Zooplankton community response to eddy during dinoflagellate Noctiluca scintillans blooms off Pakistan,northern Arabian Sea

Eddies are major elements of ocean dynamics that affect ocean production.Understanding their effects on plankton distribution may help understand the dynamics of harmful phytoplankton blooms.Previous studies on the effects of eddies in the northern Arabian Sea have primarily focused on the zooplankton community,and few have observed zooplankton dynamics during winter blooms of Noctiluca scintillans.We investigated zooplankton community structure and the related environmental variability during a N.scintillans bloom that was affected by an eddy in February 2018.The sampling stations were deployed at eddy core and eddy edge distinguished in salinity,temperature,and velocity.Results show that N.scintillans bloomed at the eddy core with high-velocity currents induced by warm eddies that moved from eddy core to eddy edge.As a result,blooms significantly changed the zooplankton community structure.Non-bloom stations had higher zooplankton diversity than bloom stations.Zooplankton at non-bloom stations were dominated by either tunicates or copepods,such as Thalia democratica and Pleuromamma gracilis.In addition to the influence of N.scintillans blooms,the velocity of eddy currents was a crucial factor on the similarities in the zooplankton community composition between eddy edge and eddy core.Moreover,the lower abiotic factors in bloom area contribute to the structuring of the zooplankton community during N.scintillans blooms.

Morphotaxonomy and seasonal distribution of planktonic and benthic Prorocentrales in Karachi waters,Pakistan Northern Arabian Sea

Morphotaxonomy and seasonal abundance of dinoflagellates of the genera Prorocentrum and Mesoporos （Prorocentrales） were studied from nutrient-rich waters, Karachi Harbor and the mouth of the Manora Channel, Pakistan during May 2002-July 2003. Using both light and scanning electron microscopy, 13 species of Prorocentrales were identified according to cell shape, size, ornamentation of thecal plates, and architecture of apical platelets, apical pore area, marginal pores, and intercalary bands. P. sigmoides, P. arcuatum, P. scutellum, P. donghaiense, P. balticum, P. minimum, P. emarginatum, P. lima, P. faustiae, and Mesoporos perforatus constitute new records for sindh coast of Pakistan. The most abundant species were P. minimum/P, balticum （4.5x103 cells/L）, P. micans （1.1~103 cells/L）, P. gracile/P, sigmoides （2.5 x 102 cells/L） and P. donghaiense （6.6 x 103 cells/L） at temperatures of 29-31 ~C and salinities of 35-40. Maximum abundance was observed in winter and lower abundance in summer. There was no significant change in the distribution of species between stations except for the benthic species which occurred close to Karachi Harbor waters. Significant positive correlations were observed between Prorocentrum spp. and temperature （R2=0.27） and negative correlations with salinity （R2=-0.32） except for P. minimum and P. emarginatum which has negative correlation with temperature （R2=-0.24） and positive with salinity （R2=0.08, 0.19）. The finding of potential okadaic-acid producing species of benthic Prorocentrum call for monitoring for possible human health problems in this region.

Length-weight relationship of eleven species of marine catfishes from the northern Arabian Sea coast of Pakistan

This study records length-weight relationships （LWRs） for eleven commercially important marine catfish species of the family Ariidae （sea catfishes） and Plotosidae （eel catfishes） from the northern Arabian Sea coast of Pakistan. The specimens were sampled from December 2014 to November 2015, using bottom trawls with various mesh sizes by commercial vessels. The species were Nemapteryx caelatus, Sciades sona, Arius gagora, Batrachocephalus mino, Neturna thalassina, N. bilineata, Osteogeneiosus militaris, Plicofollis dussumieri, P. tenuispinis, Plotosus limbatus, and P. lineatus. Of the eleven species, two species A. gagora and N. bilineata were recorded for the first time and LWRs for four species A. gagora, N. bilineata, S. sona, and B. mino still have no data in the FishBase database. In addition, new maximum length for each of the three species N. bilineata, O. militaris andB. mino was also found.

Assessment of heavy metals concentration in holothurians, sediments and water samples from coastal areas of Pakistan (Northern Arabian Sea)

