Seawater carbonate chemistry and egg production, hatching and metabolic rates of a Mediterranean copepod species (Acartia clausi) in a laboratory experiment

This study includes the first information on the combined effect of low pH and raised temperature on egg production rate (EP), hatching success (HS), excretion and respiration of the Mediterranean copepod Acartia clausi. Adult individuals of A. clausi and fresh surface seawater were collected at a coastal station in Saronikos Gulf during April 2012. Four different conditions were applied: two different pH levels (present: 8.09 and future: 7.83) at two temperature values (present: 16°C and present+4 °C= 20°C). EP and HS success decreased significantly over the duration of exposure at future pH at both temperature conditions. However, the analysis of the combined effect of pH, T, chlorophyll a and the duration of the experiments on EP and HS revealed that ocean acidification had no discernible effect, whereas warming; food and the duration of exposure were more significant for the reproductive output of A. clausi. Temperature appeared to have a positive effect on respiration and excretion. Acidification had no clear effect on respiration, but a negative effect on the A. clausi excretion was observed. Acidification and warming resulted in the increase of the excretion rate and the increase was higher than that observed by warming only. Our findings showed that a direct effect of ocean acidification on copepod's vital rates was not obvious, except maybe in the case of excretion. Therefore, the combination of acidification with the ambient oligotrophic conditions and the warming could result in species being less able to allocate resources for coping with multiple stressors.

Assessment of Acartia tonsa effect on Necora puber zoeal stages

A navalheira (Necora puber) é uma das espécies mais consumidas em Portugal, sendo que a maioria dos organismos consumidos é atualmente importada de países do Norte da Europa. Para o sucesso da sua produção em aquacultura, é indispensável a administração de presas adequadas à dimensão das fases larvares e que respondam às suas necessidades nutricionais. Os benefícios da administração de copépodes têm vindo a ser reconhecidos, uma vez que os calanóides possuem um largo espectro de tamanhos, movimentos naturais que promovem a sua captura e elevados níveis de ácidos gordos essenciais. Acartia tonsa é uma das espécies de copépodes mais recomendadas para administrar nos primeiros estágios larvares, mas os seus protocolos de cultivo em grande escala ainda requerem otimização. Neste enquadramento, o presente estudo teve como objetivo a seleção da microalga mais adequada para o cultivo de A. tonsa, possibilitando a avaliação do seu efeito no desenvolvimento larval de N. puber, quando comparado com a administração de Artemia franciscana. Inicialmente, os copépodes foram submetidos a duas dietas distintas: Rhodomonas lens e Tetraselmis chuii, a uma densidade de 1x104 cell.mL-1, tendo sido avaliadas as taxas de eclosão, sobrevivência e produção de ovos. A microalga que promoveu uma melhor performance foi administrada nos cultivos contínuos de A. tonsa. Em relação ao desenvolvimento larvar de N. puber, foram avaliadas as taxas de crescimento, percentagem de estágios ao longo do tempo, bem como a correlação entre o peso e o comprimento das larvas, quando alimentadas com A. tonsa e A. franciscana. Adicionalmente, foi avaliado o perfil de ácidos gordos de ambas as espécies de microalgas e de zooplâncton. R. lens permitiu um melhor desempenho enquanto alimento para cultivos de A. tonsa, promovendo uma taxa de eclosão perto de 90%, enquanto que, com T. chuii os copépodes apenas sobreviveram até ao oitavo dia. Tais resultados poderão dever-se à dimensão celular de R. lens, bem ao seu elevado conteúdo de DHA. Em relação ao desenvolvimento larvar de N. puber, Acartia tonsa promoveu uma taxa de sobrevivência de 89 ± 1,63% em zoea V e o encurtamento da fase larvar. Com ambas as dietas foi demonstrada uma forte correlação entre o peso o tamanho. Foi observada uma melhor performance larvar a partir de zoea II, quando as larvas foram alimentadas com A. tonsa, devido à elevada presença de C 20:5 n3 e C 22:6 n3 e movimentos naturais que promovem a sua captura. Assim, foi possível concluir que as A. tonsa é uma presa adequada para larvas de pequenas dimensões, promovendo elevadas sobrevivências e redução da fase larvar.

