Population structure and temporal variation of the roughneck shrimp Rimapenaeus constrictus (Decapoda: Penaeoidea) in a coastal bay of the Southwestern Atlantic

Few studies have been performed regarding long-term variation of penaeids in coastal areas, especially of the marine shrimp Rimapenaeus constrictus, which is distributed along the western Atlantic Ocean (Canada to Brazil). This is the first study of R. constrictus in the Guanabara Bay, a tropical bay on the southern coast of Rio de Janeiro state, Brazil. We aimed to describe its population structure, focusing on sex ratio, abundance, size class and allometry, as well as its relationship with abiotic factors, over five years. Monthly trawls were carried out from January 2011 to December 2015, using a shrimp fishing boat equipped with a single-rig net. The shrimps were identified and sexed and the carapace length and total weight were measured. A total of 6358 individuals were sampled. Females were more abundant and larger than males, a common pattern found in penaeids. The annual abundance peak, which occurred in 2013, was influenced by total rainfall and seasonal peaks occurred in winter and spring. Abundance was positively related to salinity (r_s: 0.31, p?<?0.05), suggesting that the shrimp’s presence near shallower coastal regions is due to the presence of marine water at the bottom and/or a stronger stratification of the water column in the bay. A low seasonal variation in female allometry can be the result of a constant investment in gametogenesis, and a high seasonal variation in allometry for males can be due to their short life cycle, as was found in previous studies of the same species in other coastal regions worldwide.     

A mantle length structured stock assessment model for the jumbo squid,Dosidicus gigas,fishery of the Ecuadorian Pacific: a limited data approach

The jumbo squid Dosidicus gigas is a new fishery resource in Ecuador; the species is harvested from January to December every year. Biological sampling was carried out each month during March–December (2013) and January–December (2014) in different coastal zones off Ecuador, and the monthly mantle length (ML) composition was obtained from field data in the coastal areas. The catch-at-mantle length data were analysed based on the mantle length structured model (CAMLA). The results showed that the biomass of D. gigas in Pacific Ecuadorian waters was 641,915 t (2013) and 1,866,857 t (2014). For 2013, for squid smaller than 30?cm ML the biomass was greater than 30,000 t, while individuals between 35 and 48?cm ML had an estimated biomass varying between 35,000 and 45,000 t. During 2014, the biomass estimated for squid smaller than 30?cm ML was low (40,000 t or less); however, squid between 38 and 48?cm ML showed a change in biomass compared with the previous fishing season, varying from 100,000 to 190,000 t. The harvested rate-at-mantle length for squid larger than 35?cm ML was higher than for individuals between 12 and 30?cm ML. The CAMLA model was found to be appropriate for modelling catch-at-mantle length of jumbo squid in Ecuadorian waters, and the model can be used to obtain harvest management quantities, as well as quantitative outputs useful for Ecuadorian stakeholders.     

Age estimation methods in the marine gastropod Buccinanops globulosus comparing shell marks and opercula growth rings

Age determination in gastropods is an essential tool for understanding the main aspects of population dynamics that allow for the formation of fisheries policies. Small-scale fisheries of the nassariid gastropod Buccinanops globulosus from northern Patagonia are not yet regulated, although it is locally consumed while an incipient commercialization is taking place. The aim of this study was to show the suitability of opercula readings for age estimation in B. globulosus, compared with shell marks, previously validated by the analysis of the stable isotope of oxygen. The individual age estimated by the opercula rings reading method did not match the estimation made by the shell marks reading method. Stable isotope analyses confirmed that shell marks were deposited annually. Proper age estimation for B. globulosus, based on recognizable external shell marks, reached up to 9 years.     

