江苏海门蛎岈山牡蛎礁生态现状评价

基于2013—2014年间的生态调查结果,评价了江苏海门蛎岈山牡蛎礁的生态现状。无人机航拍结果显示,江苏海门蛎岈山分布有750个潮间带区牡蛎礁斑块,总面积约为201519.37 m2;与2003年相比,海门蛎岈山牡蛎礁面积约下降了38.8%。活体牡蛎的平均盖度约为66%,2013年5和9月熊本牡蛎Crassostrea sikamea的平均密度分别为(2199±363)个/m2和(2894±330)个/m2。2013年5月海门蛎岈山熊本牡蛎种群的平均肥满度(CI)和性腺指数(GI)分别为(9.76±0.95)%和(1013±82)mg/g,均显著低于浙江象山港养殖的熊本牡蛎种群(P0.05)。海门蛎岈山熊本牡蛎的单倍体多样性和核苷酸多样性指数分别为0.119和0.00028,均高于长江口野生种群和浙江象山港养殖种群。海门蛎岈山熊本牡蛎种群受到尼氏单孢子虫(Haplosporidium nelson)的轻度浸染,其感染率(17.2%)低于浙江象山港养殖群体(47.3%)。泥沙沉积和人类捕捞是江苏海门蛎岈山牡蛎礁面临的主要胁迫因子,今后牡蛎礁恢复的重点是增加附着底物的数量。     

河北唐山曹妃甸-乐亭海域自然牡蛎礁分布及生态意义

牡蛎礁是生态系统服务价值最高的海洋生境之一,目前我国自然牡蛎礁分布和生态现状的基础信息仍然较缺乏。于2019年3月对河北唐山曹妃甸-乐亭海域自然牡蛎礁的空间分布、生态环境、牡蛎生物学和礁体动物群落开展了调查,并评估了该牡蛎礁的生态系统服务价值。该海域自然牡蛎礁分布于溯河(SR)、溯河口海域(SRE)和捞鱼尖海域(LYJ),总面积约15 km~2,是目前我国面积最大的自然牡蛎礁。基于96个牡蛎样品的16S rDNA检测,共识别出92个长牡蛎Crassostrea gigas、3个侏儒牡蛎Nanostrea fluctigera和1个巨蛎属未知种Crassostrea sp.。自然牡蛎礁中牡蛎平均密度介于104—3912个/m~2之间,不同礁区间牡蛎平均密度的大小排序为：SRE>SR>LYJ (P<0.05),平均生物量的大小排序为：SR>SRE>LYJ (P<0.05),平均壳高的大小排序为：SR>SRE=LYJ (P<0.05)。在该牡蛎礁内记录到49种礁体动物,其中软体动物16种、节肢动物16种、环节动物8种、棘皮动物5种、腔肠动物2种...     

鲢鳙鱼养殖小型水库底栖动物群落季节动态

底栖动物是鱼类重要的天然饵料,评估水体中底栖动物的现存量可以指导渔业生产中鱼类的放养数量。为了探究淡水生态养殖水库中底栖动物群落的季节动态,于2013年4月、7月、10月和2014年1月对三河水库的底栖动物群落进行了调查分析。研究共采集到7个属的底栖动物,隶属于颤蚓科、摇蚊科和蠓科,未采集到软体动物。相对重要性指数(IRI)计算结果表明,菱跗摇蚊属Clinotanypus(IRI=7136)、颤蚓属Tubifex(IRI=6734)和尾鳃蚓属Branchiura(IRI=1384)是优势类群,分别占总捕获数量的34.26%、50.38%和10.96%。不同季节之间底栖动物的总密度和生物量差异显著(P0.05),均为冬季春季夏季秋季。冬季总密度(4100个/m~2)和总生物量(10.14 g/m~2)最高,春季(1446个/m~2;1.07 g/m~2)次之,夏季(579个/m~2;0.66 g/m~2)较低,秋季(492个/m~2;0.64 g/m~2)最低。非度量多维尺度分析(MDS)和群落相似性分析表明底栖动物群落结构季节差异显著(P=0.001),2013年三河水库的底栖动物群落可明显划分为3个:春季群落、夏秋季群落和冬季群落。皮尔森相关分析表明,底栖动物总密度与溶氧和营养盐呈正相关关系,与其他水理化因子呈显著负相关关系(P0.05)。冗余分析表明,氨氮、盐度、pH和浊度是三河水库底栖动物群落季节差异的显著影响因子(P0.05),总氮对底栖动物群落的季节差异具有边缘显著影响(P=0.08)。     

