In Russia the Far East Marine Reserve (FEMR) is the Federal Nature Reserve with the richest but insufficiently studied biodiversity. Spatiotemporal variations in the zooplankton dwelling in the area were sporadically observed over 20 years ago. The recent investigation focused on the species composition, population density and distribution of copepods – the basic member of zooplankton in FEMR. Samples of plankton were taken from 10 stations above the 50-m isobath monthly during June – September 2012, the months when temperature in the seawater area varies widest. The Calanoida and Cyclopoida copepods were represented by 17 and by 4 species, respectively; 21 species altogether. Genera Acartia and Oithona had larger diversity – by 4 species each. Marine species dominated in the samples (80 % of the total species number), neritic – in the biotope (58 %). The copepods were boreal (55 %) and tropical + subtropical (45 %). Species number increased to 16 in June and dropped to 5 in September. Oithona similis and Pseudocalanus newmani dominated during June – July, Paracalanus parvus, Oithona brevicornis and O. similis – in August, and P. parvus and O. brevicornis – in September. The abundance and diversity decreased in all areas of the reserve from June to September. In June, when the cold-water O. similis, P. newmani, Acartia hudsonica и Eurytemora pacifica prevailed, the average population density (20959±3007 ind.·m-3) maximally increased and in September it was minimal. Concentrations of copepods were largest (to 36 thousand ind.·m-3) above the 10-m depth in the Gulf of Posyet (western FEMR) in June. Cluster analysis applied to the total seawater area of the reserve evaluated Bray – Curtis coefficient as 60 %; three plankton copepod complexes were determined, species composition in each formed under the influence of the water mass. The complexes from the west and the east of FEMR had larger species richness and population density. In the shallow-water western complex high densities of brackish-water copepods (genera Acartia, Eurytemora, Centropages, Tortanus and Pseudodiaptomus) suggested presence of estuarine and coastal waters whereas tropical and subtropical O. nana, Mesocalanus tenuicornis, Pseudodiatomus inopinus – warm-water intrusion from the East Korea current. The concurrent presence of cold- and warm-water copepods in the deep-water eastern complex in summer evidenced the water stratification effect when cold water from the Sea of Japan dominated in the depth and its warmer modification – in the upper seawater layer. The diversity and density were poorest in the southern complex, largely of Panthalassa and neritic copepods. In summer, large presence of cold-water copepods O. similis and P. newmani indicated the cold-water mass penetration to near-bottom layer; numbers estimates of these copepods can represent the degree of the cold-water effect in the south of the reserve. The copepod distribution, stable abundance and diversity in the seawater area south of FEMR suggested desalination by the river influx and, possibly, harmful impact of pollutants. Species composition and quantitative characteristics of copepods can be used for environmental quality determination in different areas of FEMR.
The sequence of local recolonization of warm-water marine molluscan species during a deglacial warming climate phase: a case study from the early Pleistocene of the Sea of Japan