Algae as Living Sensors: What Microscopic Blooms Can Reveal About the Health of the Black Sea
Algae are usually noticed when they become impossible to ignore: a green layer on the water surface, seaweed washed onto the shore, an unpleasant smell near the coast, or a bloom that suddenly changes the colour of the sea. Yet for scientists, algae are not only a visible sign that something is happening in the marine environment. They are also among the first organisms to respond when conditions in the water begin to change.
This makes them powerful biological indicators. Algae react quickly to shifts in nutrients, temperature, sunlight, oxygen, salinity and pollution pressure. A rapid increase in algal biomass can point to nutrient enrichment from agricultural runoff, wastewater or river discharge. A change in the species present can suggest that water quality is changing. A bloom may reflect a combination of warmer temperatures, stable water layers, high nutrient availability and human pressure along the coast.
In the Black Sea, these signals are especially important. The basin is semi-enclosed, with limited water exchange with the Mediterranean and strong influence from major rivers such as the Danube, Dnieper and Dniester. These conditions make the region sensitive to eutrophication and algal bloom events. When blooms become excessive, they can reduce water quality, block light, contribute to oxygen depletion and affect biodiversity, fisheries, aquaculture, tourism and coastal communities.
However, algae should not be seen only as a problem. They are part of the natural functioning of marine ecosystems and form the base of many aquatic food webs. The challenge is to understand when normal growth becomes a warning signal. This requires looking not only at how much algae is present, but also at which species are appearing, where they are accumulating and what environmental conditions are driving their growth.
This is where field science becomes essential. Within the AlgaeRevive project, monitoring activities along the Romanian Black Sea coastline have started to turn visible coastal changes into measurable scientific evidence. Between May and August 2025, researchers from Ovidius University of Constanța carried out systematic fieldwork at five monitoring stations between Cape Midia and Vama Veche. Four samples per month were collected at each station, with each sample measuring 400 cm³ and preserved for further laboratory analysis.
Initial results identified 13 algal species. Green algae dominated the samples, with eight species representing 61.54% of the identified taxa. Red algae accounted for three species, or 23.08%, while brown algae were represented by Scytosiphon lomentaria, making up 15.38%. The estimated quantities of stranded algae ranged from 0.22 kg/m² to 3.46 kg/m².
These figures show why algae monitoring matters. What may look like ordinary seaweed accumulation on the beach can contain valuable information about species composition, biomass, decomposition patterns and ecosystem pressure. Over time, this type of data can help scientists identify trends, compare locations and better understand the environmental drivers behind bloom formation.
At the same time, algae monitoring is becoming increasingly digital. Satellite data can provide large-scale information on chlorophyll-a, phytoplankton biomass, sea surface temperature and other indicators across broad areas. Chlorophyll-a is especially useful because it is widely used as a proxy for phytoplankton biomass. When combined with field observations and water-quality measurements, it can help researchers detect changes that may not be visible from the coast.
Through AlgaeSense, the AlgaeRevive project is working to connect these different layers of information. The tool is designed to support algal bloom analysis and forecasting by combining historical environmental data, satellite information, in-situ measurements and artificial intelligence. Instead of looking at algae only after a bloom has already appeared, this approach aims to improve early detection and support more informed decision-making.
For coastal regions, this matters far beyond scientific research. Earlier and more accurate monitoring can help public authorities plan responses, support environmental agencies in assessing water quality, and provide useful information for fisheries, aquaculture, tourism and coastal communities. It can also help communicate environmental risks more clearly, especially in areas where pollution, climate pressure and human activity overlap.
The ALGAE K-HUB supports this wider effort by making algae-related knowledge, field data, reports, tools and learning materials more accessible to researchers, public institutions, SMEs and environmental organisations. By bringing scientific resources into a shared space, the platform helps transform algae monitoring from a specialised research activity into a practical source of knowledge for the Black Sea region.
Algae are small, but the signals they carry are significant. They can show when ecosystems are under pressure, when pollution is changing coastal waters and when environmental conditions are moving toward imbalance. If we learn to read these signals early enough, algae can become more than a symptom of marine stress. They can become part of the solution.
Sources and Further Reading
- NOAA Ocean Service, “What are harmful algal blooms?”
https://oceanservice.noaa.gov/education/tutorial-coastal/harmful-algal-blooms/habs01.html - NOAA Ocean Service, “Are all algal blooms harmful?”
https://oceanservice.noaa.gov/facts/habharm.html - NOAA Ocean Service, “Why do harmful algal blooms occur?”
https://oceanservice.noaa.gov/facts/why_habs.html - NOAA Fisheries, “Effects of Harmful Algal Blooms on West Coast Fishing Communities”
https://www.fisheries.noaa.gov/west-coast/science-data/effects-harmful-algal-blooms-west-coast-fishing-communities - European Commission / CINEA, “Study to Support a Sustainable EU Algae Industry”
https://cinea.ec.europa.eu/publications/digital-publications/study-support-eu-sustainable-algae-industry_en - Copernicus Marine Service
https://marine.copernicus.eu/ - AlgaeRevive project reporting materials, Period 3, May–September 2025
Photo by Solen Feyissa on Unsplash
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