Aboulghasem Roohi

Bio: Aboulghasem Roohi is an academic researcher. The author has contributed to research in topics: Zooplankton & Mnemiopsis. The author has an hindex of 4, co-authored 9 publications receiving 134 citations.

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

Abstract: 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 ~70% from 69,070 ± 20,270 t during 1995–2000 to 23,430 ± 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.

Long-term changes in fecundity of the Kutum, Rutilus frisii kutum Kamensky, 1901, in the Caspian Sea (Osteichthyes: Cyprinidae)

Abstract: Changes in length, weight and fecundity of mature females of the Kutum (Rutilus frisii kutum) were compared for the periods 1948–1950, 1974 and 2007 in Iranian waters of the Caspian Sea. The average fork length decreased from 54.1 over 44.7 to 43.9 cm and the average weight from 2181 over 1295 to 1210 g. However, the average condition factor has remained fairly constant and varied between 1.35 and 1.38. The potential fecundity of the Kutum for the three periods also decreased from 106,800 over 74,600 to 64,400 eggs. Size and fecundity of the Caspian Kutum has therefore sharply declined during the last six decades. The reduction of fecundity is apparently the consequence of the shift towards smaller fish size.

Mnemiopsis leidyi Invasion and Biodiversity Changes in the Caspian Sea

Abstract: 1.1 Caspian Sea The complex history of the Caspian Sea formation has lead to a variety of different habitats. Like Australia, the Caspian Sea became isolated thousands of years ago (Plate 1). This isolation led to the speciation of many rare animals in particular the sturgeon. The Caspian Sea is the biggest enclosed body of water on Earth, having an even larger area than that of the American Great Lakes or that of Lake Victoria in East Africa. It is situated where the South-Eastern Europe meets the Asian continent, between latitudes 47 .07N and 36 .33N and longitudes 45 .43E and 54 .20E. It is approximately 1,030 km long and its width ranges from 435 km to a minimum of 196 km. It has no connection to the world’s oceans and its surface level at the moment is around _26.5 m below MSL. At this level, its total coastline is some 7,000 km in length and its surface area is 386,400 km2. The water volume of the lake is about 78,700 km3.

The Effect of the Ctenophore Mnemiopsis leidyi (Ctenophora: Lobata) on the Population Density and Species Composition of Mesoplankton in Inshore Waters of the Caspian Sea

Abstract: This paper examined the qualitative and quantitative of food composition of the ctenophore Mnemiopsis leidyi, as well as its feeding intensity and predatory impact on selected mesoplankton species in the inshore waters of the southern Caspian Sea. The ctenophore Mnemiopsis leidyi initially increased during 2001-2002 with the abundance and biomass of 381-480 ind.m-3 and 15.1-27.7 g.m-3, respectively, and during recent years (2012-2013) its population and biomass reached at a low level with an average of 5-46 ind.m-3 and 0.6-4.0 g.m-3. The highest summer–autumn average of M. leidyi abundance was observed in 2002 with 1338 ± 334 ind.m-3 and the maximum biomass in 2001 with 77.5±19.4 g.m-3. Over the years, 2003-2012, M. leidyi population did not reach to its initial value and the mean range of abundance and biomass 5-25 ind.m-3 and 0.6-19.2 g.m-3. Interannual and interspecies differences in the intensity of predatory impact on zooplankton were found. Copepod nauplii of Acartia (Acanthacartia) tonsa, the cladocerans Podon (Pleopsis) polyphemoides, experienced the highest pressure from ctenophore predation. Zooplankton species composition showed there were 36 species before the M. leidyi introduction, while now days it is 12 species. Food spectra of M. leidyi consisted of zooplankton in which the copepods were the main in the southern Caspian Sea. The mass development of M. leidyi defines the qualitative and quantitative composition of zooplankton community through the control of abundance of copepod and cladoceran nauplii, which, in turn, results in changes in the trophic structure of the whole food chain.

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

Abstract: 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 -1 which 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 influencing the M. leidyi decreased after initial bloom invasion in the southern Caspian Sea.

Increasing jellyfish populations: trends in Large Marine Ecosystems

Abstract: Although there are various indications and claims that jellyfish (ie, scyphozoans, cubozoans, most hydrozoans, ctenophores, and salps) have been increasing at a global scale in recent decades, a rigorous demonstration of this has never been presented Because this is mainly due to scarcity of quantitative time series of jellyfish abundance from scientific surveys, we attempt to complement such data with non-conventional information from other sources This was accomplished using the analytical framework of fuzzy logic, which allows the combination of information with variable degrees of cardinality, reliability, and temporal and spatial coverage Data were aggregated and analyzed at the scale of Large Marine Ecosystem (LME) Of the 66 LMEs defined thus far that cover the world’s coastal waters and seas, trends of jellyfish abundance after 1950 (increasing, decreasing, or stable/variable) were identified for 45, with variable degrees of confidence Of those 45 LMEs, the majority (28 or 62%) showed increasing trends These changes are discussed in the context of possible sources of bias and uncertainty, along with previously proposed hypotheses to explain increases in jellyfish

