Mesozooplankton distribution,metabolism and grazing in an anticyclonic slope water oceanic eddy (SWODDY) in the Bay of Biscay

Mesozooplankton distribution, metabolism and feeding were investigated in the slope water oceanic anticyclonic eddy (SWODDY) AE6 during the cruise Gigovi-0898, which was conducted in August 1998 in the Bay of Biscay. According to the distribution of isotherms at 200 m depth, the sampling area was divided into three zones: SWODDY centre (C), edge (E) and outside the SWODDY (O). Multivariate analysis identified four different zooplankton assemblages. Such separation was closely related to the structure of the SWODDY, with each grouping associated to a particular zone of this mesoscale structure. Thus, two of the groups were located at the SWODDY centre and outside (groups C and O, respectively), whereas the two remaining station groupings (T_WE and T_NS) were situated at the SWODDY margin. The assemblages C and O differed clearly from each other in their taxonomic composition. In contrast, T_WE and T_NS were separated because of the differences observed in numerical abundance rather than by a different composition. Some taxa were found exclusively outside the SWODDY, while others were confined to the centre, suggesting a large degree of isolation of the SWODDY with respect to the surrounding waters. Phytoplankton and mesozooplankton biomass followed a similar pattern, with highest values in the SWODDY centre, although the differences between zones were significant only for phytoplankton. The highest grazing impact for both phytoplankton standing stock (3.4%) and primary production (12.7%) was observed outside the SWODDY. Ammonium released by mesozooplankton accounted for between 25.3% (outside the SWODDY) and 44.4% (SWODDY centre) of total phytoplankton nitrogen demands. The percentage of total phosphorus required to be fulfilled by phosphate excretion ranged from 14.0% at the edge to 17.5% outside. Mesozooplankton underwent intense vertical migrations, especially at the SWODDY edge. The role of the mesozooplankton in the biological pump releasing metabolic end-products below 200 m at night time is proposed as one of the main sources of downward export of biogenic material in these systems.Communicated by S.A. Poulet, Roscoff     

Upper-slope distributions of oceanic lanternfishes (family: Myctophidae)

In order to determine the effects of bottom depth and water column structure on slope distributions, lanternfishes in the Cape Canyon and Cape Point Valley (eastern South Atlantic) and from the Feni Ridge and Hebridean Terrace (eastern North Atlantic) were sampled with commercial midwater nets fished 10 m above the bottom at preselected depths. Fifty-one species were taken in the eastern South Atlantic and 17 species in the eastern North Atlantic. Analyses of the samples included clustering and multi-dimensional scaling ordination of the root-root transformed densities using the Bray-Curtis similarity index. In the eastern South Atlantic (March 1988), where the horizontal and vertical temperature structuring of the water column was marked, oceanic myctophids were not taken shallower than the 300 m-depth horizon and less than one-third of the total number of species occurred inside the 500 m-depth horizon. Temperatures and bottom depths correlated with the downslope distributions of the species. Down-slope zonation was apparent. In the eastern North Atlantic (May 1983), where the temperature structure of the water column was similar at all stations, no oceanic species were taken at the 200 m-depth horizon and more than one-half of the total number of species was taken at the 300 m-depth horizon. Species distributions correlated with depth, and downslope zonation was not evident. The data sets, as well as information from the West Florida slope, suggest that both the depth and the regional temperature structure of the water column effect the upper slope distributions of oceanic myctophids. Long-slope, ribbon distribution patterns (generalized down-slope zonation) in myctophids may therefore be localized artifacts produced by the interaction of these factors.     

