Benthic communities, critical to the health and function of marine ecosystems, are under increasing pressure from anthropogenic impacts such as pollution, eutrophication and climate change. In order to refine predictions of likely future changes in benthic communities resulting from these impacts, we must first better constrain their responses to natural seasonality in environmental conditions. Epibenthic time series data (July 2008–May 2014) have been collected from Station L4, situated 7.25 nautical miles south of Plymouth in the Western English Channel. These data were analysed to establish patterns in community abundance, wet biomass and composition, and to link any observed patterns to environmental variables. A clear response to the input of organic material from phytoplankton blooms was detected, with sediment surface living deposit feeders showing an immediate increase in abundance, while predators and scavengers responded later, with an increase in biomass. We suggest that this response is a result of two factors. The low organic content of the L4 sediment results in food limitation of the community, and the mild winter/early spring bottom water temperatures allow the benthos to take immediate advantage of bloom sedimentation. An inter-annual change in community composition was also detected, as the community shifted from one dominated by the anomuran Anapagurus laevis to one dominated by the gastropod Turitella communis. This appeared to be related to a period of high larval recruitment for T. communis in 2013/2014, suggesting that changes in the recruitment success of one species can affect the structure of an entire community.

Cosmopolitan habitat-forming taxa of algae such as the genus Corallina provide an opportunity to compare patterns of biodiversity over wide geographic scales. Nematode assemblages inhabiting Corallina turves were compared between the south coasts of the British Isles and South Korea. A fully nested design was used with three regions in each country, two shores in each region and replicate samples taken from three patches on each shore to compare differences in the taxonomic and biological trait composition of nematode assemblages across scales. A biological traits approach, based on functional diversity of nematodes, was used to make comparisons between countries, among regions, between shores and among patches. The taxonomic and biological trait compositions of nematode assemblages were significantly different across all spatial scales (patches, shores, regions and countries). There is greater variation amongst nematode assemblages at the scale of shore than at other spatial scales. Nematode assemblage structure and functional traits are influenced by the local environmental factors on each shore including sea-surface temperature, the amount of sediment trapped in Corallina spp. and tidal range. The sea-surface temperature and the amount of sediment trapped in Corallina spp. were the predominant factors determining nematode abundance and composition of assemblages and their functional diversity.

Reef encrusting calcifiers (non-scleractinian species) constitute assemblages that participate in the carbon cycle at coral reefs. Despite their apparent secondary role in building the reef framework, they contribute to the reef consolidation binding sediments and inducing larval recruitment from other epilithic invertebrates. The contribution of encrusting calcifiers on reef accretion was examined by the assessment of their rate of carbonate deposition on four different simulated reef microhabitats using calcification accretion units (CAUs) during 12 months at Playa Las Gatas and Islote Zacatoso, two coral communities from the coast of the Mexican Pacific. Encrusting calcifiers from Playa Las Gatas, the most impacted site, showed a rate of carbonate deposition (mean ± SD) four times higher than at Islote Zacatoso (10.02 ± 3.22 g CaCO3 m−2 d−1vs 2.48 ± 1.01 g CaCO3 m−2 d−1). Overall, the rate of carbonate deposition on surfaces protected from sedimentation and light was up to 1.8 times higher than on exposed ones (11.40 ± 4.35 g CaCO3 m−2 d−1vs 6.18 ± 3.13 g CaCO3 m−2 d−1). Carbonate deposition by calcareous algae was higher on the well-lit exposed surfaces while filter-feeding invertebrates showed the major contribution on the shaded cryptic surfaces. Although rate of carbonate deposition by encrusting calcifiers seems to be lower than hermatypic corals, it seems to be relevant on coral reefs affected by anthropogenic impacts where coral calcification is low. Under global demise of coral reefs by environmental degradation and climate change, encrusting calcifiers may become relevant for the process of carbonate deposition.

The South China Sea (SCS) is a biodiversity hotspot, however, most biodiversity surveys in the region are confined to shallow water reefs. Here, we studied the benthic habitat and fish assemblages in the upper mesophotic coral ecosystems (MCEs; 30–40 m) and SWRs (8–22 m) at three geographic locations (Luzon Strait; Palawan; and the Kalayaan Group of Islands) in the eastern SCS (also called the West Philippine Sea) using diver-based survey methods. Mean coral genera and fish species richness ranged from 17–25 (per 25 m2) and 11–17 (per 250 m2) in MCEs, respectively; although none of these were novel genera/species. Coral and fish assemblages were structured more strongly by location than by depth. Location differences were associated with the variability in benthic composition, wherein locations with higher hard coral cover had higher coral genera richness and abundance. Locations with higher algae and sand cover had higher diversity and density of fish herbivores and benthic invertivores. Fishing efforts may also have contributed to among-location differences as the highly exploited location had the lowest fish biomass. The low variation between depths may be attributed to the similar benthic composition at each location, the interconnectivity between depths due to hydrological conditions, fish motility, and the common fishing gears used in the Philippines that can likely extend beyond SWRs. Results imply that local-scale factors and anthropogenic disturbances probably dampen across-depth structuring in coral genera and fish species assemblages.

