Recent studies of hydrozoans suggest that metabolic factors associated with the physiology of gastrovascular fluid transport play a role in regulating morphogenetic development of colonies. In that context, the objective of this study was to develop a system to experimentally control diets of hydrozoans in culture that could be used to test effects of specific compounds. This diet delivery system consisted of a known concentration of homogenate of brine shrimp nauplii that was solidified in a 1% agar block cut to the size of, and containing the equivalent of, a single, 2-day old brine shrimp nauplius larva. We tested the utility of this system by comparing the frequencies of ingestion, and rates of gastrovascular transport and growth following feeding, between polyps of Podocoryna carnea fed either a single brine shrimp nauplius (controls) or an agar cube including brine shrimp homogenate. Polyps fed experimental diets showed similar rates of gastrovascular transport (6 and 12 h after feeding) and growth (24 h after feeding) to those of polyps fed a brine shrimp nauplius suggesting that no significant artefacts existed associated with these response variables. However, the frequency of ingestion of experimental foods by polyps was much less than that by control polyps. These results imply that this system of delivery of experimental diets has potential as a means to manipulate physiological state and assay the effects on morphogenesis of hydrozoan colonies, but must first overcome limitations of low ingestion frequency.
Monthly samples were taken in the surf zone of sandy beaches along the Belgian coast from May 1996 until July 1997 at four selected stations. Temporal patterns of the macrocrustacean and fish species residing the surf zone were investigated, as well as the abiotic variables structuring the community. In total 34 species were recorded belonging to caridean shrimps (3), anomuran and brachyuran crabs (5), cephalopods (2) and fish (24). The brown shrimp Crangon crangon dominated almost all samples (>80%). Total densities often exceeded 400 ind per 100 m2, and if C. crangon was excluded 10 ind per 100 m2. Notwithstanding the harsh hydrodynamic conditions, the surf zone of Belgian sandy beaches is used intensively by a number of epibenthic macro-crustaceans and demersal fish species. Seven resident and ten migrant species were identified. As mainly juvenile fishes were present, the surf zone of the Belgian sandy beaches may act as a nursery for longer (e.g. plaice Pleuronectes platessa) or shorter (e.g. brill Scophthalmus rhombus) periods. However, its nursery function should be studied in more detail, since the highly dynamic circumstances and more specifically wave height and wind speed may be important structuring factors for the epibenthic communities. The surf zone of Belgian sandy beaches also seems to function as a transient area to other nurseries (e.g. bass Dicentrarchus labrax) or between a nursery and the true marine environment (e.g. dab Limanda limanda).Temporal variation in community structure was greatly masked by spatial differences between sites. Although variables such as salinity and hydrodynamic factors may have influenced the data, clear temperature-related, seasonal patterns occur. Most likely, extreme winter conditions and subsequent migration of organisms to deeper waters caused a decline in winter in both density and diversity.
This study tested the hypothesis that regularly-shaped sandstone blocks in intertidal boulder-fields are colonized by mobile macrofauna at a similar rate to colonization of natural boulders. In addition, the sessile component on these plates (three levels of sessile assemblages) and their position in the boulder-field (three different positions relative to other boulders) were varied to test hypotheses about effects of these features on colonization. The epibiota varied among the three sets of plates and the natural boulders at the start of the experiment. The boulders were very rapidly colonized by a suite of mobile animals, particularly chitons, gastropods and echinoderms. Colonization was sparse and patchy to start with, causing great variability among replicates. Nevertheless, it did not differ among any of the treatments, indicating that even at this early stage, colonization did not differ between natural boulders and blocks, nor according to the sessile assemblage, or the proximity of other boulders. By six months, there was little variability among replicates and the assemblages had converged. This indicates that sandstone plates/blocks can form a standardized unit of habitat which can be used to test models about spatial variation in this relatively specialized fauna.
The two new species, Gymnodinium vitiligo and G. veneficum, which are described below, are both small and highly motile, and in other respects very similar. The greatest difference between them is physiological, as G. vitiligo is harmless, whereas G. veneficum produces a very powerful toxin which is lethal to fish. There are also small morphological differences which are visible when the organisms are in culture, confirming the existence of two separate species.
