Temporal variability of water quality of submarine groundwater discharge in Ubatuba,Brazil

Measurements of electric resistivity of the seabed and of the electric conductivity of submarine groundwater discharge (SGD) collected in seepage meters have been made to evaluate temporal variability of the origin and quality of submarine groundwater discharge in Ubatuba, Brazil. A diurnal variation of SGD conductivity was found under the condition of semi-diurnal tidal changes over a period of 4 days. Both the ground resistivity and the conductivity of the discharged groundwater indicated that the freshwater–saltwater interface moved towards offshore at high tide, i.e. in the direction opposite to commonly made observations. SGD comprised a combination of Submarine Fresh Groundwater Discharge (SFGD) of terrestrial origin, and of Recirculated Saline Groundwater Discharge (RSGD) of marine origin. The maximum of the terrestrially derived fraction SFGD/SGD was found at a distance of 50 m offshore. A lower SFGD/SGD ratio was found closer to shore, where the highest SGD flux was measured. SGD conductivity and ground resistivity displayed a diurnal cyclicity at semi-diurnal tidal water level variations, indicating that tidal water level fluctuations may not be the primary driver of SGD flux, but preferential flow in volcanic hydrogeologic setting at Ubatuba.     

Defining dynamic pelagic habitats in oceanic waters off eastern Australia

Although many species in the pelagic ocean are widespread, they are not randomly distributed. These species may have associations with particular water masses or habitats, but to best understand patterns in the ocean, these habitats must be identified. Previous efforts have produced static or seasonal climatologies, which still represent smearing over habitats. The Eastern Tuna and Billfish Longline Fishery (ETBF) targets a range of high trophic level species in oceanic waters off eastern Australia. In this study, dynamic ocean habitats in the region were identified for each month based on cluster analysis of five oceanographic variables averaged at a monthly time scale and a spatial scale of 0.5° for the period 1995-2006. A total of seven persistent habitats were identified off eastern Australia with intra and interannual variation in size and location, indicating the importance of spatial and temporal variation in the dynamics of the region. The degree to which these dynamic habitats were distinguished was tested using (i) stable isotope analysis of top fish predators caught in the region and (ii) estimates of variation in estimated abundance generated from catch data from the fishery. More precise estimates (measured as lower total CV) of isotopic values from swordfish (Xiphias gladius), yellowfin tuna (Thunnus albacares) and albacore (Thunnus alalunga) were obtained for 4 of 6 isotope comparisons using the dynamic habitat groupings, which indicate that stratifying by pelagic habitat improved precision. Dynamic habitats produced more precise abundance estimates for 7 of 8 large pelagic species examined, with an average reduction in total CV of 19% compared to when abundance was estimated based on static habitat stratification. These findings could be used to guide development of effective monitoring strategies that can distinguish patterns due to environmental variation, and in the longer term, climate change.     

Surface cyclopoid copepod assemblages in relation to environmental conditions near undisturbed coral reefs of Minicoy,southeastern Arabian Sea,a part of the Indian Ocean

The cruise conducted in the spring inter-monsoon (pre-monsoon) of April 2015 in the frame of a funded project epitomized an open ocean survey that allowed procuring a quasi-synoptic picture of cyclopoid copepod community structure in 18 open ocean stations of the Minicoy Island, Lakshadweep archipelago, off the southwestern Indian coast, based on the analysis of standing stock and composition in the integrated 0–10 m water column. The main objective was to explore the community structure of cyclopoid copepods prevailing here and which environmental variable influences the same. It is witnessed that sea surface temperature (SST) (30.42 ± 0.19°C), sea surface salinity (SSS) (33.56 ± 1.15 psu), and dissolved oxygen (DO) (4.32 ± 0.06 ml/L) with SSS and DO are the best matching variables diversifying cyclopoid copepod species (av. abundance 700 ± 386 no. of individuals/100 m³). Average zooplankton biomass (0.03 ml/m³) and abundance (8,989 ± 3,866 no. of individuals/100 m³) were also observed. Fifty-one cyclopoid copepod species belonging to four families and seven genera were identified, with the dominance of high saline species such as Sapphirina, Copilia, Farranula, and Oncaea. An abundance biomass curve (ABC) plot analysis indicated an undisturbed community with normal environmental conditions. TAXDTEST (taxonomic distinctness) depicted a diverse condition where all points clustered together within a 95% confidence level. Our results indicate that the cyclopoid copepod assemblage near Minicoy Island is a diverse, undisturbed community and hypothesize that the stable environmental conditions during pre-monsoon (spring inter-monsoon) preferred the diversification of cyclopoid copepods with the prevalence of high saline species. The data evolved could be used as a standard reference/benchmark to detect any deviation from an undisturbed/diverse community status of Minicoy Island in the looming scenario of climate change in and around the Indian Ocean.     