Organic content and biomass of abyssal holothuroids (Echinodermata) from the Bay of Biscay

The levels of ash, lipid, carbohydrate, protein and calories in the body walls of 3 abyssal holothuroids of the Bay of Biscay [Benthogone rosea Koehler, Paelopatides gigantea (Verrill) and Psychropotes longicauda Theel] are similar to those found in the body walls of shallow-water holothuroids. The biomass of abyssal holothuroids in terms of calories comprises an important fraction of the total biomass in the deep sea; at 2 000 m depth, the holothuroids correspond to one-sixth of the total biomass. However, the numerical and caloric densities of abyssal holothuroids are 4 orders of magnitude less than those of shallow-water holothuroids, although the sizes and caloric contents of individuals are of similar magnitude.Contribution No. 742 of Centre Océanologique de Bretagne     

Variability of biochemical composition and size distributions of seston in the euphotic zone of the Bay of Biscay: implications for microplankton trophic structure

Particle-size distributions and several biochemical components of seston were studied from October 1986 to December 1987 in surface waters of the Bay of Biscay. Variance partitioning of hydrographic and seston parameters indicates that, although seasonal variability related to the thermal cycle was important, most of the differences in seston concentration were caused by spatial components of variance. Changes in the vertical structure of the water column appeared to be the principal source of variability. Phytoplankton blooms in spring and fall and the effects of the coastal upwelling and the thermocline during summer were traced using seston concentration and biochemical composition. The different seston measurements were scaled according to their correlations with total concentration and particle size. Photosynthetic pigment biomass was related to both large and small partieles. However, concentrations of particulate proteins, lipids and carbohydrates were more related to small particles. Although not specifically analysed, low concentrations of inorganic particles and detritus can be expected in the study area, thus most of the particulate organic matter was associated with small, non-pigmented organisms, particularly in surface waters during the period of thermal stratification. The variability in concentrations of total seston and particulate organic matter was mainly due to variations in particulate proteins, lipids and carbohydrates; pigment concentrations were of secondary importance. Expressed as the ratio chlorophyll a: particulate protein-nitrogen, phytoplankton constituted an important fraction of the microplankton biomass only during spring blooms, when it averaged 75% of the particulate protein-nitrogen. In constrast, <30% of protein-nitrogen was related to chlorophyll a during the summer. These results suggest that an oligotrophic structure based on the microbial-loop prevails in microplankton assemblages of surface waters for most of the year.     

Small-scale spatial and temporal interactions among benthic crustaceans and one fish species in the Bay of Biscay

In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasière) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus suggested reduced competition for food but also space as both are burrowing species. The observed temporal and spatial activity patterns may contribute to regulating assemblage structure as competing species may be actively foraging at different times and locations thus reducing direct competition.     

Deep distributions of oceanic cirripede larvae in the Sargasso Sea and surrounding North Atlantic Ocean

From deep ( 1000 m), multi-depth zooplankton samples taken in the Azores frontal region from November 1980 to June 1981, high numbers of the two larval forms ofLepas pectinata, the commonest lepadid cirripede in this area, were sampled. The nauplii and cyprid larvae are large and long-lived. Nauplii were sampled where they feed, in the upper 150 m, closely associated with the fluorescence maximum. The cyprids were mainly sampled between 300 and 400 m, with a sharp cut-off in numbers just below the distribution peak. This deep distribution is intriguing, as the cyprids, which were not migrating diurnally, are non-feeding. To complete their life cycle they must settle on floating debris at the surface, where very few were sampled. They are negatively buoyant and there is no apparent physical reason for this deep distribution. There was no obvious pattern of changes in individual length or length/dry weight distribution with depth, the population appeared homogeneous. There was also no accumulation of other zooplankton at the same depth, or evidence from gut contents of large carnivores that the distribution pattern was caused by selective predation. A close association exists betweenL. pectinata andSargassum spp. weed, the cyprids preferentially settling on small fragments of weathered weed, the supply of which may be enhanced after winter. During winter, the harsh environment at the surface of the northern Sargasso Sea may discourage cyprid settlement. The deep distribution may be an ontogenetic migration conferring some survival advantage and saving energy due to the lower temperature and oxygen levels at depth. If it is a behavioural mechanism, duration of the cyprid stage will be extended until a more clement time of year, allowing them to settle over a longer period. The cyprids of other species were also sampled at depth, so the phenomenon appears to be widespread. If subsequent research confirms these observations as an ontogenetic migration, our current understanding of the fouling behaviour of oceanic lepadid cirripedes would be considerably modified.     

