Elsa Vázquez

The gonads of the purple sea urchin Paracentrotus lividus are considered a delicacy in some European countries. Combined with rising international demand, their harvesting has become unsustainable in most regions. Despite recent fishing bans and seeding programmes using juveniles reared in hatcheries, challenges such as poaching, the long time to reach marketable size and insufficient genetic variability have required alternative approaches. Translocation of adult individuals from stable populations is emerging as a solution to restore overfished stocks, but high plasticity is required to cope with novel environmental conditions. As ocean warming is the major concern for shallow‐water invertebrate communities, this study addressed the effects of varying seawater temperatures on the survival, physiology and reproduction of adult P. lividus through a 28‐day controlled common garden experiment. Sea urchins from upwelling‐influenced northwestern Spain (stable stock; Cabo Estai, Galicia) and upwelling‐independent northern Spain (depleted stock; Bay of Biscay, Basque Country) were exposed to basal and heatwave temperatures recorded at their respective locations to investigate potential thermal adaptability. Mortality was marginal and not attributable to temperature treatments in individuals from both origins, which stabilised their physiological values over time. However, most individuals in the warmest treatment showed higher activity and faster righting time, indicating some extra energy expenditure in response to warming. Despite these metabolic differences, successful fertilisation and viability of blastula‐stage cells occurred regardless of origin or treatment, confirming the species' rapid thermal plasticity. Therefore, this study provides valuable information for fishery managers to support controlled translocation measures aimed at restoring sustainable sea urchin stocks in northern Spain.

Studying the early stages of the introduction of non-indigenous species (NIS) is crucial as it allows immediate management actions aimed at preventing NIS spread at a time when these actions are more likely to be effective. Recent species introductions present unique opportunities to study key aspects of the invasion process. However, comprehensive information on how and when NIS are first introduced remains rare. We assessed the characteristics of the introduction of a member of the widespread Pyura stolonifera species group (Chordata, Tunicata) in Europe. These ascidians are important bioengineer species that can attain amongst the highest benthic biomass per surface area ever reported. We collected introduced individuals on the coast of the northwestern Iberian Peninsula, an area with high shipping traffic and one of the world’s most important mussel farming regions. The specimens were analysed using taxonomic and genetic tools. Both field surveys and taxonomic analysis showed that one of the African members of the species group, Pyura herdmani, has recently been introduced to Europe and, although it does not yet form the large aggregates found in the native range, it is already well-established. Genetic data revealed that only the northwest African lineage of P. herdmani has been introduced to Europe. Considering the low dispersal capabilities of the early life-history stages of P. herdmani, the introduction of this species into Europe can only be explained via human mediated transport of NIS. In order to prevent any detrimental effects on both native biota and/or economically-important anthropogenic activities, regular monitoring of recent NIS introductions is urgently required.

Wave climate is shifting over the last decades along the Atlantic coasts of Europe ultimately driven by large-scale patterns of atmospheric variability forced by anthropogenic global warming. Changes in wave height and surf zone orbital currents are hypothesized to drive marked shifts in the shape of intertidal organisms such as the stalked barnacle Pollicipes pollicipes, whose quality and market price are known to decrease non linearly with the peduncle length: width ratio S. This study evaluates wave trends in NW Iberian Peninsula, using the Spanish Port System 2006–2020 SIMAR wave hindcast. On the other hand, trends in stalked barnacle morphology and quality are estimated from 26 sites at the management regions of Baiona and A Guarda between 2011 and 2020. Results show evidence of temporal changes in barnacle quality and, especially, morphometry caused by simultaneous shifts in winter wave induced orbital currents. Because of the non linear relationship between S and the high quality threshold, large increases in S are usually translated to small reductions in quality. However, we identified a tipping point around S = 2.4 that if surpassed can lead to great drops in barnacle quality. In addition, changes in wave forcing will have different effects at each extraction site, as trends in wave climate are decoupled from barnacle morphometry at steeper sites sheltered from the predominant wave direction. In conclusion, this knowledge could be applied to develop site specific barnacle harvesting strategies based on annual wave climate forecasts. Graphical abstract

