Modeled Buoyancy of eggs and larvae of the deep-sea shrimp Aristeus antennatus (Crustacea: Decapoda) in the northwestern Mediterranean Sea

Information on the buoyancy of eggs and larvae from deep-sea species is rare but necessary for 30 explaining the position of non-swimming larvae in the water column. Due to embryonic 31 morphology and ecology diversities, egg buoyancy has important variations within one species and 32 among other ones. Nevertheless, it has hardly been explored if this buoyancy variability can be a 33 strategy for deep-sea larvae to optimize their transport beyond their spawning areas. In the 34 northwestern Mediterranean Sea, protozoea and mysis larvae of the commercial deep-sea shrimp 35 Aristeus antennatus were recently found in upper layers, but to present, earlier stages like eggs and 36 nauplii have not been collected. Using a Lagrangian transport model and larval characteristics, we 37 evaluate the buoyancy and hydrodynamic effects on the transport of A. antennatus larvae in the 38 northwestern Mediterranean Sea. The transport models suggested that 75% of buoyant eggs 39 released between 500 and 800 m depth (i.e., known spawning area), reached the upper water layers 40 (0-75 m depth). Then, according to the modeled larval drifts, three spawning regions were defined 41 in the studied area: 1) the northern part, along a continental margin crossed by large submarine 42 canyons; 2) the central part, with two circular circulation structures (i.e., eddies); and 3) the 43 southern part, with currents flowing through a channel. The number of larvae in the most upper 44 layer (0-5 m depth) was higher if the larval transport model accounted for the ascent of eggs and 45 nauplii (81%) instead of eggs reaching the surface before hatching (50%). The larvae reaching the 46 most water upper layer (0-5 m depth) had higher rates of dispersal than the ones transported below 47 the surface layer (deeper than 5 m depth). The results of larval dispersal simulations have 48 implications for the understanding of A. antennatus larval ecology and for management decisions 49 related to the shrimp fisheries in the northwestern Mediterranean S

Comparison between ROV video and Agassiz trawl methods for sampling deep water fauna of submarine canyons in the Northwestern Mediterranean Sea with observations on behavioural reactions of target species

In this paper we present a comparison between Remotely Operated Vehicle (ROV) and Agassiz trawling methods for sampling deep-water fauna in three submarine canyons of the Northwestern Mediterranean Sea and describe the behavioural reactions of fishes and crustacean decapods to ROV approach. 10 ROV dives, where 3583 individuals were observed and identified to species level, and 8 Agassiz trawls were carried out in a depth range of 750-1500 m. As noticed in previous studies, abundances of fishes and decapod crustaceans were much higher in the ROV videos than in Agassiz trawl samples, as the latter are designed for the retrieval of benthic, less motile species in permanent contact with the bottom. In our observations fish abundance was one order of magnitude higher with ROV (4110.22 ind/km2) than with Agassiz trawl (350.88 ind/km2), whereas decapod crustaceans were six times more abundant in ROV videos (6362.40 ind/km2) than in Agassiz samples (1364.52 ind/km2). The behaviour of highly motile fishes was analysed in terms of stationary positioning over the seafloor and avoidance or attraction to ROV approach. The most frequently occurring fish species Coelorinchus mediterraneus, Nezumia aequalis, Bathypterois dubius, Lepidion lepidion, Trachyrincuss scabrus and Polyacanthonotus rissoanus did not react to the presence of the ROV in most cases (>50%). Only B. dubius (11%), Lepidion lepidion (14.8%), P. rissoanus (41%) and T. scabrus (14.3%) reacted to ROV approach. More than 60% of less motile species, such as crustacean decapods, did not respond to ROV presence either. Only 33.3% of Geryon longipes, 36.2% of Munida spp. and 29.79% of Pagurus spp. were observed avoiding or defensively reacting to the ROV. The comparison of results obtained with ROV and trawl sampling is of ecological relevance since ROV can report observations in areas where trawling is technically unfeasible. The lack of reaction by most fish and crustacean decapod specimens further confirms that ROV surveying is an efficient technique to assess abundance and species composition in deep-sea waters for these motile species and questions trawl-based estimations

Visual faunistic exploration of geomorphological human-impacted deep-sea areas of the north-western Mediterranean Sea

This study reports the composition and distribution of demersal megafauna from various north-western Mediterranean submarine areas such as canyons, seamounts and landslides between 60-800 m depth, based on remotely operated vehicle (ROV) observations. From a total of 30 h of video, 4534 faunistic observations were made and analysed in relationship to environmental factors (i.e. topography, substrate type and depth). In addition, anthropogenic impact was quantified by grouping observations in four categories: fishing nets, longlines, trawl marks and other litter. The different targeted environments showed similarities in faunal composition according to substrate, depth and topography. Our results also indicated the presence of anthropogenic impact in all the sampled areas in which litter and trawl marks were the most observed artefacts

Dynamics of oligotrophic pelagic environments:North western Mediterranean sea and subtropical north Atlantic