Diversity of bacterial communities related to the nitrogen cycle in a coastal tropical bay

A culture-independent molecular phylogenetic analysis was carried out to study for the first time the diversity of bacterial ammonia monooxygenase subunit A (amoA) and nitrogenase reductase subunit H (nifH) genes from Urca inlet at Guanabara Bay in Rio de Janeiro, Brazil. Most bacterial amoA and nifH sequences exhibited identities of less than 95% to those in the GenBank database revealing that novel ammonia-oxidizing bacteria and nitrogen-fixing microorganisms may exist in this tropical marine environment. The observation of a large number of clones related to uncultured bacteria also indicates the necessity to describe these microorganisms and to develop new cultivation methodologies.     

Bivalve suspension-feeding dynamics and benthic-pelagic coupling in an eutrophicated marine bay

The open exposed Laholm Bay in the Kattegat is eutrophicated through riverine input, mainly of N. The benthic macrofauna down to 10 m depth (60 km²) is dominated by the suspension-feeding bivalves Cardium edule and Mya arenaria. To estimate the seasonal and annual consumption of seston by the suspension-feeders in Laholm Bay, we carried out three sets of observations. (1) The abundance and biomass of the macrofauna in this depth interval were assessed along eight transects. (2) The secondary production of the two bivalves was estimated over a 10-month period in two sampling squares. (3) The filtration rate of C. edule was determined in natural seawater in laboratory experiments during different seasons. The bivalves can in theory filter all of the water volume down to 10 m in 3 days and, thus, make a significant impact on the phytoplankton concentration. In our study, however, they filtered only approximately half of their potential feeding capacity, perhaps because food availability was low due to low turnover close to the bottom or due to physical disturbance. The majority of the phytoplankton is exported from the bay. Bivalve abundance, biomass, production and growth rate were moderate and generally lower than in adjacent areas to the north. In autumn, the bivalves consumed >90% of the seston in comparison with net-zooplankton consumption. An energy-flow diagram for the bivalves is presented including estimates of bivalve N excretion and biodeposition.     

Structuring of bacterioplankton diversity in a large tropical bay

Structuring of bacterioplanktonic populations and factors that determine the structuring of specific niche partitions have been demonstrated only for a limited number of colder water environments. In order to better understand the physical chemical and biological parameters that may influence bacterioplankton diversity and abundance, we examined their productivity, abundance and diversity in the second largest Brazilian tropical bay (Guanabara Bay, GB), as well as seawater physical chemical and biological parameters of GB. The inner bay location with higher nutrient input favored higher microbial (including vibrio) growth. Metagenomic analysis revealed a predominance of Gammaproteobacteria in this location, while GB locations with lower nutrient concentration favored Alphaproteobacteria and Flavobacteria. According to the subsystems (SEED) functional analysis, GB has a distinctive metabolic signature, comprising a higher number of sequences in the metabolism of phosphorus and aromatic compounds and a lower number of sequences in the photosynthesis subsystem. The apparent phosphorus limitation appears to influence the GB metagenomic signature of the three locations. Phosphorus is also one of the main factors determining changes in the abundance of planktonic vibrios, suggesting that nutrient limitation can be observed at community (metagenomic) and population levels (total prokaryote and vibrio counts).     

Relative growth and size at onset of sexual maturity of the brown crab,Cancer pagurus in the Isle of Man,Irish Sea

In this study, the relative growth, size–weight relationships and size at onset of maturity of the brown crab Cancer pagurus were investigated in the Isle of Man. For the analyses of relative growth and size at onset of maturity, the samples were collected seasonally between autumn 2012 and spring 2013 using several methods: pot surveys, dredge and trawl surveys, market surveys and shore surveys. Results showed that allometric growth occurred in the chelipeds of males (n?=?87) and in the abdomen of females (n?=?222). Four different measures of maturity (behavioural, functional, morphometric and physiological) were examined. With respect to the behavioural maturity, the smallest female crab found with a sperm plug measured 110?mm CW, whereas in terms of functional maturity the smallest ovigerous female had a CW of 134?mm. Based on direct observations of gonad maturity, 50% of females were mature at 108?mm CW, whereas 50% of males were mature at 89?mm CW. The size at the onset of maturity measurements of female and male C. pagurus based on gonad development is smaller than the current minimum landing size (130?mm), and therefore this suggests that the current minimum landing size is an adequate management measure.     

