Recent Large Scale Environmental Changes in the Mediterranean Sea and Their Potential Impacts on Posidonia Oceanica

Climate related changes can have significant effects on Posidonia oceanica, an endemic seagrass species of the Mediterranean Sea (MEDIT). This seagrass is very important for many aspects of functioning of the sea but there is an increasing number of reports about the ongoing loss of its biomass and area coverage. We analysed multiyear data of the sea surface temperature (SST), sea level anomalies, ocean colour MODIS-A and ERA-Interim reanalysis. The results provide a description of current environmental conditions in the MEDIT and their spatial and temporal variability, including long-term trends. We defined regions where the extent of the P. oceanica meadows may be limited by specific environmental conditions. Light limitation is more severe near the northern and western coasts of the MEDIT, where the vertical diffuse attenuation coefficient is large. In the zone extending from the Gulf of Lion towards the south, significant wave heights reach large values. Wave action may destroy the plants and as a result the shallow water depth limit of P. oceanica meadows is most likely deeper here than in other regions. The highest SST values are documented in the south-eastern part of the Mediterranean Sea. In this area P. oceanica meadows are more endangered by the climate warming than in other regions where SSTs are lower. The absence of P. oceanica meadows in the south-eastern edge of the Mediterranean Sea can be attributed to high temperatures. Our conclusions are partly confirmed by the information about P. oceanica from the literature but more monitoring efforts are needed to fully describe current extent of the meadows and their shifts. Results presented in this paper can help with designing special programs to confirm the role of environmental conditions on the spatial distribution of P. oceanica and their future trends in the Mediterranean Sea

Análise de redes da paisagem submarina de canhão : implicações para o planeamento e gestão da biodiversidade

