The technical difficulties of performing underwater observation mean that marine ecologists have long relied on behavioural experiments to study reactions of marine organisms. In this article, we examine the underlying complexity of assumptions made in raceway experiments and we propose a statistical inference procedure tailored to this type of experimental protocol. As an example, experiments were performed to test if light of two different intensities affects the proximal behaviour (i.e. direct, local and immediate) of two species of crustaceans, the hermit crab (Pagurus bernhardus), and the green crab (Carcinus maenas). Individuals were collected in the vicinity of the Sven Loven Marine Center in Tjarnö (Sweden). Their movements in raceways were recorded and the statistical distance between the resulting experimental distribution and a simulated null distribution was used to compare their behaviour in two situations: dim (when they were expected to feed) and bright light (when they were expected to shelter). Initial tests indicated no differences of behaviour between dim and bright light for the two species. However, when compared with the reference state (here, a null distribution) the behaviour in dim light deviates significantly from the null distribution suggesting non-random behaviour. Our results suggest that efforts should be made to understand the behaviours of the individuals of these two species to establish a comprehensive reference state as a basis for comparison. This fundamental information should be a prerequisite before implementing experiments testing how potential disturbances affect individual organisms in behavioural ecology.

The present study aims to assess the environmental quality of six estuaries in north-eastern Brazil, using biochemical composition and quantity of organic matter in tropical sediments. Samples were collected monthly during spring low tide from August 2011 to July 2012, in the mid-littoral. Concentrations of organic matter and its biochemical composition reflected the degree of anthropogenic pressure. Although total concentrations of proteins and carbohydrates were similar among estuaries with contrasting levels of anthropogenic pressure, the protein to carbohydrates (PRT : CHO) ratio effectively reflected the trophic state of these areas. PRT : CHO ratios >1 were observed in all studied areas suggesting eutrophic conditions or an initial stage of eutrophication in all of them. Low Chl-a/Phaeo ratios may be associated with the level of eutrophication of each area, however it may also reflect the natural productivity or the presence of mangrove debris. These results were compared with those obtained in previous environmental assessments of the same estuarine areas using the AZTI Marine Biotic Index and monitoring reports showing good agreement. The present study confirmed for the first time in tropical estuarine areas that the biochemical approach can be successfully used to assess the trophic state of the benthic compartment.

Although necessary for sustainable management of coastal ecosystems the understanding of trophic ecology of kelp fishes remains largely limited in the NE Atlantic. In this paper, stable isotope ratios of carbon (C) and nitrogen (N), complementarily with analyses of stomach contents, were used to investigate the trophic ecology of an Atlantic kelp forest fish assemblage targeted by spear fishers in Galicia (NW Spain). Trophic habits of the fishes were consistent across the species ranges and six trophic niches were identified. Chelon labrosus was the only pelagic omnivore, while Conger conger and Dicentrarchus labrax were the principal predators, preying on benthic osteichthyes. The intermediate carnivorous Diplodus sargus mainly preyed on benthic molluscs, while Labrus bergylta exploited a wider range of prey. Although associated with different trophic niches, the two morphotypes of L. bergylta showed some degree of diet overlap, providing little support to the hypothesis of their separate management. Moreover, L. bergylta can be a keystone species whose adequate management has relevant implications for the sustainable use of the European kelp forest ecosystems.

The worldwide population of the leatherback turtle (Dermochelys coriacea) encompasses seven subpopulations among the Pacific, Atlantic and Indian Oceans. It has experienced declines across parts of its distribution, with the subpopulation of the South-west Atlantic listed as critically endangered by the IUCN Red List. The main threats to this subpopulation include its interaction with fisheries, coastal development, pollution and climate change. In this study, we sequenced mitochondrial DNA from 52 leatherback turtles in Brazil and combined these with published data from other Atlantic Ocean rookeries. The haplotype diversities of the Atlantic population rookeries ranged from 0.112 to 0.533 and are not directly proportional to current rookery sizes. The Brazilian rookery, despite recording low nest numbers per year, had the second-highest haplotype diversity among all Atlantic rookeries (h = 0.532). A mixed-stock analysis revealed that the South American pelagic aggregate is primarily composed of individuals from West Africa (84%), with contributions from the North Atlantic rookeries (14%). Leatherback turtles appear to have a complex phylogeographic pattern, showing evidence of multiple colonization events and a lack of isolation by distance. Our novel dataset, based on DNA sequences of 695 base pairs, will provide baseline data needed to understand population dynamics in the region, building comprehensive population assessments to support and develop management strategies. Having both the only known regular rookery in the South-west Atlantic, and a mixed-origin foraging area for the species along its coast, Brazil has a key role in the conservation of the leatherback turtle.

