Population Dynamic And Effects Of The Invasive Species Ctenophore Mnemiopsis Leidyi In The Southern Caspian Sea

In this study, M. leidyi population, plankton abundance, biomass and species composition and interaction between environmental and biological characteristics were evaluated in the Iranian coasts of the Caspian Sea from 2001 until 2006. Dalam kajian ini, populasi M. leidyi, kelimpahan plankton, biojisim dan komposisi spesies serta interaksi antara persekitaran dan aspek biologi telah dikaji di persisiran pantai Laut Caspian, Iran pada tahun 2001 hingga 200

Monitoring and rearing survey of Mnemiopsis leidyi in the southern of Caspian Sea

With the arrival of the invasive comb jelly Mnemiopsis leidyi in the Caspian Sea in 1991, extensive changes have been occurred. Therefore, this project aims to investigate the comb jelly M. leidyi monitoring and rearing in the southern Caspian Sea in 2013. To survey of M. leidyi and zooplankton abundance and biomass, sampling was carried out during the four seasons at spring, summer, autumn and winter in 4 half-transect (Anzali, Tonekabon, Noshar and Amirabad) and also samples for the ctenophore rearing was done at depths of 5, 10 and 20m. Sampling was performed with a 500 and 100 μ plankton net vertically at layers of 0-5, 0-10 and 0-20 m. 12 aquaria of 50 L volume were designed with salinity of the Caspian Sea to study the breeding and fecundity with aeration. 3 of aquariums with salinity of 9±1pp, 3 with 11±1ppt and 3 of 12±1 ppt filled with Caspian Sea water. Water temperature in each of the three treatments was set in 20±2oC, 23±2^oC and 25±2^oC. 3 of aquaria were set at the salinity of 12.5 ppt and at the same temperature of the Caspian Sea (20, 23, 25^oC) as control. Mean annually Mnemiopsis abundance and biomass were 16.8±1.5 ind.m^3 (139.5±41.1 ind.m^2) and 1.9±0.1 g.m^3. (5.3±0.7 g.m^2). Maximum mean abundance was recorded in autumn with 36.6.7±13.8 ind.m^3 (355.1±103.6 ind.m^2) and maximum biomass was observed in summer of 1.9±0.2 g.m^3(15.0±1.5 g.m^2). Minimum mean abundance was found in spring with 1.3±0.5 ind.m^3 and minimum biomass was in winter of 0.01±0.005 g.m^3. Regional distribution of M. leidyi in the southern Caspian Sea showed aggressive area in terms of density and biomass are areas with significant differences (P<0.05). Comb jelly population showed that both West and East in terms of abundance and biomass were similar but different with the central region. Eastern and western regions compared to the central region have the higher abundance. Laboratory studies on M. leidyi reproduction of different sizes at different temperatures showed an average of 12 eggs per day spawning. Maximum spawning rate was registered with 115 eggs per day, for M. leidyi of 46-15 mm (0/7-9/7 g) which increased with increasing size. Average M. leidyi spawning recorded in 11ppt with 25oC was twice in 12ppt (14 eggs. Day^-1 ) while in salinity of 12ppt of 23^oC the fecundity was two half-times in temperature of 25oC and equal of 20oC. Maximum M. leidyi fecundity was recorded at 23^oC with salinity of 12±1ppt with 22.8±35.5 eggs.day^-1. There was a direct regression between size and weight fecundity of M. leidyi, in which fecundity of more than 16 mm length showed the maximum spawning. Based on the study looks at the rise and persistence parameters of comb jelly, it seems two main factors such as water temperature to the desired value, especially in summer (22-30°C), and food availability (zooplankton) have more roles in the increasing of M. leidyi the southern of the Caspian Sea. After the invasion of M. leidyi into the Caspian Sea, not only the abundance and biomass of zooplankton decreased but also the species diversity decreased from 36 to 15 species. Hence, it seems the decline in the South Caspian comb jelly was due to decreased of fecundity for lack of zooplankton feeding resources

Factors Influencing the Invasion of the Alien Ctenophore Mnemiopsisleidyi Development in the Southern Caspian Sea

