Recovery of fishery-stressed seagrass meadows is driven by improvements in wastewater management

As ecosystem engineers, seagrasses provide major benefits to coastal habitats worldwide. Nonetheless, their dynamics remain poorly understood in local areas. Three seagrass (Zostera noltei) meadows located within shellfish beds in Galicia (NW Spain) were selected to assess the intra and inter-annual changes in the habitats by considering the effects of harvesting, temperature and sewage pollution. Seagrass cover increased between April and October, when the sediment temperature ranged from 15 to 20 °C, while in terms of long-term dynamics there was a mean gain of 3 % year−1 between 2004 and 2023. Shellfishing caused mechanical disturbance within the meadows, but the seasonal changes in cover depended on temperature. However, we pointed out the built of new wastewater treatment plants since 1990 that improved water quality as the main driver of the long-term increase in seagrass cover. Environmental policies that enhance seawater quality and limit harvesting pressure are essential to maintain this positive trendAgencia Estatal de Investigación | Ref. RTI2018-095583-B-I00Xunta de Galicia | Ref. ED481A-2020/199Xunta de Galicia | Ref. ED431C 2021/4

Rapid diagnosis of the geospatial distribution of intertidal macroalgae using large-scale UAVs

Macroalgae have been used as indicators of the health of coastal ecosystems, they function as sinks of CO2 and are essential contributors to primary production. With the increase in anthropogenic activities, it is crucial to assess the impact of such activities on these ecosystems. As traditional surveying techniques, although accurate, are time-consuming and their area coverage is limited, novel techniques are required to monitor the coverage and diversity of intertidal macroalgae. We propose a methodology using the free-source Semi-Automatic Classification Plugin from QGIS to use UAV and multispectral cameras for the spatiotemporal monitoring of intertidal macroalgae. We also compared the performance of six classifiers: Minimum Distance (MD), Maximum Likelihood (ML), Spectral Angle Mapping (SAM), Multi-Layer Perceptron (MLP), Random Forest (RF) and Support Vector Machine (SVM), for three types of macroalgae classification: general, taxonomical groups and species. As proof of concept, an intertidal rocky shore in a marine protected area (NW Spain) was studied for four months. RF and SVM achieved similar results, with both being recommended for the general (OASVM = 97.4±1.7 and OARF = 98.3±1.7) and taxonomical groups (OASVM = 91.6±1.9 and OARF = 89.2±4.5). SVM and ML were found to be more suitable for species classification (OASVM = 77.4±11.4 and OAML = 74.2±9.7). SAM and MLP provided the least performant species classifiers because of the overlap in the macroalgae spectral signatures. The plugin showed limitations when tuning the input parameters of the MLP classifier and did not let to add a validation dataset. Additionally, we present an open-access GIS web application, Alganat 2000 GIS web, to facilitate the monitoring and management of coastal areas. We conclude that the proposed methodology using the SVM or ML classifiers is an effective tool for assessing intertidal macroalgal assemblages. Its easy and rapid implementation is beneficial for researchers who are not very familiar with coding and machine learning frameworks and reduces the time and cost of fieldwork. As future work, we propose the combination of the multispectral bands with topographic and spectral indices and to research the application of deep learning models to the classification of intertidal macroalgaeAgencia Estatal de Investigación | Ref. PRTR-C17.I1Universidade de Vigo/CISU

Monitoring and mapping of intertidal macroalgae using low-cost geospatial automated techniques

The global extent of macroalgae is declining with important consequences on marine biodiversity and ecosystem processes. Tracking the status and trends of macroalgal cover is, therefore, an emerging priority for ocean and coastal management. A remote sensing technique combining UAVs surveys with in situ data acquisition was developed to map intertidal macroalgae from rocky shores in a marine protected area, the Atlantic Islands of Galicia National Park (Illas Cíes, NW Spain). The classifcation by groups (brown and green macroalgae) achieved a good precision. A more precise classifcation would be achieved by focusing on those spectral bands where the highest diferences between species appeared.Peer Reviewe

Population structure and habitat assessment for two commercial clam species exploited in small-scale fisheries

Small-scale fisheries play a crucial role in providing food and jobs in local communities worldwide. Nonetheless, their environmental impact remains poorly understood. To assess the effect of different levels of harvesting pressure on clam population dynamics, we selected three areas for study within each of three intertidal shellfish beds (in NW Spain) on the basis of historical harvesting pressure. The abundance (up to 149 ind m −2 ) of the introduced clam Ruditapes philippinarum of marketable size was much greater than that of the native R. decussatus (up to 20 ind m −2 ) in all three beds, which is consistent with the low level of recruitment of the native species. Our results suggest that the harvesting pressure did not significantly affect reproduction, which was asynchronous across beds, and that the reproductive period was longer in R. philippinarum than in R. decussatus . Nonetheless, the intertidal system was strongly affected by harvesting, as bare sediment was typical in frequently harvested areas, while sparse or dense patches of the seagrass Zostera noltei occurred in areas where harvesting pressure was scarce or null. The abundance and diversity of non-commercial infaunal species were greatest in unharvested areas. However, commercial clams were not abundant in these areas, possibly due to natural habitat preferences or artificial seeding and movement of clams along the beds. Management plans based on local knowledge of ecosystems are needed to maintain sustainable stocks of R. decussatus and also to limit the effects of harvesting on the systems.Ministerio de Ciencia e Innovación | Ref. RTI2018-095583-B-I00CRUE-CSICXunta de Galicia | Ref. ED481A-2020/199Xunta de Galicia | Ref. ED431C 2021/42NASA | Ref. 80NSSC20K007

Are clam-seagrass interactions affected by heatwaves during emersion?