Climate change and heavy anthropic pressures are giving rise to important modifications in the rocky benthic communities of the Mediterranean Sea. In particular, sponge assemblages have been deeply affected due to the susceptibility of some species to dramatic phenomena such as mass mortalities or widespread variations in the abundance of other species. For this reason, long-term biodiversity monitoring of the sponge assemblages is important for understanding the direction of changes over time. We studied the sponge fauna living off Tricase Porto (Otranto Strait) and compared its composition with the results of a study conducted in the same area 50 years ago. The comparison indicated that the sponge diversity of this area has strongly increased in the last 50 years and a large number of the sponges recorded in the old survey are still present in the recent community. This evidence matches with other results obtained from different localities of the Mediterranean Sea indicating an increase of sponge diversity, possibly due to the present water warming. The description of two new Demosponge species, Diplastrella boeroi sp. nov. and Spirastrella angulata sp. nov., is also provided.

The physiology of mesophotic Scleractinia varies with depth in response to environmental change. Previous research has documented trends in heterotrophy and photosynthesis with depth, but has not addressed between-site variation for a single species. Environmental differences between sites at a local scale and heterogeneous microhabitats, because of irradiance and food availability, are likely important factors when explaining the occurrence and physiology of Scleractinia. Here, 108 colonies of Agaricia lamarcki were sampled from two locations off the coast of Utila, Honduras, distributed evenly down the observed 50 m depth range of the species. We found that depth alone was not sufficient to fully explain physiological variation. Pulse Amplitude-Modulation fluorometry and stable isotope analyses revealed that trends in photochemical and heterotrophic activity with depth varied markedly between sites. Our isotope analyses do not support an obligate link between photosynthetic activity and heterotrophic subsidy with increasing depth. We found that A. lamarcki colonies at the bottom of the species depth range can be physiologically similar to those nearer the surface. As a potential explanation, we hypothesize sites with high topographical complexity, and therefore varied microhabitats, may provide more physiological niches distributed across a larger depth range. Varied microhabitats with depth may reduce the dominance of depth as a physiological determinant. Thus, A. lamarcki may ‘avoid’ changes in environment with depth, by instead existing in a subset of favourable niches. Our observations correlate with site-specific depth ranges, advocating for linking physiology and abiotic profiles when defining the distribution of mesophotic taxa.

The present study is the first attempt to describe beta-diversity patterns in polychaetes of the Caribbean Sea, analysing depth changes in species composition of the Eunicida and Amphinomida inhabiting dead coral in Chinchorro Bank, southern Mexican Caribbean. In April 2008, dead coral fragments were collected by scuba diving in eight stations along two bathymetric gradients (4–9 m and 7–16.2 m depth); 755 individuals from 53 species of the families Amphinomidae, Dorvilleidae, Eunicidae, Lumbrineridae, Oenonidae and Onuphidae were identified. The highest number of species (32) and individuals (514) were found in the family Eunicidae. The Northern transect harboured 36 species, on average 18.75 ind. L−1, which decreased linearly with depth; the Central transect had 43 species, on average 19.01 ind. L−1, which increased at middle depths. The species inhabiting both these zones were moderately different (βsor = 0.603): 49.06% of the fauna occurred on both transects, but the components of beta-diversity, turnover and nestedness, displayed distinct patterns: in the Northern one replacement was the dominant factor (βsim = 0.3–1; βnes = 0–0.091), practically representing all faunal differences (βsor = 0.391–1); in the Central, dissimilarity due to nestedness increased (βnes = 0.031–0.829), mainly at the shallowest stations, but from 5 m depth, beta-diversity was almost completely explained by species replacement (βsim = 0.417–0.5; βnes = 0.031–0.318). Faunal differences were mostly related to higher abundances of Lysidice caribensis, Eunice goodei and Lumbrineris floridana in the Northern zone, and Lumbrineris perkinsi, Nicidion obtusa, Lysidice caribensis, Lumbrineris floridana, Lysidice unicornis and Eunice mutilata in the Central zone.

