Ecological niches and areas of overlap of the squat lobster ‘munida’ (Pleuroncodes monodon) and anchoveta (Engraulis ringens) off Peru

The world’s largest mono-specific fishery, the Peruvian anchovy or anchoveta (Engraulis ringens) fishery, has been the subject of many studies since the 1960s. Details of its relationship with other species have mainly focused on alternations with sardine, Sardinops sagax, and little effort has so far been paid to interactions with other species sharing the same ecosystem. This is the case for Pleuroncodes monodon, the crustacean squat lobster or ’munida’, which has become highly abundant along the Peruvian coast since the mid-1990s. Munida is now an important prey for seabirds, mammals and coastal predatory fish. Knowledge of patterns of distribution and ecological niche of munida is scarce however off Peru. Here we describe and compare spatial patterns of distribution of anchoveta and munida and their ecological niches based on data from 26 acoustic surveys performed along the Peruvian coast between 1998 and 2006. The results indicate that munida and anchoveta share ecological niches but that munida is restricted to the coldest part of the productive cold coastal waters whereas anchoveta do not present any temperature preference over a large range (14–23 °C). The recent increase in munida abundance off Peru is concomitant with colder conditions; with their onset munida extended its range from central Chile northwards. Off Peru the very shallow oxycline keeps munida from its usual bottom habitat and has forced it to adopt pelagic behaviour.     

东南太平洋秘鲁鳀资源量预报模型的构建

秘鲁鳀（Engraulis ringens）是栖息于东南太平洋沿岸的一种小型中上层鱼类。有效地对秘鲁鳀资源量进行预报将有助于为我国鱼粉进口企业提供决策支撑。为此,本研究结合秘鲁鳀生物（上一个渔汛季度的资源量、渔获物中的幼鱼比例）和环境（渔场水温和nino1+2区的温度距平）因素及捕捞量为预报因子,利用主成分分析和多元线性回归的方法对17个渔汛季度（2006年至2014年第一渔汛季度）秘鲁鳀的资源量建立预报模型并利用主成分分析的结果对影响秘鲁鳀资源变动的因子进行初步评价。研究表明,随着时间的推移样本量的增加,模型拟合资源量与真实资源量的平均相对误差逐渐下降,拟合资源量序列与真实资源量序列的相关系数逐渐增加。最终模型5（建模数据为2006-2013年第二渔汛季度的数据,验证数据为2014年第一渔汛季度的数据）能够很好地拟合出秘鲁鳀资源量的大小及变动趋势拟合资源量序列与真实资源量序列的相关系数为0.861;拟合资源量序列与真实资源量序列的平均相对误差为12%;预报得到的2014年第一渔汛季度的数据与真实值相比,相对误差为1%。结合主成分分析的结果对影响秘鲁鳀资源变动的因素进行评价结果表明,第一主成分的方差贡献率为46%,其中环境因素占据了最大的载荷;第二主成分的方差贡献率为23%,同样环境因素占据了最大载荷,但是,排名第二和第三的因素分别是上一个渔汛季度的资源量和捕捞量,其载荷相当;第三和第四主成分的方差贡献率分别为9%和7%,其中幼鱼比例占的载荷最大。根据各主成分得分序列与资源量序列的相关系数结果,环境因子对秘鲁鳀资源变动有重要影响。     

An individual-based model study of anchovy early life history in the northern Humboldt Current system

We used an individual-based model of anchovy (Engraulis ringens) early life history coupled with hydrodynamic outputs from the regional oceanic modeling system (ROMS) to investigate the factors driving variability in egg and larval survival rates in the northern Humboldt upwelling region off Peru. Individuals were released within a coastal area and followed for a period of 30 days. Those that were still in the coastal area at that time were considered as retained. We investigated the spatial and temporal variability in the release locations of the individuals retained, and compared these to observed egg concentration patterns reconstructed from a 40-year period of monitoring. A first set of simulations using passive particles to represent anchovy eggs and larvae revealed a large sensitivity of the results to the initial vertical distribution of particles. We then conducted two additional sets of simulations that included the effect of egg buoyancy, larval vertical swimming behavior and lethal temperature. We obtained (1) maximal coastal retention close to the surface in winter and in deeper layers in summer, (2) a large influence of egg buoyancy and of larval vertical behavior on coastal retention in all seasons, (3) a partial match between dates and locations of enhanced retention and observed egg concentration patterns and (4) a low effect of lethal temperature on survival except when associated with high egg density. The model suggests that an optimal temporal spawning pattern for maximizing coastal retention would have two maximums, the most significant in austral winter and the second in summer. This pattern agrees roughly with observed spawning seasonality, but with temporal discrepancy of about two months in the peaks of both series. Spatially, we obtained higher retention from 10 S to 20 S, whereas the observed maximum egg concentration was located between 6°S and 14°S. Among the three sets of simulations, the one taking into account larval vertical swimming behavior lead to the best match with the data.     

