Ostracods in the Plankton of the Sivash Bay (The Sea of Azov) During Its Transformation From Brackish to Hypersaline State

Abstract

<jats:p>Bay Sivash (the Sea of Azov), the largest lagoon in Europe, demonstrates a sharp ecosystem change due to anthropogenic impact. A pronounced salinity increase occurs as a result of the decision to stop supplying Dnieper water into the North-Crimean Canal. Salinity has increased from 20–22 g/L to 55–75 g/L in the lagoon. This led to the changes of biotic composition. The authors used data on ostracod species composition and abundance in samples of 2014–2016 samples with comparison with data from samples collected in 2004, before the salinity increase. The identification of ostracod species in the Sivash Bay was first made; five species was found in 2004–2016: Cyprideis torosa (Jones, 1850), Loxoconcha bulgarica Caraion, 1960, Loxoconcha aestuarii Marinov, 1963, Cytherois cepa Klie, 1937, Leptocythere devexa Schornikov, 1966. In June and August 2004, the average ostracod abundance in plankton was 22 ind./m3 (CV = 1.506). In October 2014, the ostracod abundance in the plankton reached 210 ind./m3, and in August 2015 – average of 1273 ind./m3 (CV = 1.220). In some plankton samples, ostracods dominated in numbers and reached 3850 ind./m3. In the salinity range of 50–80 g/L, a significant positive correlation was observed between total ostracod abundance in plankton and salinity.</jats:p>

Do separated taxa react differently to a long-term salinity increase? The meiobenthos changes in Bay Sivash, largest hypersaline lagoon worldwide

“…in some samples (Drapun et al, 2017). Similar trends in the changes of the bottom meiobenthos were observed in the Aral Sea during a long-term salinity increase from brackish water up to 88-109 g l À1 (Mokievsky, 2009).…”

“…In 2015, the average contribution of Ostracoda to the total abundance of the bottom meiobenthos was 17% varying from <1 to 56% in the samples . In 2015, ostracods were also abundant in plankton, dominating FO À frequency of occurrence; D À species was dominant; SD À species was subdominant; 1data from Kolesnikova et al, 2017 andDrapun et al, 2017;2 -data for 2004; ** À found only in the plankton samples at salinity of 30 g l À1 ; * À found only in the plankton samples at salinity of 52 g l À1 ; *** À found only at salinity of 30 g l À1 ; **** À without species found only at salinity 30 g l À1 .…”

“…High TSS and its sedimentation rate suppress distribution and abundance of the phytobenthos and the meiobenthos more than salinity changes (Gambi et al, 2003) due to depressing primary production as well as feeding and reproduction of animals (Gambi et al, 2003;Shadrin and Litvinchuk, 2005;Farkas et al, 2017). Floating mats of filamentous green algae C. siwaschensis became an important component of the Sivash ecosystem from 2015 and occupy large areas reaching high biomass of up to 2 to 3 kg m À2 (wet mass) (Drapun et al, 2017;. Such floating mats also played a very important role in hypersaline Bay Sivash before construction of the North-Crimea Canal (Vorobyev, 1940).…”

“…A study conducted in 2015 showed that salinity increased in the Bay fluctuating between 28 and 75 g l À1 in 2015 . A new ecosystem transformation had begun in the lagoon with changes occurring in all ecosystem components including the meiobenthos (Drapun et al, 2017;Kolesnikova et al, 2017;Sergeeva et al, 2019). From 2015, filamentous green algae Cladophora siwaschensis C. Meyer again formed floating mats with biomass (ww) up to 2.5-3.0 kg m À2 and which occupy large areas in the bay; hypoxic and even anoxic conditions often occur beneath them (Drapun et al, 2017;.…”

Photosynthetic Activity of Green Filamentous Algae Mats in the Hypersaline Lake Сhersonesskoye (Crimea)

“…Какая часть этой первичной продукции потребляется в озере гетеротрофами, а какая захоранивается в донных отложениях? В крымских гиперсоленых водоемах, включая озеро Херсонесское, в матах нитчатых зеленых водорослей наблюдали очень высокие численности животных и инфузорий, намного превышающие таковые в планктоне (Ivanova et al, 1994;Kolesnikova et al, 2008;Павловская и др., 2009;Шадрин и др., 2016;Drapun et al, 2017;Kolesnikova et al, 2017;Shadrin et al, 2017). Зная средние размеры животных и хорошо известные зависимости массы тела от его длины, интенсивности метаболизма и скорости роста от массы тела в различных группах беспозвоночных животных (Винберг, 1979;Ivanova et al, 1994;Балушкина и др., 2009), можно рассчитать примерный суммарный рацион, животных, обитающих в матах.…”