Interactions between harmful algae and calanoid copepods in the Baltic Sea

The aim of the studies reported in this thesis was to examine the feeding interactions between calanoid copepods and toxic algae in the Baltic Sea. The central questions in this research concerned the feeding, survival and egg production of copepods exposed to toxic algae. Furthermore, the importance of copepods as vectors in toxin transfer was examined. The haptophyte Prymnesium parvum, which produces extracellular toxins, was the only studied species that directly harmed copepods. Beside this, it had allelopathic effects (cell lysis) on non-toxic Rhodomonas salina. Copepods that were exposed to P. parvum filtrates died or became severely impaired, although filtrates were not haemolytic (indicative of toxicity in this study). Monospecific Prymnesium cell suspensions, in turn, were haemolytic and copepods in these treatments became inactive, although no clear effect on mortality was detected. These results suggest that haemolytic activity may not be a good proxy of the harmful effects of P. parvum. In addition, P. parvum deterred feeding, and low egestion and suppressed egg production were consequently observed in monospecific suspensions of Prymnesium. Similarly, ingestion and faecal pellet production rates were suppressed in high concentration P. parvum filtrates and in mixtures of P. parvum and R. salina. These results indicate that the allelopathic effects of P. parvum on other algal species together with lowered viability as well as suppressed production of copepods may contribute to bloom formation and persistence. Furthermore, the availability of food for planktivorous animals may be affected due to reduced copepod productivity. Nodularin produced by Nodularia spumigena was transferred to Eurytemora affinis via grazing on filaments of small N. spumigena and by direct uptake from the dissolved pool. Copepods also acquired nodularin in fractions where N. spumigena filaments were absent. Thus, the importance of microbial food webs in nodularin transfer should be considered. Copepods were able to remove particulate nodularin from the system, but at the same time a large proportion of the nodularin disappeared. This indicates that copepods may possess effective mechanisms to remove toxins from their tissues. The importance of microorganisms, such as bacteria, in the degradation of cyanobacterial toxins could also be substantial. Our results were the first reports of the accumulation of diarrhetic shellfish toxins (DSTs) produced by Dinophysis spp. in copepods. The PTX2 content in copepods after feeding experiments corresponded to the ingestion of <100 Dinophysis spp. cells. However, no DSTs were recorded from field-collected copepods. Dinophysis spp. was not selected by the copepods and consumption remained low. It seems thus likely that copepods are an unimportant link in the transfer of DSTs in the northern Baltic Sea.

The feeding ecology of some zooplankters that are important prey items of larval fish

Diets of 76 species of fish larvae from most oceans of the world were inventoried on the basis of information in 40 published studies. Although certaln geographlc, size- and taxon-specific patterns were apparent, certain zooplankton taxa appeared in the diets of larvae of a variety of fish species in numerous localities. Included were six genera of calanoid copepods (Acartia, Calanus, Centropages, Paracalanus, Pseudocaianus, Temora), three genera of cyclopoid copepods (Corycaeus, Oilhona, Oncata), harpacticoid copepods, copepod nauplii, tintinoids, cladocerans of the genera Evadne and Podon, barnacle nauplii, gastropod larvae, pteropods of the genus Limacina, and appendicularians. Literature on feeding habits of these zooplankters reveals that most of the copepods are omnivorous, feeding upon both phytoplankton and other zooplankton. Some taxa, such as Calanus, Paracalanus, Pseudocalanus, and copepod nauplii appear to be primarily herbivorous, while others, such as Acartia, Centropages, Temora, and cyclopoids exhibit broad omnivory or carnivory. The noncopepod zooplankters are primarily filter-feeders upon pbytoplankton and/or bacterioplankton. Despite the importance of zooplankters in larval fish food webs, spectic knowledge of the feeding ecology of many taxa is poor. Further, much present knowledge comes only from laboratory investigations that may not accurately portray feeding habits of zooplankters in nature. Lack of knowledge of the feeding ecology of many abundant zooplankters, which are also important in larval fish food webs, precludes realistic understanding of pelagic ecosystem dynamics. (PDF file contains 34 pages.)

Premiers résultats sur l'excrétion et la production du zooplancton de la Lagune Ebrié (Côte d'Ivoire)

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators.

On four species of Copepoda new to Chesapeake Bay, with a description of a new variety of Paracalanus crassirostris Dahl

At this time, four additional species, unreported by Wilson [1932], can be added to the list of those species to be found within the limits of the bay. These are Acartia tonsa Dana, Cyclops vernalis Fischer, Diaptomus spatulocrenatus Pearse, and Paracalanus crassirostris Dahl var. nudus nov. The specimens from which identifications were made were collected by means of Clarke-Bumpus nets, in use on the motor ship "Mahatru."