表层水温结构变化对东南太平洋秘鲁鳀渔场的影响

秘鲁鳀（Engraulis ringens）是栖息于东南太平洋沿岸的小型中上层鱼类,掌握其渔场变化及其与海洋环境因子的关系有利于企业把握该渔业的生产情况。研究结合2005-2014年渔汛期间秘鲁各港口出港的船数及其所获得的秘鲁鳀渔获量和表层水温数据（海表面温度,sea surface temperature,SST）,以单位捕捞努力量的渔获量（catch per unit effort,CPUE）和捕捞努力量（Effort）数据构建的渔场指数（fishing ground index,FGI）为渔场指标,对秘鲁鳀的渔场类型进行分类,探讨水温结构变化对秘鲁鳀渔场的影响。方差分析表明:渔场指数在不同渔汛阶段（渔汛前期、中期和末期,P<0.01）和不同捕捞区域（北部、中部和南部,P<0.01）都有着极显著的差异。以表层水温大于20℃的海水是否入侵到近岸为标志,可以将秘鲁鳀渔场分成两种类型:大于20℃的海水没有入侵到沿岸（A型渔场）和入侵到沿岸（B型渔场）。研究表明,在渔汛前期和中期阶段,A型渔场的出现有利于渔场的形成,其中渔汛前期沿岸19℃或20℃等温线的出现以及渔汛中期沿岸18℃或19℃等温线的出现可以作为中心渔场形成的指标。     

Patterns in the spatial distribution of Peruvian anchovy (Engraulis ringens) revealed by spatially explicit fishing data

Peruvian anchovy (Engraulis ringens) stock abundance is tightly driven by the high and unpredictable variability of the Humboldt Current Ecosystem. Management of the fishery therefore cannot rely on mid- or long-term management policy alone but needs to be adaptive at relatively short time scales. Regular acoustic surveys are performed on the stock at intervals of 2 to 4 times a year, but there is a need for more time continuous monitoring indicators to ensure that management can respond at suitable time scales. Existing literature suggests that spatially explicit data on the location of fishing activities could be used as a proxy for target stock distribution. Spatially explicit commercial fishing data could therefore guide adaptive management decisions at shorter time scales than is possible through scientific stock surveys. In this study we therefore aim to (1) estimate the position of fishing operations for the entire fleet of Peruvian anchovy purse–seiners using the Peruvian satellite vessel monitoring system (VMS), and (2) quantify the extent to which the distribution of purse–seine sets describes anchovy distribution. To estimate fishing set positions from vessel tracks derived from VMS data we developed a methodology based on artificial neural networks (ANN) trained on a sample of fishing trips with known fishing set positions (exact fishing positions are known for approximately 1.5% of the fleet from an at-sea observer program). The ANN correctly identified 83% of the real fishing sets and largely outperformed comparative linear models. This network is then used to forecast fishing operations for those trips where no observers were onboard. To quantify the extent to which fishing set distribution was correlated to stock distribution we compared three metrics describing features of the distributions (the mean distance to the coast, the total area of distribution, and a clustering index) for concomitant acoustic survey observations and fishing set positions identified from VMS. For two of these metrics (mean distance to the coast and clustering index), fishing and survey data were significantly correlated. We conclude that the location of purse–seine fishing sets yields significant and valuable information on the distribution of the Peruvian anchovy stock and ultimately on its vulnerability to the fishery. For example, a high concentration of sets in the near coastal zone could potentially be used as a warning signal of high levels of stock vulnerability and trigger appropriate management measures aimed at reducing fishing effort.     