Mnemiopsis leidyi population activities first were recorded during the coastal observations in 2001 in which its population considerably increased afterward and now sustained the southern Caspian Sea. Maximum summer-autumn M. leidyi abundance was recorded in euphotic layer in 2002 (851±85 ind.m-3) and maximum biomass was in 2001 with 48.1±14.4 g.m-3) while minimum were in aphotic layer. In years 2003 to 2011, M. leidyi abundance and biomass sharply declined to 1-843 ind.m-3 and 0.07-37.7 g.m-3, respectively. The length-frequency distribution of Mnemiopsis showed larval, juveniles and transitional stages that made up 98.6% of the total population. In the southern Caspian Sea, Acartia tonsa was the highest number of mesozooplankton species (36 species) which decreased tenfold after Mnemiopsis invasion during 2001-2010. Fecundity experiments of Mnemiopsis showed the average of 8 eggs. day-1, with a maximum of 35 eggs.day-1which increased with increasing body length. The main food was larger amounts of zooplankton prey such as copepodites and adult of A. tonsa. It seems the sharp decreased of Mnemiopsis abundance could be related the decreasing of ova reproduction; and food ability is the main reasons of M. leidyi sustained in the southern Caspian Sea. The objective of present study was to provide information about parameters influencingthe M. leidyi decreased after initial bloom invasion in the southern Caspian Sea

The response of phytoplankton assemblages to environmental parameters in the Azad Dam Lake in the west of Iran

Seasonal variations of phytoplankton abundance, species composition, and their interaction with environmental parameters were investigated in the Azad Dam Lake, in the West of Iran during 2015–2016. Sampling was conducted seasonally at five stations in the lake. Multivariate statistical analyses were carried out to define the abiotic variables influencing phytoplankton community composition. A total of 51 taxa of phytoplankton belonging to six phyla were identified. Bacillariophyta (diatoms) were most diverse with 22 taxa, comprised more than 90% of the total density. Despite the low Shannon–Wiener index (H ′) diversity (0.10–1.54), pointing out the dominant density of Bacillariophyta resulted in high water quality. Statistical analysis showed seasonal phytoplankton assemblages differences indicating a biogeographical gradient. Distance-based Linear Model (DisTLM) analysis displayed six environmental variables showing significant relationships with the phytoplankton abundance in the resemblance matrix (p < 0.05). Based on Akaike's information criterion (AIC), the combination of total phosphorus (TP), water temperature (WT), Secchi disc depth (SD), total nitrogen (TN), nitrite (NO2−), and dissolved oxygen (DO) by the DisTLM model elucidated 63.1% of the total variability. Since the dam is newly constructed and has not yet been exploited, and the factors caused by human activities that threaten the lake have not yet spread much, findings of the present study suggest Azad Dam Lake appears to have been not highly affected by anthropogenic activities up to now.This paper investigates the variation of the phytoplankton community and its interaction with environmental parameters in the Azad Dam Lake in Iran. We show that the diversity index was low, pointing out a high level of Bacillariophyta dominance. Moreover, environmental variables show significant relationships with phytoplankton abundance

Changes in biodiversity of phytoplankton, zooplankton, fishes and macrobenthos in the Southern Caspian Sea after the invasion of the ctenophore Mnemiopsis Leidyi

Monitoring for 6 years (2001-2006) showed that the population explosion of the alien ctenophore Mnemiopsis leidyi in the southern Caspian Sea coincided with a decline in the abundance and species number of mesozooplankton. While this decline appeared to have reduced the nourishment of sprat (also known as kilka), it seemed to have affected phytoplankton favorably mainly due to the decrease in grazing pressure. During 2001-2002, when M. leidyi abundance and biomass were at their highest levels, abundance of dinoflagellates and cyanophytes exceeded that of diatoms. Before the invasion (1996) and in some years after the invasion (2003, 2004 and 2006) diatom abundance was higher than the abundance of other groups. In September 2005, an unprecedented bloom of the toxic cyanophyte Nodularia sp. was observed in the southern Caspian Sea. Disappearance of edible zooplankton such as Eurytemora spp. was among the first changes observed after the expansion of M. leidyi in the area. Some changes in the macrobenthic fauna were also conspicuous after the increase of this ctenophore. While the biomass of some deposit feeders, such as the polychaete Nereis diversicolor and oligochaete species increased, benthic crustaceans decreased sharply in abundance during 2001-2003 and completely disappeared during 2004-2006. Iranian catches of kilka, the most abundant and widespread zooplanktivorous fish, decreased significantly in the southern Caspian Sea after 1999. Iranian landings of kilka dropped similar to 70% from 69,070 +/- A 20,270 t during 1995-2000 to 23,430 +/- A 12,240 t during 2001-2006, resulting in a loss of at least 125 million US dollars to the economy. There were also changes in the total catches of large predators such as the kutum and mullet, which mainly feed on kilka, between 1991 and 2006