Submarine canyons are complex and heterogeneous geomorphologic structures highly relevant for the biodiversity and productivity of continental margins. These marine ecosystems play a key role providing invaluable goods and services for human well-being but are also increasingly subjected to the effects of anthropogenic pressure and climate change. The natural isolation of canyons may act synergistically with these changes with implications for population connectivity and the maintenance of biodiversity. The understanding of the causes and ecological consequences of such changes requires holistic and interdisciplinary approaches. I mapped the landscape of submarine canyon research based on a comprehensive bibliographic data set and using data mining techniques and network analysis. The existing knowledge clusters, historical trends, emergent topics and knowledge gaps in canyon research were identified and characterized. Topics such as “Geology & Geophysics”, “Oceanographic Processes” and “Biology & Ecology” were among the most studied while, for instance, “Biogeochemistry” and ecological modelling were among the less explored. Topics regarding anthropogenic impacts and climate-driven processes were only detected on publication of the last decade. The knowledge network reflects a latent interdisciplinarity in canyon research that developed mostly in the new millennium, supported by a well implemented and international collaboration network. The research efforts have been mainly directed towards only a few canyon systems and a thematic bias was identified, with specific topics addressed preferentially in particular canyons. This spatial and thematic bias, together with the paucity of truly inter-disciplinary studies, may be the most important limitation to the integrated knowledge and development of canyon research and hinders a global, more comprehensive understanding of canyon patterns and processes. The scientific landscape mapping and the complementary results are made available online as an open and interactive platform. In order to assess the importance of submarine canyons for the conservation and management on the deep sea, a study area and a modelling species were selected: the Mediterranean Sea and Lophelia pertusa, a cold-water coral species. The Mediterranean Sea encompasses several submarine canyon systems and L. pertusa is an ecosystem engineering species that occurs frequently in these geomorphological features and provides refuge, nursery grounds and physical support for a remarkable diversity of other life forms. Considering that the distribution of L. pertusa in the Mediterranean Sea is probably underestimated and that this information is crucial to assess the relevance of canyons in the Mediterranean seascape, I estimated the habitat suitability and draw uncertainty maps for this region based on environmental predictors and an ensemble approach of three machine-learning algorithms. The results suggest that in the Mediterranean Sea, L. pertusa encounters environmental settings close to its physiological limits but, despite the highly variable quality of the seascape, submarine canyons were identified as high suitability areas, especially across the Western and Central Mediterranean margins. In addition to the environmental suitability, the ecosystem connectivity determines the species distribution, the metapopulation dynamics and population resilience. I simulated the transport of L. pertusa larvae in the Mediterranean Sea using a biophysical model to estimate their potential dispersal as well as a network analysis to evaluate the habitat availability based on parameters such as suitability, spatial configuration of the seascape and the oceanographic conditions variability. The results suggest that connectivity among Mediterranean ecoregions is weak and that the intensification of climate-driven events (e.g., dense shelf water cascading) may worsen this scenario. However, the potential exchange of larvae between colonies within the same ecoregion was significant, favoring population resilience to local disturbances. Habitat areas with high quality and larval flux were identified as a priority for the conservation of L. pertusa, and subsequently also for their associated fauna. Once again, I showed that habitat areas on submarine canyons may play an important role in the connectivity of L. pertusa Mediterranean populations. However, these habitat areas are subjected to intense anthropogenic pressures, which allied to the effects of climate change, may impose greater challenges to their conservation. Apart from three French marine protected areas in the Gulf of Lion, the development of conservation efforts considering submarine canyon in the Mediterranean Sea is negligible. The knowledge produced in this thesis provides scientific evidence to support decision-making in conservation and planning of marine protected areas networks in the Mediterranean Sea and illustrates the relevance of submarine canyon for the management and conservation of deep-sea biodiversity.Os canhões submarinos são estruturas geomorfológicas complexas localizadas nas margens continentais. São reconhecidos como zonas importantes de biodiversidade no mar profundo onde os níveis de produtividade biológica são de modo geral superiores às áreas adjacentes. Estes ecossistemas marinhos desempenham um papel fundamental na prestação de bens e serviços essenciais ao bem-estar humano. Não obstante, estes ecossistemas estão cada vez mais sujeitos a efeitos nefastos que advêm de ações diretas das atividades humanas, mas também, resultantes de alterações climáticas. O