Effects of short-term hyposalinity stress on four commercially important bivalves: A proteomic perspective.

Increased heavy rainfall can reduce salinity to values close to 0 in estuaries. Lethal and sublethal physiological and behavioural effects of decreases in salinity below ten have already been found to occur in the commercially important clam species Venerupis corrugata, Ruditapes decussatus and R. philippinarum and the cockle Cerastoderma edule, which generate an income of ∼74 million euros annually in Galicia (NW Spain). However, studies of the molecular response to hyposaline stress in bivalves are scarce. This 'shotgun' proteomics study evaluates changes in mantle-edge proteins subjected to short-term hyposaline episodes in two different months (March and May) during the gametogenic cycle. We found evidence that the mantle-edge proteome was more responsive to sampling time than to hyposalinity, strongly suggesting that reproductive stages condition the stress response. However, hyposalinity modulated proteome profiles in V. corrugata and C. edule in both months and R. philippinarum in May, involving proteins implicated in protein folding, redox homeostasis, detoxification, cytoskeleton modulation and the regulation of apoptotic, autophagic and lipid degradation pathways. However, proteins that are essential for an optimal osmotic stress response but which are highly energy demanding, such as chaperones, osmoprotectants and DNA repair factors, were found in small relative abundances. In both months in R. decussatus and in March in R. philippinarum, almost no differences between treatments were detected. Concordant trends in the relative abundance of stress response candidate proteins were also obtained in V. corrugata and C. edule in the different months, but not in Ruditapes spp., strongly suggesting that the osmotic stress response in bivalves is complex and possibly influenced by a combination of controlled (sampling time) and uncontrolled variables. In this paper, we report potential molecular targets for studying the response to osmotic stress, especially in the most osmosensitive native species C. edule and V. corrugata, and suggest factors to consider when searching for biomarkers of hyposaline stress in bivalves.

Spotting intruders: Species distribution models for managing invasive intertidal macroalgae.

Invasive macroalgae represent one of the major threats to marine biodiversity, ecosystem functioning and structure, as well as being important drivers of ecosystem services depletion. Many such species have become well established along the west coast of the Iberian Peninsula. However, the lack of information about the distribution of the invaders and the factors determining their occurrence make bioinvasions a difficult issue to manage. Such information is key to enabling the design and implementation of effective management plans. The present study aimed to map the current probability of presence of six invasive macroalgae: Grateloupia turuturu, Asparagopsis armata, Colpomenia peregrina, Sargassum muticum, Undaria pinnatifida, and Codium fragile ssp. fragile. For this purpose, an extensive field survey was carried out along the coast of the north-western Iberian Peninsula. Species distribution models (SDMs) were then used to map the presence probability of these invasive species throughout the study region on the basis of environmental and anthropogenic predictor variables. The southern Galician rias were identified as the main hotspots of macroalgal invasion, with a high probability of occurrence for most of the species considered. Conversely, the probability of presence on the Portuguese coast was generally low. Physico-chemical variables were the most important factors for predicting the distribution of invasive macroalgae contributing between 57.27 and 85.24% to the ensemble models. However, anthropogenic factors (including size of vessels, number of shipping lines, distance from ports, population density, etc.) considerably improved the estimates of the probability of occurrence for most of the target species. This study is one of the few to include anthropogenic factors in SDMs for invasive macroalgae. The findings suggest that management actions aimed at controlling these species should strengthen control and surveillance at ports, particularly in southern Galician rias. Early detection should be of main concern for risk assessment plans on the Portuguese coast.

Does global warming threaten small-scale bivalve fisheries in NW Spain?

Shellfisheries of the intertidal and shallow subtidal infaunal bivalves Ruditapes decussatus, Ruditapes philippinarum, Venerupis corrugata and Cerastoderma edule are of great socio-economic importance (in terms of landings) in Europe, specifically in the Galician Rías Baixas (NW Spain). However, ocean warming may threaten these fisheries by modifying the geographic distribution of the species and thus affecting productive areas. The present study analysed the impact of rising ocean temperature on the geographical distribution of the thermal comfort areas of these bivalves throughout the 21st century. The Delft3D model was used to downscale climate data from CORDEX and CMIP5 and was run for July and August in three future periods (2025-2049, 2050-2074 and 2075-2099) under the RCP8.5 scenario. The areas with optimal temperature conditions for shellfish harvesting located in the middle and outer parts of the rias may increase in the near future for R. decussatus, V. corrugata and C. edule and decrease in the far future for R. philippinarum. Moreover, shellfish beds located in the shallower areas of the inner parts of the Rías Baixas could be affected by increased water temperature, reducing the productive areas of the four species by the end of the century. The projected changes in thermal condition will probably lead to changes in shellfish harvesting modality (on foot or aboard vessels) with further socio-economic consequences.

