Sea
Biodiversity loss is a critical global challenge, particularly in oceans and seas, due to human-induced habitat degradation. UNESCO warns that without intervention, over half of marine species could face extinction by 2100. Oceans and seas play a significant role in climate regulation, absorbing about a third of yearly carbon dioxide emissions. Marine and coastal ecosystems support diverse plant and animal species, providing valuable ecosystem services. These services, including coastal erosion prevention and nutrient cycling, rely on maintaining a healthy environment. For example, mangroves act as natural barriers and whale faeces provide essential iron for phytoplankton growth, crucial for carbon storage. Figure 4-9 illustrates an exhaustive list of these ecosystem services (NatureScot, 2022).
Beyond safeguarding ecosystems and maintaining high water quality, it may be possible to restore biodiversity in marine areas that have undergone degradation. The MERCES project focuses on rejuvenating biologically depleted regions in Europe's seas by reintroducing key species, such as plants and corals. Successful habitat rejuvenation offers hope for ecosystems to recover from human-induced damage. In Mediterranean, Baltic, and North Atlantic seagrass meadows, seaweed species are being replanted, while gorgonians (sea fans) and other corals are reintroduced in hard-bottom and deep-sea habitats, respectively. These efforts have shown promising results, with population resurgence ranging from 50% to 90% depending on the species involved (EU Horizon, 2019).
Preventing overfishing through enforced policies constitutes a key measure for biodiversity restoration. According to a 2015 report by the European Commission, a significant 74% of fish stocks in the Black Sea were categorized as over-exploited, fully exploited, or depleted, with only 17% having managed to recover from damage. In 2021, the European Parliament's Committee on Fisheries (PECH) approved a report by Bulgarian MEP Hristov, addressing challenges and opportunities within the Black Sea fisheries sector. The report underlines the prevalent issue of overfishing in the Black Sea and calls for prompt action to tackle the matter.
In the Black Sea, algae blooms are a significant concern, triggered by favorable environmental conditions like increased nutrients, warm temperatures, abundant light, and low wind. Human activities, such as agricultural runoff or malfunctioning septic systems, exacerbate this issue by introducing excessive nutrients, leading to eutrophication and intensified algal blooms. Harmful algal blooms can have toxic effects on aquatic life, including people, fish, shellfish, marine mammals, and birds. Even non-toxic blooms can deplete oxygen levels, obstruct light access, and hinder fish gill function. A satellite image from 2016 (Figure 4-10) shows light blue hues around the sea's midpoint, likely indicating blooming phytoplankton (NASA Earth Observatory, 2016). The Black Sea hosts over 150 types of phytoplankton, supporting diverse marine life. Coccolithophores, microscopic plankton with white calcium carbonate plates, contribute to visible white blooms. While the central region of the sea remains deep and anoxic, shallower areas near coasts experience mixing and sediment disturbance, visible as brown and green hues after heavy rainfall or near major river mouths like the Danube. Increased interest in water quality in coastal and marine areas stemming from the Water Framework Directive and the Marine Strategy Framework Directive has led to important questions in relation to policies that address nutrient loadings.
Nature-based Solutions can safeguard biodiversity and water quality in the Black Sea through the utilisation of excessive algae. While there are practical challenges with diverting seawater there is potential for the harvesting and production of algae for use in bioenergy production, a subject which continues to receive worldwide attention. Due to high growth rates and productivity of biofuel pre-cursor molecules, microalgae potentially represent a valuable feedstock for renewable energy production (Arora et al., 2021). Furthermore, algae can also be used for animal and human food. It is the original source of omega-3 in fish oil food supplements, spirulina and other so-called “superfoods”. Algae can also produce natural food pigments, including the natural blue colour and has many other uses in pharmaceuticals and cosmetics industries. The output from such an algae plant could be filtered and cleaned seawater, discharged back into the Black Sea. The potential of algae in bioremediation while being a useful by-product is discussed by Alazaiza et. al, (2022).