泉州湾蟳埔潮间带大型底栖动物群落的时空分布

为了比较泉州湾蟳埔潮间带沙滩、互花米草滩和牡蛎石泥滩3种生境(3个潮层)的大型底栖动物群落,2011年4月至2012年1月对3种生境的大型底栖动物进行了季度定量取样。在3种生境共获得85种大型底栖动物,其中环节动物39种,软体动物20种,节肢动物21种,刺胞动物、扁形动物、纽虫动物、星虫动物和脊索动物各1种。多维标度排序(MDS)分析表明,春季和冬季泉州湾蟳埔潮间带3种生境的大型底栖动物群落相似性较低;夏季和秋季互花米草滩与牡蛎石泥滩的大型底栖动物群落相似性较高,而与沙滩的大型底栖动物群落相似性较低。沙滩大型底栖动物群落的季节变化较明显,其次是牡蛎石泥滩,而互花米草滩大型底栖动物群落的季节变化较不明显。大型底栖动物栖息密度和生物量随着潮层降低而增加。单变量双因素方差分析(Two-way ANOVA)表明,不同生境之间的大型底栖动物物种数、栖息密度、多样性指数、均匀度指数和丰度指数有显著差异,但生物量无显著差异,这是因为沙滩的物种数较少,栖息密度较低,但优势种弧边招潮蟹(Uca arcuata)个体较大,互花米草滩和牡蛎石泥滩的优势种为加州中蚓虫(Mediomastus californiensis),个体相对弧边招潮蟹小。不同季节之间大型底栖动物物种数、栖息密度、生物量和丰度指数有显著差异,但多样性指数和均匀度指数元显著差异,这是因为沙滩物种数少,但个体分布比较均匀,而互花米草滩和牡蛎石泥滩物种数较多,个体分布较不均匀。以上结果表明,潮汐、沉积物粒径和生境是影响潮间带大型底栖动物群落的主要因素。潮汐导致潮间带的空间异质性,空间异质性导致大型底栖动物群落的差异。     

东寨港红树林小型底栖动物丰度与Chla、有机质的相关性

于2015年4月(春季)、2015年6月(夏季)、2015年10月(秋季)、2016年1月(冬季),在海南东寨港红树林保护区潮间带进行多次采样,分选小型底栖动物,并测定沉积物中有机质和叶绿素a含量,分析不同季节东寨港红树林小型底栖动物丰度与有机质、Chla的相关性。研究结果,沉积物中小型底栖动物主要包括自由生活线虫、桡足类、涡虫、多毛类、寡毛类,线虫为优势类群;有机质含量为25.22%—93.41%,平均值为46.6%; Chla含量为0.188—6.303μg/g,平均值为1.731μg/g。相关性分析显示,春季小型底栖动物的丰度和Chla含量呈显著正相关(Pearson's r=0.684; P0.05),夏季小型底栖动物的丰度与有机质含量呈显著负相关(Pearson's r=-0.518; P0.05)。     