Biofilm-dwelling protozoa are a primary component of microbiota and play important roles in the functioning of microbial food webs such as the mediation of carbon and energy flux from plankton to benthos in marine ecosystems. To demonstrate the vertical pattern of the protozoan communities, a 1-month baseline survey was carried out in coastal waters of the Yellow Sea, northern China. A total of 40 samples were collected using glass slides as artificial substrates at four depths: 1, 2, 3.5 and 5 m. A total of 50 species were identified, comprising seven dominant and eight commonly distributed species. Species richness and individual species abundances showed a clear decreasing trend down the water column from 1 to 5 m, although the former peaked at a depth of 2 m. Multivariate approaches revealed that protozoan community structure differed significantly among the four depths, except for those at 2 and 3.5 m. Maximum values of species richness, diversity and evenness generally decreased with depth although they peaked at either 2 or 3.5 m. These results suggest that water depth may significantly shape the community patterns of biofilm-dwelling protozoa in marine ecosystems.

A study was conducted over eight consecutive days in February 2010 in which daily variations in the vertical distributions of heterotrophic bacteria, mesozooplankton and ichthyoplankton at 1–1200 m in the South-western Atlantic Ocean were investigated. Diurnal and nocturnal samples were collected at an oceanographic station at four regional depths: Tropical Water (TW) (1 m), South Atlantic Central Water (SACW) (250 m), Antarctic Intermediate Water (AAIW) (800 m) and Upper Circumpolar Deep Water (UCDW) (1200 m). Bacterial, mesozooplankton and larval fish densities significantly differed between sample depths but not between sampling tow times. In total, 154 zooplankton species and 18 larval fish species were identified. The highest number of taxa was obtained from the night-time TW trawls. This depth zone had the highest densities of mesozooplankton, larval fish and bacterioplankton (auto and heterotrophic), associated with the highest temperature and salinity and the lowest inorganic nutrient concentrations. Two sample groups were identified based on their mesozooplankton and larval fish compositions: night-time TW and other water masses (daytime TW, SACW, AAIW and UCDW). Thirty-two indicator species were detected in night-time TW. The copepod Nullosetigera impar was, to the best of our knowledge, identified for the first time on the Brazilian coast. Our results showed significant variability in the abundance and vertical distribution of mesozooplankton, bacterioplankton and larval fish along the water column in an oceanic area. We have provided new data and insights on the composition and vertical distribution of mesozooplankton, larval fish and bacterioplankton in deep waters in the South-western Atlantic Ocean.

Siphonophores are colonial hydrozoans that feed on zooplankton including fish larvae, and occur throughout the world's oceans from surface waters to ocean depths. Here we describe the composition of hyponeustonic siphonophores (0–3 m depth) from the tropical Colombian Pacific Ocean based on 131 plankton samples collected between June–October from 2001–2004. Samples were dominated by species of Calycophorae, with only three species of Physonectae identified, consistent with their deeper depth distribution. Muggiaea atlantica, Chelophyes contorta, Diphyes dispar, and Eudoxoides mitra were the most common of the 21 species identified. We found moderate structuring of the siphonophore community by the salinity gradient from inshore to offshore, and greater richness during the night because of diel vertical migration. Temperature did not play a significant role in structuring siphonophore communities, perhaps because of the narrow temperature range observed (3.5 °C). We extend the known temperature and salinity range of several species, including M. atlantica up to temperatures of 28.6 °C and salinities down to 24.7. Interestingly, only polygastric stages of M. atlantica were found, suggesting the reproductive stage of M. atlantica in tropical waters might be found in deeper waters. Chelophyes appendiculata was rare in our study and C. contorta was common, providing evidence they have a potential allopatric relationship, with C. contorta replacing C. appendiculata in warm water. Finally, we found siphonophore abundance was positively related to the abundance of copepods and fish eggs, with the top 13 most abundant species all having positive correlations, suggesting siphonophore abundances are tightly controlled by their food.

