When I was for the first time on the Black Sea I was a little bit surprised to see so few signs of life on the beach. Also between the stones of the rare breakwaters nothing phenomenal. While I know more or less to identify more than a couple of lower animals near the breakwaters of the North Sea, I couldn’t find anything like that neither in Sunny Beach nor in Burgas. Back in the hotel where I looked it up I as surprised to read about the abundance of different species that find their habitat in the Black Sea and in perfect ecological harmony whereas the same species in other parts of the world rather cause an ecological disequilibrium.
The main phytoplankton groups present in the Black Sea are dinoflagellates, diatoms, coccolithophores, and cyanobacteria. Generally, the annual cycle of phytoplankton knows a significant diatom and dinoflagellate-dominated spring production. During summer months there is a weaker mixed assemblage of community development below the seasonal thermocline. In autumn a surface-intensified production. This pattern of productivity is also augmented by an Emiliania huxleyi bloom during the late spring and summer months.
Annual dinoflagellate distribution is defined by an extended bloom period in subsurface waters during the late spring and summer. In November, subsurface plankton production is combined with surface production. This is due to vertical mixing of water masses and nutrients such as nitrite.
The major bloom-forming dinoflagellate species in the Black Sea is Gymnodinium sp. Estimates of dinoflagellate diversity in the Black Sea range from 193 to 267 species. This level of species richness is relatively low in comparison to the Mediterranean Sea, which is attributable to the brackish conditions, low water transparency and presence of anoxic bottom waters. It is also possible that the low winter temperatures below 4 °C (39 °F) of the Black Sea prevent thermophilous species from becoming established. The relatively high organic matter content of Black Sea surface water favour the development of heterotrophic (an organism which uses organic carbon for growth) and mixotrophic dinoflagellates species (able to exploit different trophic pathways), relative to autotrophs. Despite its unique hydrographic setting, there are no confirmed endemic dinoflagellate species in the Black Sea.
The Black Sea is populated by many species of marine diatom, which commonly exist as colonies of unicellular, non-motile auto- and heterotrophic algae. The life-cycle of most diatoms can be described as ‘boom and bust’ and the Black Sea is no exception, with diatom blooms occurring in surface waters throughout the year, most reliably during March.
The phase of rapid population growth in diatoms is caused by the in-wash of silicon-bearing terrestrial sediments. When the supply of silicon is exhausted, the diatoms begin to sink out of the photic zone and produce resting cysts. Additional factors such as predation by zooplankton and ammonium-based regenerated production also have a role to play in the annual diatom cycle. Typically, Proboscia alata blooms during spring and Pseudosolenia calcar-avis blooms during the autumn.
Coccolithophores are a type of motile, autotrophic phytoplankton that produce CaCO3 plates, known as coccoliths, as part of their life cycle. In the Black Sea, the main period of coccolithophore growth occurs after the bulk of the dinoflagellate growth has taken place.
In May, the dinoflagellates move below the seasonal thermocline, into deeper waters, where more nutrients are available. This permits coccolithophores to utilise the nutrients in the upper waters, and by the end of May, with favourable light and temperature conditions, growth rates reach their highest. The major bloom forming species is Emiliania huxleyi, which is also responsible for the release of dimethyl sulfide into the atmosphere. Overall, coccolithophore diversity is low in the Black Sea, and although recent sediments are dominated by E. huxleyi, Braarudosphaera bigelowii, Holocene sediments have also been shown to contain Helicopondosphaera and Discolithina species.
Cyanobacteria are a phylum of picoplanktonic (plankton ranging in size from 0.2 to 2.0 µm) bacteria that obtain their energy via photosynthesis, and are present throughout the world’s oceans. They exhibit a range of morphologiies, including filamentous colonies and biofilms.
In the Black Sea, several species are present, and as an example, Synechococcus spp. can be found throughout the photic zone, although concentration decreases with increasing depth. Other factors which exert an influence on distribution include nutrient availability, predation, and salinity.
Zebra mussels are filter-feeding organisms. They remove particles from the water column. The zebra mussels process up to one liter of water per day, per mussel. Some particles are consumed as food, and feces are deposited on the lake floor. Nonfood particles are combined with mucus and other matter and deposited on lake floors as pseudofeces.
The lifespan of a zebra mussel is four to five years. A female zebra mussel begins to reproduce within 6–7 weeks of settling. An adult female zebra mussel can produce 30,000 to 40,000 eggs in each reproductive cycle, and over 1 million each year. Free-swimming microscopic larvae, called veligers, drift in the water for several weeks and then settle onto any hard surface they can find.
Zebra mussels also can tolerate a wide range of environmental conditions and adults can even survive out of water for about 7 days. Research on natural enemies, both in Europe and North America, has focused on predators, particularly birds (36 species) and fish (15 and 38 species eating veligers and attached mussels).
The Zebra Mussel is native to the Black and Caspian Sea. Everywhere else it was introduced and has become an invasive species as in North America, Great Britain, Ireland, Italy, Spain, and Sweden. They disrupt the ecosystems by monotypic colonization. They damage harbors and waterways, ships and boats, and water treatment and power plants.
The Common Carp’s native range extends to The Black Sea along with the Caspian Sea and Aral Sea. Like the Zebra mussel the Common Carp is an invasive species when introduced to other habitats.
The round goby is another native fish that is also found in the Caspian Sea. It preys upon Zebra mussels. Like the mussels and common carp it has become invasive when introduced to other environments, like the Great Lakes.
Marine mammals present within the basin include two species of dolphins (common and bottlenose) and harbour porpoise inhabit the sea although all of these are endangered due to pressures and impacts by human activities. All the three species have been classified as a distinct subspecies from those in the Mediterranean and in Atlantic Seas and endemic to Black and Azov Seas.
Critically endangered Mediterranean monk seals were historically abundant in Black Sea, and are regarded to have become extinct from the basin since in 1997. Monk seals were present at the Snake Island until 1950s, and several locations such as the Danube plavni nature reserve and Doğankent were last of hauling-out sites in post-1990. Very few animals still thrive in the Sea of Marmara.
Various species of pinnipeds, sea otter, and beluga whales were introduced into Black Sea by mankind and later escaped either by accidental or purported causes. Of these, grey seal and beluga whales have been recorded with successful, long-term occurrences.