Deep-sea hydrothermal vents display extreme and highly variable environmental conditions that are expected to be among the most important factors structuring associated benthic populations and communities. We tested this assumption,focusing Oil the distribution of gastropods, as well as on the demographic population structure and reproductive biology of one dominant gastropod species ill zones characterized by alvinellid polychaetes and vcstimentiferan tubeworms. A total Of 14 biological samples from both types of habitats were collected at three sites oil the East Pacific Rise 13 degrees N vent field in May 2002. At all vents except one, the physico-chemical environment was described in two steps: (1) pH, total sulphide and reduced iron concentrations have been measured in situ in Alvinella habitats and correlations to temperature were assessed at the scale of each sampled vent, and (2) assuming the consistency of these relationships within a single edifice, ranges of physicochemical factors were estimated for each biological sample from the corresponding fine scale temperature measurements. A total Of 11 gastropod species were identified from all samples and 2 main faunal assemblages were distinguished: one dominated by Lepetodrilus elevatus in the alvinellid zone as well as in the vestimentiferan zone, and one dominated by the peltospirids Nodopelta heminoda, N. subnoda and Peltospira operculata confined to the alvinellid zone. Peltospirid gastropods were dominant over lepetodrilid gastropods in the more acidic, sulphide-richer, and hotter environments. Although this pattern could be related to specific physiological tolerances to temperature and sulphide toxicity, the weak correlation between community structure and physico-chemical variables suggests that additional factors are also involved. Particularly, the lost, species richness and the overwhelming dominance of L. elevatus in one faunal assemblage suggest that this species may outcompete peltospirids and greatly affect community structure. This hypothesis is supported by large differences in the demographic structure and reproductive biology of L. elevatus between the 2 faunal assemblages.
The life-cycle of the harpacticoid copepod Tisbe furcata (Baird, 1837) at 18°C was studied quantitatively. Stage durations were determined by two different methods, using synchronous cohorts. Combined nauplius stages last for 80.4h; the successive copepodite stages take 23.0, 23.2, 28.0 (females) to 23.2 (males), 33.4 (females) to 24.2 (males) and 48.8 (females) to 34.7 (males) h, respectively. Females develop more slowly but more synchronously than males. Age-specific survival and fertility rates were used to calculate the stable stage distribution in an exponentially growing population. From life-table data the following demographic parameters were computed: intrinsic rate of natural increase r<sub>m</sub> = 0.233 day<sup>-1</sup>; net reproductive rate R<sub>0</sub> = 94; minimum generation time T<sub>min</sub> = 14.9 days; parameters related to "generation time": T = 19.5 days, T(mean) = 16.4 days, T<sub>e</sub> = 25.4 days.
The spatial pattern of the ostracod Cyprideis torosa (Jones. 1850) is aggregated and can be described by the negative binomial distribution. The fit of the observed distribution to the negative binomial is less well for the total number of females because females that are not carrying eggs tend to be independently distributed from both females carrying eggs and males. The aggregations are roughly circular with a radius of about 13 cm and may be themselves aggregated. A method to picture the aggregations is described.
Regular sea temperature measurements have been made since 1975 at Gravelines (French coast of the Southern Bight of the North Sea) within the framework of a research programme aimed at monitoring the influence of the thermal discharge of a nuclear power plant. The sampling has yielded a 28-year time-series. Pluriannual natural fluctuations of temperature show cyclic patterns and long-term trends in good accordance with global climatic changes as revealed by the NAO (North Atlantic Oscillation) annual index.
Size-based analyses of marine animals are increasingly used to improve understanding of community structure and function. However, the resources required to record individual body weights for benthic animals, where the number of individuals can reach several thousand in a square metre, are often prohibitive. Here we present morphometric (lengthweight) relationships for 216 benthic species from the North Sea to permit weight estimation from length measurements. These relationships were calculated using data collected over two years from 283 stations. For ten abundant and widely dispersed species we tested for significant spatial and temporal differences in morphometric relationships. Some were found, but the magnitude of differences was small in relation to the size-ranges of animals that are usually present and we recommend that the regression relationships given here, based on pooled data, are appropriate for most types of population and community analyses. Our hope is that the availability of these morphometric relationships will encourage the more frequent application of size-based analyses to benthic survey data, and so enhance understanding of the ecology of the benthic/demersal component of marine ecosystems and food webs.