isolamento natural dos canhões submarinos em conjunto com estas mudanças, pode ter implicações para a conectividade das populações biológicas que os habitam, bem como para a manutenção da biodiversidade associada. Avaliar as causas e efeitos ecológicos de tais mudanças só será possível através de uma abordagem holística e interdisciplinar. Partindo de uma base de dados bibliográfica abrangente de publicações dedicadas ao estudo de canhões submarinos, usei técnicas de data mining e de análise de redes para mapear o conhecimento reunido até agora. Foram identificados clusters de conhecimento, a evolução histórica da investigação em canhões submarinos, bem como, os tópicos emergentes e lacunas no conhecimento sobre estas estruturas. Os tópicos mais desenvolvidos dizem respeito a áreas associadas à “Geologia e Geofísica”, “Processos Oceanográficos” e “Biologia e Ecologia”. Por outro lado, temas como “Biogeoquímica” e modelação ecológica estão entre os menos explorados. Estudos referentes a impactos antropogénicos nestes ecossistemas e alterações induzidas por processos climáticos foram detetados apenas em publicação datadas da última década. A rede de tópicos gerada reflete uma interdisciplinaridade latente na investigação associada a canhões que se desenvolveu principalmente durante o século XXI, apoiada por colaborações internacionais da comunidade científica. No entanto, a investigação científica em canhões submarinos apresenta uma tendência clara direccionada para determinados temas e áreas geográficas. Tópicos específicos são abordados preferencialmente em determinados canhões, enquanto que um número muito pequeno destas estruturas concentra a maior parte dos trabalhos desenvolvidos. Este resultado juntamente com o número reduzido de estudos interdisciplinares, foi a mais importante limitação detetada que poderá dificultar a integração do conhecimento já reunido sobre estas estruturas, impedido uma compreensão mais abrangente dos padrões e processos associados aos canhões submarinos. Os resultados alcançados foram disponibilizados numa plataforma online aberta para exploração interativa e direcionada dos conteúdos. No sentido de avaliar a importância dos canhões para a conservação e gestão da biodiversidade no mar profundo, foi definida como área de estudo o Mar Mediterrâneo e selecionada como espécie modelo, um coral de água fria: Lophelia pertusa. O Mar Mediterrâneo engloba vários sistemas de canhões submarinos enquanto que L. pertusa é uma espécie engenheira de ecossistemas que cria refúgio, áreas de berçário e habitat para uma panóplia de outras espécies, ocorrendo frequentemente em canhões. Uma vez que a distribuição de L. pertusa no Mar Mediterrâneo está provavelmente subestimada e que esta informação é fundamental para avaliar a relevância dos canhões na área de estudo, desenvolvi um modelo de nicho ecológico baseado em variáveis ambientais e uma abordagem conjunta de três algoritmos. Os resultados obtidos foram mapas de adequação ambiental, bem como, de avaliação da capacidade de previsão do modelo. Os resultados sugerem que no mar Mediterrâneo, esta espécie de coral encontra condições ambientais próximas dos seus limites fisiológicos. Apesar disso, áreas com condições favoráveis à ocorrência de L. pertusa foram detetadas em canhões submarinos, principalmente no Mediterrâneo Ocidental e Central. A par da qualidade dos habitats, a distribuição dos organismos, a dinâmica metapopulacional e a resiliência das populações a perturbações estão fortemente relacionadas com a conectividade dos ecossistemas. Neste contexto, simulei o transporte de larvas de L. pertusa no Mar Mediterrâneo usando um modelo biofísico para estimar o seu potencial de dispersão. Com os resultados do modelo e usando análises de rede, avaliei a disponibilidade de habitat com base em parâmetros como a qualidade, configuração espacial da paisagem marinha e variabilidade oceanográfica. Os resultados sugerem que a conectividade entre as eco-regiões do Mar Mediterrâneo é baixa e que a intensificação de eventos impulsionados por condições climáticas (por exemplo, dense shelf water cascading) pode agravar este cenário. No entanto, a potencial troca de larvas entre colónias dentro da mesma eco-região foi significativa, podendo favorecer a resiliência das populações a perturbações locais. Áreas de habitat com boa qualidade e com fluxo de larvas foram identificadas como prioritárias para a conservação de L. pertusa, com benefícios eventuais também para a fauna associada a este coral. Mais uma vez, áreas de habitat incluídas em canhões submarinos foram identificadas como as mais relevantes no Mar Mediterrâneo, devendo desempenhar um papel importante na conectividade de populações desta espécie. Contudo, estas áreas estão igualmente sujeitas de forma intensa a atividades humanas com efeitos prejudiciais nos ecossistemas, e que, aliadas aos efeitos das alterações climáticas, podem dificultar a implementação de medidas de conservação eficazes. Com a exceção de três áreas marinhas protegidas francesas no Golfo do Leão, o desenvolvimento de esforços de conservação no Mar Mediterrâneo que incluam áreas com canhões submarinos é ainda negligenciável. Os resultados apresentados nesta tese fornecem evidências científicas que poderão apoiar medidas de conservação e gestão com vista à criação de redes de áreas marinhas protegidas no Mar Mediterrâneo. Neste sentido, proponho os canhões submarinos como áreas prioritárias para a conservação da biodiversidade de mar profundo na área de estudo.PEst-C/MAR/LA0017/2013 e UID/AMB/50017/2013Programa Doutoral em Biologia e Ecologia das Alterações Globai