The increased frequency of heatwaves expected in the context of global warming will affect socio-ecological systems such as shellfish beds at intertidal seagrass meadows. A mesocosm experiment was performed to assess the effects of a simulated atmospheric heatwave during low tide on the bioturbation indicators and growth of the commercial juvenile native Ruditapes decussatus and the introduced clam R. philippinarum, and on their interactions with the seagrass Zostera noltei. Under the heatwave, heat dissipation at 5 cm depth was significantly greater in the sediments below Z. noltei than below bare sand, the photosynthetic efficiency (Fv/Fm) of Z. noltei decreased and the clams tended to grow less. Furthermore, after the heatwave clams below bare sand tended to burrow deeper than those below Z. noltei, indicating that seagrass provided a refuge for clams. Ruditapes philippinarum grew less, and did not burrow as deeply as R. decussatus, which may imply greater vulnerability to desiccation and heat at low tide. The particle displacement coefficient (PDC) of R. philippinarum indicated lower bioturbation values in Z. noltei than in bare sand and was a suitable bioturbation indicator for juvenile Ruditapes spp. clams. In Z. noltei coexisting with R. philippinarum, the Fv/Fm values were higher than without clams after a recovery period, which may be linked to the assimilation of phosphate excreted by the clams and suggests a facilitative interaction. No such interaction was observed with R. deccusatus, probably because of its deeper burrowing depth. The findings suggest reciprocal facilitative interactions between R. philippinarum and Z. noltei and the potential contribution of Z. noltei to the sustainability of clams under global warming scenarios, which may support management actions aimed at enhancing the coexistence between shellfishing activities and seagrass conservation.Agencia Estatal de Investigación | Ref. RTI2018-095583-B-I00Xunta de Galicia | Ref. ED431C 2021/42Xunta de Galicia | Ref. ED481A-2020/199Universidade de Vigo/CISU

Effects of warming on biological interactions between clams and the seagrass Zostera noltei: A case study using open top chambers

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGBivalves and seagrasses can interact through diverse environmentally-modulated mechanisms. To assess the effects of climate warming on bivalve-seagrass interactions, we carried out a pioneering field experiment in which open top chambers (OTCs) were used to increase air and sediment temperature in a shellfish bed in NW Spain during two consecutive spring tides (16 days of exposure to OTCs). The temperature increase produced by OTCs was significant, as observed in the daily maximum and mean temperature and in degree hours, although the difference was greater in air and at the sediment surface (up to 8 ◦C and 3 ◦C, respectively) than at 5 cm depth (up to 1 ◦C). Warming was less acute in boxes with the seagrass Zostera noltei, which acted as a thermal buffer, reducing the mean temperature by 1 ◦C at the sediment surface in OTC boxes and control boxes (without OTCs). Although the short-term increase in temperature did not greatly affect physiological responses of Z. noltei, the carbohydrate reserves and nutrient content increased in the presence of clams. Growth of the native clam Ruditapes decussatus was significantly slower in OTC boxes with bare sediment, and the seagrass thus buffered the negative effect of warming on growth. The presence of Z. noltei may save clams from having to spend energy to burrow deeper to encounter cooler conditions, leaving more energy available for growth. Conversely, growth of the introduced clam R. philippinarum did not differ between habitats or treatments. Our findings confirm a twoway facilitative interaction that may be particularly important in relation to the resilience of both species in the current context of global warming.Ministerio de Ciencia e Innovación | Ref. RTI2018-095583-B-I00Xunta de Galicia-FEDER | Ref. ED431C 2021/42Xunta de Galicia | Ref. ED481A- 2020/199NASA | Ref. 80NSSC20K007

The stress response of the seagrass Zostera noltei and three commercial clam species to low salinity associated with heavy rainfall

Abstract The maintenance of stocks of estuarine species strongly depends on the ability of the species to cope with environmental stress. In NW Spain, commercial clam beds, which are usually co-occupied by the seagrass Zostera noltei, are often exposed to reduced salinity caused by intense rainfalls. Our goals were to evaluate the effects of low salinity events on both juvenile clams and Z. noltei, including their interactions. A mesocosm experiment was performed to simulate three salinity decreases (35–35, 25–10, and 20–5), and several indicators of clam and seagrass performance were measured after 3 and 6 days of exposure and again after a recovery period of 4 days. No differences were observed in the non-native clam Ruditapes philippinarum, while oxygen consumption, clearance rate and growth decreased significantly in the native clams R. decussatus and Venerupis corrugata in response to low salinity stress. Zostera noltei indicators did not vary in response to low salinity exposure, except the sucrose content, which decreased. Moreover, the seagrass buffered juvenile clams from salinity fluctuations in the short term, although the interactions were weak. The species-specific sensitivity to low salinity should be a major concern in future management plans for the shellfish beds in the context of climate change.Agencia Estatal de Investigación | Ref. RTI2018-095583-B-I00Xunta de Galicia | Ref. ED481A-2020/199Xunta de Galicia | Ref. ED431C 2021/4