新疆巩乃斯河枯、丰水期大型底栖动物群落结构与环境因子的关系

为探究新疆巩乃斯河的生态状况, 团队先后在2018年10月(枯水期)和2019年6月(丰水期)对大型底栖动物群落和环境因子进行了调查, 分析大型底栖动物群落结构、功能摄食类群、生活类型组成及其与环境因子的关系。研究河段共采集到大型底栖动物40种, 隶属3门4纲8目27科, 主要以节肢动物门为主, 其中直突摇蚊亚科(Orthocladiinae spp.)、长跗摇蚊族(Tanytansini sp.)、四节蜉属(Baeits sp.)、亚美蜉属(Ameletus sp.)和Cheilotrichia sp.是优势类群。经过分析发现枯、丰水期巩乃斯河大型底栖动物群落结构差异显著, T检验结果显示: 枯水期大型底栖动物群落的生物密度和物种丰富度显著低于丰水期(P<0.05), 两个时期大型底栖动物的生物多样性指数和均匀度无显著性差异(P>0.05)。巩乃斯河大型底栖动物功能摄食类群完整, 枯、丰水期均以收集者为主; 在生活类型方面, 枯水期时固着型动物最相对丰度最大为43.20%, 丰水期时蔓生型动物相对丰度最大为57.53%。经过对大型底栖动物和环境因子之间进行典范对应分析发现, 水温是影响巩乃斯河大型底栖动物群落变化的关键环境因子。研究成果可为巩乃斯河后续相关研究以及伊犁河水系生态保护提供基础数据支持及参考。     

东寨港红树林小型底栖动物丰度与Chla、有机质的相关性

于2015年4月(春季)、2015年6月(夏季)、2015年10月(秋季)、2016年1月(冬季),在海南东寨港红树林保护区潮间带进行多次采样,分选小型底栖动物,并测定沉积物中有机质和叶绿素a含量,分析不同季节东寨港红树林小型底栖动物丰度与有机质、Chla的相关性。研究结果,沉积物中小型底栖动物主要包括自由生活线虫、桡足类、涡虫、多毛类、寡毛类,线虫为优势类群;有机质含量为25.22%—93.41%,平均值为46.6%;Chla含量为0.188—6.303μg/g,平均值为1.731μg/g。相关性分析显示,春季小型底栖动物的丰度和Chla含量呈显著正相关(Pearson′sr=0.684;P0.05),夏季小型底栖动物的丰度与有机质含量呈显著负相关(Pearson′sr=-0.518;P0.05)。     

空间和环境因子对黄河口自然和淡水恢复湿地底栖动物群落的差异影响

生物多样性的形成和维持机制是生态学研究的核心问题,其中环境和空间因子在群落构建中的相对重要性是生态学家面临的重要挑战。为探究黄河口湿地底栖动物群落的关键影响因子,及环境和空间因子对底栖动物群落结构的相对调控作用。于2017年10月与2018年5月对黄河口湿地32个样点（淡水恢复湿地19个和自然湿地13个）的底栖动物和水体理化指标进行采集分析。非度量多维标度排序（NMDS）结果显示,黄河口淡水恢复湿地和自然湿地的底栖动物群落结构显著不同。典范对应分析（CCA）表明,影响淡水恢复湿地底栖动物群落结构的环境因子主要为电导率、盐度和氧化还原电位;而自然湿地底栖动物群落结构主要受pH和无机碳的影响;盐度是两类湿地底栖动物群落组成差异的关键因子。变差分解（VPA）结果显示,环境过滤对淡水恢复湿地底栖动物群落起主导作用;在自然湿地中,空间因子对底栖动物群落具有主要的调控作用,同时环境和空间因子的相互作用也至关重要。本研究明确了黄河口的自然和恢复湿地中环境和空间因素对底栖动物群落特征的相对作用,对黄河三角洲河口湿地中生物多样性的保护和生态系统管理提供参考。     