胶州湾四种哲水蚤种群动态的研究

本文研究了胶州湾内1988年5月至1989年5月，小拟哲水蚤[Paracalanus parvus(Claus)]、双刺纺锤水蚤[Acartia bifilosa (Giesbrecht)]、太平洋纺锤水蚤(A. pacifica steuer)和1982年5月至1983年4月中华哲水蚤(Calanus sinicus Brodsky)的种群结构和种群数量的季节变化。双剌纺锤水蚤和太平纺锤水蚤在胶州湾是季节性出现的种类，它们能产生休眠卵，本文对其休眠卵数量的季节变化以及影响休眠卵产生和孵化的因素进行了初步的探讨。本文还研究了体长的季节变化以及温度和食物条件对体长的影响。

长江口北港和北支浮游动物群落生态学比较研究

浮游动物是河口生态系统的重要组成部分，在食物网中，浮游动物是浮游植物捕食者，对浮游植物有摄食压力，所以控制浮游植物数量的增长。同时，浮游动物还是鱼类的饵料，从而影响渔业资源的数量。长江口是各种经济鱼、虾和蟹的重要产卵场、索饵场和洄游场。长江口各个分汊的分流量的差异较大，导致不同分汊的水文环境明显不同，其中最为明显就是北港和北支水域。然而以往对浮游动物的研究仅限于某一水域，没有对整体水域进行研究，本文选择最具代表性的北港和北支水域，对两水域浮游动物的群落生态特征进行比较研究。 本论文的数据来源于2004年5、8、11月和2005年2月在长江口北港和北支水域4个航次的海洋综合调查资料。通过采用优势度和优势种贡献率等生态学指标，同时结合逐步回归分析，讨论了温、盐与浮游动物总丰度变化的关系。结果表明，就四季而言，浮游动物总丰度和盐度呈显著正相关，和温度负相关。而就单个季节而言，除了5月和2月落潮，总丰度和盐度均呈显著正相关，与温度相关关系不显著。调查水域优势种主要为河口半咸水种或近海种。北港的盐度约为0-5, 表现为长江淡水特征；北支的盐度约为12-28，表现为长江径流和外海水团混合水团的特征。上述优势种的盐度适应和水团分布特征决定了长江口浮游动物分布的时空变化，即盐度较高的水域往往有较高的丰度，北支的总丰度和生物量均大于北港。此外，在长江口口内水域，水温较低的枯水期，浮游动物丰度高于水温较高的丰水期，温度的季节波动，以及主要优势种中华华哲水蚤（Sinocalanus sinensis）对低温环境的适应，是调查水域浮游动物总丰度季节变化的重要因素。 另一方面，本论文通过物种多样性、累积优势度曲线等群落水平的指标和相似性检验分析（ANOSIM），对长江口北港和北支浮游动物群落及其主要优势种的差异，以及主要生态因子对浮游动物群落的影响进行了分析。结果表明，北港主要由潮汐影响的淡水和低盐水组成，北支由中、高盐水组成。春季，北港浮游动物丰度和多样性均低于北支，主要优势种为中华华哲水蚤；北支优势种种数较多，主要是真刺唇角水蚤（Labidocera euchaeta）。夏季，北港和北支的多样性较接近，但是种类组成差别较大，北港以中华华哲水蚤和太平洋纺锤水蚤（Acartia pacifica）为主构成河口半咸水群落，北支以由火腿许水蚤（Schmackeria poplesia）、虫肢歪水蚤（Tortanus vermiculus）和太平洋纺锤水蚤等构成河口低盐群落。秋季，北港的丰度和多样性均低于北支，两个水域的群落差异明显，北港主要由中华华哲水蚤构成，北支由小拟哲水蚤（Paracalanus parvus）、针刺拟哲水蚤（Paracalanus aculeatus）、真刺唇角水蚤和中华哲水蚤（Calanus sinicus）等近岸和外海种组成。冬季，两个水域种数和多样性均较低，群落差别达四季最小，中华华哲水蚤占绝对优势。温度和盐度及其相互作用是决定长江口浮游动物群落特征的最主要因素。其中温度是造成研究水域浮游动物群落季节变化的主要因素，而由径流和外海水之间的消长引起的盐度变化是造成北港和北支浮游动物群落区域变化的决定因素。