Extreme climate events, such as heatwaves and torrential rain, affect the physiology and functioning of marine species, especially in estuarine habitats, producing severe ecological and socioeconomic impacts when the affected species support important fisheries, such as artisanal shellfisheries. Studies of the impact of sudden decreases in salinity and increases in temperature were reviewed with the aim of producing comprehensive conceptual maps to aid the management of fisheries of the native clams Ruditapes decussatus and Venerupis corrugata, the introduced Ruditapes philippinarum, and the cockle Cerastoderma edule in Galicia (NW Spain). The maps show the effects on mortality, scope for growth, ability to burrow, changes in gonad development or predation risk. While V. corrugata will generally be more affected by low salinity (5 to 15) or high temperature (30 °C) during only two tidal cycles, C. edule populations may recover. Both species are also expected to become more vulnerable to predators. The clams R. philippinarum and R. decussatus will be more resistant, unless extreme events occur after massive spawning episodes; however, the presence of the intertidal seagrass Zostera noltei may buffer the negative effects of high sediment temperature on the growth of some species, such as R. decussatus. Finally, recommendations for assessing climate risk and designing management actions for shellfisheries are given.

Increased heavy rainfall can cause huge decreases in salinity in estuaries. Lethal and sublethal physiological and behavioural effects of decreases in salinity to below 10 have already been found to occur in the commercially important clam species V. corrugata , R. decussatus and R. philippinarum and the cockle C. edule , which inhabit estuaries and generate ~74 million euros annually in Galicia (NW Spain). However, the response of these bivalves to hyposalinity stress has never been described at the molecular level. In this "shotgun" proteomics study, changes in protein expression were evaluated in the four abovementioned species subjected to brief episodes of low salinity in March and May, and both species- and temporal-specific molecular responses were detected. Significant alterations were observed in V. corrugata and C. edule , previously described as poorly tolerant of hyposalinity, with disruptions at the membrane level and in the unfolded protein response. In the introduced clam, R. philippinarum , the NudC-like protein, a chaperone that may confer protection against low salinity, was overexpressed, while in R. decussatus , no differentially expressed proteins were detected. This research identified new molecular targets that could act as biomarkers of low salinity in bivalves. The study findings are useful in relation to the management and conservation of native species, mainly V. corrugata and C. edule , which are particularly sensitive to decreased salinity.

The impacts of climate change on the structure and functioning of estuaries is a major focus of concern, even more when the affected species support important fisheries as the bivalves Ruditapes decussatus, Ruditapes philippinarum, Venerupis corrugata, and Cerastoderma edule in Europe. Their reproductive performance, in the context of climate stressors, had not been investigated so far. Our objective was to experimentally evaluate acute stress effects over gonad development after 6 days of low salinity stress in autumn, winter and spring as well as 4 days of heatwave stress during emersion in summer. These are the most probable extreme events that bivalves should face in our latitudes. Four different salinity ramps (5–20, 10–25, 15–30, 30–30) were created during simulated tidal cycles in mesocosms for the low salinity experiments. Also four sediment heatwaves at emersion (20–20, 20–27, 20–32, 20–37°C) were done during simulated tidal cycle. Both low salinity and heatwave stresses over such short periods compromised reproduction; the acute response was species-specific and varied with the time of the year, and therefore, with the stage of the gametogenic cycle. In December, during sexual resting and the beginning of gametogenesis, a delay in gametogenesis at lower salinities was recorded in the four species. However, at the peak of the reproductive period (March and May), different responses were observed: abnormal oocytes in R. decussatus and resorption of gametes with haemocytic infiltration in R. philippinarum and V. corrugata. Likewise sediment temperatures higher than 32°C provoked gonadal resorption and severe haemocytic invasion in V. corrugata, R. decussatus, and C. edule but had no effect in R. philippinarum. These responses to both environmental stressors might be related to the allocation of energy from reproduction toward defense and repair mechanisms to ensure survival. Contrastingly, low salinities triggered massive spawning in C. edule that could lead to a mismatch between the presence of larvae and phytoplankton, causing potentially starvation and thus reducing recruitment success. Reproduction of theses bivalves would be compromised if low salinity episodes in winter and spring, even for short periods of time such as those in these experiments, are followed by a heatwave in summer. Furthermore the impact would be magnified if this situation happens during consecutive years preventing replenishment of the shellfish beds.