Early development of the polychaetes Capitella sp. TF from Tampa, Florida and Capitella sp. TV from Tamiahua Lagoon, Veracruz was studied under laboratory conditions. Our observations indicate that hermaphrodites occur in Capitella sp. TF, but not in Capitella sp. TV. Length and volume of larvae and early juveniles were measured daily. Both species appear to have lecithotrophic development. Sizes and duration of the developmental stages varied widely, as in most known species of Capitella. Characteristic features of Capitella sp. TF include very small hermaphrodites with a distinct dorsal pigmentation pattern and characteristically shaped brood tubes with a centrally thickened region. Embryos forced to abandon the brood did not survive more than 3 days, and handling the brood produced alterations in timing. Ciliated metatrochophores from Capitella sp. TV survived inside the brood without the female for at least 14 days and some larvae hatched and died during settling. Some of these larvae were abnormal, with two rounded protuberances in the two ends. Mortality was high. Fungi and protozoans appeared in the dishes and probably partially induced the production of thicker mucus in the brood tubes, delay in metamorphosis, juvenile mortality, worm length and failure in coupling. Size and duration of the developmental stages were distinctly different from the other putative lecithotrophic species of the complex. These differences and other characteristics of each species discard the possibility that they belong to a previously described species. Our results are applicable to future ecological, morphological and molecular studies of each species, habitat and phylogenetics.

The amphinomid fireworm Hermodice carunculata is a potentially invasive species reported throughout the subtropical Atlantic Ocean and the Mediterranean Sea, which is known as a generalist predator and opportunistic feeder. The ongoing climate changes and seawater warming may favour fireworm poleward range expansions and density increases. Our results provide the first investigation into a population which has purportedly been spreading widely in the Salento Peninsula (Apulia, Italy). The specimens were analysed using allometric variables and molecular markers. The best morphometric parameters to estimate individual size were determined as key information for future studies on fireworm population dynamics. To phylogeographically characterize the Apulian population, sequences of the mitochondrial COI and 16S rDNA regions were obtained from a pool of individuals and treated together with those of Atlantic specimens retrieved from GenBank. The estimates of genetic variability for Apulian population were consistent with those recently reported in the literature. Inferences on demographic history analysis confirmed a recent expansion event in Apulia, as has been recounted by fishermen and scuba divers during recent years. Overall, these results constitute a crucial step in the characterization of present-day H. carunculata populations, and provide greater insight into fireworm population ecology.

Understanding variations in the reproductive cycle of commercial and ecologically important bivalve species is essential to address fisheries management and climate oscillation issues. Spatial and temporal trends in the reproductive cycle of Callista chione were analysed using standard histological procedures and gonadosomatic index (GSI) for two consecutive years at two coastal sites in the Adriatic Sea. Reproductive output and fecundity were analysed quantitatively to gain better insight into the seasonal energy balance with respect to gametogenesis. A seawater temperature difference of ~4°C between the two sites likely influenced the onset and duration of spawning. At Cetina (milder temperatures), spawning was prolonged and occurred between spring and July, whereas at Pag there was only one main spawning peak in July. Both histology and GSI showed similar trends, indicating GSI to be a reliable method for analysing the main characteristics of the reproductive cycle. Conversely, the use of the body mass index (BMI) as an indicator of gonad development should be addressed carefully. Intraspecific variation in energy allocation between populations suggested life strategies modified to different habitat conditions. A higher reproductive investment and output in the Pag population directed gonadal resorption to ensure the generation of a new cycle, whereas the higher fecundity at the Cetina site indicated the production of gonads from newly available food. These results suggest successful physiological acclimatization to recent increasing temperatures.

Molluscan shells showing phenotypic variations are ideal models for studying evolution and plasticity. In north-eastern Asia, genetic and morphological diversity of the gastropod, Monodonta labio, were assumed to be influenced by both palaeoclimatic changes and current ecological factors. In this study, we examined spatial variations in shell shape of M. labio using general measurement and geometric morphometric analysis. We also investigated whether shell shape variation is best explained by environmental gradients or by genetic structuring, based on our prior molecular phylogeographic study. Two common morphological forms were observed among Chinese populations and in the adjacent Asian areas. Both the analyses revealed separation patterns in morphological variations of shell shape among the clades and populations. Environmental modelling analysis showed a significant correlation between shape variations and local maximum temperatures of the warmest month, indicating the role of natural selection in the evolution of this species. Data obtained in this study, combined with the cytochrome oxidase subunit I (COI) molecular phylogenetic data from the prior study, showed that morphological variations in M. labio were constrained by both local adaptation and phenotypic plasticity. We hypothesized that geographic separation by the Dongshan Landbridge was the first step towards its diversification, and that the temperature gradient between the East China Sea and South China Sea probably was the selective force driving the divergence of its morphological variations.