Objective: To determine heavy metal concentrations in holothurians (Holothuria arenicola, Holothuria pardalis, Holothuria verrucosa, Holothuria atra, Ohshimella ehrenbergii, Holothuria cinerascens, Stolus buccalis and Holothuria leucospilota), sediments and sea water samples from both Buleji and Sunehri coasts bordering Northern Arabian Sea during January to December 2014 and to assess the level of bioaccumulation using bioaccumulation factors. Methods: Fe, Mn, Zn, Cu, Cd and Pb levels were determined by Perkin Elmer AAnalyst 700 Atomic Absorption Spectrophotometer. Biota concentration factor (BCF) and biota sediment accumulation factor (BSAF) were also calculated. Results: The mean concentrations of heavy metals in body wall of sea cucumber ranged from 0.11 to 2.67, 0.43 to 8.93, 14 to 73, 0.76 to 7.12, 0.52 to 3.02 and 11 to 46 μg/g dry wright for Cd, Cu, Fe, Mn, Pb and Zn, respectively. The greatest biota-sediment bioaccumulation factor (BSAF) value for Zn (3.29) was observed in H. leucospilota at Buleji during pre-monsoon, indicating the species as microconcentrator. The BSAF values for Cd in sea cucumber ranged from 0.042 to 1.492. Conclusions: The results suggested that the studied sea cucumber species ranged from being microconcentrators to deconcentrators. The BSAF values of Cu, Fe, Mn and Pb were low, indicating the species as deconcentrators. Zn in all species from Sunehri coast is 'very bioaccumulative' (BCF > 5000) during all sampling periods. Cu, Fe, Mn and Pb can be considered 'bioaccumulative' (BCF < 5000).

北印度洋净热通量的季节、年际和年代际变化

根据月平均热通量(TropFlux)资料,使用相关分析和线性倾向估计以及经验正交分解(EOF)等方法,标记5个特征海区,以反映北印度洋净热通量的季节、年际和年代际变化特征。结果显示:冬季阿拉伯海失热区比孟加拉湾失热区失热多;夏季只有亚丁湾海域失热,斯科特拉区得热量值和赤道区相当。北印度洋净热通量季节分布呈现春季峰值大于秋季的双峰分布。近些年来,阿拉伯海和亚丁湾海域失热减小,孟加拉湾失热增多,赤道得热有下降的趋势。阿拉伯海、孟加拉湾和亚丁湾失热区净热通量的季节、年际和年代际变化主要由潜热和感热决定,亚丁湾夏季失热还与长波辐射有关。冬季净热通量异常场分解出3个独立模态,累计贡献率可达53.87%,第一模态为主模态,阿拉伯海失热区失热减少、孟加拉湾失热区失热增多的年代际变化特征。夏季净热通量异常场前3个模态的累计贡献率为57.42%,第一模态为主模态,北印度洋全场一致性得热,且以热带印度洋西部为最强的年代际变化。

阿拉伯北部公海海域鸢乌贼渔场分布及其与海洋环境因子关系

根据2004年9~12月在阿拉伯北部公海海域鸢乌贼资源的探捕生产情况,分海区初步分析了海洋环境因子与中心渔场之间的关系。调查表明,中心渔场分布在62°E^64°E、12°N^13°N,59°E^62°E、15°N^18°N和62°E^64°E、18°N^20°N三个海区。中心作业渔场基本分布在冷水与暖水交汇边缘处,并处于冷水涡边缘一侧。中心渔场的适宜表温27~29℃、表层盐度35.5~36.5。不同作业渔场的温盐结构不同。北部渔场的表温相对要高于南部渔场,但是50m以下水层的温度则相反;中部渔场的各层盐度明显低于南部和北部渔场。GAM模型分析表明,产量与表温、50m水温和200m水温以及各层盐度的关系密切。

阿拉伯海北部公海海域鸢乌贼资源密度及其分布

根据2004年9—12月阿拉伯海北部公海海域鸢乌贼资源的调查和渔获统计资料，采用效能比方法，对鸢乌贼资源密度指标CPUE值进行了估算。结果发现，调查海域的鸢乌贼资源密度较高，其CPUE值为0．2～8．3尾／（线·h），CPUE优势组为1．0～4．0尾／（线·h），约占总站数的63．1%，总体平均CPUE值为2．22尾／（线·h）。资源密度的随海域而不同。高于2尾／（线·h）的CPUE值分布在12°N．58～62°E；14～16°N，59～61°E；18～20°N，62～64°E海域。

阿拉伯海北部马克兰增生楔G16站位地球化学特征及其对天然气水合物的指示

阿拉伯海马克兰海域是具有天然气水合物勘查潜力的重要区域之一。对该海域G16站位沉积物样品的碎屑矿物、钼、有机碳和顶空气甲烷含量以及孔隙水总碱度和阴阳离子等地球化学特征进行综合分析。结果表明:Mg^(2+)和Ca^(2+)的浓度随深度明显降低,总碱度、Mg^(2+)/Ca^(2+)随深度显著增加;在硫酸盐-甲烷界面(SMI),SO4^(2−)的浓度线性降低至0.31 mmol/L,甲烷含量急剧增加至784μmol/L,黄铁矿含量达到最大值并形成一个Mo峰。研究区硫酸根浓度线性降低和强烈亏损梯度以及Mg^(2+)、Ca^(2+)、总碱度和有机碳含量的变化特征,指示研究区存在强烈的甲烷厌氧氧化反应(AOM),并形成浅的SMI(估算深度4.62 mbsf)。孔隙水样品的地球化学异常与沉积物自生黄铁矿和Mo含量存在耦合现象,表明本站位深部沉积物中可能赋存有天然气水合物藏。