Annual biomass and production of the oceanic copepod community off Discovery Bay,Jamaica

Monthly samples were collected in oceanic waters off Discovery Bay, Jamaica, in 60- and 200-m vertical hauls, using 200- and 64-m mesh plankton nets, from June 1989 to July 1991. Length-weight regressions were derived for twelve genera of copepods (R²=0.79 to 0.97). For eight occasions spanning the study period, biomass estimates generated from these length-weight regressions differed by only 3% from direct weight determinations. The mean ash content of copepods was 7.1%, and the energy density was 20.8 kJ g^-1 ash-free dry weight (AFDW). Mean annual biomass of the total copepod community in the upper 60 m was 1.83 mg AFDW m^-3 (range 1.14 to 2.89 mg AFDW m^-3), and for the 200-m water column was 0.96 mg AFDW m^-3 (range 0.12 to 1.99 mg AFDW m^-3). Estimates of generation times for five common taxa ranged from 16.1 to 33.4 d. None of the taxa investigated displayed isochronal development; in general, stage duration increased in later copepodite stages. Weight increments showed a significant decrease in later copepodite stages, but with strong reversal of the trend from stage 5 to adult female in most species. Daily specific growth rates also declined in later copepodite stages, and ranged from 1.49 d^-1 in stage 1–2 Paracalanus/Clausocalanus spp. to 0.04 in stage 5-female of Oithona plumifera. Progressive food limitation of somatic copepodite growth and egg production is postulated. Naupliar production was 50.4 to 59.5% of copepodite production, and egg production was 35.1 to 27.7% of copepodite production in the 60-and 200-m water columns, respectively. Total annual copepod production, including copepodites, nauplii, eggs and exuviae, was 160 kJ m^-2 yr^-1 for the upper 60 m and 304 kJ m^-2 yr^-1 for the upper 200 m. Secondary production of the copepod community in oceanic waters off Discovery Bay approaches 50% of the corresponding value in tropical neritic waters.     

杭州湾南岸滩涂环境状况及与贝类养殖的关系

浙江省慈溪市滩涂环境与贝类养殖的调查结果显示,杭州湾海域水中石油类及无机氮含量介于Ⅱ、Ⅲ类海水水质标准之间,无机磷平均含量超过Ⅳ类海水水质标准。滩涂底质总体上符合海洋沉积物第一类标准,但一些样点多氯联苯(PCBs)超标。分离到2 976株细菌,隶属17个属及肠杆菌科的部分属,具有明显的陆源性特点。发现浮游生物71种,主要为硅藻类等广盐性种类,大部分为贝类的主要天然饵料。石油类、Cd、Cr、Hg、Cu及PCBs残留量在一些贝体内不同程度地超过GB 18421—2001《海洋生物贝类质量标准》。为有效改良和保育滩涂环境,提高养殖贝类的产量和质量,在揭示滩涂环境与贝类养殖关系的基础上,提出了一些统筹兼顾的措施和建议。     

莱州湾南岸滨海湿地的生物多样性特征分析

通过2005年、2006年的实地调查和整理相关文献资料分析了莱州湾南岸滨海湿地的生物多样性总体特征,湿地维管束植物和水禽的区系组成特点,并与黄河三角洲滨海湿地的生物多样性特征进行了对比。莱州湾南岸滨海湿地维管束植物区系科的分化程度较低,属的分化程度较高,湿生植物、水生植物在区系中占据重要地位;从生活型角度分析,区系中草本植物、地下芽植物和一年生植物占据优势;从维管束植物区系的地理分布成分看,以温带分布属和世界分布属为主;莱州湾南岸滨海湿地水禽区系的居留型构成以旅鸟和候鸟为主,地理分布成分构成以古北界种为主。莱州湾南岸滨海湿地的维管束植物和水禽种类都明显少于相邻的黄河三角洲滨海湿地。     

