Bloom dynamics of an exceptional red tide of the toxigenic dinoflagellate

The toxic dinoflagellate Alexandrium minutum generally proliferates in semi-enclosed sites such as estuaries, harbours and lagoons, where stratification, restricted circulation and accumulation of resting cysts set suitable conditions for its development. In the Galician Rías (NW Iberian Peninsula), its blooms follow also this pattern. They are recurrent in small, shallow estuarine bays inside the Rías, but rarely detected, and if so in minor amount, out of these areas. However, a massive proliferation of A. minutum from June to July 2018 in the Rías Baixas (Vigo and Pontevedra) changed this picture. The bloom initiated in semi-enclosed waters, as previously described for this species, but thereafter spread to the whole embayments where persisted more than one month. It generated a noticeable red tide with disperse patches that became heavily concentrated inside the port of Vigo. During that period shellfish harvesting closures and paralytic shellfish toxins in certain marine invertebrates and fish were reported for the first time in Spain. Meteorological conditions (higher than usual rains/runoff, sustained temperature increment and oscillating wind pattern promoting a series of upwelling-relaxation cycles) fostered optimal circumstances for the outbreak of A. minutum: strong vertical stratification and the alternation of retention and dispersion processes. Simulations from a particle tracking model portrayed the observed bloom development phases: onset, transport within the surface layer towards the interior parts of the Ría of Vigo, and dispersion all over the embayment. High concentrations of resting cysts were detected several months after the bloom, which may have favoured flourish of A. minutum in the following years, markedly in 2020

HABs in coastal upwelling systems: Insights from an exceptional red tide of the toxigenic dinoflagellate Alexandrium minutum

Alexandrium minutum blooms generally occur in semi-enclosed sites such as estuaries, harbours and lagoons, where enhanced stratification, restricted circulation and accumulation of resting cysts in the sediment set suitable habitat conditions for the proliferation of this paralytic shellfish poisoning toxigenic species. In the Galician Rías Baixas (NW Iberian Peninsula), according to weekly time-series between 1994 and 2020, blooms of A. minutum were recurrent in small, shallow estuarine bays inside the Rías de Vigo and Pontevedra, but rarely detected, and if so at low concentrations, out of these environments. However, from May to July 2018 it developed as usual in the small inner bays but then spread over both Rías (Vigo and Pontevedra) causing discoloured waters during one month and prolonged harvesting closures. Meteorological conditions during that period (rains / runoff higher than climatological averages, sustained temperature increment and oscillating wind pattern –i.e., series of upwelling-relaxation cycles), fostered optimal circumstances for the development of that extensive and massive proliferation: strong vertical stratification and the alternation of retention and dispersion processes. Simulations from a particle tracking model portrayed the observed bloom development phases: onset and development inside a small inner bay; transport within the surface layer, from these sites towards the interior parts of the Ría; and dispersion all over the embayment. Seedbeds with high concentrations of resting cysts were detected several months after the bloom, which may have favoured flourishment of A. minutum in the following two years, markedly in 2020. The present work contributes to the general understanding of the dynamics of harmful algal blooms (HABs), from which surveillance indicators of the state of marine ecosystems and their evolution can be derived. We hypothesize that the intensity and frequency of A. minutum proliferations in the Galician Rías could increase under projected climate trends.Postprint2,69

Red tides in the Galician rías: historical overview, ecological impact, and future monitoring strategies

The Galician rías (NW Iberia, Spain) are coastal embayments at the northern boundary of the Canary Current upwelling system. Their favourable conditions for phytoplankton growth turn them into a suitable area for the development of aquaculture activities and a site of most of the national shellfish production. Phytoplankton blooms, a natural phenomenon inside the rías, under certain conditions eventually lead to seawater discolourations (colloquially known as "red tides"). Because of their transient nature, available records derive mainly from opportunistic samplings or casual observations, and are scattered in the literature. As a rule of thumb, red tides in the NW Iberian Peninsula are of non-toxic nature and are not systematically monitored. However, in recent years striking exceptions such as those of the toxic dinoflagellate Alexandrium minutum, a producer of paralytic shellfish toxins, have been registered. The present study goes through a historical overview of red tides in the Galician rías, describing their colouring, responsible organisms, seasonal and geographical occurrence, and their association with other features (harmful algal blooms, biotoxins and shellfish harvesting closures, bioluminescence, etc.), ending with social challenges and proposals for improving the monitoring of red tides in the future.Funding was provided by the EU INTERREG Atlantic Area project PRIMROSE (EAPA 182/2016), BIOTOX (PID2021-125643OB-C22; Proyectos de generación de conocimiento 2021, MICINN), TOXEMER (PGIDIT-CIMA 21/01) and GPC (IN607B2023/11). This is a contribution to SCOR WG #165 MixONET, supported by grant OCE-214035 (NSF to SCOR) and contributions from SCOR National Committees.Peer reviewe

Amphibians in the diet of European Barn Owls

We present a review of the propensity to eat amphibians in the Barn Owl Tyto alba in Europe. Based on the analysis of 596 published studies reporting 3.32 million prey items identified in pellets, 17 869 amphibians (0.54%) were found. An analysis of 9036 amphibians identified to the species level showed that Barn Owls avoid consuming toxic species, and they are able to capture tree frogs (Hylidae) only rarely. The true frogs (Ranidae) are by far the most frequently captured amphibians followed by spadefoot toads (Pelobatidae) and Parsley frogs (Pelodytidae)