Anoxia in a coastal bay: case study of a seasonal event

Bahía Concepción (Gulf of California) was studied to describe some extremely low dissolved-oxygen values at the bottom of the bay. Surveys included measurements of vertical distribution of temperature, dissolved oxygen, nitrate, nitrite, phosphates and hydrogen sulfide. Thermal stratification from early spring to autumn and a well-mixed water column during the winter were present. Dissolved-oxygen concentration was homogeneous in the water column from winter to spring (5-7 mg L-1). From summer to autumn, bottom dissolved oxygen (> 20 m) decreased to reach conditions of hypoxia (1-2 mg L-1) or anoxia; nitrate, nitrite, and phosphates increased (up to 13, 1.7 and 2.2 microM) followed by a last short period of a deep hydrogen sulfide layer (up to 3.1 mg L-1). A back calculation to estimate the input of organic matter in the deep layer showed that 18 g C m-2 y-1 needed to be trapped in the bottom to induce such an oxygen depletion. This period is thought to be unfavorable for bottom infauna in this bay.     

Spatial variations in macrobenthic fauna recolonisation in a tropical mangrove bay

Recolonisation by crab species and sediment-infauna taxa (at class level) in artificially regenerated mangrove stands of Avicennia marina, Rhizophora mucronata and Sonneratia alba (5 yr old) were studied using respective bare sites (open without mangroves or denuded) and natural sites (relatively undisturbed) as controls. The controls were chosen based on site history, physical proximity and tidal inundation class in reference to the particular reforested mangrove stand and samples randomly taken. A number of environmental variables were measured; interstitial water salinity and temperature (measured at low tide) were lower, whereas sediment organic matter content was higher in the areas with mangrove cover, with the natural sites having the highest content. The bare sites were generally sandier, whereas the areas with mangrove cover had higher proportions of clay and silt. Generally, there was a higher crab density in the reforested sites than in the bare sites, whereas crab species diversity (Shannon diversity index) did not vary from one site to another for any of the mangrove species. In terms of crab species composition, the reforested sites were more similar (Sørensen similarity coefficient) to the natural sites and less to the bare controls. For sediment-infauna, the reforested sites had a significantly higher density than the respective bare controls, while the natural sites had the highest density. The number of sediment-infauna taxa in both the reforested and natural sites of all the mangrove species was similar and higher than in the comparable bare sites. The results suggest that the reforested sites are supporting more faunal recolonisation, and therefore becoming more akin to the natural mangrove sites in terms of the investigated functional indicators. The findings seem to support the use of artificial mangrove regeneration (in areas where natural regeneration has been impeded by physical conditions or otherwise) as an effective management tool in the restoration and conservation of the functional integrity of degraded mangrove habitats.Key words: Crabs, Environmental variables, Kenya, Recolonisation, Restored mangroves, Sediment-infauna     

Phylogeny and historical biogeography of the loliginid squids (Mollusca: cephalopoda) based on mitochondrial DNA sequence data