Predicting suitable habitat for the European lobster (Homarus gammarus), on the Basque continental shelf (Bay of Biscay), using Ecological-Niche Factor Analysis

Predicting species distribution and habitat suitability (HS) modelling, across broad spatial scales, is now a major challenge in marine ecology. The resulting knowledge is of considerable use in supporting the implementation of environmental legislation, integrated coastal zone management and ecosystem-based fisheries management. This contribution considers the identification of seafloor morphological characteristics, together with wave energy conditions, that determine the presence of European lobster (Homarus gammarus); and it predicts suitable habitats over the Basque continental shelf (Bay of Biscay), in summer. The results obtained, by applying Ecological-Niche Factor Analysis (ENFA), indicate that lobster habitat differs considerably from the mean environmental condition over the study area; likewise, that it is restrictive in terms of the range of conditions in which they dwell. The best of the environmental predictors found to be: distance to the rock substrate; Benthic Position Index; wave flux over the seafloor; and the underlying bathymetry. A habitat suitability map was produced, with a high model quality (Boyce index: 0.98 ± 0.06). The most suitable habitat for European lobster are locations at the boundary between sedimentary- and rocky-bottoms, coincident with seafloor depressions with a steep slope, with medium to high wave energy conditions, and located within a range of water depths of 35–40 m. This approach demonstrates the applicability of the method in case studies where only presence data are available, together with the inclusion of environmental variables obtained from different sources.     

Seasonal changes in movements and habitat preferences of the scalloped hammerhead shark (Sphyrna lewini) while refuging near an oceanic island

Movements and habitat preferences of sharks relative to a central location are widely documented for many species; however, the reasons for such behaviors are currently unknown. Do movements vary spatially or temporally or between individuals? Do sharks have seasonal habitat and environmental preferences or simply perform movements at random at any time of the year? To help understand requirements for the designation of critical habitats for an endangered top predator and to develop zoning and management plans for key habitats, we examined vertical and horizontal movements, and determined habitat and environmental preferences of scalloped hammerhead sharks (Sphyrna lewini). We tracked seven hammerheads for 19–96 h at Wolf Island (1.38ºN, 91.82ºW) between 2007 and 2009 using ultrasonic transmitters with depth and temperature sensors, and we profiled temperature through the water column. Movements of individual hammerheads fell in two classes: constrained (remaining near the island) and dispersive (moving offshore to pelagic environments). The central activity space or kernel off the southeast side of Wolf Island was small and common to most, but the area varied among individuals (mean ± SE 0.25 ± 0.2 km²), not exceeding 0.6 km² for any of the sharks, and not changing significantly between seasons. In general, hammerheads showed preference for the up-current habitat on the eastern side of Wolf Island in both the warm and cold seasons. However, the depth of sharks varied with season, apparently in response to seasonal changes in the vertical structure of temperature. Hammerheads performed frequent vertical excursions above the thermocline during offshore movements and, in general, were observed to prefer temperatures of 23–26 °C found above the thermocline. At times, though individuals moved into the thermocline and made brief dives below it. Our results provided evidence that hammerheads (1) are highly selective of location (i.e., habitat on up-current side of island) and depth (i.e., top of the thermocline) while refuging, where they may carry out essential activities such as cleaning and thermoregulation, and (2) perform exploratory vertical movements by diving the width of the mixed layer and occasionally diving below the thermocline while moving offshore, most likely for foraging.     