Carbon, nitrogen and phosphorus stoichiometry in Japanese anchovy (Engraulis japonicus) from the Huanghai Sea, China

Generally, nutrient cycle is closely related to the element distribution in biomass and the population dynamics in ecosystems. Carbon, nitrogen and phosphorus in Japanese anchovy (Engraulis japonicus) of different body lengths from the Huanghai Sea (Yellow Sea) were determined to better understand their variability and reasons during its life history. The mean content was 45.12%, 10.12% and 2.02% for C, N and P, respectively. Significant differences in C, N and P elemental composition were found among different sizes, which could be explained by varying proportions of storage compounds in whole body fish, and varying degrees of ossification. Considering abundant resources in Japanese anchovy, it was an important P-pool in the cycle of P. Moreover, the excreted N/P ratio was significantly different in fishes of different sizes, especially at high gross growth efficiency. In the past two decades, overexploitation tended to cause smaller body length in the community structure of anchovy, which presumably changed the nutrient cycle in food webs of the Huanghai Sea. Exptrapolation of the results indicates that Japanese anchovy may be important for conveying nutrient in the Huanghai Sea.     

Reproductive cycle and minimal length at sexual maturity of Engraulis encrasicolus (L.) in the Zrmanja River estuary (Adriatic Sea, Croatia)

The reproductive cycle of anchovy, Engraulis encrasicolus (L.), was studied from monthly random samples of purse seine catches. A total of 1477 anchovy specimens were collected from January to December 2003 in the Zrmanja River estuary (Novigrad Sea). The analysis was based on the temporal evolution of gonadosomatic index, mass and stage of gonads. The total length of anchovy ranged from 4.5 to 14.5 cm and mass from 0.56 to 19.80 g. Sex ratio was slightly different from 1:1; the females were insignificantly predominated (♂/♀ = 0.99). The period of reproductive activity was from April to September coinciding with the most developed stages of gonads as well as with the highest gonad weights, and gonadosomatic indices. To estimate the length at maturity, a sub sample of 454 anchovy was taken from May to July (peak of anchovy spawning period). The length at which 50% of anchovy were mature (L₅₀) was calculated to be 8.2 cm. The length–weight relationship of anchovy was described by the expression: W = 3.51 × 10⁻³ L_T^3.211 (r² = 0.998). The relationships between total length–standard length and total length–fork length are L_T = 1.1405L_S + 0.2420 and L_T = 1.0425 L_F + 0.3944, respectively.     

Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers

Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management.     

Size increment of jumbo flying squid Dosidicus gigas mature females in Peruvian waters, 1989–2004

Changes in population structure of the jumbo flying squid Dosidicus gigas in Peruvian waters were studied based on size-at-maturity from 1989 to 2004. From 1989 to 1999, mature squid belonging to the medium-sized group prevailed, but from 2001 on, mature squids were larger. This change is not related to the changes in sea surface temperature and we hypothesized that it was caused by the population increase of mesopelagic fishes as prey.     

Schooling behaviour and environmental forcing in relation to anchoveta distribution: An analysis across multiple spatial scales

The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO₂ sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales.     

A time series of prokaryote secondary production in the oxygen minimum zone of the Humboldt current system, off central Chile

Because the marine picoplanktonic communities are made up of phylogenetically different microbial groups, the re-evaluation of key processes such as bacterial secondary production (BSP) has become an important contemporary issue. The difficulty of differentiating the metabolic processes of Bacteria from the rest of the microorganisms in the water column (i.e., Archaea and Eukarya) has made it difficult to estimate in situ BSP. This work presents the seasonal variability of the prokaryote secondary production (PSP) measured by the incorporation of ¹⁴C-leucine in the oxygen minimum zone (OMZ) off central-southern Chile. The BSP and potential archaeal secondary production (PASP) were determined through the combined use of ¹⁴C-leucine and N¹-guanyl-1, 7-diaminoheptane (GC₇), an efficient inhibitor of archaeal and eukaryote cell growth. BSP accounted for the majority of the PSP (total average, 59 ± 7.5%); maximum values were ∼600 μg C m⁻³ h⁻¹ and, on several dates, BSP represented 100% of the PSP. Similarly, PASP was also an important fraction of the PSP (total average, 42.4 ± 8.5%), although with levels that ranged from not detectable (on given dates) to levels that represented up to ∼97% of PSP (winter 2003). Our results showed that both Bacteria and Archaea accounted for almost equal portions of the prokaryote heterotrophic metabolism in the OMZ, and that PASP is notoriously enhanced through temporal pulses of heterotrophy. This indicates that, at least in marine systems with high abundance of Archaea (e.g., mesopelagic realm), the secondary production obtained through methods measuring the uptake of radiolabeled substrates should be considered as PSP and not as BSP. If the latter is the target measurement, then the use of an inhibitor of both archaeal and eukaryote cell growth such as GC₇ is recommended.     

