A Multi-Species Investigation of Sponges’ Filtering Activity towards Marine Microalgae

Chronic discharge of surplus organic matter is a typical side effect of fish aquaculture, occasionally leading to coastal eutrophication and excessive phytoplankton growth. Owing to their innate filter-feeding capacity, marine sponges could mitigate environmental impact under integrated multitrophic aquaculture (IMTA) scenarios. Herein, we investigated the clearance capacity of four ubiquitous Mediterranean sponges (Agelas oroides, Axinella cannabina, Chondrosia reniformis and Sarcotragus foetidus) against three microalgal substrates with different size/motility characteristics: the nanophytoplankton Nannochloropsis sp. (~3.2 μm, nonmotile) and Isochrysis sp. (~3.8 μm, motile), as well as the diatom Phaeodactylum tricornutum (~21.7 μm, nonmotile). In vitro cleaning experiments were conducted using sponge explants in 1 L of natural seawater and applying different microalgal cell concentrations under light/dark conditions. The investigated sponges exhibited a wide range of retention efficiencies for the different phytoplankton cells, with the lowest average values found for A. cannabina (37%) and the highest for A. oroides (70%). The latter could filter up to 14.1 mL seawater per hour and gram of sponge wet weight, by retaining 100% of Isochrysis at a density of 105 cells mL−1, under darkness. Our results highlight differences in filtering capacity among sponge species and preferences for microalgal substrates with distinct size and motility traits.

Globally consistent assessment of coastal eutrophication

Eutrophication is an emerging global issue associated with increasing anthropogenic nutrient loading. The impacts and extent of eutrophication are often limited to regions with dedicated monitoring programmes. Here we introduce the first global and Google Earth Engine-based interactive assessment tool of coastal eutrophication potential (CEP). The tool evaluates trends in satellite-derived chlorophyll-a (CHL) to devise a global map of CEP. Our analyses suggest that, globally, coastal waters (depth ≤200 m) covering ∼1.15 million km2 are eutrophic potential. Also, waters associated with CHL increasing trends—eutrophication potential—are twofold higher than those showing signs of recovery. The tool effectively identified areas of known eutrophication with severe symptoms, like dead zones, as well as those with limited to no information of the eutrophication. Our tool introduces the prospect for a consistent global assessment of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs) and the application of Earth Observations in support of SDGs.

Globally Consistent Assessment of Coastal Eutrophication

Eutrophication associated with increasing anthropogenic nutrient loading is an emerging global concern. Often, eutrophication is concomitant with negative impacts on ecosystems and human well-being. Nevertheless, the impacts and the extent of eutrophication are limited to regions with dedicated monitoring programmes. Here we introduce the Global Eutrophication Watch, the first global and interactive assessment map of coastal eutrophication potential (CEP). It is constructed on Google Earth Engine and it evaluates temporal trends in satellite chlorophyll-a (CHL), a proxy for phytoplankton biomass, to devise a global map of CEP. Our analyses suggest that, globally, coastal waters (depth ≤200 m) covering ~1.15 million km2 are eutrophic potential. We found that waters associated with CHL increasing trends—those with potential for further deterioration of water quality—are twofold higher than those showing signs of recovery. The tool effectively identified areas of known eutrophication with severe symptoms, such as dead zones, as well as those with limited to no information of the eutrophication. Our tool introduces the prospect for a consistent global assessment of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs). This work contributes to the application of Earth Observations in support of SDGs.

Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modelling approach using C-GEM

Estuaries are key reactive ecosystems along the land–ocean aquatic continuum, with significant ecological and economic value. However, they have been facing strong morphological management changes as well as increased nutrient and contaminant inputs, possibly leading to ecological problems such as coastal eutrophication. Therefore, it is necessary to quantify the ingoing and outgoing fluxes of the estuaries, their retention capacity, and estuarine eutrophication potential. A 1-D Carbon–Generic Estuary Model (C-GEM) was used to simulate the transient hydrodynamics, transport, and biogeochemistry for estuaries with different sizes and morphologies along the French Atlantic coast during the period 2014–2016 using readily available geometric, hydraulic, and biogeochemical data. These simulations allowed us to evaluate the budgets of the main nutrients (phosphorus [P], nitrogen [N], silica [Si]) and total organic carbon (TOC), and their imbalance with respect to estuarine eutrophication potential. Cumulated average annual fluxes to the Atlantic coast from the seven estuaries studied were 9.6 kt P yr−1, 259 kt N yr−1, 304 kt Si yr−1, and 145 kt C yr−1. Retention rates varied depending on the estuarine residence times, ranging from 0–27 %, 0–34 %, 2–39 %, and 8–96 % for TP, TN, DSi, and TOC, respectively. Large-scale estuaries had higher retention rates than medium and small estuaries, which we interpreted in terms of estuarine residence times. As shown by the indicator of eutrophication potential (ICEP), there might be a risk of coastal eutrophication, i.e., the development of nonsiliceous algae that is potentially harmful to the systems studied due to the excess TN over DSi.

Globally Consistent Assessment of Coastal Eutrophication

Eutrophication associated with increasing anthropogenic nutrient loading is an emerging global concern. Often, eutrophication is concomitant with negative impacts on ecosystems and human well-being. Nevertheless, the impacts and the extent of eutrophication are limited to regions with dedicated monitoring programmes. Here we introduce the Global Eutrophication Watch, the first global and interactive assessment map of coastal eutrophication potential (CEP). It is constructed on Google Earth Engine and it evaluates temporal trends in satellite chlorophyll-a (CHL), a proxy for phytoplankton biomass, to devise a global map of CEP. Our analyses suggest that, globally, coastal waters (depth ≤ 200 m) covering ~ 1.15 million km2 are eutrophic potential. We found that waters associated with CHL increasing trends—those with potential for further deterioration of water quality—are twofold higher than those showing signs of recovery. The tool effectively identified areas of known eutrophication with severe symptoms, such as dead zones, as well as those with limited to no information of the eutrophication. Our tool introduces the prospect for a consistent global assessment of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs). This work contributes to the application of Earth Observations in support of SDGs.