The response of phytoplankton to various ecological forcings was examined in the upper waters of the NW Mediterranean (MED) and the subtropical North Atlantic (NA) from field observations, analysis of historical data sets and numerical simulations. Particular emphasis was given to the role played by the water column structure in controlling the nitrogen diffusion and new production. Using numerical simulations, the effects of different levels of heating of surface waters and nutrient concentrations in waters below the euphotic zone were examined.Spring microplankton metabolism of surface mixed waters in MED was studied. The system was heterotrophic explained by dark community respiration (DCR) rates higher than gross primary production (GPP) rates. The GPP to DCR ratio was ~0.53, indicating that the system was far from balance between carbon production (photosynthesis) and consumption (respiration), probably caused by organic matter accumulation in the mixed layer favouring respiration over production processes. Summer primary production and nitrogen fluxes in stratified water layers in NA were analysed. The nitrogen flux fuelling new primary production was closely linked to vertical turbulent diffusion at the nitracline rather than at the thermocline. Upward diffused nitrogen inducing new production explaining 21% of total primary production. The vertical turbulent diffusion model used to estimate new production did not explain new production in the Canary Current zone, where laterally advected nutrients from coastal upwelling areas altered the vertical nitrate gradients.A numerical ecological model of the pelagic domain was developed to assess the plankton response to different environmental pressures. The model represents the vertical dimension of the upper and intermediate water layers of the open ocean. A comparative study of the plankton functioning in MED and NA sites was carried out using the model. The nitrate entering the euphotic zone through the lower boundary explained the low but continuous primary production in the two systems. The latitudinal variability of plankton scenarios implied a year round different solar heating of the upper waters, altering both phytoplankton photosynthesis and mixed layer processes in the water column, with the latter dominating over the former in controlling the phytoplankton biomass. The balance of light availability and nutrient concentration controlled the chlorophyll maximum depth, but the zooplankton grazing prevented this maximum to reach greater concentrations. The model structure and functioning makes it suitable for comparative ecological studies and is expected to be applicable to other studies related to coastal and marine environmental issues

The Potential Use of Mangrove Forests as Nitrogen Sinks of Shrimp Aquaculture Pond Effluents: The Role of Denitrification

Este artículo contiene 14 páginas, 6 tablas, 1 figura.A generalized nitrogen budget was constructed to evaluate the potential role of mangrove sediments as a sink for dissolved inorganic nitrogen (DIN) in shrimp pond effluents. DIN concentrations were measured in pond effluents from three semi-intensive shrimp ponds along the Caribbean coast of Colombia between 1994-1995. Mean NH4+ concentrations in the discharge water for all farms were significantly higher (67 f 12 pgL) than in the adjacent estuaries (33 f 8 p&). Average NH4+ concentrations in the pond discharge over all growout cycles were similar, representing an approximate doubling in relation to estuarine water concentrations. In contrast, NO,- + NO,- concentrations were similar in both pond effluent and estuarine waters. Dissolved inorganic nitrogen loading of the ponds was similar. The estimated reduction of DIN in pond effluents by preliminary diversion of outflow to mangrove wetlands rather than directly to estuarine waters would be 2 190 mg N/m2 per d. Based on this nitrogen loss and depending upon the enrichment rate, between 0.04 to 0.12 ha of mangrove forest is required to completely remove the DIN load from effluents produced by a 1- ha pond.Partial support for this work was provided by INVEMAR and CENIACUA through a cooperative agreement with the University of Southwestern Louisiana. COLCIENCIAS provided financial support through the research project “Desarrollo y optimization del cultivo de camarones marinos (Penaeus vannamei, P. stylirostris, y P. schmitti)” directed by Federico Newmark (Code No. 2105-09-030-93).Peer reviewe

Comparison between ROV video and Agassiz trawl methods for sampling deep water fauna of submarine canyons in the Northwestern Mediterranean Sea with observations on behavioural reactions of target species

In this paper we present a comparison between Remotely Operated Vehicle (ROV) and Agassiz trawling methods for sampling deep-water fauna in three submarine canyons of the Northwestern Mediterranean Sea and describe the behavioural reactions of fishes and crustacean decapods to ROV approach. 10 ROV dives, where 3583 individuals were observed and identified to species level, and 8 Agassiz trawls were carried out in a depth range of 750-1500 m. As noticed in previous studies, abundances of fishes and decapod crustaceans were much higher in the ROV videos than in Agassiz trawl samples, as the latter are designed for the retrieval of benthic, less motile species in permanent contact with the bottom. In our observations fish abundance was one order of magnitude higher with ROV (4110.22 ind/km2) than with Agassiz trawl (350.88 ind/km2), whereas decapod crustaceans were six times more abundant in ROV videos (6362.40 ind/km2) than in Agassiz samples (1364.52 ind/km2). The behaviour of highly motile fishes was analysed in terms of stationary positioning over the seafloor and avoidance or attraction to ROV approach. The most frequently occurring fish species Coelorinchus mediterraneus, Nezumia aequalis, Bathypterois dubius, Lepidion lepidion, Trachyrincuss scabrus and Polyacanthonotus rissoanus did not react to the presence of the ROV in most cases (>50%). Only B. dubius (11%), Lepidion lepidion (14.8%), P. rissoanus (41%) and T. scabrus (14.3%) reacted to ROV approach. More than 60% of less motile species, such as crustacean decapods, did not respond to ROV presence either. Only 33.3% of Geryon longipes, 36.2% of Munida spp. and 29.79% of Pagurus spp. were observed avoiding or defensively reacting to the ROV. The comparison of results obtained with ROV and trawl sampling is of ecological relevance since ROV can report observations in areas where trawling is technically unfeasible. The lack of reaction by most fish and crustacean decapod specimens further confirms that ROV surveying is an efficient technique to assess abundance and species composition in deep-sea waters for these motile species and questions trawl-based estimations