The aim of this study was to determine the abundance of cyanophages over an annual cycle in the Red Sea from the period April 1999 to December 1999 at a range of depths. Cyanophage numbers from 71 water samples were determined by the use of plaque assays using four different Synechococcus strains. The results indicate that cyanophage are found throughout the water column from surface waters to depths of 150 m, with a discrete maximum in the number of cyanophages in the summer months of July, August and September at a depth of 30 m. Eighty-seven cyanophages were isolated and characterized in terms of host range, genome size and possession of a myoviral portal vertex gene. Cyanophages were found to infect multiple strains of Synechococcus from different phylogenetic clades. The genome sizes of cyanophages were also found to be bigger than previously estimated.
Ashadze-1 (128 580N 448 510W, 4080 m) on the Mid-Atlantic Ridge (MAR) is the deepest known ctive hydrothermal vent ield. The first observations on this site were numerous clear and black smokers and surprisingly few nown symbiotic species ominant in other vent areas on the MAR. The species most abundant at Ashadze-1 are those usually ound at the periphery f hydrothermal communities: sea-anemones Maractis rimicarivora and chaetopterid polychaetes hyllochaetopterus sp. ov. This study comprised site mapping and faunal sampling and Ashadze-1 was completely mapped y using the Remote perated Vehicle ‘Victor 6000’ and a new high resolution tool available for deep-sea research. A photo-mapping survey was carried out with a long range optical black and white camera. Digitization of substrata and sea-anemones visible on the images was performed by GIS. Spatial distribution of Ma. rimicarivora was distinguished by high densities of 32 ind.m22 on the western side of the main smoker area. Submersible sampling operations allowed taxonomic identification within a 200 × 110 m area. Carbon, nitrogen and sulphur isotopic ratios were measured in four dominant species to identify their trophic position. The present paper gives the complete maps and describes the faunal community of the Ashadze-1 vent field. The results obtained led us to consider this site as an ecosystem in its declining stage. Finally we compare the similarities of this community to other hydrothermal communities on the northern MAR.
Cyanophage abundance has been shown to fluctuate over long timescales and with depth, but little is known about how it varies over short timescales. Previous short-term studies have relied on counting total virus numbers and therefore the phages which infect cyanobacteria cannot be distinguished from the total count.
In this study, an isolation-based approach was used to determine cyanophage abundance from water samples collected over a depth profile for a 24 h period from the Indian Ocean. Samples were used to infect Synechococcus sp. WH7803 and the number of plaque forming units (pfu) at each time point and depth were counted. At 10 m phage numbers were similar for most time-points, but there was a distinct peak in abundance at 0100 hours. Phage numbers were lower at 25 m and 50 m and did not show such strong temporal variation. No phages were found below this depth. Therefore, we conclude that only the abundance of phages in surface waters showed a clear temporal pattern over a short timescale. Fifty phages from a range of depths and time points were isolated and purified. The molecular diversity of these phages was estimated using a section of the phage-encoded psbD gene and the results from a phylogenetic analysis do not suggest that phages from the deeper waters form a distinct subgroup.