Benthic Associations of the Shelfbreak and Upper Slope off Ubatuba-SP, South-eastern Brazil

The composition and distribution of the benthic communities at the shelfbreak and upper slope of the Ubatuba region (south-eastern Brazil) were studied from a limited set of 15 dredge hauls taken between 130 and 600 m depth. Data analysis using multivariate methods showed the presence of three distinct benthic associations, related to depth and substratum. The first, between 130 and 180 m depth, was associated with the presence of large amounts of calcareous algal blocks, serving as a shelter for most of the organisms sampled, as well as an important substratum for sessile and filter-feeding animals. The second association was from the slope (240–350 m) comprising organisms exclusive to that area, and species common on shallower stations. The major faunal changes were observed in the third association at 500 m, which presented a fauna totally distinct from the former regions. It is suggested that this area is probably an upper limit for deep-living organisms in the region.     

Reproductive traits of Euterpina acutifrons in a coastal area of Southeastern Brazil

We investigated the reproductive biology of the planktonic harpacticoid copepod Euterpina acutifrons, including morphometric data, egg production rates (EPR) and viability, and weight‐specific egg production. Experiments were carried out during 1 year in an inner‐shelf area off Ubatuba (SE Brazil), a site seasonally influenced by bottom intrusions of the relatively cold and nutrient‐rich South Atlantic Central Water (SACW). We hypothesized that E. acutifrons attain higher reproductive rates when SACW penetrates in this region. Live females were incubated individually in cell culture plates during two periods of 24 h each, under controlled temperature and light conditions. Euterpina acutifrons carried on average 16.9 ± 6.9 eggs·sac^?1, ranging between 10.8 ± 5.7 and 30.8 ± 7.4 eggs·sac^?1. Estimated EPRs ranged from 6.3 ± 3.4 to 13.6 ± 4.2 eggs·female^?1·day^?1, with mean weight‐specific egg production rates of 0.06 ± 0.04 and 0.17 ± 0.08 per day. Euterpina acutifrons was not directly influenced by SACW intrusions, but body length and clutch size were positively related to temperature and chlorophyll content. Egg hatching time was clearly dependent on water temperature, as a 2 °C increase resulted in a decrease of 15 h in egg hatching time. This shows that even a small variation in temperature may considerably affect E. acutifrons population dynamics. Reproductive traits of this pelagic harpacticoid seem, therefore, to be controlled by the trade‐offs between increased food supply and the metabolic demands at low temperatures associated with SACW bottom intrusions toward this coastal area.     

Harpacticoid copepod response to epiphyte load variations in Posidonia oceanica (L.) Delile meadows

We conducted a field experiment to assess the response of phytal harpacticoids to nutrient‐driven increases of epiphyte load in Posidonia oceanica meadows. First, we evaluated differences in species richness, diversity and assemblage structure of phytal harpacticoids in P. oceanica meadows with differing epiphyte loads. Secondly, we conducted a field experiment where epiphyte load was increased through an in situ addition of nutrients to the water column and evaluated the responses of the harpacticoid assemblages. We predicted that there would be changes in the harpacticoid assemblages as a result of nutrient‐driven increases of epiphyte load, and that these changes would be of a larger magnitude in meadows of low epiphyte load. Our results show that the harpacticoid fauna (>500 μm) present in P. oceanica meadows in the Bay of Palma comprised taxa which are considered phytal and other less abundant ones previously described as sediment dwellers or commensal on other invertebrate species. Nutrient addition had an overall significant effect on epiphyte biomass and on harpacticoid abundance, diversity and assemblage structure, possibly as a response to the increased resources and habitat complexity provided by epiphytes. The abundance of dominant species at each location was favoured by nutrient addition and in some cases correlated with epiphytic biomass, although never strongly. This may indicate that structural complexity or diversity of the epiphytic cover might be more important than the actual epiphytic biomass for the harpacticoid species investigated. More species‐specific studies are necessary to ascertain this and clarify the relationships between harpacticoids and epiphytes in seagrass meadows. To our knowledge, this is the first account of harpacticoid species associated with P. oceanica leaves and the epiphytic community they harbour in the Mediterranean Sea.     