Succession of macrofauna on macroalgal wrack of an exposed sandy beach: effects of patch size and site.

In this study, we used experimental manipulation of algal wrack to test hypotheses about influences on macrofaunal assemblages inhabiting the upper shore level of different sites along an exposed sandy beach. First, we hypothesized that decomposition of algal wrack depends on wrack patch size and site. With respect to macrofauna, we tested the hypotheses that (1) abundance of colonising individuals and species vary with wrack patch size, (2) succession (i.e. sequence of colonisation and species replacement) depends on time, and (3) as a result, macrofaunal assemblages associated with wrack patches vary with the patch size and time. We also predicted that responses could be different across sites because of their slightly different environmental conditions. The decomposition of wrack patches was similar in all sites and was dependent on wrack patch size. It was strongly influenced by time-specific environmental and/or biological factors. The pattern of colonisation, i.e. total number of species and individuals, varied among wrack patch sizes. Small patches had fewer species and individuals than medium and large patches. Nevertheless, pattern of colonisation varied among species, across sites and through time. Colonisation of wrack patches was rapid (i.e. within 3 days) for most species. There was some evidence to support the hypothesis that macrofaunal assemblages change in response to patch size and time.

Appropriate experimental design to evaluate preferences for microhabitat: an example of preferences by species of microgastropods.

The intertidal microgastropods Eatoniella atropurpurea, Amphithalamus incidata and Eatonina rubrilabiata are principally found at mid- to low-shore levels in coralline turf and in patches of sediment close to algal turf on rocky shores. All three species are more abundant in coralline turf (i.e. algal beds composed primarily of Corallina officinalis Linnaeus, often containing patches of sediment) than in sediment, although the latter two are also quite abundant in patches of sediment. Eatoniella atropurpurea seem to live on branches of coralline algae, whereas Eatonina rubrilabiata and A. incidata seem to inhabit the sediment. In this study, we investigated whether or not behaviour of these animals accounts for the patterns observed in the field. Particularly, this study deals with choices amongst three microhabitats (coralline algae, coralline algae plus sediment and sediment) by these three species of microgastropods. Laboratory experiments were designed to examine preferences. The designs of such experiments are complex because demonstrating preference necessitates demonstrating different behaviour when confronted with choices from that showed when no choice is available. This study describes an appropriate series of hypotheses about preferences and experimental designs to test them. Preferences were indicated by differences in occupancy of the microhabitats when presented with a mixture and when each type is presented alone. In such experiments, snails did show preferences, except for A. incidata which did not show a pattern. Thus, the behaviour could, at least partially, account for the patterns of distribution in the field. The designs of experiments used here may be of value in other studies of preferences among habitats.

Invasion of Sargassum muticum in intertidal rockpools: patterns along the Atlantic Iberian Peninsula.

Spatial patterns of non-indigenous species show scale-dependent properties. Sargassum muticum is an invasive macroalga widely distributed along the Atlantic Iberian Peninsula. Despite being quite abundant from Norway to South Portugal, there is little information about its patterns of distribution, particularly at a large spatial scale (i.e. thousands of kilometres). Here, we examined the spatial variation in the invasion success of S. muticum from rockpools at multiple spatial scales using a hierarchical design. In addition, we analysed how the richness of native assemblages was related to its invasion success and how this relationship changed over different scales. Most of the variation in the invasion success was found at the smallest scales of pool and plot. Furthermore, the invasibility of native macroalgal assemblages was related to the native species richness, but causes that determined invasion success could not be separated from the effects provoked by the invader. Results suggest that small-scale (centimetres to metres) processes contribute considerably to the heterogeneity of S. muticum invasion success.