新疆伊犁河不同生境大型底栖动物群落及其影响因素

于2014和2015年7月对新疆伊犁河支流喀什河和巩乃斯河共14个采样点的大型底栖无脊椎动物进行了调查研究, 比较分析了自然、受损、坝下和保护区4种生境的大型底栖动物群落结构特征。共采集大型底栖动物14435头, 属10目39科81属(种), 其中水生昆虫、软体动物、寡毛类分别占93.8%、2.5%和3.7%。对不同生境大型底栖动物群落结构特征进行了分析比较, 结果表明: 自然生境在物种数、优势物种数、EPT物种数、密度和物种多样性方面均高于其他3种生境, 而坝下生境均最低, 保护区生境底栖动物群落结构优于受损生境和坝下生境。冗余分析(RDA)结果共解释了物种数据累计方差的54.1%, 流速、电导率、水温和海拔是影响伊犁河底栖动物分布的主要因素(F=2.28—4.34, P<0.05)。     

象山港不同养殖类型海域大型底栖动物群落比较研究

于2009年2月在象山港顶部海域分别对海带、牡蛎和鱼类网箱3种不同养殖区进行了大型底栖动物调查。调查共鉴定大型底栖动物73种,隶属8门12纲53科,以软体动物和环节动物为主。海带养殖区优势种有5种;牡蛎养殖区有4种;网箱养殖区有9种。海带、牡蛎和网箱养殖区大型底栖动物平均栖息密度分别为(132±71)个/m²、(94±91)个/m²和(210±132)个/m²;平均生物量分别为(26.51±11.06) g/m²、(53.03±61.94) g/m²和(108.80±73.56) g/m²。栖息密度和生物量不同养殖区和不同调查站位间差异显著。Tukey多重比较结果显示,栖息密度海带养殖区与牡蛎和网箱养殖区间均无显著差异,而牡蛎与鱼类网箱养殖区间存在显著差异;生物量海带养殖区与牡蛎养殖区间无显著差异,海带养殖区和牡蛎养殖区与网箱养殖区间均显著差异。典范对应分析结果表明,对大型底栖动物群落起主要影响的环境因子有温度、盐度、总氮和总磷等,排序轴对物种-环境关系的贡献率计算结果表明环境变量可以较好的解释主要类群的变化情况。丰度/生物量比较曲线(ABC曲线)分析结果表明,网箱养殖区大型底栖动物群落受较明显扰动,而海带和牡蛎养殖区大型底栖动物群落未受扰动。     

3种无脊椎动物对近江牡蛎Crassostrea ariakensis和熊本牡蛎C. sikamea的捕食研究

捕食是影响牡蛎种群建立和牡蛎礁发育的重要生物因子之一。通过室内受控实验测定了日本蟳（Charybdis japonica）、脉红螺（Rapana venosa）和黄口荔枝螺（Thais luteostoma）对4组规格（W1：壳高10-20mm;W2：壳高20-30mm;W3：壳高30-40mm;W4：壳高>40mm）近江牡蛎（Crassostrea ariakensis）和熊本牡蛎（C.sikamea）的捕食偏好性和捕食效率。双因子方差分析结果表明,日本蟳对2种牡蛎的捕食效率没有显著性差异（P>0.05）,但牡蛎规格大小显著影响着日本蟳的捕食效率（P<0.05）,即日本蟳对W1组近江牡蛎的捕食效率显著高于W2和W4组（P<0.05）,W3组的被捕食效率介于中间（P>0.05）;日本蟳对W1组熊本牡蛎的捕食效率显著高于W2和W3组（P<0.05）,W4组的被捕食效率与其他处理组均没有显著性差异（P>0.05）。牡蛎种类（P=0.590）和规格大小（P=0.357）对脉红螺的捕食效率均无显著性影响,不同规格的两种牡蛎均呈现较低的被捕食效率。黄口荔枝螺对2种牡蛎的捕食效率无显著性差异（P=0.917）,但牡蛎规格大小显著影响其捕食效率（P=0.035）,即对W1组熊本牡蛎捕食效率显著高于其他3个规格组（P<0.05）,但其对不同规格近江牡蛎的捕食效率没有显著性差异（P>0.05）。2种牡蛎的壳厚与其壳高之间均存在极显著的正相关关系（P<0.001）。研究结果表明,3种无脊椎动物捕食者对近江牡蛎和熊本牡蛎并未表现出差异性的捕食偏好,但对不同规格牡蛎的捕食效率具有种间差异。     

