Abstract
Aim The unique aquatic Pontocaspian (PC) biota of the Black Sea Basin
(BSB) is in decline. Lack of detailed knowledge on the status and trends
of species, populations and communities hampers a thorough risk
assessment and precludes effective conservation. This paper aims to
review PC biodiversity trends using endemic molluscs as a model group.
We aim to assess changes in PC habitats, community structure and species
distribution over the past century and to identify direct anthropogenic
threats. Location Black Sea Basin (Bulgaria, Romania, Moldova, Ukraine
and Russia). Methods Presence/absence data of target mollusc species was
assembled from literature, reports and personal observations. PC
biodiversity trends in the NW BSB coastal regions were established by
comparing 20th and 21st century occurrences. Direct drivers of habitat
and biodiversity change were identified and documented. Results A very
strong decline of PC species and communities during the past century is
driven by a) damming of rivers, b) habitat modifications negatively
affecting salinity gradients, c) pollution and eutrophication, d)
invasive alien species and e) climate change. Four out of 10 studied
regions, namely, the Danube Delta – Razim Lake system, Dniester Liman,
Dnieper-South Bug Estuary and Taganrog Bay-Don Delta contain the entire
spectrum of ecological conditions to support PC communities and still
host threatened endemic PC mollusc species. Distribution data is
incomplete, but the scale of deterioration of PC species and communities
is evident from the assembled data, as are major direct threats. Main
conclusions PC biodiversity in the BSB is profoundly affected by human
activities. Standardised observation and collection data as well as
precise definition of PC biota and habitats are necessary for targeted
conservation actions. This study will help to set the research and
policy agenda required to improve data collection to accommodate
effective conservation of the unique PC biota.