Remote sensing and bio-geo-optical properties of turbid, productive inland waters: a case study of Lake Balaton

Algal blooms plague freshwaters across the globe, as increased nutrient loads lead to eutrophication of inland waters and the presence of potentially harmful cyanobacteria. In this context, remote sensing is a valuable approach to monitor water quality over broad temporal and spatial scales. However, there remain several challenges to the accurate retrieval of water quality parameters, and the research in this thesis investigates these in an optically complex lake (Lake Balaton, Hungary). This study found that bulk and specific inherent optical properties [(S)IOPs] showed significant spatial variability over the trophic gradient in Lake Balaton. The relationships between (S)IOPs and biogeochemical parameters differed from those reported in ocean and coastal waters due to the high proportion of particulate inorganic matter (PIM). Furthermore, wind-driven resuspension of mineral sediments attributed a high proportion of total attenuation to particulate scattering and increased the mean refractive index (n̅p) of the particle assemblage. Phytoplankton pigment concentrations [chlorophyll-a (Chl-a) and phycocyanin (PC)] were also accurately retrieved from a times series of satellite data over Lake Balaton using semi-analytical algorithms. Conincident (S)IOP data allowed for investigation of the errors within these algorithms, indicating overestimation of phytoplankton absorption [aph(665)] and underestimation of the Chl-a specific absorption coefficient [a*ph(665)]. Finally, Chl-a concentrations were accurately retrieved in a multiscale remote sensing study using the Normalized Difference Chlorophyll Index (NDCI), indicating hyperspectral data is not necessary to retrieve accurate pigment concentrations but does capture the subtle heterogeneity of phytoplankton spatial distribution. The results of this thesis provide a positive outlook for the future of inland water remote sensing, particularly in light of contemporary satellite instruments with continued or improved radiometric, spectral, spatial and temporal coverage. Furthermore, the value of coincident (S)IOP data is highlighted and contributes towards the improvement of remote sensing pigment retrieval in optically complex waters

Remote sensing, numerical modelling and ground truthing for analysis of lake water quality and temperature