Environmental factors associated with a distinct decline in pelagic fish abundance as detected by aerial fish spotting in February and March 1982 off northern South West Africa

Aerial fish-spotting flights were carried out between Cape Frio and Palgrave Point, off the northern coast of South West Africa, during February and March 1982. Results showed a pronounced drop in the number of shoals of pelagic fish (anchovy Engraulis capensis and pilchard Sardinops ocellata) within the area from one month to the next. Consideration of available hydro-acoustic survey data, environmental data and egg counts led to the conclusion that the decline in shoal abundance was brought about by a southward migration of shoals, and that the migration was possibly triggered by environmental changes between January and February 1982. The implied time lag of 14—32 days is difficult to explain, but it could have been a consequence of favourable spawning conditions which still prevailed during February, coupled with the development of dense phytoplankton to the south of the survey area during March.     

Short-term responses to sewage discharge and storms of subtidal sand-bottom macrozoobenthic assemblages off Mar del Plata City, Argentina (SW Atlantic)

This work describes short-term responses of sandy-bottom infaunal macrobenthic communities to environmental disturbances, such as episodic storms and the intertidal sewage discharge of the Mar del Plata City (38° S, 57° W, Argentina). Sewage discharge increases by up to 60% every summer due to tourism pressure. Episodic storms affect the area during autumn-winter and arguably have a cleaning effect on the water and sediment quality. Quantitative data on benthic communities (based on Van Veen grab samples), water and sediment variables were obtained in November 1999 and March 2000. During March the sampling was carried out before and after a storm. Parametric and non- parametric tests showed highly significant differences in both environmental (pH, dissolved oxygen, salinity, temperature, grain size and total organic carbon of sediments) and biological data (species distribution and abundances, density, species number, diversity and evenness), reflecting changes that might be related to increasing sewage discharge between November and March, and to storm effects of March. High values of pH and dissolved oxygen, including a slight stratification in the water column, as well as high values of mean grain size and total organic carbon were observed in March with the increasing sewage volume. Nevertheless, diversity and evenness showed low values, but higher density. The ratio crustacean/polychaetes + molluscs also showed low values compared to November data. Maldanid polychaetes (indicator of low content of organic matter in sediments) dominated in November, but they were replaced by the polychaete Prionospio spp. (indicator of organic enrichment in subtidal areas) and the tanaidacean Kalliapseudes schubarti in March. Before the storm event, values of both environmental and biological data returned to relatively normal conditions, but without reaching the November values, reflecting the disturbance produced by a moderate northern storm. In spite of an inappropriate replication in time, the present results strongly suggest that these changes were related to both sewage disturbance and storm effects. These data are in agreement with and explain the pattern observed in shallow-shelf benthic communities of the SW Atlantic. Implications for environmental management and decision making are discussed, because a pulse disturbance (storms) becomes a press disturbance, keeping the environment healthy in spite of strong pressure and pulse sewage-disturbances.     

Big fish (and a smallish skate) eat small fish: diet variation and trophic level of Sympterygia acuta,a medium‐sized skate high in the food web

The bignose fanskate, Sympterygia acuta, is a small‐to‐medium‐sized species endemic to shallow coastal waters of the Southwest Atlantic. Sympterygia acuta displays a clear seasonal reproductive cycle, characterized by maximum egg‐laying activity in spring and hatching in summer. We hypothesized that diet and feeding activity change with maturity stage and season and that, given its smallish size, the trophic level is low. Using a multiple‐hypothesis modeling approach, the diet of S. acuta in relation to sex, body size, maturity stage, region (i.e. north and south) and season was analysed; and a potential relationship between feeding activity and the seasonal reproductive cycle was assessed. Sympterygia acuta fed on a broad spectrum of prey, but teleosts were more important (47.97% index of relative importance, %IRI), followed by decapods (39.84%IRI), cumaceans (8.31%IRI) and isopods (1.89%IRI). Maturity stage was a strong determinant of the ontogenetic diet shift of S. acuta, and relationships between number of prey consumed with season and region were found.. Feeding activity was higher in the cold season than in the warm season, and was less important in the south region than in the north region. Unexpectedly, the specific trophic level was high (3.87). Sympterygia acuta shifts its diet with maturity stage, possibly by a combination of an improved ability to capture prey and a change in energy demand of mature individuals. Despite being a small‐to‐medium‐sized skate, S. acuta showed a trophic level similar to that of large‐bodied marine predators. It reduces its feeding activity seasonally because in the warm season this species may experience an increased predation risk from large sharks.     