Occurrence of symbiotic turbellarians in the oyster,Crassostrea virginica

Crassostrea virginica was collected from several locations where it is cultured, both along the Northumberland Strait of New Brunswick and Malpeque Bay on the coast of Prince Edward Island. The oysters were found with two turbellarians on their gills. Urastoma cyprinae (Graff) was found in the oysters mostly during the warmer months of the year in numbers averaging as high as 50 worms per host (N = 50) and with as much as 78% of the host population infected (N = 100). Paravortex gemellipara (Linton) was also found during warmer months, but much less frequently or abundantly.Both male and female oysters were found to have U. cyprinae. No eggs or recent young of U. cyprinae were found in hosts; female-mature individuals of P. gemellipara with young were found from June through August.     

Cryopreservation of heart cells from the eastern oyster

Summary Conditions were developed to cryopreserve cells from pronase-dissociated atria and ventricles of eastern oysters (Crassostrea virginica). The effect of three concentrations (5, 10, 15%) of the cryoprotectants (dimethyl sulfoxide, glycerol, and propylene glycol), three thawing temperatures (25, 45, 75°C), and three cooling rates (slow, medium, fast) were compared. Cells were frozen at −80°C and plunged in liquid nitrogen. Thawed cells were seeded in 96-well plates and primary cultures were evaluated after 3 d by measuring the metabolic activity using a tetrazolium compound, 3-(4,5-dimethylthiazol-2-yl)-5-( 3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, and by comparing the relative spreading of cells between treatments. The best conditions for freezing and thawing of cells for each cryoprotectant were selected and a final study was performed to compare cryoprotectants. For this final study, we measured the number of cells and their viability 3 d after thawing, in addition to determining cell metabolic activity and cell spreading. Primary cultures of cells frozen without cryoprotectant and of nonfrozen cells were used as controls in all studies. Atrial cells were best cryopreserved with glycerol at a concentration of 10%, a medium cooling rate, and thawing at 45°C. After thawing, atrial cells showed 53±5% of the metabolic activity, 84±5% of the number, and 92±2% of the viability of nonfrozen cells. For ventricular cells, 10% glycerol, a medium cooling rate, and thawing at 25°C yielded the best results. The thawed ventricular cells showed 83±5% of the metabolic activity, 91±5% of the number, and 96±2% of the viability of nonfrozen cells.     

Cultivation of the oyster mushroom (Pleurotus ostreatus) on wood substrates in Hawaii

Summary Five non-native, aggressively growing trees, Falcataria moluccana (Miquel) Barneby & Grimes, Casuarina equisetifolia L. ex J. R. & G. Forst, Eucalyptus grandis Hill ex Maid, Psidium cattleianum Sabine, and Trema orientalis (L.) Blume, were evaluated for suitability as substrate for outdoor cultivation of the oyster mushroom, Pleurotus ostreatus (Jacq.: Fr.) Kumm., in Hawaii. An existing shade house was modified for mushroom production and proved to be an adequate fruiting site. Nitrogen-fixing trees (C. equisetifolia, T. orientalis, and F. moluccana) supported greater yield (275.5, 272.4 and 268.8 g/bag, respectively), biological efficiency (70.1, 78.5, and 74.0%, respectively), and flush number (3.0, 3.2, and 3.5) than non-fixers. P. cattleianum supported significantly lower yield (190.5 g/bag) and biological efficiency (44.2%). Mean crop period was 51 days and was not affected by the wood substrate. Similarly, substrate did not have a significant impact on the concentration of nutrients or moisture in fruit bodies. Taste preferences were noted in mushrooms grown on different substrates; those grown on C. equisetifolia were most flavourful and preferred in one taste test.     