It has been suggested that the large grey seal colonies around the British Isles form local populations within a metapopulation, and that seal movements outside the breeding season lead to considerable overlap between individual home ranges. Individual behaviour and population dynamics of small peripheral colonies may also play a role in the metapopulation. We studied the French grey seal colony of the Molene archipelago, at the southern-most limit of the species' range. We analysed photo-identification data with capture-mark-recapture techniques in order to estimate the total seasonal abundance of grey seals in the archipelago and to quantify the seasonal rates of occurrence or movements of male and female seals. We found that between 58% (95% confidence interval: 48-71) and 98 (95% CI: 75-175) individuals hauled out in the archipelago during the summers of 1999 and 2000. the use of multistate models allowed the assessment of seasonal site fidelity and indicated that it varied between key periods of the annual cycle, particularly for females. Males showed a constant fidelity rate of 56% from one season to another. Hence, even though they showed high inter-annual site fidelity, they did not seem to have a preferred season for using the archipelago. On the contrary, female grey seals showed the highest site fidelity between moult and summer (around 80%), and the lowest fidelity between summer and the breeding period (34-43%). Thus, females seem to use the Molene archipelago preferentially in summer and leave the site before the breeding season, which explains the very low local pup production. Philopatry may explain this pre-breeding emigration, and we suggest that most grey seals observered in the Molene archipelago were born and breed in other local breeding populations, probably the south-western British Isles.
Information on cetaceans off Gabon in tropical West Africa is summarized from boat-based surveys carried out between 7 March and 7 August 2009. Thirteen cetacean species were positively identified comprising two baleen whale species, one sperm whale species and ten species of delphinid. Bryde's whale (Balaenoptera brydei) and humpback whale (Megaptera novaeangliae) were the most frequently encountered species. Cetaceans were found throughout a range of sea surface temperature between 20.5°C and 27.5°C and a wide range of depths with the majority of effort and sightings occurring seaward of the shelf break. Of particular interest from the study were the following: (1) Gabonese waters have a broad cetacean diversity, especially with a large and diversified delphinid community in the northern part of the study area; (2) the variations in oceanographic conditions within Gabonese waters are likely to result in a temporal variation in species composition; (3) the sightings of Atlantic spotted dolphin (Stenella frontalis) are the first at-sea sightings confirmed for these waters, although not unexpected given their distribution and abundant presence in surrounding waters; and (4) the poorly known Clymene dolphin (Stenella clymene) was sighted on four occasions in deep oceanic waters and was the most abundant cetacean. These are the first confirmed records of Clymene dolphins in Gabonese waters.
The abundance, composition and metabolic activity of plankton were assessed in the Tribulation zone of the central Great Barrier Reef (16°-17°S). Wet phytoplankton biomass ranged in shallow reef waters from 30 to 70mgm -3, and from 60 to 270mgm-3 in the deep lagoon and in the estuarine areas which are dominated by pico- and nano-algae. Wet bacterioplankton biomass varied from 70 to 290mgm-3. Wet meroplankton biomass was less than 10mgm-3. Wet daytime mesozooplankton biomass ranged from 100 to 300mgm-3 in the deep lagoon. In the estuarine area, it reached 400 to 1300mgm-3and in the shallow inner lagoon of the Low Isles ring reef it varied from 10 to 30mgm-3. Zooplankton density increased at night and was 3 to 5 fold greater in the deep lagoon, for about 2 orders of magnitude greater over the reef shallows and up to 3 orders of magnitude greater in mangrove habitats, due to the emergence of demersal components from the benthos. The biomass of zooplankton hidden in the benthic substrates during the day reached 10 to 40gm-2. Pelagic primary production in the deep lagoon varied between 0.2 and 0.5gCm-2d -1. A calculation of the energy balance suggests that the basic energy source for heterotrophic plankton production in the deep lagoon is the organic matter exported from surrounding reef benthic communities and from mangroves. The trophic status of coral reef pelagic ecosystem might range from mesotrophic to eutrophic.
Interannual and spatial differences in the abundance of Metridialucens are reported from the Irish Sea from 1996 to 2001. In most years the abundance in spring is very low (<50 m2), however in 2001 the abundance was high and this enabled a rare study of the vertical distribution of M.lucens in coastal waters. The vertical distribution differs with time of day and water column structure. Abundances were always higher in stratified deeper waters compared with mixed or coastal waters.