小型桡足类种群动力学研究

小型桡足类在生态系统中的重要作用近年来得到了广泛的关注，在近岸生态系统中，小型桡足类起着相当重要的作用。但关于小型桡足类种群动力学的研究在国内还处于起步阶段，因此我们选取了国内沿岸海域常见优势种小拟哲水蚤、双刺纺锤水蚤、太平洋纺锤水蚤及强额拟哲水蚤等四种小型桡足类为研究对象，探讨其种群动力学相关方面的变动机制。本文在2005年10月－2006年9月选取胶州湾为主要的研究海域，进行了一周年的小型桡足类的采样和培养实验研究。在胶州湾，小拟哲水蚤（Paracalanus parvus）全年出现，其种群数量变动呈现双峰型，在夏季（6月和8月）达数量高值，在冬季（1月）有一个小的高峰。种群数量在4月达全年最低值，在7月份数量也有一个明显的数量降低。从空间分布上来讲，该水蚤在冬季主要以CV期桡足幼体存在于湾南和湾外区域，湾北数量很少；从春末开始，各期幼体开始在各海区广泛分布。小拟哲水蚤在胶州湾几乎全年产卵（2月份除外），但较高的产卵率主要集中在春末到秋初，最大产卵率出现在5月，达27.9 eggs female-1d-1。总体来讲，在胶州湾小拟哲水蚤的产卵率与温度、叶绿素及体长均呈显著正相关，但与盐度呈负相关关系。从不同的区域来看，胶州湾湾北区域小拟哲水蚤产卵率较高，最高值出现在湾北6月份，产卵率达到了60.8 eggs female-1d-1。大于10 eggs female-1d-1的产卵率在湾北持续了6个月（4－9月），在湾口持续了5个月（4－8月），而在湾外只持续了3个月（5－7月）。小拟哲水蚤生物量在6月份达到最高值（6.15 mg C m-3），在4月达到全年最低值（0.028 mg C m-3）。次级生产的变动从4月到9月与生物量的变动趋势完全相似，但冬季生物量的高峰并没有伴随次级生产的高峰值，分析其原因是由于冬季低的生长率所致。小拟哲水蚤在整个胶州湾平均的年次级生产为158.41 mg C.m-3yr -1。强额拟哲水蚤（Paracalanus crassirostris）在胶州湾只在夏末到秋季出现，最大数量出现在8月份。从强额拟哲水蚤的分布区域来看，从湾内到湾外有递减趋势。在2006年9月份，只有湾北有部分种群，其他区域几乎没有该种出现。该种最大产卵率出现在8月，达11.2 eggs female-1d-1。强额拟哲水蚤生物量的变动与次级生产的变动趋势相似，最大值也都出现在8月份。该水蚤在胶州湾平均年次级生产仅为2.12 mg C m-3yr-1。双刺纺锤水蚤(Acartia bifilosa)在胶州湾是全年出现，其种群数量在5－6月份突发性增加达全年最高值（>8000 ind. m-3），之后又急剧下降。从该种的区域分布来看，5－6月份数量的高峰主要出现在湾北区域，7月份虽然各区域数量均下降，但大部分种群集中在湾外区域。双刺纺锤水蚤在胶州湾几乎全年产卵（1－2月除外），产卵率的最高值出现在4月，达16.5 eggs female-1d-1。4月份雌体高的产卵率为5月份种群数量的大量增加提供了补充。双刺纺锤水蚤生物量与次级生产的变动趋势一致，在5－6月份达到高值，在秋冬季次级生产较低。双刺纺锤水蚤在整个胶州湾平均的年次级生产为114.61 mg C m-3yr-1。太平洋纺锤水蚤（Acartia pacifica）在胶州湾季节性出现，在冬春季节消失，从夏季开始出现。该种在5月零星出现，种群数量在6月份开始增多，到7月份达到最高值2356 ind. m-3，之后在8月数量锐减至196 ind. m-3。从区域分布来看，该水蚤在胶州湾只出现在湾北和湾南区域，湾外区域几乎没有，而且呈现湾北到湾南递减的趋势。6月份数量大部分出现在湾北区域，到7月份才有一部份在湾南出现。太平洋纺锤水蚤在其出现季节均产卵，最大产卵率出现在6月份，达37.17 eggs female-1 d-1，部分补充了7月份太平洋纺锤水蚤种群数量的大量增加。太平洋纺锤水蚤生物量与次级生产的变动趋势相似，在7月份达到了最高值，在11月达到最低值。太平洋纺锤水蚤在胶州湾平均的年次级生产为45.63 mg C m-3yr-1。胶州湾四种小型桡足类总的年次级生产为~320 mg C m-3 yr-1。

