marine phytoplankton over a vast region of the western Mediterranean Sea. Direct aerosol measurements were combined with satellite observations, resulting in the detection of significant declines in phytoplankton biomass after atmospheric aerosol events characterized by high Cu concentrations. The declines were more evident during summer, when nanoflagellates predominate in the phytoplankton population and stratification and oligotrophic conditions prevail in the study region. Together with previous findings concerning atmospheric Cu deposition, these results demonstrate that the toxicity of Cu-rich aerosols can involve large areas of the world’s oceans. Moreover, they highlight the present vulnerability of oceanic ecosystems to Cu-rich aerosols of anthropogenic origins. Because anthropogenic emissions are increasing, large-scale negative effects on marine ecosystems can be anticipated.

Eddy and deep chlorophyl maximum response to wind-shear in the lee of Gran Canaria

The physical and biological properties of the warm wake of Gran Canaria were examined during a survey carried out in June 1998. The sampling region was dominated by the presence of a warm triangular region downwind the island and an anticyclonic eddy spun off the island. Convergent and divergent frontal regions were generated by the wind shear zones extending along either side of the sheltered region of the warm wake. With increasing distance from shore, evidence of convergent/divergent frontal regions weakened, but the influence of the eddy increased. Both structures, frontal regions and the eddy, clearly altered the vertical phytoplankton biomass distribution as indicated by chlorophyll-fluorescence. Downwelling on the convergent boundary moved the 26.2 kg m � 3 isopycnal and its associated deep chlorophyll maximum (DCM) below the 1% light zone. Upwelling at the divergent boundary not only elevated the DCM with its associated isopycnal but also, because of the increased light levels, allowed a shift in the DCM to higher (deeper) density surfaces (26.4 kg m � 3 ). However, the highest integrated chlorophyll occurred in the

Population genetic structure and connectivity of the harmful dinoflagellate Alexandrium minutum in the Mediterranean Sea

The toxin-producing microbial species Alexandrium minutum has a wide distribution in the Mediterranean Sea and causes high biomass blooms with consequences on the environment, human health and coastal-related economic activities. Comprehension of algal genetic differences and associated connectivity is fundamental to understand the geographical scale of adaptation and dispersal pathways of harmful microalgal species. In the present study, we combine A. minutum population genetic analyses based on microsatellites with indirect connectivity (Ci) estimations derived from a general circulation model of the Mediterranean sea. Our results show that four major clusters of genetically homogeneous groups can be identified, loosely corresponding to four regional seas: Adriatic, Ionian, Tyrrhenian and Catalan. Each of the four clusters included a small fraction of mixed and allochthonous genotypes from other Mediterranean areas, but the assignment to one of the four clusters was sufficiently robust as proved by the high ancestry coefficient values displayed by most of the individuals (>84%). The population structure of A. minutum on this scale can be explained by microalgal dispersion following the main regional circulation patterns over successive generations. We hypothesize that limited connectivity among the A. minutum populations results in low gene flow but not in the erosion of variability within the population, as indicated by the high gene diversity values. This study represents a first and new integrated approach, combining both genetic and numerical methods, to characterize and interpret the population structure of a toxic microalgal species. This approach of characterizing genetic population structure and connectivity at a regional scale holds promise for the control and management of the harmful algal bloom events in the Mediterranean Sea.

Seasonal Dynamics of a Microtidal Pocket Beach with Posidonia oceanica Seabeds (Mallorca, Spain)

Abstract In this work, we analyze the seasonal evolution of a Mediterranean pocket beach and its response to different storm episodes. Magalluf, an intermediate medium sand beach located in the Bay of Palma (Balearic Islands) was monitored by topographic levelling during 14 months. Near the beach, a Posidonia oceanica meadow covers most of the seabed and appears to influence the cross-shore beach adjustment. The low variability observed during the sampling period was perturbed by two storm events that caused significant beach evolution and sediment transport. The first storm gave rise to waves from the SE, significant height = 2.4 m, cross-shore sediment transport and along-shore net sediment exchange that resulted in decreased dry beach extension to a minimum. The second storm was characterized by strong northeasterly winds and generated a set-up of 0.5 m and a nearshore drift reversal that redistributed sediment from the berm crest to the beach face, thereby increasing beach extension. Results from numerical simulations of wave propagation show the circulation patterns during both events and their influence on the beach morphology. In general terms, the beach exhibited a homeostatic behaviour characteristic of an equilibrium system.

Phytoplankton biomass and production during late austral spring (1991) and summer (1993) in the Bransfield Strait

Abstract Phytoplankton biomass and productivity were measured during two cruises in the Bransfield Strait in December 1991 (D91) and January/February 1993 (J93). Strong seasonal variability in productivity values was observed due to differences in the physiological response of phytoplankton. However, although the photosynthetic capacity of phytoplankton was markedly lower in D91 [PmB=0.61 ± 0.25 mg C (mg Chla)−1 h−1] than in J93 [PmB=2.18 ± 0.91 mg C (mg Chla)−1 h−1], average water column chlorophyll values in different areas of the strait were approximately similar in D91 (49–78 mg Chla m−2) and J93 (22–76 mg Chla m−2). The spatial distribution of chlorophyll was patchy and generally associated with the influence of the different water masses that meet together in the Bransfield Strait. No correlation was found between the mixed layer depth and either the integrated chlorophyll or the productivity. Our results suggest that major phytoplankton blooms in the Bransfield Strait are advected from the nearby Gerlache Strait or Bellingshausen Sea following the main eastward surface currents.

Contribution of groundwater discharge to the coastal dissolved nutrients and trace metal concentrations in Majorca Island: karstic vs detrital systems.

Submarine groundwater discharge (SGD) and derived nutrient (NO2(-), NO3(-), NH4(+), PO4(3-), and SiO2) and trace element (Cd, Co, Cu, Fe, Mo, Ni, Pb, V and Zn) loadings to the coastal sea were systematically assessed along the coast of Majorca Island, Spain, in a general survey around the island and in three representative coves during 2010. We estimated that brackish water discharges through the shoreline are important contributors to the DIN, SiO2, Fe, and Zn budgets of the nearshore waters. Furthermore, our results showed that SGD-derived elements are conditioned by the hydrogeological formations of the aquifer and discharge type. Thus, while rapid discharges through karstic conduits are enriched in SiO2 and Zn, the large detrital aquifers of the island typically present enhanced concentrations of Fe. The estimated total annual inputs of chemicals constituents discharged by SGD to the coastal waters were as follows: DIN: 610 × 10(3) kg yr(-1), SiO2: 1400 × 10(3) kg yr(-1), Fe: 3.2 × 10(3) kg yr(-1), and Zn: 2.0 × 10(3) kg yr(-1). Our results provide evidence that SGD is a major contributor to the dissolved pool of inorganic nutrients and trace metals in the nearshore waters of Majorca.