Chapter A2.2: Benthic Habitats

Shallow-water coastal benthic habitats, which can comprise seagrasses, sandy soft bottoms, and coral reefs are essential ecosystems, supporting fisheries, providing coastal protection, and sequestering blue carbon. Multispectral satellite imagery, particularly with blue and green spectral bands, can penetrate clear, shallow water, allowing us to identify what lies on the seafloor

Cubesats Allow High Spatiotemporal Estimates of Satellite-Derived Bathymetry

High spatial and temporal resolution satellite remote sensing estimates are the silver bullet for monitoring of coastal marine areas globally. From 2000, when the first commercial satellite platforms appeared, offering high spatial resolution data, the mapping of coastal habitats and the extraction of bathymetric information have been possible at local scales. Since then, several platforms have offered such data, although not at high temporal resolution, making the selection of suitable images challenging, especially in areas with high cloud coverage. PlanetScope CubeSats appear to cover this gap by providing their relevant imagery. The current study is the first that examines the suitability of them for the calculation of the Satellite-derived Bathymetry. The availability of daily data allows the selection of the most qualitatively suitable images within the desired timeframe. The application of an empirical method of spaceborne bathymetry estimation provides promising results, with depth errors that fit to the requirements of the international Hydrographic Organization at the Category Zone of Confidence for the inclusion of these data in navigation maps. While this is a pilot study in a small area, more studies in areas with diverse water types are required for solid conclusions on the requirements and limitations of such approaches in coastal bathymetry estimations

Mind the gap in data poor Natura 2000 sites and how to tackle them using Earth Observation and scientific diving surveys

Charismatic species drives decisions for the conservation of marine areas in the view of the coverage of the Natura 2000 sites in the European Union and other forms of Marine Protected Areas in Europe. However, when used solely, critical seascapes and habitats are systematically ignored and practically it can take decades to fulfill baseline needs on habitats distributions, habitats conservation status and species distributions and biodiversity assessments. Luckily, in the last decade, the use of new technologies in conjunction with scientific diving and budget friendly hydroacoustic tools and applications, has allowed to fill the gap in knowledge in such situations and seascapes. The current work demonstrates the use of Earth Observation and Science Dive to fill the gap of knowledge in a newly established Natura 2000 area in Crete, Greece, East Mediterranean, paving the road for replicable approaches in similar situations

Earth Observation for Seagrass Blue Carbon Assessment in East Africa

The plan to mitigate the rise in global temperature includes nature-based solutions such as the blue carbon stocks of coastal ecosystems. Seagrass meadows rank among the most efficient organic carbon sinks on Earth. However, due to the high costs of the required equipment and enormous environmental challenges, field data collection of underwater habitats are expensive. In order to fill the knowledge gap, we utilized openly available Earth Observation data and algorithms which enabled us to remotely assess the blue carbon stocks here. In this study, we opted for the Sentinel-2 optical satellite images to map the national extent of seagrass meadows across the East African coastline. We developed and applied our mapping framework in the geospatial cloud platform Google Earth Engine of which processors are capable of processing 16,453 images available from 2018-2020 at 10-m spatial resolution. We estimated a regional extent of 4,316 km^2 of shallow water seagrass meadows along the coastlines of Kenya, Tanzania, Mozambique, and Madagascar with the overall accuracy of 84.3%, up to 23 m of depth. By pairing the country-specific in situ soil carbon data, we estimated regional seagrass blue carbon stocks between 11.2-40.2 million MgC in East Africa. Our regional seagrass map and its resulting blue carbon stock estimates are useful to highlight the importance of seagrass restoration and conservation for coastal biodiversity and blue carbon ecosystem services worldwide

DEIMS-SDR – A web portal to document research sites and their associated data

Climate change and other drivers are affecting ecosystems around the globe. In order to enable a better understanding of ecosystem functioning and to develop mitigation and adaptation strategies in response to environmental change, a broad range of information, including in-situ observations of both biotic and abiotic parameters, needs to be considered. Access to sufficient and well documented in-situ data from long term observations is therefore one of the key requirements for modelling and assessing the effects of global change on ecosystems. Usually, such data is generated by multiple providers; often not openly available and with improper documentation. In this regard, metadata plays an important role in aiding the findability, accessibility and reusability of data as well as enabling reproducibility of the results leading to management decisions. This metadata needs to include information on the observation location and the research context. For this purpose we developed the Dynamic Ecological Information Management System – Site and Dataset Registry (DEIMS-SDR), a research and monitoring site registry (https://www.deims.org/) that not only makes it possible to describe in-situ observation or experimentation sites, generating persistent, unique and resolvable identifiers for each site, but also to document associated data linked to each site. This article describes the system architecture and illustrates the linkage of contextual information to observational data. The aim of DEIMS-SDR is to be a globally comprehensive site catalogue describing a wide range of sites, providing a wealth of information, including each site's location, ecosystems, facilities, measured parameters and research themes and enabling that standardised information to be openly available

The origin and dispersal pathway of the spotted sea hare Aplysia dactylomela (Mollusca : Opisthobranchia) in the Mediterranean Sea