Ctenophore relationships and their placement as the sister group to all other animals

Abstract: Ctenophora, comprising approximately 200 described species, is an important lineage for understanding metazoan evolution and is of great ecological and economic importance. Ctenophore diversity includes species with unique colloblasts used for prey capture, smooth and striated muscles, benthic and pelagic lifestyles, and locomotion with ciliated paddles or muscular propulsion. However, the ancestral states of traits are debated and relationships among many lineages are unresolved. Here, using 27 newly sequenced ctenophore transcriptomes, publicly available data and methods to control systematic error, we establish the placement of Ctenophora as the sister group to all other animals and refine the phylogenetic relationships within ctenophores. Molecular clock analyses suggest modern ctenophore diversity originated approximately 350 million years ago ± 88 million years, conflicting with previous hypotheses, which suggest it originated approximately 65 million years ago. We recover Euplokamis dunlapae—a species with striated muscles—as the sister lineage to other sampled ctenophores. Ancestral state reconstruction shows that the most recent common ancestor of extant ctenophores was pelagic, possessed tentacles, was bioluminescent and did not have separate sexes. Our results imply at least two transitions from a pelagic to benthic lifestyle within Ctenophora, suggesting that such transitions were more common in animal diversification than previously thought. Newly sequenced transcriptomes are combined with existing data to establish Ctenophora as the sister group to all other animals and suggest a radiation around 350 Ma as well as multiple transitions from a pelagic to a benthic lifestyle.

Transitions of Mnemiopsis leidyi (Ctenophora: Lobata) from a native to an exotic species: a review

Abstract: The genus Mnemiopsis is comprised of a single species, Mnemiopsis leidyi A. Agassiz, 1865, that has recently made the transition from a distribution limited to the Atlantic coasts of North and South America to an invasive range that includes the Black, Caspian, Mediterranean, North, and Baltic seas. We review the foundations of the ctenophore’s invasive success, which include the source-sink dynamics that characterize Mnemiopsis populations in temperate coastal waters where the ctenophore achieves its highest biomass levels and ecosystem impacts. Within its native temperate range, Mnemiopsis is frequently a dominant, seasonal, colonizing species with limited dispersal capacities. Cross-oceanic transport within ballast waters of intercontinental shipping vessels has altered this dispersal limitation and initiated a rapid global spread of Mnemiopsis. Owing to continuing transport via transoceanic shipping, we anticipate continued range expansion and review the variables most likely to determine whether introduction of Mnemiopsis to a novel community results in an inconspicuous addition or a disruptive invasion.

Stealth predation and the predatory success of the invasive ctenophore Mnemiopsis leidyi

Abstract: In contrast to higher metazoans such as copepods and fish, ctenophores are a basal metazoan lineage possessing a relatively narrow set of sensory-motor capabilities. Yet lobate ctenophores can capture prey at rates comparable to sophisticated predatory copepods and fish, and they are capable of altering the composition of coastal planktonic communities. Here, we demonstrate that the predatory success of the lobate ctenophore Mnemiopsis leidyi lies in its use of cilia to generate a feeding current that continuously entrains large volumes of fluid, yet is virtually undetectable to its prey. This form of stealth predation enables M. leidyi to feed as a generalist predator capturing prey, including microplankton (approximately 50 μm), copepods (approximately 1 mm), and fish larvae (>3 mm). The efficacy and versatility of this stealth feeding mechanism has enabled M. leidyi to be notoriously destructive as a predator and successful as an invasive species.

Invasive copepods in the Lower Columbia River Estuary: Seasonal abundance, co-occurrence and potential competition with native copepods

Abstract: As part of a multi-year field study to investigate plankton dynamics in the Lower Columbia River Estuary (LCRE), we conducted monthly sampling of the mesozooplankton (> 73 μm) at a station near Astoria, Oregon. The planktonic copepod community was numerically dominated by three non-indigenous species (NIS), Pseudodiaptomus forbesi, Limnoithona tetraspina, and Sinocalanus doerrii, and two native species, Eurytemora affinis and Diacyclops thomasi. However, seasonal co-occurrence of non-indigenous and native copepods was highly variable between species-pairs. The native E. affinis and the non-indigenous S. doerrii showed the greatest temporal overlap (March-October), but other species-pairs also showed periods of considerable overlap during some seasons (e.g., E. affinis and P. forbesi in June-September). Spatial co-occurrence of native and non-indigenous species was also examined in temperature and salinity “space” (rather than geographic space): all six species-pairs (3 non-indigenous species × 2 native species) showed some degree of overlap, with the greatest (proportional) overlap occurring between the native E. affinis and the two nonindigenous species, S. doerrii and P. forbesi. This suggests the potential for competition to occur between native and non-native copepods in the LCRE, although with variation between seasons and species. Future studies are recommended that explicitly test for and distinguish between the relative importance of biological (e.g., competition and predation) and physico-chemical processes (e.g., freshwater runoff, eutrophication) in regulating the population dynamics of native and invasive copepods in the LCRE.