Pierre Gernez

Beyond key ecological services, marine resources are crucial for human food security and socio-economical sustainability. Among them, shellfish aquaculture and fishing are of primary importance but become more vulnerable under anthropogenic pressure, as evidenced by reported mass mortality events linked to global changes such as ocean warming and a...

Accurate habitat mapping methods are urgently required for the monitoring, conservation, and management of blue carbon ecosystems and their associated services. This study focuses on exposed intertidal seagrass meadows, which play a major role in the functioning of nearshore ecosystems. Using Sentinel-2 (S2) data, we demonstrate that satellite remo...

Seagrass meadows are monitored in the frame of several environmental programs worldwide, including the Water Framework Directive (WFD), to evaluate the ecological status of European coastal and transitional water bodies. The large size, spatial complexity, and interannual variability of seagrass ecosystems significantly challenge field monitoring....

Taking into account trophic relationships in seagrass meadows is crucial to explain and predict seagrass temporal trajectories, as well as for implementing and evaluating seagrass conservation policies. However, this type of interaction has been rarely investigated over the long term and at the scale of the whole seagrass habitat. In this work, rec...

Harmful algal blooms (HABs) have severe environmental and economic impacts worldwide. Improving HAB detection is crucial because massive blooms are likely to increase in both frequency and amplitude in the next decades due to global warming and escalating coastal eutrophication. While satellite remote sensing has proved useful to detect red tides a...

Coastal areas support seagrass meadows, which offer crucial ecosystem services, including erosion control and carbon sequestration. However, these areas are increasingly impacted by human activities, leading to habitat fragmentation and seagrass decline. In situ surveys, traditionally performed to monitor these ecosystems, face limitations on tempo...

Intertidal areas, which emerge during low tide, form a vital link between terrestrial and marine environments. Seagrasses, a well-studied intertidal habitat, provide a multitude of different ecosystem goods and services. However, owing to their relatively high exposure to anthropogenic impacts, seagrasss meadows and other intertidal habitats have s...

Seagrasses are marine flowering plants that form extensive meadows from the inter-tidal zone up to ~50 m depth. As biological and ecological Essential Biodiversity Variables, seagrass cover and composition provide a wide range of ecosystem services. Inter-tidal seagrass meadows provide services to many ecosystems, so monitoring their occurrence, ex...

Mesodinium rubrum is a kleptoplastidic ciliate that sequesters the chloroplasts and nuclei of cryptophyte algae to perform photosynthesis. Blooms of M. rubrum can cause red tides in coastal oceans worldwide. Such red tides are detectable by remote sensing, and studying M. rubrum pigments and optical properties is a crucial step toward characterizin...

This poster summerise the work done by the RSBE² team of Nantes university as part of BiCOME project. It about spectral discrimination of green macrophyte based on hyperspectral and multispectral drone data.

Monitoring biodiversity and how anthropogenic pressures impact this is critical, especially as anthropogenically driven climate change continues to affect all ecosystems. Intertidal areas are exposed to particularly high levelsof pressures owing to increased population density in coastal areas. Traditional methods of monitoring intertidalareas do n...

At the end of July 2021, a bloom of Lingulodinium polyedra developed along the French Atlantic coast and lasted six weeks. The REPHY monitoring network and the citizen participation project PHENOMER contributed to its observation. A maximum concentration of 3,600,000 cells/L was reached on the 6th of September, a level never recorded on French coas...

Rugulopteryx okamurae is a species of brown macroalgae belonging to the Dictyotaceae family and native to the north-western Pacific. As an Invasive Alien Species (IAS), it was first detected in the Strait of Gibraltar in 2015. Since then, R. okamurae has been spreading rapidly through the submerged euphotic zone, colonizing from 0 to 50 m depth and...

Use of Earth Observation and remote sensing techniques for monitoring the marine invasive alien macrophyte R. okamurae in Tarifa (Spain). Use of multispectral (Landsat-8 and Sentinel-2) and hyperspectral (UAV) data and machine learning methods for classification mapping.

