Seasonal variability of the zooplankton community in the southwest of the Huanghai Sea (Yellow Sea) Cold Water Mass

Samples were collected with a plankton net in the four seasonal cruises during 2006-2007 to study the seasonal variability of the zooplankton community in the southwest part of Huanghai Sea Cold Water Mass (HSCWM, Yellow Sea Cold Water Mass). The spatial and temporal variations of zooplankton species composition, biomass, abundance and biodiversity were examined. A total of 122 zooplankton species and 30 pelagic larvae were identified in the four cruises. Calanus sinicus and Aidanosagitta crassa were the most dominant species, and Themisto gaudichaudi and Euphausia pacifica were widely distributed in the HSCWM area. The spatial patterns of non-gelatinous zooplankton (removing the high water content groups) were similar to those of the total zooplankton biomass in autumn, but different significantly in the other three seasons. The seasonal means of zooplankton biomass in spring and summer were much higher than that in autumn and winter. The total zooplankton abundance averaged 283.5 ind./m~3 in spring (highest), 192.5 ind./m~3 in summer, 165.5 ind./m~3 in autumn and 65.9 ind./m~3 in winter (lowest), and the non-gelatinous groups contributed the most total abundance. Correlation analysis suggests that the non-gelatinous zooplankton biomass and abundance had a significant positive correlation in the whole year, but the relationship was insignificant between the total zooplankton biomass and abundance in spring and summer. The diversity index H of zooplankton community averaged 1.88 in this study, which was somewhat higher than historical results. Relatively low diversity in summer was related to the high dominance of Calanus sinicus, probably due to the strongest effect of the HSCWM in this season.     

Diel vertical migration of medusae in the open Southern Adriatic Sea over a short time period (July 2003)

Diel vertical migration (DVM) of medusae was investigated at a fixed station in the oligotrophic Southern Adriatic Sea at several depths during summer (July) 2003. We hypothesized that medusan DVM is considerably influenced by environmental variables such as hydrographic features, light intensities, and potential prey densities. We used short-term repetitive sampling as an approach to detail these relationships. Of the 26 species collected, the highest abundance was in the layer between the thermocline (15 m) and 100 m depth, where Rhopalonema velatum predominated, reaching the maximum count of 93 individuals per 10 m³. Seven species were observed over a wide depth range: Solmissus albescens (15–1200 m), R. velatum (0–800 m), Persa incolorata (50–1200 m), Octophialucium funerarium (200–1200 m), Arctapodema australis (200–1200 m), Amphinema rubra (100–800 m), and Rhabdoon singulare (15–600). According to the medusan weighted mean depth (WMD) calculations, the longest DVMs were noted for the deep-sea species S. albescens , O. funerarium , and A. australis . The shallowest species, Aglaura hemistoma , was primarily non-migratory. Certain medusan assemblages were associated consistently with a particular depth layer characterized by a particular light intensity. The interplay of environmental factors and trophic relationships explains some of the features of medusan migratory patterns. These findings thus contribute to understanding the variables that determine patterns of medusan vertical migratory behavior.     

Origin and characteristics of the zooplankton phosphatase activity in a coastal ecosystem of the Mediterranean sea (Toulon Bay)

In Toulon Bay (France), very high phosphatase activities have been found in the zooplankton fraction>90 microm. This work was intended to specify their origin. For that purpose, larvae, juvenile and adult Crustacea (Copepods: Calanoids, Cyclopoids, Branchiopods: Cladocera, and Cirripeds) were isolated. Their activities were measured using paranitrophenyl phosphate dissolved in sea water in order to calculate Km (the enzyme half saturation concentration) and Vmax (the reaction rate when the enzyme is saturated with substrate). Vmax were referred to protein contents of the isolated organisms to calculate specific activities. For all zooplankton groups high and low affinity phosphatase activities were found. The low affinity enzyme was responsible for at least 70% of the total phosphatase activity. Its specific activity was higher for larvae than for copepodites and adults. In Cirriped nauplii this activity was particularly high with values which were several hundred times higher than that in other Crustacea. These enzymes had optimum pH close to 8.4, magnesium requirement and were competitively inhibited by orthophosphate. Experiments with intact and lysed Cirriped nauplii confirmed that living organisms had only a weak external activity and showed that most of the activity of these larvae was primarily intracellular.     

南海浮游被囊动物火体虫科(Pyrosomatidae)一新记录种的形态特征

火体虫科(Pyrosomatidae),隶属于脊索动物门、尾索动物亚门、海樽纲、磷海樽目,全球海域已报道8种。本文描述了采自南海火体虫科一新记录种短轮火体虫(Pyrosomella verticillata)群体和单体的形态特征,分析了其群体长度、宽度与轮数的关系,并比较了该种与已在南海发现的大西洋火体虫(Pyrosoma atlanticum)的形态差异。研究标本保存在南海海洋生物标本馆。     

Distribution and texture of the bottom sediments in a semi-enclosed coastal inlet, the Izmit Bay from the eastern sea of Marmara (Turkey)

Thirty-one surficial sediment samples were collected from the floor of Izmit Bay with a grab onboard the R/V Bilim in summer 1987 and analysed for their grain size, total carbonate, and organic carbon distribution.Low calcareous-terrigenous mud (2–45% CaCO₃) with a relatively high silt percentage was the principal sediment type found on the floor of Izmit Bay. Sediments rich in sand and gravel usually occur in the narrow and shoal areas of the bay, where biogenic and topography-related hydrodynamic conditions are dominant factors controlling the nature of bottom deposits. The carbonates are made up almost entirely of the remains of calcareous organisms. Organic carbon concentrations of the sediments (0·35-1·62%) are probably associated with the high primary production rates in this region. Thus, the rates of sedimentation in the Izmit Bay calculated from the organic carbon and primary productivity data are estimated to be up to 70 cm/1000 years.     

Differential feeding rates of native and alien predators on the invasive Asian date mussel Arcuatula senhousia (Benson in cantor, 1842) in a Mediterranean coastal lagoon

The alien Asian date mussel Arcuatula senhousia inhabits several coastal environments worldwide. This species can form dense mats where individuals attach through byssus threads, thus altering the structure, functioning and biodiversity of the native communities. We investigated the feeding preference of different predators on this alien species in a Mediterranean coastal lagoon. To do this, a mesocosm experiment was conducted using two crab species (the Mediterranean green crab Carcinus aestuarii) and the Say mud crab Dyspanopeus sayi, and one gastropod, the banded dye-murex Hexaplex trunculus as predators of A. senhousia with or without byssus mats. Our data suggest that C. aestuarii is a more effective predator against A. senhousia than D. sayi, and that H. trunculus is almost ineffective. A possible implication of this result is the potential use of the native crab C. aestuarii for limit the formation of the byssus mats, thus mitigating their potential negative effects on the native communities.