糖原含量与糖原磷酸化酶基因(GPH)和己糖激酶基因(HK)的表达在福建牡蛎生殖周期中的相关性分析

Glycogen, a polymer of glucose, is an important means of storing energy. It is degraded by glycogen phosphorylase (GPH) and hexokinase (HK), glycogen phosphorylase, and hexokinase cDNAs (Ca-GPH andCa-H...     

副溶血弧菌攻毒过程中文蛤肝胰腺弧菌载量变化的分析

文蛤(Meretrixpetechialis)是我国一种重要的海水养殖贝类,其养殖过程中病害导致的规模性死亡时有发生,已有的工作证实致病性弧菌是导致文蛤大规模死亡最为常见的病原。在本研究中,我们通过浸泡感染实验模拟了文蛤在自然条件下的弧菌胁迫环境,明确了攻毒水体中弧菌生长变化规律;攻毒过程中宿主载菌量分析显示,文蛤肝胰腺组织弧菌载量在攻毒后呈第1天急剧上升,第3天迅速下降的变化趋势,而且不同个体间载菌量差异较大;通过不同弧菌含量攻毒实验,发现在攻毒早期文蛤体内弧菌载量与水体环境的弧菌含量之间呈显著的正相关(Spearman’sρ=0.899,P=0.000),而在感染中后期不同攻毒强度组之间无显著差异,且呈现较低水平,为0～205CFU/mg,预示着宿主免疫系统和肝胰腺微生物群落可将致病菌的数量控制在一定的范围。上述研究为开展文蛤感染发病过程中弧菌载量和免疫抗性评价相关研究提供了参考。     

孔鳐雄性生殖系统解剖学与组织学观察

本研究对成年雄性孔鳐(Okamejei kenojei)的生殖系统进行解剖学和组织学观察,结果表明,孔鳐的生殖系统主要由精巢、附睾、输精管、储精囊、间质腺、鳍脚腺和鳍脚组成。其中孔鳐的精巢中的精小囊,按照成熟度依次由中心向小叶外周辐射状排列,其精子发育成熟过程根据精巢支持细胞的位置、精小囊的大小和精小囊中的生精细胞所处的状态可划分为7个时期:精巢支持细胞未迁移期、精巢支持细胞迁移期、精巢支持细胞定植早期、精巢支持细胞定植晚期、精子变形期、精子迁移期、精子聚拢期。变态成熟的精子最终每59~64根精子组成精子束进入附睾。精子束在附睾中经历“游离-聚拢-游离”3个过程后,最终储存在储精囊中。鳍脚是孔鳐的外生殖器,主要有鳍扇、扇盾等结构组成,它与储精囊相连,是将精液输送至体外的器官。     

贝藻混养生态系统模拟实验研究

2013年4~6月,在室内采用实验生态学的方法进行了海湾扇贝(Argopecten irradias)和孔石莼(Ulva pertusavar)4种配比模式的混养实验。各实验组扇贝密度均为48只/m3,孔石莼密度分别为55、121、255和338g/m3。每周采样测定水体中营养盐(NH4-N、NO3-N、NO2-N、PO4-P)的含量及养殖生物的生长情况。扇贝与孔石莼的混养实验结果表明,在养殖系统中引入孔石莼可以改善养殖环境,扇贝和孔石莼的适宜混合比例为1︰1(贝肉湿质量:藻类湿质量)能取得较好的生态效应。     

Nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) in the Eastern-Central Mediterranean Sea