This study evaluated the population structure, growth and longevity of Xiphopenaeus kroyeri in the State of Sergipe. The obtained data were compared with other populations on a latitudinal scale in order to evaluate whether the latitudinal paradigm applies to this species. Shrimp sampling took place monthly from September 2013 to August 2014, in nine stations distributed at 5, 15 and 30 m depths, using a shrimp fishery boat equipped with a ‘double rig’ net. Sexual maturity was estimated by the logistic function y = a/(1 + b*exp(-cx)), and the sex ratio was analysed with the Chi-square test. The individual growth rate was estimated using the von Bertalanffy model, and the longevity was estimated by the inverse form of this formula. A total of 6418 (3457 females and 2961 males) was analysed. The size at onset of sexual maturity was 12 mm of carapace length (CL) for males and 12.5 mm CL for females. The total sex ratio did not differ from the expected (1:1). Males exhibited higher growth coefficients (k) and smaller asymptotic growth (CC∞ = 28.74 mm, k = 0.0081 day−1) than females (CC∞ = 30.79 mm, k = 0.0058 day−1). The estimated longevity (years) was 1.55 for males and 2.15 for females. No evident latitudinal pattern was observed regarding the size at onset of sexual maturity or the growth parameters for X. kroyeri. The information found, besides contributing to the knowledge about the biology of this shrimp, can also clarify hypotheses presented in relation to the latitudinal paradigm along the Brazilian coast.

Details on size at first maturity, embryo number and size, brood chamber volume and reproductive output of deep-sea armoured shrimp, Glyphocrangon investigatoris caught off the south-east coast of India by using EXPO trawl from 633 m depth in FORV ‘Sagar Sampada’ are reported here. Eighty-four female shrimps ranging from 17.29–36.31 mm carapace length and 2.28–16.54 g weight formed 7.73% of total catch, 30% of which was constituted by embryo-bearing females. Regression of weight on carapace length revealed negatively allometric growth (r2 = 0.85, P < 0.01). The size at first maturity was estimated as 19.96 mm. The embryo number ranged from 55 to 233 with a mean of 120.24 ± 34 embryos and showed a positive correlation to body size. Embryo diameter varied between 1.0 to 3.34 mm and more than 50% of embryos constituted the 2.0–2.5 mm size class. Brood chamber volume and percentage frequency of embryo stage development revealed a linear relationship with carapace length. Based on dry weight, mean reproductive output was estimated to be 0.16. The female armoured shrimps showed a high reproductive investment evidenced from few, large, yolky embryos, indicating their deep-sea adaptation.

The population and reproductive characteristics of the hermit crab Pagurus proximus Komai, 2000 have been examined in the northern part of the species range (Vostok Bay, Peter the Great Bay, Sea of Japan). The average population density was 4–5 ind m−2 in winter and spring, 10 ind m−2 in summer and autumn; the biomass was 7–9 and 18–19 g m−2, respectively. Hermit crabs were found at a depth of 0 to 12 m but were most numerous at about 3 m depth with an average population density of up to 26 ± 7 ind m−2. The shield length of males varied from 1.3 to 7.8 mm and females from 1.2 to 6.7 mm. The male to female ratio was close to 1 but varied with size and season. Females attained sexual maturity at a shield length of more than 1.3 mm. Ovigerous females were found from December to August. The proportion of ovigerous females increased from 7% in December to 93% in late April; however, the embryos in clutches remained at early developmental stage until May. The mass release of larvae was observed at the beginning of June. A subsequent spawning probably took place in July. The main factors contributing to the high abundance of P. proximus in the investigated area are the presence of the embryonic diapause synchronizing the release of larvae at the most favourable time for their development, high fecundity, the presence of at least two egg clutches during the reproductive season, and total absence of parasites.