The combined use of satellite-derived environmental data and a dynamic energy budget (DEB) model to determine Pacific oyster growth potential was adapted for the South African marine environment. Study areas consisted of the West Coast (high-chlorophyll, low temperature) and the South Coast (variable chlorophyll, higher temperature) ecoregions. Chl...

Blooms of the marine dinoflagellate Lepidodinium chlorophorum cause green seawater discolorations affecting the recreational use and the tourism economy along southern Brittany (NE-Atlantic, France). Hypoxic conditions associated with phytoplankton biomass recycling are suspected to cause fauna mortalities. An in situ monitoring was performed in 20...

Habitat engineers make strong and far-reaching imprints on ecosystem processes. In intertidal mudflats, the dominant primary producer, microphytobenthos (MPB), often forms high biomass patches around oyster reefs. We evaluate multiple hypotheses linking MPB with oyster reefs, including oyster biodeposition, meiofaunal grazing, and abiotic factors,...

The presence of hydrosols, taken as suspension of micro- or macroscopic material in water, strongly alters light propagation and thus the radiance distribution within a natural or artificial water volume. Understanding of hydrosols’ impacts on light propagation is limited by our ability to accurately handle the angular scattering phase function inh...

A R T I C L E I N F O Keywords: Bivalve Pacific oyster Dynamic energy budget (DEB) Marine spatial planning (MSP) Offshore aquaculture Site selection, climate change A B S T R A C T Aquaculture development in Europe, while critical to the European Union (EU) Blue Growth strategy, has stagnated over the past decades due largely to high competition fo...

Oyster production has historically taken place in intertidal zones, and shellfish farms already occupy large extents of the French intertidal space. The expansion of French shellfish aquaculture within intertidal areas is therefore spatially limited, and moving production to the subtidal offshore environment is considered to be a possible solution...

Aquaculture increasingly contributes to global seafood production, requiring new farm sites for continued growth. In France, oyster cultivation has conventionally taken place in the intertidal zone, where there is little or no further room for expansion. Despite interest in moving production further offshore, more information is needed regarding th...

Plain Language Summary Intertidal mudflats support a high biological productivity sustained mainly by microalgae living in the sediment. Microalgae form a dense biofilm at the surface of the mud during daytime low tides and fix a high quantity of inorganic carbon into organic carbon through photosynthesis. Microalgae can be resuspended along with t...

Executive summary and recommendations The EU Water Framework Directive 1 (WFD) is an ambitious legislation framework to achieve good ecological and chemical status for all surface waters and good quantitative and chemical status for groundwater by 2027. A total of 111,062 surface waterbodies are presently reported on under the Directive, 46% of whi...

For most people, the reflection of the Sun (or Moon) light on the sea surface is an open place for romanticism and reveries. From beaches to space, the sparkling patch of sunlight reflected on the wavy ocean can be readily observed by any kind of optical imager; from the naked eye to modern sensors embarked on satellites. For most oceanographers, t...

The potential for and productivity of shellfish aquaculture is strongly influenced by sea surface temperature (SST), and the concentration and nature of suspended particulate matter (SPM), which can both be monitored from space to determine shellfish growth conditions. Phytoplankton is a main food source for suspension-feeding bivalves. In too high...

In Europe, oyster production has historically taken place in intertidal zones. Shellfish farms already occupy large extents of intertidal space, and sometimes have for more than a century. The possibility of expanding shellfish aquaculture in intertidal areas is therefore spatially limited, and is also constrained by carrying capacity, water qualit...

Marine diseases have major impacts on ecosystems and economic consequences for aquaculture and fisheries. Understanding origin, spread and risk factors of disease is crucial for management, but data in the ocean are limited compared to the terrestrial environment. Here we investigated how the marine environment drives the spread of viral disease ou...

Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating on smaller scales however, such as the impact of benthic macrofauna on MPB development, to d...

The implementation of accurate atmospheric correction is a prerequisite for satellite observation and water quality monitoring in coastal areas. The potential of the fast-line-of-sight atmospheric analysis of spectral hypercubes (FLAASH) was investigated here for the medium resolution imaging spectrometer (MERIS). As the comparison between discrete...

Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats, and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating at smaller scales however, such as the impact of benthic macrofauna on MPB development, to...

The algorithms of Novoa et al. (2017) and Gons et al. (2005) were recalibrated and applied to Sentinel2 data to retrieve suspended particulate matter (SPM) and chlorophyll a (chl a) concentration in the environmentally and economically important intertidal zones. Sentinel2-derived chl a and SPM concentration distributions were analyzed at the scale...

The accurate measurement of suspended particulate matter (SPM) concentrations in coastal waters is of crucial importance for ecosystem studies, sediment transport monitoring, and assessment of anthropogenic impacts in the coastal ocean. Ocean color remote sensing is an efficient tool to monitor SPM spatio-temporal variability in coastal waters. How...

Monte Carlo simulations are used to compute the uncertainty associated to light backscattering measurements in turbid waters using the ECO-BB (WET Labs) and Hydroscat (HOBI Labs) scattering sensors. ECO-BB measurements provide an accurate estimate of the particulate volume scattering coefficient after correction for absorption along the short instr...

The invasion of the wild oyster Crassostrea gigas along the western European Atlantic coast hasgenerated changes in the structure and functioning of intertidal ecosystems. Considered as an invasivespecies and a trophic competitor of the cultivated conspecific oyster, it is now seen as a resource byoyster farmers following recurrent mass summer mort...

AimThe spread of non-indigenous species in marine ecosystems world-wide is one of today's most serious environmental concerns. Using mechanistic modelling, we investigated how global change relates to the invasion of European coasts by a non-native marine invertebrate, the Pacific oyster Crassostrea gigas. LocationBourgneuf Bay on the French Atlant...

At the end of the SPOT4 mission, a four-month experiment was conducted in 2013 to acquire high spatial (20 m) and high temporal (5 days) resolution satellite data. In addition to the SPOT4 (Take5) dataset, we used several Landsat5, 7, 8 images to document the variations in suspended particulate matter (SPM) concentration in the turbid Gironde and L...

High resolution satellite data of the Medium Resolution Imaging Spectrometer in full resolution mode (MERIS FR, pixel size is 300 m) were used to study the impact of suspended particulate matter (SPM) on oyster-farming sites in a macrotidal bay of the French Atlantic coast where SPM concentration can exceed 100 g m-3. Because MERIS standard SPM con...

We examined the within-day variability in seawater optical properties and biogeochemical constituents for a high-latitude location in the Ross Sea, Antarctica, during development of the annual spring phytoplankton bloom. Measurements of particulate organic carbon concentration POC, chlorophyll-a concentration Chl, and particle size distribution wer...

Benthic microalgae can make a substantial contribution to the food web in coastal ecosystems, in particular diatoms, which dominate photo‐autotrophic assemblages in intertidal mudflats. They form dense biofilms in the most superficial sediment layers and contribute to their stabilization. Many studies investigated the spatio‐temporal dynamics of th...

Optical variability occurs in the near-surface and upper ocean on very short time and space scales (e.g., milliseconds and millimeters and less) as well as greater scales. This variability is caused by solar, meteorological, and other physical forcing as well as biological and chemical processes that affect optical properties and their distribution...

Time series measurements of fluctuations in underwater downward irradiance, Ed, within the green spectral band (532 nm) show that the probability distribution of instantaneous irradiance varies greatly as a function of depth within the near-surface ocean under sunny conditions. Because of intense light flashes caused by surface wave focusing, the n...

The changes in shape, amplitude, and timing in the diel variability of the particulate beam attenuation coefficient (cp) were investigated at 4 and 9 m during two seasonal cycles at an oceanic site in the northwestern Mediterranean Sea under contrasting physical and trophic situations. We observed a diel cycle in cp during the winter mixing of the...

1] A field characterization of the amplitude and periods of the underwater light field fluctuations is presented on the basis of field measurements of the downward and upward irradiances at a deep-sea mooring in the Mediterranean Sea (BOUSSOLE site). The optical time series at this site includes multispectral irradiance measurements at two depths a...