The spatial pattern of the nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) (Linnaeus, 1758) and deep-water rose shrimp (Parapenaeus longirostris) (Lucas, 1846) was studied in the South Adriatic and North Ionian Seas (Eastern-Central Mediterranean) applying geostatistical techniques and data from time series trawl surveys conducted in the area. The analysed variables were: R (number of recruits/km²) and R/Tot (fraction of recruits on the total sampled population). The structural analysis showed a spatial pattern of both variables characterized by continuity on a small scale. Predictions of nursery area localization with probability of finding recruits at different threshold values were obtained through median indicator kriging. For the red mullet the nurseries were mainly identified in the South Adriatic Sea off the Gargano peninsula and between Molfetta and Monopoli within 50 m in depth. The main concentration of hake juveniles was found to be between 100 and 200 m in depth along the Gargano peninsula and between Otranto and Santa Maria di Leuca, where a nursery of deep-water rose shrimp was also detected. An overlapping depth, between 100 and 200 m, was identified for hake and deep-water rose shrimp nurseries. Protection of these areas through limitations of fishing pressure is discussed.     

大黄鱼cGAS-like基因isofrom X1的克隆鉴定及在感染刺激隐核虫后的表达变化

cGAS(cyclic GMP-AMP synthase)基因是近几年来新发现的先天免疫中一个新型的信号分子。作者基于大黄鱼(Larimichthys crocea)基因组信息,用cDNA末端快速扩增(RACE)技术在鳃组织中克隆鉴定了cGAS基因cDNA全长序列:包含1个231 bp的5′端-非翻译区(5′-UTR)、207 bp的3′-UTR和1 488 bp的开放阅读框(ORF),命名为Lc-cGAS-like X1。该基因编码1个由495个氨基酸残基组成的多肽,预测的分子量(Mw)大小为56.57kDa,理论等电点(pI)为9.45;序列分析表明其预测的蛋白无信号肽,第115～431位氨基酸序列为Mab-21功能域,第470～492位氨基酸序列为跨膜结构域。基因组全长3 153 bp,包含8个外显子和7个内含子,所有内含子的剪切特点都符合GT-AG规则。同源比对结果显示:Lc-cGAS-likeX1与鱼类cGAS的相似性大于66%,与高等脊椎动物的相似性较低。系统进化分析表明Lc-cGAS-like X1与鱼类cGAS聚成一支。荧光定量PCR(qPCR)检测显示Lc-cGAS基因(X1/X2两种剪切体)在大黄鱼9种组织中均有表达,其中在鳃中的表达量最高;刺激隐核虫感染后,大黄鱼免疫器官头肾中Lc-cGASmRNA分别在刺激隐核虫幼虫感染阶段和滋养体脱落阶段出现了极显著上调(P0.01);解毒器官肝脏中分别在滋养体脱落阶段和细菌感染阶段出现极显著上调变化(P0.01)。本研究结果暗示大黄鱼cGAS基因参与了大黄鱼感染刺激隐核虫的免疫防御过程,为进一步了解鱼类cGAS基因的多样化功能提供参考。     

针胞藻海洋卡盾藻(Chattonella marina)和硅藻中肋骨条藻(Skeletonema costatum)藻际细菌的分离、鉴定及影响研究

对实验室培养的两株海洋微藻海洋卡盾藻和中肋骨条藻的可培养细菌进行了分离鉴定,分别在海洋卡盾藻和硅藻中肋骨条藻不同生长时期分离得到48株和34株可培养细菌,去除重复序列后得到12株不同的菌株。这些菌株分属α-变形杆菌纲、γ-变形杆菌纲、拟杆菌和放线菌。α-变形杆菌纲在两种藻的藻际环境中占据优势,其中红杆菌科是最为常见的科,中肋骨条藻的藻际细菌比海洋卡盾藻更为多样化。海洋卡盾藻生长后期细菌密度大幅度上升,可能导致了藻细胞的衰亡。中肋骨条藻相关细菌中有一株对旋链角毛藻的生长具有明显抑制作用,而大部分海洋卡盾藻相关细菌对角毛藻的生长具有抑制作用。本研究结果说明海洋卡盾藻的藻际细菌也许对其与硅藻的种间竞争中具有一定作用。     

Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l^− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l^− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.