Mitochondrial and nuclear DNA phylogeography of Crassostrea angulata, the Portuguese oyster endangered in Europe

The respective status of the Portuguese oyster, Crassostrea angulata, and the Pacific oyster, Crassostrea gigas, has long been a matter of controversy. Morphological and physiological similarities, homogeneity of allozyme allelic frequencies between populations of the two taxa and the demonstration of hybridization lead most authors to suggest that they should be regrouped within the same species. The risk of introgression and the present expansion of C. gigas aquaculture in Europe raises the question of the need for preservation of C. angulata in Europe, as only a few populations remain. We studied European and Asian populations of C. gigas and C. angulata using microsatellite and mitochondrial DNA markers to estimate their genetic diversity and differentiation. The analysis of genetic distances and the distribution of allelic and haplotype frequencies revealed significant genetic differences between taxa, showing two clusters: (1) C. gigas French and Japanese populations and (2) C. angulata Portuguese and Taiwanese populations. The Asian origin of the Crassostrea angulata taxa is therefore confirmed. Unlike previous studies based on allozymes, significant nuclear genome differences were noted between C. angulata and C. gigas. Despite the presumed history of the introduction of C. angulata into Southern Europe, these populations did not show any significant reduction of variability compared to Taiwanese populations. Any conservation plans for European C. angulata populations should take its non-native origin into account. They represent a valuable genetic resources for European breeding program.     

Invasive species cause large-scale loss of native California oyster habitat by disrupting trophic cascades

Although invasive species often resemble their native counterparts, differences in their foraging and anti-predator strategies may disrupt native food webs. In a California estuary, we showed that regions dominated by native crabs and native whelks have low mortality of native oysters (the basal prey), while regions dominated by invasive crabs and invasive whelks have high oyster mortality and are consequently losing a biologically diverse habitat. Using field experiments, we demonstrated that the invasive whelk’s distribution is causally related to a large-scale pattern of oyster mortality. To determine whether predator–prey interactions between crabs (top predators) and whelks (intermediate consumers) indirectly control the pattern of oyster mortality, we manipulated the presence and invasion status of the intermediate and top trophic levels in laboratory mesocosms. Our results show that native crabs indirectly maintain a portion of the estuary’s oyster habitat by both consuming native whelks (density-mediated trophic cascade) and altering their foraging behavior (trait-mediated trophic cascade). In contrast, invasive whelks are naive to crab predators and fail to avoid them, thereby inhibiting trait-mediated cascades and their invasion into areas with native crabs. Similarly, when native crabs are replaced with invasive crabs, the naive foraging strategy and smaller size of invasive crabs prevents them from efficiently consuming adult whelks, thereby inhibiting strong density-mediated cascades. Thus, while trophic cascades allow native crabs, whelks, and oysters to locally co-exist, the replacement of native crabs and whelks by functionally similar invasive species results in severe depletion of native oysters. As coastal systems become increasingly invaded, the mismatch of evolutionarily based strategies among predators and prey may lead to further losses of critical habitat that support marine biodiversity and ecosystem function. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cytometric investigations on hemocytes of the American oyster, Crassostrea virginica

Pericardial hemolymph was obtained from American Oysters (Crassostrea virginica) and the hemocytes characterized by flow cytometry. The cells were found to have a broad unimodal size distribution with a median diameter of 7 micrometers. Total protein measured by flow cytometric fluorescence of dansylated cells also revealed a broad unimodal distribution similar to that obtained for size. The proportion of hemocytes in each stage of the cell cycle was measured using DNA-specific DAPI fluorescence. Histograms showed a single peak representing the G(0)/G(1) population. There was no evidence of S or G(2)+M phases of the cell cycle, nor was polyploidy seen. The forward and orthogonal light scatter of fixed hemocytes showed no evidence of sub-populations on the basis of cytoplasmic granularity. Thus, in terms of these parameters, oyster hemocytes appear to represent a single population exhibiting graded cellular differences.     