Freshwater accounts for just 2.5% of the earth’s water resources, and its quality and availability are becoming an issue of global concern in the 21st century. Growing human population, over-exploitation of water sources and pressures of global warming mean that both water quantity and quality are affected. In order to effectively manage water quality there is a need for increased monitoring and predictive modelling of freshwater resources. To address these concerns in New Zealand inland waters, an approach which integrates biological and physical sciences is needed. Remote sensing has the potential to allow this integration and vastly increase the temporal and spatial resolution of current monitoring techniques, which typically involve collecting grab-samples. In a complementary way, lake modelling has the potential to enable more effective management of water resources by testing the effectiveness of a range of possible management scenarios prior to implementation. Together, the combination of remote sensing and modelling data allows for improved model initialisation, calibration and validation, which ultimately aid in understanding of complex lake ecosystem processes. This study investigated the use of remote sensing using empirical and semi-analytical algorithms for the retrieval of chlorophyll a (chl a), tripton, suspended minerals (SM), total suspended sediment (SS) and water surface temperature. It demonstrated the use of spatially resolved statistical techniques for comparing satellite estimated and 3-D simulated water quality and temperature. An automated procedure was developed for retrieval of chl a from Landsat Enhanced Thematic Mapper (ETM+) imagery, using 106 satellite images captured from 1999 to 2011. Radiative transfer-based atmospheric correction was applied to images using the Second Simulation of the Satellite in the Solar Spectrum model (6sv). For the estimation of chl a over a time series of images, the use of symbolic regression resulted in a significant improvement in the precision of chl a hindcasts compared with traditional regression equations. Results from this investigation suggest that remote sensing provides a valuable tool to assess temporal and spatial distributions of chl a. Bio-optical models were applied to quantify the physical processes responsible for the relationship between chl a concentrations and subsurface irradiance reflectance used in regression algorithms, allowing the identification of possible sources of error in chl a estimation. While the symbolic regression model was more accurate than traditional empirical models, it was still susceptible to errors in optically complex waters such as Lake Rotorua, due to the effect of variations of SS and CDOM on reflectance. Atmospheric correction of Landsat 7 ETM+ thermal data was carried out for the purpose of retrieval of lake water surface temperature in Rotorua lakes, and Lake Taupo, North Island, New Zealand. Atmospheric correction was repeated using four sources of atmospheric profile data as input to a radiative transfer model, MODerate resolution atmospheric TRANsmission (MODTRAN) v.3.7. The retrieved water temperatures from 14 images between 2007 and 2009 were validated using a high-frequency temperature sensor deployed from a mid-lake monitoring buoy at the water surface of Lake Rotorua. The most accurate temperature estimation for Lake Rotorua was with radiosonde data as an input into MODTRAN, followed by Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2, Atmospheric Infrared Sounder (AIRS) Level 3, and NASA data. Retrieved surface water temperature was used for assessing spatial heterogeneity of surface water temperature simulated with a three-dimensional (3-D) hydrodynamic model (ELCOM) of Lake Rotoehu, located approximately 20 km east of Lake Rotorua. This comparison demonstrated that simulations reproduced the dominant horizontal variations in surface water temperature in the lake. The transport and mixing of a geothermal inflow and basin-scale circulation patterns were inferred from thermal distributions from satellite and model estimations of surface water temperature and a spatially resolved statistical evaluation was used to validate simulations. This study has demonstrated the potential of accurate satellite-based thermal monitoring to validate water surface temperature simulated by 3-D hydrodynamic models. Semi-analytical and empirical algorithms were derived to determine spatial and temporal variations in SS in Lake Ellesmere, South Island, New Zealand, using MODIS band 1. The semi-analytical model and empirical model had a similar level of precision in SS estimation, however, the semi-analytical model has the advantage of being applicable to different satellite sensors, spatial locations, and SS concentration ranges. The estimations of SS concentration (and estimated SM concentration) from the semi-analytical model were used for a spatially resolved validation of simulations of SM derived from ELCOM-CAEDYM. Visual comparisons were compared with spatially-resolved statistical techniques. The spatial statistics derived from the Map Comparison Kit allowed a non-subjective and quantitative method to rank simulation performance on different dates. The visual and statistical comparison between satellite estimated and model simulated SM showed that the model did not perform well in reproducing both basin-scale and fine-scale spatial variation in SM derived from MODIS satellite imagery. Application of the semi-analytical model to estimate SS over the lifetime of the MODIS sensor will greatly extend its spatial and temporal coverage for historical monitoring purposes, and provide a tool to validate SM simulated by 1-D and 3-D models on a daily basis. A bio-optical model was developed to derive chl a, SS concentrations, and coloured dissolved organic matter /detritus absorption at 443 nm, from MODIS Aqua subsurface remote sensing reflectance of Lake Taupo, a large, deep, oligotrophic lake in North Island, New Zealand. The model was optimised using in situ inherent optical properties (IOPs) from the literature. Images were atmospherically corrected using the radiative transfer model 6sv. Application of the bio-optical model using a single chl a-specific absorption spectrum (a*ϕ(λ)) resulted in low correlation between estimated and observed values. Therefore, two different absorption curves were used, based on the seasonal dominance of phytoplankton phyla with differing absorption properties. The application of this model resulted in reasonable agreement between modelled and in situ chl a concentrations. Highest concentrations were observed during winter when Bacillariophytes (diatoms) dominated the phytoplankton assemblage. On 4 and 5 March 2004 an unusually large turbidity current was observed originating from the Tongariro River inflow in the south-east of the lake. In order to resolve fine details of the plume, empirical relationships were developed between MODIS band 1 reflectance (250 m resolution) and SS estimated from MODIS bio-optical features (1 km resolution) were used estimate SS at 250 m resolution. Complex lake circulation patterns were observed including a large clockwise gyre. With the development of this bio-optical model MODIS can potentially be used to remotely sense water quality in near real time, and the relationship developed for B1 SS allows for resolution of fine-scale features such turbidity currents