We analysed the morphological variations through geometric morphometric approaches of the dorsal and ventral views of growing male and female Callinectes danae Smith 1869, based on the hypothesis that swimming crabs present polymorphism during growth. Our research identified six instars for females, seven instars for males and one instar for unsexed individuals (young). The sixth instar of females and the seventh instar of males were composed of adults. We identified 20 landmarks from the dorsal view, and 16 landmarks from the ventral view. Based on canonical analysis and Procrustes distance, we observed the formation of clearly separated instars (both views), indicating a significant change during ontogeny, not only in the pubertal moult. The most prevalent changes occurred in the abdomen, with males thinning and females broadening the abdomen during growth. In the dorsal view, we observed a displacement of anterolateral spines to the posterior region throughout the growth period and that the anterolateral and frontal teeth of juveniles were more ornate than those of adults. The ontogenetic trajectories for males and females have similar origins and follow different directions over the instars, with maximum distance after the pubertal moult (P < 0.05).

Brown crab contributes to small-scale fisheries in the Isle of Man and landings (495 t) were worth in excess of £0.5 million in 2012. The present study sought to fill evidence gaps needed to improve the scientific understanding of this fishery. Observer data were collected to examine the spatial and temporal variations in the size distribution and sex ratio of crabs around the Isle of Man. This study also aimed to evaluate the catch characteristics of brown crab using logbook data (2007–2012), observer data (2012–2013) and questionnaire survey data (2013). The sex ratio is highly variable in different areas across seasons and was perhaps indicative of migration patterns in relation to mating. This change was most notable with a strong increase in the proportion of females to the south and west of the Isle of Man in the autumn months. The depth and pot volume were important factors that influenced the catch per unit effort (CPUE). Future survey designs would need to ensure adequate spatial coverage of the east and west coast of the Isle of Man together with a seasonal sampling regime that captures the spatial change in the distribution and abundance of male and female crabs.

The gastropod shell influences important aspects of the hermit crab's life; however, the shells are commonly a limited resource. Therefore, different hermit crab species that coexist in intertidal areas are commonly involved in intraspecific and interspecific competition for shells. We assess if differences in shell preference, exploitation ability, or competition by interference can explain the partitioning of shells between the coexisting species Calcinus californiensis and Clibanarius albidigitus. Clibanarius preferred shells of Nerita funiculata among the six gastropod shells tested, while Calcinus did not establish a hierarchy in shell preference. Therefore, the preference for gastropod shell species does not seem to diminish the competition for shells in the wild. Clibanarius identified and attended to chemical cues signalling potential sites of available shells (chemical cues of dead gastropods); Calcinus did not respond to these cues (competition by exploitation). However, Calcinus was more successful in obtaining a new shell by interspecific shell fighting than Clibanarius. Consequently, the use of better quality shells (intact shells) by Calcinus in the wild can be explained by its greater fighting ability compared with Clibanarius. The bias in shell distributions through dominance by shell fighting, more than by exploitation ability, has also been suggested for other hermit crab species of these genera.

The aim of this study was to analyse the population dynamics of Xiphopenaeus kroyeri in Sergipe, Brazil. Four samples were collected monthly from shrimp trawlers based in the municipality of Pirambu from March 2015 to May 2016. Carapace length (CL), total length (TC), live weight (LW), sex and maturity stages were obtained for each specimen. A total of 13,035 individuals were analysed with an overall sex ratio of 1:1. However, this ratio favoured females in larger sizes, which reflects a reproductive strategy, as their larger size allows for larger gonads, higher fertility and production of more eggs. An inflexion point was observed in the relationship between total and carapace length, probably related to reproduction, as this occurred after first maturity. A reproduction peak was observed in August–September, which does not correspond to the closed season. The parameters estimated for a seasonally oscillating version of the von Bertalanffy growth function were CL∞ = 33 mm and K = 1.5 year−1 for females, and CL∞ = 31 mm and K = 1.7 year−1 for males (C = 0.6 and WP = 0.8 for both sexes). These estimates do not support the latitudinal rule in terms of larger sizes in higher latitudes, which may be associated to methodological differences, occurrence of more than one species along the South-western Atlantic coast, sampling bias, exploitation status and unbalanced availability of studies. The instantaneous total mortality rate was high and should be further investigated to allow for the definition of the exploitation status of seabobs in Sergipe.