Grazing impact of copepods on phytoplankton in the Bohai Sea

During spring (April/May 1999) and autumn (September/October 1998) cruises in the Bohai Sea, China, copepods were the dominant components of mesozooplankton, the most abundant species being Calanus sinicus, Centropages mcmurrichi, Paracalanus parvus, Acartia bifilosa and Oithona similis. Pigment ingestion rates by three size classes of copepods (200-500, 500-1000 and > 1000 mum) were measured. In the south of the investigation area, gut pigment content (GPC), individual pigment-specific ingestion rates and grazing impacts on phytoplankton were lower in spring than in autumn. In the central area, GPC and individual pigment-specific ingestion rates were higher in spring than in autumn. The grazing impact on phytoplankton by the copepod assemblages was lower in spring than in autumn, however, because of the relatively smaller biomass in spring. In the western area where the Bohai Sea joins the Yellow Sea, GPC, individual pigment-specific ingestion rates and grazing impacts on phytoplankton were higher in spring than in autumn. Among the three size groups, the small-sized animals (200-500 mum) contributed more than 50% (range 38-98%) of the total copepod grazing during both cruises. The grazing impact on phytoplankton by copepods was equivalent to 11.9% (range 3.0-37.1%) of the chlorophyll-a standing stock and 53.3% (range 21.4-91.4%) of the primary production during the spring cruise. Grazing impact was equivalent to 6.3% (range 2.0-11.6%) of the chlorophyll-a standing stock and >100% (range 25.7-141.6%) of the primary production during the autumn cruise. The copepod community apparently consumed only a modest proportion of the standing stock of phytoplankton during spring and autumn blooms. They did, however, sometimes graze a significant proportion of daily primary production and hence were presumably able to limit the rate of further accumulation of phytoplankton, or even to prevent it. (C) 2003 Elsevier Ltd. All rights reserved.

Diel vertical migration of zooplankton following optimal food intake under predation

A model is developed to investigate the trade-offs between benefits and costs involved in zooplanktonic diel vertical migration (DVM) strategies. The 'venturous revenue' (VR) is used as the criterion for optimal trade-offs. It is a function of environmental factors and the age of zooplankter. During vertical migration, animals are assumed to check instantaneously the variations of environmental parameters and thereby select the optimal behavioral strategy to maximize the value of VR, i.e. taking up as much food as possible with a certain risk of mortality. The model is run on a diel time scale (24 h) in four possible scenarios during the animal's life history. The results show that zooplankton can perform normal DVM balancing optimal food intake against predation risk, with the profile of DVM largely modified by the age of zooplankter.

Feeding activities of zooplankton in the Bohai Sea

The Bohai Sea was the site of the Chinese national GLOBEC programme. During the June 1997 cruises of R/V Science No.1, observations and experiments on zooplankton feeding were conducted. At five 48 h time-series stations the following observations and measurements on zooplankton were carried out: (1) diurnal vertical migration, by collecting samples at different layers every 3 h with a closing net; (2) diurnal feeding rhythms, by gut pigment analysis; and (3) ingestion rate, by both gut pigment analysis and the dilution method. A classification by body size was used to deal with the diversity of species and developmental stages of zooplankton assemblages. Samples were separated into three size groups: small (200-500 mu m), medium (500-1000 mu m) and large (> 1000 mu m). The results showed that the copepods (Calanus sinicus, Paracalanus parvus, Acartia bifilosa and Centropages mcmurrichi) performed clear diurnal vertical migrations. However, their behaviour was different at different stations. The variation in gut pigment content over the 24 h cycle showed strong diurnal feeding rhythms, particularly for the large size group. Gut pigment contents reached their daily maximum during the time from dusk to midnight (18:00-24:00). The peak value was about 10 times the minimum observed in the daytime. The in situ daily grazing rate, based on gut pigment contents and evacuation experiments, was 4.00-12.65 ng chla ind(-1) day(-1) for the small size group, 5.99-66.58 ng chla ind(-1) day(-1) for the medium size group and 31.31-237.13 ng chla ind(-1) day(-1) for the large size group. The copepods consumed only a small part (2.90-13.52%) of the phytoplankton biomass hut about 77% of the daily production. The grazing mortality rate of phytoplankton by microzooplankton (<200 mu m) measured by the dilution method ranged from 0.43 to 0.69 day(-1) The calculated daily consumption of phytoplankton biomass was 35-50%, and 85-319% of the potential production.