Molecular characterization and mRNA expression of catalase from pearl oyster Pinctada fucata

Catalase (EC 1.11.1.6) is an important antioxidant enzyme that protects aerobic organisms against oxidative damage by degrading hydrogen peroxide to water and oxygen. In the present study, a catalase cDNA of peal oyster Pincatada fucata (designated as PoCAT) is cloned and characterized by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) methods. PoCAT is 2428 bp long and consists of a 5′-UTR of 140 bp, an unusually long 3′-UTR of 749 bp, and an open reading frame (ORF) of 1539 bp. The ORF of PoCAT encodes a polypeptide of 512 amino acids with molecular weight of 58.1 kDa and the theoretical isoelectric point of 8.4. PoCAT shares 62.3–82.2% identity and 73.0–92.0% similarity to other catalase amino acid sequences. Sequence alignment indicates that PoCAT contains the proximal heme-ligand signature sequence (R³⁵¹LFSYSDT³⁵⁸), the proximal active site signature (F⁶¹NRERIPERVVHAKGGGA⁷⁸), and the three catalytic amino acid residues (His⁷², Asn¹⁴⁵, and Tyr ³⁵⁵). PoCAT has two potential glycosylation sites (N⁴³⁶YS⁴³⁸ and N⁴⁷⁸FS⁴⁸⁰) and a peroxisome targeting signal (ASL). PoCAT mRNA was ubiquitously expressed in all detected tissues, and the expression level of PoCAT mRNA was higher in intestine and mantle. The expression profile analysis showed that the expression level of PoCAT mRNA in intestine was significantly up-regulated at 2, 4 and 12 h after Vibrio alginolyticus stimulation. These results demonstrated that PoCAT is a typical member of catalase family and might be involved in innate immune responses of pearl oyster.     

In vitro effects of noradrenaline on Sydney rock oyster (Saccostrea glomerata) hemocytes

Our prior work has shown that the catecholamine hormone, noradrenaline, mediates environmental stress responses in Sydney rock oysters, resulting in impaired immunological function. In the current study, we tested the cellular basis of this stress response. Hemocytes were exposed to noradrenaline in vitro before cell morphology and viability were analyzed. Noradrenaline was shown to induce apoptotic markers, including the loss of mitochondrial membrane potential, DNA fragmentation and plasma membrane blebbing. F-actin appeared to play an important role in the changes observed in hemocytes, being concentrated mostly in the plasma membrane blebs of noradrenaline-treated hemocytes. This may explain why hemocyte adhesion and pseudopodia formation were inhibited by noradrenaline. Cellular dysfunction induced by norarenaline mainly affected the hyalinocyte sub-population of hemocytes, whilst the other major cell type, granulocytes, remained unaffected. Given that hyalinocytes are important immunological effectors, the results of this study help to explain why immunosuppression accompanies noradrenaline-mediated stress responses in oysters.     

Histopathology in Pacific oyster (Crassostrea gigas) spat caused by the dinoflagellate Prorocentrum rhathymum

The recognition of an apparent association between seasonal oyster spat mortalities (up to 40%) and high Prorocentrum rhathymum density in the Little Swanport Estuary, Tasmania, prompted further experimental investigation into the toxicity by this dinoflagellate. Standard brine shrimp, haemolysis assays and intraperitoneal mouse bioassays revealed fast acting toxins in methanol but not aqueous extracts of P. rhathymum, with mice dying in less than 20 min. Oyster bioassays involved feeding spat (4 mm shell width) for 21 consecutive days on a diet of cultured P. rhathymum at simulated bloom densities (10⁴ cells ml⁻¹). No oyster mortality was observed, however, histopathological signs of thin, dilated gut tubules and sloughing of gut cells resembled those seen in affected field samples. In contrast to field samples, gill pathology was also observed in experimental exposure oysters.