The harbour porpoise is the only resident cetacean species in the German Baltic Sea. Within the last several decades this harbour porpoise stock declined drastically, causing deep concern about its status. Plans of the German government for proposing Marine Protected Areas (MPAs) to implement Natura2000 and for assessing the impact of offshore windmill constructions on the marine environment led to an increased research effort on the harbour porpoise in German waters. For the first time, long-term passive acoustic monitoring has been conducted in the German Baltic Sea from the Kiel Bight to the Pomeranian Bay from August 2002 to December 2005. Porpoise detectors (T-PODs) have been installed five to seven metres below the water surface at up to 42 measuring positions throughout the investigated area, registering the exact times of echolocation signals of passing harbour porpoises. The proportion of monitored days with porpoise detection in each quarter of the years has been analysed. A correlation of the results with the longitude of the measuring position revealed a significant decrease from west to east in the percentage of days with porpoise detections. Comparison of data gathered in the first quarters with the third quarters of the monitoring years displayed a seasonal variation with fewer days of porpoise detections in winter time than in summer time. Nevertheless, harbour porpoises have been detected year-round at most of the measuring positions in the German Baltic Sea. The present study clearly indicates a regular use of the German Baltic Sea by harbour porpoises with a geographical and seasonal variation in the usage of the German Baltic Sea. The larger numbers of harbour porpoise detections in spring to autumn compared with winter suggests that the German Baltic Sea is an important breeding and mating area for these animals.
The John dory, Zeus faber, has a pair of intrinsic sonic muscles on the swimbladder wall and produces sounds by rapid contractions of the muscles. The physical properties of the sounds and the detailed innervation pattern to the sonic muscle were investigated. The dory emitted two types of the sounds: “bark” and “growl”. The bark consisted of continuous multiple pulses and lasted about 85ms on the average. The growl consisted of a group of intermittent single-pulses and lasted for 50 ms to 1.2 s. The main frequencies of both sounds were almost similar and ranged between 200 to 600 Hz. The sonic muscles were innervated by the sonic branches of the 1st.4th spinal nerves. Interestingly, the innervation from the first spinal nerve was newly revealed in the present study. Total of 1,700 myelinated axons innervated the sonic muscles on both sides. There was no sex difference in the sonic muscle size as judged by the sonic muscle-somatic index (SMSI, male: 0.675%, female: 0.670%). The sounds in the dory possibly function as a threatening means. Journal of the Marine Biological Association of the UK, 84(4), 2004, pp. 843-850
Patella ferruginea is an endangered marine gastropod, distributed on the western Mediterranean coasts, whose range has progressively contracted, due to intense human exploitation. A genetic analysis was performed on two unidentified young individuals belonging to the genus Patella found attached to the shell of an adult of P. ferruginea , with a twofold aim: (i) to achieve their correct taxonomic attribution by means of the DNA barcoding; and (ii) to shed some light on the hypothesized larval philopatry and/or juveniles phoresis in P. ferruginea . The survey was carried out comparing the sequences of the cytochrome c oxidase subunit I (COI) Folmer region obtained for the two juveniles with those obtained for adults of P. ferruginea , P. caerulea , P. rustica , and P. ulyssiponensis , from different sites of the western Mediterranean, by means of maximum likelihood cluster analysis and a Bayesian-based assignment test. Results obtained evidenced that: (i) COI may be used with confidence as DNA barcoding in the genus Patella ; and (ii) the two juveniles studied are not conspecific: one belonged to P. ferruginea , the other to P. rustica . The latter finding raises doubts about the juvenile phoresis and about the occurrence of larval philopatry in P. ferruginea , suggesting that an extensive use of a molecular approach for a better evaluation of the recruitment features of this endangered species should be adopted.
A new species of calanoid copepod, Centropages aegypticus sp. nov. collected from the Egyptian coasts of the northern Red Sea is described. This species is unique in having two pointed conical processes on the dorsal surface of cephalosome in both sexes, female genital compound somite with irregular-surface outline of the right swelling part and transverse dorsolateral row of spinules on the left side, 2-segmented exopod of the female leg 5, asymmetrical medial processes of the female leg 5, of which the left one is longer and medially-curved and the right one with oblique row of thick spinules, and a club-shaped medial seta on the third exopodal segment of the male leg 5. The new species is similar to C. tenuiremis, but is not assigned to the same species group as the latter species or to any other groups.