Sensing the ocean biological carbon pump from space: A review of capabilities, concepts, research gaps and future developments

The element carbon plays a central role in climate and life on Earth. It is capable of moving among the geosphere, cryosphere, atmosphere, biosphere and hydrosphere. This flow of carbon is referred to as the Earth’s carbon cycle. It is also intimately linked to the cycling of other elements and compounds. The ocean plays a fundamental role in Earth’s carbon cycle, helping to regulate atmospheric CO2 concentration. The ocean biological carbon pump (OBCP), defined as a set of processes that transfer organic carbon from the surface to the deep ocean, is at the heart of the ocean carbon cycle. Monitoring the OBCP is critical to understanding how the Earth’s carbon cycle is changing. At present, satellite remote sensing is the only tool available for viewing the entire surface ocean at high temporal and spatial scales. In this paper, we review methods for monitoring the OBCP with a focus on satellites. We begin by providing an overview of the OBCP, defining and describing the pools of carbon in the ocean, and the processes controlling fluxes of carbon between the pools, from the surface to the deep ocean, and among ocean, land and atmosphere. We then examine how field measurements, from ship and autonomous platforms, complement satellite observations, provide validation points for satellite products and lead to a more complete view of the OBCP than would be possible from satellite observations alone. A thorough analysis is then provided on methods used for monitoring the OBCP from satellite platforms, covering current capabilities, concepts and gaps, and the requirement for uncertainties in satellite products. We finish by discussing the potential for producing a satellite-based carbon budget for the oceans, the advantages of integrating satellite-based observations with ecosystem models and field measurements, and future opportunities in space, all with a view towards bringing satellite observations into the limelight of ocean carbon research

Feasibility Study for an Aquatic Ecosystem Earth Observing System Version 1.2.

International audienceMany Earth observing sensors have been designed, built and launched with primary objectives of either terrestrial or ocean remote sensing applications. Often the data from these sensors are also used for freshwater, estuarine and coastal water quality observations, bathymetry and benthic mapping. However, such land and ocean specific sensors are not designed for these complex aquatic environments and consequently are not likely to perform as well as a dedicated sensor would. As a CEOS action, CSIRO and DLR have taken the lead on a feasibility assessment to determine the benefits and technological difficulties of designing an Earth observing satellite mission focused on the biogeochemistry of inland, estuarine, deltaic and near coastal waters as well as mapping macrophytes, macro-algae, sea grasses and coral reefs. These environments need higher spatial resolution than current and planned ocean colour sensors offer and need higher spectral resolution than current and planned land Earth observing sensors offer (with the exception of several R&D type imaging spectrometry satellite missions). The results indicate that a dedicated sensor of (non-oceanic) aquatic ecosystems could be a multispectral sensor with ~26 bands in the 380-780 nm wavelength range for retrieving the aquatic ecosystem variables as well as another 15 spectral bands between 360-380 nm and 780-1400 nm for removing atmospheric and air-water interface effects. These requirements are very close to defining an imaging spectrometer with spectral bands between 360 and 1000 nm (suitable for Si based detectors), possibly augmented by a SWIR imaging spectrometer. In that case the spectral bands would ideally have 5 nm spacing and Full Width Half Maximum (FWHM), although it may be necessary to go to 8 nm wide spectral bands (between 380 to 780nm where the fine spectral features occur -mainly due to photosynthetic or accessory pigments) to obtain enough signal to noise. The spatial resolution of such a global mapping mission would be between ~17 and ~33 m enabling imaging of the vast majority of water bodies (lakes, reservoirs, lagoons, estuaries etc.) larger than 0.2 ha and ~25% of river reaches globally (at ~17 m resolution) whilst maintaining sufficient radiometric resolution