This study consisted in the characterization of reproductive aspects such as oocytes morphology, temporal variation in size and frequency of oocytes and the reproductive cycle of the mussel Brachidontes rodriguezii. This species dominates the rocky intertidal coast of Buenos Aires province, Argentine and is a prey item of several exploited species; however, due to the introduction of piers and seawalls, as a consequence of anthropogenic activities, the species also inhabits sandy coasts. Mussels were collected from May 2011 to May 2013. Gonad tissue samples were processed according to standard histological procedures. Four gonadal development stages were described for males and females. According to the significant decrease in the frequency of mature oocytes, the spawning events were detected between February and May. However, some evacuation events were recorded in June–July. This study reports the first record of two modalities of hermaphrodites in this species; individuals with male and female gonads and individuals with both types of gametes within a gonad.

Tropical coastal areas are amongst the most diverse ecosystems in the world. However, there are quite a few coasts that have rarely been studied for their macro-benthic diversity. The Indian coastline presents one such gap area. Two sub-parallel coastlines of India have a wide latitudinal span (8–23°N) and strikingly different physiographic environments. While the east coast receives a high siliciclastic input from large river systems flowing to the Bay of Bengal with fluctuating salinity, the west coast has a large shelf area and high productivity of the Arabian Sea. Such difference enables us to evaluate the effect of regional environmental parameters on marine molluscan diversity and distribution in an intra-tropical setting. Because of the wide latitudinal range, it is also possible to assess if spatial difference in species richness in such a regional scale follows the large-scale biodiversity pattern such as Latitudinal Biodiversity Gradient (LBG) despite inherent environmental variation. We used species distribution of marine bivalves, compiled using bioSearch and the Ocean Productivity database, to address this question. Our results show that intra-tropical species richness of marine bivalves is guided primarily by regional environmental parameters. Even with identical latitudinal extent, higher nutrient availability and larger shelf area, the west coast has significantly lower richness than the east coast; among environmental variables, productivity, salinity and coastline length emerged as significant predictors of species diversity. Moreover, a positive influence of a South Asian biodiversity hotspot on east coast fauna and a negative impact of the oxygen-depleted condition of Arabian Sea on west coast fauna, may have a significant contribution in developing such coastal variation in species richness. The latitudinal variation in species richness did not follow LBG. In contrast to the coast-specific diversity difference, species composition is not found to be dictated by coastal affiliation. The composition corresponds primarily to physiographic conditions. We identified three distinct eco-regions (north-western, southern, north-eastern) with characteristic species composition corresponding to unique physiography and productivity mechanism. The NW region has low siliciclastic input and high productivity associated with upwelling during winter cooling. The NE region has a distinctly high riverine input and salinity fluctuation. The southern region, in contrast, has well developed reefal system with moderate variation in salinity. Such correspondence underscores the importance of the regional environment in dictating the species diversity and distribution in the shallow marine realm.

The red-blooded limpet ‘Shinkailepas’ briandi (Neritimorpha: Phenacolepadidae) is one of the commonest gastropod species at deep-sea hydrothermal vents on the Mid-Atlantic Ridge (MAR). We investigated its population connectivity along MAR as the first such study for gastropods and explored the importance of larval migration for the distribution of vent-endemic animals. Our analyses, based on 1.3-kbp DNA sequences from the mitochondrial COI gene, showed a panmictic population throughout its geographic and bathymetric ranges that span from the northernmost and shallowest Menez Gwen vent field (38°N; 814–831 m depth) to the southernmost and deepest Ashadze field (13°N; 4090 m). Early development of this species is presumed to have a long pelagic duration as a planktotrophic larva; the hatchling with a shell diameter of 170–180 μm attains a constant settlement size of 706 ± 8 μm (mean ± SD). Retention of eye pigmentation in newly settled juveniles, along with the genetic panmixia, suggests that the hatched larva of ‘S.’ briandi migrates vertically to the surface water, presumably to take advantage of richer food supplies and stronger currents for dispersal, as has been shown for confamilial species at hydrothermal vents and cold methane seeps.