The cephalopod taxon Loliginidae (Cephalopoda: Myopsida) is a species-rich group of tropical and temperate shallow-water squids, many of which are commercial fisheries objects and neurophysiological research organisms. The worldwide distribution of these squids could make Loliginidae a useful case study in shallow-water marine biogeography, but the phylogeny of the group is unknown. To clarify loliginid phylogeny, regions of two mitochondrial genes (the 16S rRNA and the cytochrome c oxidase subunit I genes) were sequenced for members of 19 loliginid species and several outgroups. Maximum-parsimony and maximum-likelihood analyses were performed on a combined data set, as well as on each data set individually. Analyses of the combined data support loliginid monophyly and reveal four clades-one consisting primarily of species in American waters from two genera, one composed of 3 east Atlantic species, one consisting of the bioluminescent loliginids (Uroteuthis sensu Vecchione et al., 1998) plus Loliolus japonica, and one represented by a Loligo (Alloteuthis) subulata-Lolliguncula mercatoris pair. The likelihood of the unconstrained maximum-likelihood tree is not significantly better than the likelihoods of the best trees constrained to Sepioteuthis monophyly or Uroteuthis monophyly, but there is significant support for Lolliguncula polyphyly. Tests of alternative hypotheses of loliginid cladogenesis suggest that cladogenesis within Loliginidae is correlated with the widening of the Atlantic and the closure of the Tethys Sea, although dispersal from the Indo-West Pacific is a reasonable explanation for the origin of the clade of American loliginines.     

High abundance of dioecious plants in a tropical coastal vegetation

We examined the frequency of hermaphroditic, monoecious, and dioecious species of angiosperms in restinga (sandy coastal plain) vegetation in SE Brazil. The study site was a vegetation mosaic comprising nine plant formations, ranging from open types to forest. Dioecy (14% of 566 species) was similar to other tropical vegetations and strongly associated with woodiness and entomophily. However, more interestingly, there was an exceptionally high percentage (35%) of dioecious species among the dominant woody plants. This pattern has not been previously reported, and we discuss the extent to which it is ecologically driven. We argue that the high abundance of dioecious plants in this resource-poor environment can be attributed to ecological traits related to long-distance dispersal, ecological vigor, and possibly, vegetative reproduction.     

Embryonic development time of Penilia avirostris Dana, 1852 in a tropical bay in Brazil.

Development time of embryos in the brood pouch of the cladoceran Penilia avirostris Dana, 1852, was estimated by collecting zooplankton daily for 15 days in surface water of Guanabara Bay, Brazil. Each day the maturity stage of embryos of 90 parthenogenic females was noted. Total development time (egg to birth) varied from 2 to 3 days, the immature phase (stages I to IV) being generally longer (2 days) than intermediate and mature phases (1 day, stages V to XII). Similar results were obtained from Bottrell's equation, which takes water temperature into account.     

Identification of a globally distributed clinical streptomycin-resistance plasmid and other resistance determinants in a coastal bay of China

Aims: To study streptomycin‐resistant bacteria isolated from Jiaozhou Bay and their molecular determinants of resistance. Methods and Results: Twenty‐seven tetracycline‐resistant and 49 chloramphenicol‐resistant bacterial isolates from surface seawater of Jiaozhou Bay were selected for investigation. More than 88% of these isolates were resistant to streptomycin. Half of the streptomycin‐resistant bacteria harboured the strA–strB gene pair, and six isolates carried Tn5393‐like transposons by PCR detection. The p9123‐related plasmids containing the sul2–strA–strB gene cluster were characterized in two environmental Escherichia coli isolates. Transposon Tn5393 was first identified on a Klebsiella pneumoniae plasmid, which also carried Tn1721, estP and umu genes responsible for antimicrobial and insecticide resistance. Conclusions: Coresistance to streptomycin and tetracycline or chloramphenicol was found with high frequency. p9123‐related plasmid and Tn5393 transposon may contribute to the wide distribution and spread of the strA–strB gene pair in Jiaozhou Bay. The detection of streptomycin‐resistance plasmid pQ1‐1 from Jiaozhou Bay seawater bacteria and human bacterial pathogens from USA indicates its global dissemination and transmission, across different components of the microbiota on earth. Significance and Impact of the Study: Streptomycin resistance can be recognized as an important bioindicator of environmental quality, owing to its association with anthropogenic pollution and the multidrug‐resistant microbiota.     