Environmental state of an intertidal complex and anthropization in its catchment area

Environmental state analysis of an intertidal complex and the study of anthropization in its associated basin were done. The purpose was to amplify the knowledge of the relationship between land occupation changes and their effect on the marine environment. The study was divided in two stages. 1: The land use changes variation area from 1990 to 2006 in the catchment was quantified by getting the data of the Corine Land Cover (CLC) satellite images and processing them by geographical information system software. Statistical data (demographic and buildings) showed the human pressures in the area. 2: A core was collected at the intertidal complex, and the sediment was subjected to granulometric analysis, also the studies of organic matter percentage, ratios of stable carbon and nitrogen isotopes, total carbon and nitrogen, and trace metals were done. The provisional results of the CLC analysis showed that the most significant land use changes in the study period were the loss of forest soil and crops and the increase of infrastructures. In the upper 68 cm of the sediment, it was found that the grain size was finer at the upper parts of the core and the organic matter percentage decreased with depth, when the gravels appeared. The δ15N values were between 4,6 and 5,7‰ and the δ13C values were between -25,5 and -24,1‰. The C/N ratio had an increasing trend with depth with a maximum of 13.1 and a minimum of 10.2, and the inorganic elements analysis showed that the concentrations of lead, copper and zinc exceeded the background concentrations for contaminants established by the OSPAR commission

Integrated assessment of anthropization in estuarine ecosystems : land-use changes and matter inputs

Esta tesis se enfoca en el estudio del efecto de la actividad humana en zonas costeras sobre los ecosistemas de transición, con énfasis en el caso de los aportes de materia de cuencas fluviales a las marismas en varias áreas del litoral del noroeste de la Península Ibérica. La relación existente entre la presión humana y los impactos en el medio natural motivaron la definición, como objetivo principal, de la creación de variables indicadoras de antropización en ecosistemas costeros. En concreto, en estuarios con la presencia de praderas marinas influidos por distinto grado de desarrollo humano con el fin de conocer las fuentes y procesos que ocurren en las zonas evaluadas.Esta tese enfocase no estudo do efecto da actividade humana en zonas costeiras sobre os ecosistemas de transición, con énfase no caso dos aportes de materia das concas fluviais ás marismas, en varias áreas do litoral do noroeste da Península Ibérica. A relación existente entre a presión humana e os impactos no medio natural motivaron a definición, coma obxectivo principal, da creación de variables indicadoras de antropización en ecosistemas costeiros. En concreto, en estuarios coa presenza de pradeiras mariñas influidos por distinto grao de desenvolvemento humano co fin de coñecer as fontes e procesos que ocorren nas zonas evaluadas.This thesis focuses on the study of human activities in coastal zones on transitional ecosystems, with emphasis in the case of matter inputs from fluvial basins to salt marshes, in various littoral areas of northwestern Iberian peninsula. Existing relationship between human pressure and impacts in natural environment motivated the definition of anthropization indicator variables in coastal ecosystems,specifically, in estuaries with the presence of seagrasses influenced by diferent human development with the aim to know the sources and proccesses which occur in evaluated areas.Ministerio de Economía y Competitividad de España. Proyecto REIMAGE | Ref. CTM 2011-30155-C03-01Ministerio de Economía y Competitividad de España. Proyecto REIMAGE | Ref. CTM 2011-30155-C03-0

Anthropogenic nutrient inputs in the NW Iberian Peninsula estuaries determined by nitrogen and carbon isotopic signatures of Zostera noltei seagrass meadows

Coastal watersheds of the NW Iberian Peninsula have undergone increases in population densities and urbanization over the past decades. However, the effect of altered nutrient inputs to estuarine Zostera noltei ecosystems associated to these anthropogenic pressures remains largely unknown. Eleven Zostera noltei meadows located in the NW Iberian Peninsula were studied to assess the relationship between the anthropogenic pressure over coastal watersheds and the nitrogen and carbon isotopic signatures of Z. noltei meadows. Anthropogenic pressure on the watersheds was estimated from human population data and land cover classes. Carbon and nitrogen stable isotopic analyses were performed on Z. noltei leaves and in the sediments surrounding the rhizospheres. Our results indicate that the N and C isotopic signatures of Z. noltei meadows from the NW Iberian Peninsula reflect the impact of anthropogenic pressures. Nevertheless, these relationships are complex due to several processes acting simultaneously altering the expected isotopic responses.Ministerio de Ciencia e Innovación (España) | Ref. CTM2011-30155-C03-01Ministerio de Ciencia e Innovación (España) | Ref. CTM2011-30155-C03- 02Xunta de Galici