Despite the prevalence of catch per unit effort (CPUE) as a key metric in fisheries assessments it can be fraught with inherent problems that often cause its use as an index of abundance to become contentious. This is particularly the case with abalone, a sedentary shellfish targeted by commercial dive fishers around the globe. It is common practice to standardize CPUE to at least partly address issues about how well it reflects the actual abundance of a stock. Differences between standardized and unstandardized trends may lead to controversy between scientists and stakeholders when standardized trends provide a less optimistic picture of stock status. It is within this context that we applied Linear Mixed Model (LMM) and Generalized Linear Mixed Model (GLMM) methods to standardize CPUE for the Western Zone blacklip abalone fishery in Victoria, Australia. This fishery was chosen for our evaluation because it included substantial population losses from a disease shock during the middle of the time series. The effects of diver, reef location, month and their interactions with year were included as random effects in these models and the results compared with nominal geometric means. The two standardization methods provided similar standardized CPUE trends and clearly demonstrated that a large proportion of the variance could be attributed to diver and spatial effects. The GLMM seemed to explain more variability in the data and produced better precision for standardized CPUEs than LMM. The temporal trend in variability attributed to divers and spatial scales reveals the impact of disease as well as any homo/heterogeneity effect. The CPUE trends responded to the impact of disease against a backdrop of declining stock, however when compared with the inter-annual pattern in nominal CPUE, the standardized trends showed that the decline immediately following the onset of disease was less precipitous. In contrast to what appeared to be an increase in the nominal series during the more recent post-disease period, there was only a slight non-significant increase observable in the standardized trends.

Peroxisomes are cytoplasmic organelles involved in fatty acid oxidation, ether-phospholipids biosynthesis, glyoxylate metabolism and purine catabolism among other metabolic pathways. However, these organelles are still poorly studied in molluscs. During a light and electron microscopy study of the digestive glands of cephalaspidean sea slugs unusually large peroxisomes reaching about 5 µm in diameter were found in basophilic cells of Philinopsis depicta (Aglajidae), being among the biggest ever reported in metazoan cells. These round or oval peroxisomes were clearly visible with the light microscope, and their diamond shaped core was strongly stained by the tetrazonium coupling reaction for protein detection. However, in the basophilic cells of Aglaja tricolorata, another aglajid cephalaspidean, peroxisomes were more variable in shape and no bigger than 1 µm in length. Round peroxisomes with a diameter of about 0.5 µm were common in basophilic cells of Philine quadripartita (Philinidae) and Haminoea navicula (Haminoidae), whereas in Bulla striata (Bullidae) these organelles frequently had a diameter of between 1.0 and 1.5 µm. Peroxisomes were larger in basophilic cells than in digestive ones. In all these species, the electron-dense peroxisomal cores were diamond-shaped, and in H. navicula two cores could be seen in each peroxisome. The abundance and large size of peroxisomes in the digestive gland points out the importance of these organelles in the metabolism of this organ.

The bigfin reef squid Sepioteuthis lessoniana is a neritic species widely distributed in coastal waters of the Indo-Pacific region and is of interest to fisheries for its high commercial value. Squid samples were collected from Keelung (KL) and Penghu (PH), around northern Taiwan from October 2012 to September 2013. A total of 949 squid were examined, and 620 squid were aged using statoliths. The age range of the squid in KL (55–183 days) was similar to that in PH (77–186 days). The squid hatched almost year-round, except in January and December in KL. Two seasonal cohorts were identified: a spring cohort (hatched in March to May) and an autumn cohort (July to October). Concentrations of nine trace elements in statoliths were analysed using solution-based inductively coupled plasma mass spectrometry (ICP-MS). Significant differences in Fe/Ca, Cu/Ca and Sr/Ca were found between the two locations, while significant differences in concentration ratios of Sr/Ca and Ba/Ca were noted between the two seasonal cohorts. Results of a principal component analysis and cluster analysis varied in life-history traits between the two geographic stocks and in elemental concentrations between the two seasonal cohorts. Squid in KL and PH might undertake different migration routes, while seasonal variability in oceanographic conditions was apparent in the two locations.