杭州湾南岸滩涂环境状况及与贝类养殖的关系

浙江省慈溪市滩涂环境与贝类养殖的调查结果显示，杭州湾海域水中石油类及无机氮含量介于Ⅱ、Ⅲ类海水水质标准之间，无机磷平均含量超过Ⅳ类海水水质标准。滩涂底质总体上符合海洋沉积物第一类标准，但一些样点多氯联苯（PCBs）超标。分离N2976株细菌，隶属17个属及肠杆菌科的部分属，具有明显的陆源性特点。发现浮游生物71种，主要为硅藻类等广盐性种类，大部分为贝类的主要天然饵料。石油类、Cd、Cr、Hg、Cu及PCBs残留量在一些贝体内不同程度地超过GB18421-2001《海洋生物贝类质量标准》。为有效改良和保育滩涂环境，提高养殖贝类的产量和质量，在揭示滩涂环境与贝类养殖关系的基础上，提出了一些统筹兼顾的措施和建议。     

贫营养型水库中罗非鱼对浮游植物的影响:围隔实验

于2009年9～11月在贫营养型的大型深水水库(流溪河水库)中进行了围隔(体积约为85 m3)实验,分析了罗非鱼对浮游植物的影响.根据水库中现有鱼类的生物量,设置加鱼处理组(2 g/m3)和无鱼对照组两组.每组有3个重复,实验开始后每周采样一次,测定水质与采集浮游生物定性和定量样品.实验结果表明,加鱼处理组和对照组的总氮、可溶性无机氮没有明显差别,实验后期的总磷与正磷有一定差别,处理组略高于对照组.加鱼处理组浮游植物丰度及生物量、叶绿素a的含量显著高于对照组(P<0.05),且透明度低于对照组,个体小于30μm的浮游植物种类的丰度与生物量较明显增加,浮游动物丰度显著低于对照组(P<0.05),但是生物量差异不显著(P>0.05).总的来说,在贫营养条件下,低生物量的罗非鱼对水库浮游植物群落结构仍有着明显的影响,罗非鱼排泄产生的上行效应大于摄食产生的下行效应.     

Dynamics of heavy-metal transfer between biotic (Cytheria chione and Cerastoderma edule) and abiotic (water and sediment) components in marine environment (Bay of Martil, Moroccan Mediterranean coast)

This study deals with the transfer of heavy metals (Hg, Cd, Pb, Cr, Ni, Ti, Zn, and Cu) between abiotic and biotic components (Cytheria chione and Cerastoderma edule) in the inshore intertidal zones of Tetouan/Martil over 2 yr of investigation (1992-1994). Analysis of the heavy-metal accumulation kinetics in Cytheria chione and Cerastoderma edule shows that their highest contents occur during the spring-summer period when an important proliferation of the plankton biomass occurs. However, the accumulation of Cd is higher during the period between winter and spring. In general, heavy-metal concentrations are higher at Cytheria chione than at Cerastoderma edule. These results, according to previous studies, suggest the presence of significant correlations and dynamic reciprocal transfer of heavy metals among seawater, sediment, and molluscs. They also suggest that the level of contamination of decreasing heavy metals follows the sequence: sediment, organisms, and water. Among the molluscs investigated, the variability of the thallium (Tl) contents is difficult to detect due to the very weak presence of this metal in the analysed tissues.     

Interannual variation in the reproductive cycle and biochemical composition of the cockle Cerastoderma edule from Mundaca Estuary (Biscay,North Spain)

Seasonal determinants of body weight, biochemical composition and reproductive condition in the cockle Cerastoderma edule L. from the Mundaca Estuary, Spain, were performed from December 1983 to July 1985. Interannual differences in timing of gametogenesis and spawning between 1984 and 1985 were correlated with temporal variations in the cycles of storage and utilisation of carbohydrate reserves. Young individuals exhibited larger annual fluctuations in soft-body weight, displaying higher growth rates in spring and greater diminishment of energy reserves during autumn and winter than older individuals. Carbohydrate content displayed a similar tendency, levels being lower in young individuals throughout the year.