Seasonal and spatial variations of fish trophic guilds in a shallow,semi-enclosed tropical estuarine bay

A study on seasonal and spatial variations of feeding habits and trophic guilds of dominant fish species in Pattani Bay during March 2003 to February 2004 was aimed at classifying diet composition, identifying dominant food components of each species, categorizing trophic guilds of the community and evaluating effects of habitat characteristics and seasonality on guild organization. Most fishes showed high food intake, fed on a diverse range of food items but relied heavily on calanoid copepods and shrimps. All species, with the exception of Epinephelus coioides, were classified as specialist feeders. Four main dietary guilds were classified. Three of these were classified as the guilds dominated by at least two major food items. Significant variations in trophic guilds of 28 fish species based on habitat types and seasons were also identified. They could be divided into three seasonal groups and three site-groups and a single site. Trophic organization for each season and habitat ranged from two to four groups. This information identifies groups of fishes that seasonally and spatially utilize different food resources within a semi-enclosed estuarine bay ecosystem.     

Utilisation of a tropical bay as a nursery area by sharks of the families Carcharhinidae and Sphyrnidae

Synopsis At least eight species of sharks of the families Carcharhinidae and Sphyrnidae use Cleveland Bay in northern Australia as a communal nursery area.Carcharhinus dussumieri, C. fitzroyensis, C. limbatus andC. tilstoni use the bay as a seasonal primary nursery, with juveniles occurring in it for only a few months each year immediately after birth. Alternatively,Carcharhinus sorrah, Rhizoprionodon acutus andR. taylori use the bay as a year-round primary and secondary nursery, with juveniles remaining in it up to the size at maturity. AdultR. taylori also persist in the bay, a behavioural pattern possibly explained by their small maximum size. While present immediately after birth the type of utilisation pattern displayed bySphyrna lewini could not be clarified in this study. Although diets of these species in the bay are similar, there is probably little direct competition for food due to the highly productive habitats in the bay supporting an abundance of food resources. The highest numbers of juveniles occur when prey species are the most abundant, and when temporal separation of some seasonally-occurring species of sharks in effect.     

Scaling patterns of plankton diversity: a study of ciliates in a tropical coastal lagoon

Although spatial and temporal variation in plankton diversity is regularly investigated in surveys, experiments, and models, there is a lack of methods for predicting spatial patchiness of plankton diversity. We develop and apply a suite of geostatistical and multiple-regression analysis tools to assess ciliate diversity in a tropical coastal lagoon; these methods can predict spatial and temporal patterns of diversity, provide error estimates associated with these predictions, and assess which environmental factors may drive diversity patchiness. Geostatistical analysis was applied to H′ (Shannon diversity index) from 25 to 35 data collected from a sampling grid (40 × 40 m), and 10 dispersed lagoonal sites, in the dry and rainy seasons, on numerous occasions. Conditional simulation and kriging were used to predict diversity at the lagoonal and small scales, respectively. The relationship between diversity (H′) and the environment was examined by multiple-regression analysis. Thirty-six ciliate morphospecies occurred; H′ ranged from 0 to 1.9 and was patchy. Multiple regression indicated ciliate diversity changed seasonally, increasing when the sand bar was open and the lagoon was connected with the sea. Geostatistical analysis extended the recognition that seasonal changes alter diversity: when the rainy season produced a variable environment, relatively small scale patches and diversity gradients occurred; in the dry season, when the lagoon was physically uniform, larger and fewer diversity patches occurred; at the sublagoonal scale, diversity patches were similarly structured in the two seasons. Results indicate environmental variability and immigration can be the main drivers behind ciliate diversity in the lagoon. We recommend the patterns these data reveal and methods we employ be considered when further studies are continued to examine diversity on local and larger scales. Handling editor: S. Declerck     

The structure of shallow water fish assemblages in sandy beaches of a tropical bay in the southwestern Atlantic

Ichthyological Research - The spatial and seasonal dynamics of shallow water fish assemblages and their relationship with physical-chemical variables were investigated on Guanabara Bay, one of the...