渤海小型底栖动物生物量的初步研究

主要以线虫、桡足类、双壳类、多毛类和动吻5个类群对渤海小型底栖动物的生物量进行了估算,并对其水平分布进行了研究.结果表明,3个航次平均,渤海小型底栖动物年生物量为(干重)0.404g/(m2·a);1998年9～10月和1999年4～5月2个航次中小型底栖动物生物量的水平分布主要表现为渤海中东部和海峡口站位的生物量明显高于其他站位,但在1999年航次,海峡口靠近海岸的站位生物量下降,位于莱洲湾B1站位生物量明显上升.依据小型底栖动物的年生产力P=9B,估算渤海小型底栖动物的年平均生产力为(干重)3.636g/(m2·a).还对渤海小型底栖动物生物量与世界其他海域的进行了比较,认为渤海小型底栖动物生物量的数值与其他海域生物量的数值接近,但略偏低.就不同学者研究所得的线虫平均个体干重进行了比较研究.     

Benthic responses to organic matter variation in a subtropical coastal area off SE Brazil

Organic matter quality, expressed as the proportion of chlorophyll a (Chl a) to degraded organic material (i.e. phaeopigments), is known to influence the structure of benthic associations and plays an important role in the functioning of the ecosystem. This study investigates the vertical distribution of microbial biomass, meiofauna and macrofauna with respect to organic matter variation in Ubatuba, Brazil, a southeastern, subtropical coastal area. On three occasions, samples were collected in exposed and sheltered stations, at high and low hydrodynamic conditions. We hypothesize that benthic assemblages will have high meio‐ and macrofaunal densities and high microbial biomass at the sediment surface at the sheltered site, and lower and vertically homogeneous microbial biomass and densities of meio‐ and macrofauna are expected at the exposed site. The accumulation of fresh organic matter at the sediment surface was observed at both stations over the three sampling dates, which contributed to the higher densities of meiofauna in the first layers of the sediment column. Macrofauna followed the same trend only at the exposed station, but changes in the number of species, biodiversity and feeding groups were registered for both stations. Microbial biomass increased at the sheltered station over the three sampling dates, whereas at the exposed station, microbial biomass was nearly constant. Physical exposure did not influence organic matter loading at the sites and therefore did not affect overall structure of benthic assemblages, which negates our original hypothesis. Most of the benthic system components reacted to organic matter quality and quantity, but relationships between different‐sized organisms (i.e. competition and/or predation) may explain the unchanged microbial profiles at the exposed site and homogeneous vertical distribution of macrofauna at the sheltered site. In conclusion, the high quality of organic matter was a crucial factor in sustaining and regulating the benthic system, but coupled results showed that interactions between micro‐, meio‐ and macrofauna can be highly complex.     

Latitudinal changes in siphonophore assemblages across the Atlantic sector of the Southern Ocean

Siphonophores are commonly considered to be useful indicators of water masses and water-mass movement, but their employment as such across the wider Southern Ocean has not so far been attempted. We redress this here using archived samples, collected during January–February 1993 along a transect from Cape Town to the South African National Antarctic Expedition (SANAE) base in Antarctica, and compare the patterns generated with those determined from a prior analysis of whole assemblages at lower taxonomic resolution. Twenty-one species were identified from 18 of the original 53 samples collected, and two distinct assemblages were confirmed as separated by the Sub-Antarctic Front. That to the south was characterised by low diversity and high abundance and was dominated by cold-water specialists, whereas that to the north comprised a larger number of subtropical and temperate species at low abundance. Assemblage structure was strongly influenced by the mixed layer depth, sea surface salinity and chlorophyll a concentration, as well as mesozooplankton biomass. Congruence with the whole-assemblage study was high, indicating that this taxon can be suitably employed as a proxy in studies such as this. The study emphasises the value of archived plankton samples and makes a plea for better curation.     

深圳湾浮游细菌生物量的时空动态及影响因素

自2015年5月至2016年3月在深圳湾布设了3个站位,对该海域进行了每季至少1次共7个航次的浮游细菌生物量调查。结果表明:(1)深圳湾浮游细菌生物量季节均值的变化范围为(4.90~86.90)×10^-2μg·mL^-1,总均值为3.14×10^-1μg·mL^-1;(2)深圳湾浮游细菌生物量的季节变化模式为:冬季(5.98×10^-1μg·mL^-1)>秋季(3.02×10^-1μg·mL^-1)>夏季(2.79×10^-1μg·mL^-1)>春季(7.52×10^-2μg·mL^-1);(3)从空间分布来看,浮游细菌生物量湾中含量最高,湾口其次,湾顶最低;(4)深圳湾浮游细菌生物量与亚硝氮含量呈极显著的正相关(P<0.01),与氨氮含量呈显著正相关(P<0.05);(5)深圳湾水体中浮游细菌丰度季节均值变化范围为(2.45~43.50)×10⁶个·mL^-1,年均值达1.57×10⁷个·mL^-1;(6)从整体的细菌丰度及生物量来看,深圳湾海域呈现富营养化状态,湾中最严重,湾口次之,湾顶最轻。