Biodiversity, distribution and abundance of zooplankton in the Iranian waters of the Caspian Sea off Anzali during 1996–2010

Abstract

The mesozooplankton of the south-western Caspian Sea, off Anzali, sampled from 1996–2010, had undergone severe changes, especially after the year 2001, when the invasive ctenophore Mnemiopsis leidyi bloomed for the first time. Native species vanished or decreased, while invasive species such as Pleopis polyphemoides, Acartia tonsa, M. leidyi and the larvae of Balanus sp., plus Hediste diversicolor dominated the zooplankton. It could be stated that the increasing amount of nutrients since the early 1980s led to a decrease of endemic species and smoothed the way for opportunistic invader species, which outcompeted and depleted the endemic species in their turn. However, the major changes in the zooplankton community and possibly the blooming of M. leidyi during 2001–2002 were triggered by changing weather patterns, when a period with heavy rain at the end of the 1990s was followed by a prolonged drought (2001–2002). It is not clear to what extent M. leidyi was responsible for the disappearance of endemic Copepoda and Cladocera species such as Eurytemora grimmi, Limnocalanus grimaldii, Cercopagis pengoi, and Polyphemus exiguous, because the mesozooplantic invader species seemed to be more successful competitors than the endemic Caspian Sea fauna. Compared with other areas of the Caspian Sea, the development of the M. leidyi stock was moderate in the area under investigation. Mnemiopsis leidyi numbers and biomass increased from the beginning of sampling in 2001 to about 600 n.m−3 and 40–60 g wet weight m−3 until 2003. Since then the stock oscillated in this range until 2010.

Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia

“…For the Ebro river delta, abundances of > 100 individuals/m 3 were reached in 2011 and 2012 (Supporting Information Appendix S2, Table S1). Although this is an order of magnitude lower in comparison with high‐abundance areas in northern Europe and the Caspian Sea (Bagheri et al, ; Riisgård et al, ; Roohi et al, ; van Walraven et al, ), the occurrence of year‐round populations since first recording indicates that M. leidyi is established especially along the Spanish Mediterranean coastline. However, additional high‐abundance areas are likely to be detected, for example, along the Italian coast.…”

“…Mnemiopsis leidyi has established year‐round populations in the Black and Caspian Seas (Supporting Information Appendix 2, Table S1), with maximal abundances of > 1 individual/L documented for the latter area (Bagheri, Niermann, Mansor, & Yeok, ; Roohi et al, ). The invasion history in the South suggests that, aided through ocean currents, M. leidyi spread from the Black Sea to the Sea of Azov in 1988.…”

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“…For instance, the annual average temperature finding in 2003 (18.1±7.07°C) was higher than the finding in 2004 (20.3±5.42°C). But, although some researchers reported that there was an increase trend in annual average temperature values of the Caspian Sea during 2001 and 2002 (Bagheri et al, 2010(Bagheri et al, , 2014, it is difficult to say that there was an increase trend in annual average temperature values according to previous years, because there was no regular data during the period of study.…”

“…On the other hand, there are other factors such as climatological and hydrological regimes of the systems effecting contribution levels of different taxonomic groups to total phytoplankton. For instance, Bagheri et al (2010Bagheri et al ( , 2014 reported that the arresting shifts in community structure of phytoplankton in the south western Caspian Sea could be connected to changes in the atmospheric and hydrological regimes of the basin since the early 1990s in addition to anthropogenic impacts. On the other hand, there were additional silicate and phosphate inputs to the system by river discharges.…”

“…The middle Caspian (Kosarev and Yablonskaya, 1994;Dumont, 1998;Kideys and Moghim, 2003;Kideys et al, 2005a;Hosseini, 2011). Due to the extensive agricultural utilization and deforestation of woodlands, the nutrient loads of rivers have increased since the early 2000s (Kideys et al, 2008;Bagheri et al, 2014). The increased nutrient load in the south western of the Caspian Sea after 2000 caused a raise in primary production supported by high phytoplankton abundance (Bagheri et al, 2012b(Bagheri et al, , 2012c.…”