The spotted sea hare Aplysia dactylomela Rang, 1828 is a large and conspicuous opisthobranch sea slug that since 2002 has rapidly colonized the eastern Mediterranean, establishing populations in numerous localities. The source of the Mediterranean populations has been the subject of debate, with two main hypotheses considered (Atlantic and Red Sea origin). A recent study on the taxonomy of A. dactylomela has shown that the spotted sea hare is a complex of at least two genetically distinct species (A. dactylomela in the Atlantic and A. argus in the Indo-Pacific), facilitating the correct identification of Mediterranean specimens by molecular means. We used sequence data from the mitochondrial cytochrome oxidase I gene to identify the Mediterranean individuals for the first time and to infer their origin. Our results confirmed that all the specimens collected in the Mediterranean belong to A. dactylomela and therefore have an Atlantic origin. The limited sample size does not allow identification of the dispersal pathway of A. dactylomela into the Mediterranean, but the colonization sequence is consistent with a “natural” dispersal event. This hypothesis is evaluated in light of local surface circulation patterns. Possible causes for the recent and rapid invasion of the eastern Mediterranean by A. dactylomela are discussed.peer-reviewe

Population genetics of Bursatella leachii (De Blainville, 1817) and implications for the origin of the Mediterranean population

Abstract The sea hare Bursatella leachii (de Blainville 1817) (Mollusca: Gastropoda: Heterobranchia: Aplysiidae) is a pantropical sea slug that has colonized the Mediterranean Sea in modern times. Because the initial records in the non-native range started in the Eastern Mediterranean, and its pattern of spread was relatively consistent with those observed in well-known Lessepsian invaders, B. leachii is commonly considered to be a migrant from the Red Sea. In this study, we investigate for the first time the origin of the Mediterranean populations of B. leachii inferring their population structure and assessing relatedness levels of different regional populations. Sequence data from the cytochrome oxidase I were used to conduct population genetic analyses on this species, particularly by investigating the genetic structure of Atlantic, Mediterranean, and Indo-Pacific populations. Our results confirm that B. leachii is a truly pantropical species which displays geographic structure among major ocean basins. More importantly, sequenced Mediterranean and Atlantic animals share similar or identical haplotypes, which are distinct in at least 5 substitutions from haplotypes recovered from Indo-Pacific specimens. The results suggest that the Mediterranean population of B. leachii here examined probably have an Atlantic origin, and for the first time casts doubts on the assumed primary pathway of migration into the Mediterranean Sea

Pinna nobilis in the Greek seas (NE Mediterranean): on the brink of extinction?

The Mediterranean endemic fan mussel Pinna nobilis is suffering an ongoing basin-scale mass mortality event (MME) since 2016. As most Mediterranean populations have collapsed, the species has been declared as Critically Endangered in the IUCN Red List of threatened species. In an effort to track the progress of the MME and provide updated information on the status of the species in the Greek seas, data collected through dedicated surveys and opportunistic assessments during 2019 and 2020 have been compiled. During surveys conducted at 258 sites, a total of 14,589 fan mussels were recorded, of which 81.1% were dead. Of the remaining 2,762 live individuals, 256 were juveniles. Two marine areas that still sustain living populations were identified, namely Kalloni Gulf (Lesvos Island), and Laganas Bay (Zakynthos Island). The inner part of Kalloni Gulf appears to maintain the largest surviving population of the species in the eastern Mediterranean, with an abundance estimate of 684,000 individuals (95% confidence interval: 322,000-1,453,000). Solitary, potentially resistant, scattered individuals were recorded at several sites. Other previously abundant populations that had been assessed in the past, specifically those of Lake Vouliagmeni (Korinthiakos Gulf), Souda Bay (Crete) and Gera Gulf (Lesvos Island) with a total of ~350,000 individuals, have now been wiped out. Our results document the collapse of most P. nobilis populations throughout the Greek seas. The MME has progressed substantially between early 2019 and mid-2020, as indicated by the increase in mortality at sites consecutively monitored multiple times. This work highlights the urgent need for continuous monitoring of surviving populations and calls for immediate implementation of an effective protection and management strategy that will ensure the persistence of surviving individuals and the production of resistant offspring

Spatially Explicit Seagrass Extent Mapping Across the Entire Mediterranean

The Posidonia oceanica seagrass is the foundation species of the coastal Mediterranean, whose meadows support significant ecosystem services: food security, coastal protection, biodiversity maintenance, carbon sequestration, amongst others. This endemic in the basin seagrass features the largest carbon storage among seagrasses globally, contributing substantially to global blue carbon stocks.  However, climate change, coastal development, and decreasing water quality all render this slow-growing species at risk of area loss, functional extinction, and, hence, its provided services. This risk is further complicated by the current knowledge gaps in its bioregional extent, necessitating accurate, efficient and spatially explicit mapping and accounting of its distribution and trajectories at a high spatial resolution. Here, we leveraged recent Earth Observation advances—cloud computing, open satellite data, and machine learning—with field data via a cloud-based ecosystem accounting framework to map the spatially-explicit ecosystem extent of P. oceanica seagrass across the whole Mediterranean, at 10m resolution.  Employing 279,186 Sentinel-2 satellite images between 2015-2019, and a human-labelled training dataset of 62,928 pixels, we mapped 19,020 km2 of P. oceanica seagrass area in 22 countries across 56,783 km2 of mapped seabed between 0-25 m of depth. Based on 2,480 independent field-based points, we observe an overall accuracy of 72%. Using a Tier 2 assessment, we estimated the bioregional blue carbon storage of P. oceanica beds to be 722.2 million MgC.  As reference data collections, remote sensing technology and biophysical modelling improve and coalesce, such extent accounts could support physical and monetary accounting of seagrass condition and ecosystem services. We envisage that such holistic seagrass ecosystem accounts could enable effective policy uptake in national climate, biodiversity and protection strategies and necessary financing. This in turn could accelerate transparent natural climate solutions and coastal resilience, beyond the physical location of seagrass beds and the 21th century