We have monitored tributyltin (TBT) pollution in Galicia (NW Spain) for more than a decade by means of assessing gastropod imposex in populations of Nucella lapillus (N ≥ 34) and Tritia reticulata (N ≥ 18) at regular intervals. Several thousand specimens were processed to obtain their shell height (SH), penis length (PL) and vas deferens sequence (VDS); imposex indices (including the VDS index, VDSI) were subsequently calculated. The regional mean SH of both females and males has not changed significantly in either species throughout the study. This also applies to the mean male PL in N. lapillus, but male T. reticulata penises surprisingly enlarged. On the contrary, the regional mean female PL (MFPL) and all imposex indices significantly decreased in both snails. Results confirm previous conclusions based on the chemical analyses of tissues and partial imposex observations. In addition, the close correlations between MFPL and VDSI show some potential applications to TBT biomonitoring.

Hermaphroditism is thought to be an advantageous strategy common in marine molluscs that exhibit simultaneous, sequential or alternating hermaphroditism. Several species of patellid limpets have previously been shown to be protandrous hermaphrodites. The present study aimed to confirm whether this phenomenon occurs in Patella piperata. Transitional forms of simultaneous protandrous hermaphroditism were found in intermediate size classes of P. piperata, in Madeira (North-eastern Atlantic). Sequential hermaphroditism was confirmed after histological analysis. The overall sex-ratio was biased towards females but approached similar proportions in the larger size classes. Analysis of size at sex change showed that at a shell length of 36 mm 50% of the population probably have changed sex. The results reported confirm the occurrence of sequential hermaphroditism. These findings are of utmost importance to the understanding of the reproductive biology of this species with direct effect on management and conservation of this traditionally harvested limpet.

Age and growth of the little Indian squid Loliolus hardwickei (Gray, 1849) were studied using samples collected in the coastal waters of Arabian Sea. Statolith increment counts demonstrated that L. hardwickei has a fast growth rate (dorsal mantle length: 0.31–0.73 mm day−1 in females and 0.27–0.56 mm day−1 in males) and a short lifespan of less than 6 months. Females are the larger sex and their daily growth rates were higher than in males. The oldest male and female were 110 and 130 days old; the youngest mature female and male were 62 and 52 days old respectively. The oviducal fecundity ranged from 104–480 eggs, mean = 360 eggs (14–23 eggs g−1 body weight).

The burrowing shrimp Neotrypaea californiensis is an important ecosystem engineer that inhabits estuaries along the US Pacific Northwest coast. This species plays an important role in the estuarine ecosystem but negatively impacts oyster aquaculture through its burrowing activities. Development of population models for burrowing shrimp management requires more detailed life history information and accurate estimates of age. Ageing studies have been limited for crustaceans because it is generally believed that they do not retain structures with annual deposits commonly used to age other marine organisms, when they moult their exoskeletons. A mesocosm growth experiment and field surveys were combined to compare the performance of two ageing techniques, quantification of autofluorescent lipofuscin and gastric mill ossicular lamellae, for estimating age in N. californiensis. Animals of known age were grown in outdoor mesocosms and sampled regularly to correlate age metrics with body size and true age. Lipofuscin concentration increased with time across multiple cohorts at the rate of 1.430 ± 0.060 ng µg−1 year−1. Lamellae counts also increased with time (4.922 ± 0.337 lamellae year−1). While age estimates based on lipofuscin concentration and lamellae counts generally agreed, carapace size did not correlate to either age metric. Lamellae counts from field collections suggest they are added sequentially with age but the relationship can vary by location. When used together, the application of both techniques may provide robust estimates of crustacean age especially when size-based measurements are imprecise.

Natural mortality (M) is a key parameter for understanding population dynamics, especially in relation to harvested populations. Direct observations of M in crustaceans are scarce, due to the moulting process. Indirect methods to estimate M with easier-to-obtain life history attributes are therefore used routinely. Given their theoretical background, we reviewed the applicability of these methods for crustaceans. We applied the selected methods to two crustacean species harvested in Chilean waters: the yellow squat lobster (Cervimunida johni) and red squat lobster (Pleuroncodes monodon). Uncertainty of each M estimate was incorporated in the life history parameters that input into the indirect method (trait-error) and parameters defining the indirect method (coefficient-trait-error). Methods based on the relationship between total mortality and maximum age, or with different ages and based on life history theory were the most appropriate for crustaceans since they apply across taxa. M estimates showed high variability between species, sexes and areas. Estimations of M for C. johni varied from 0.13 to 0.28 (year−1) for males and 0.17 to 0.51 (year−1) for females. For P. monodon values for the north varied from 0.26 to 0.37 (year−1) for males and 0.24 to 0.45 (year−1) for females. In the south, values of M were higher for both males (0.43–0.68 year−1) and females (0.41–1.06 year−1). High variability in the M estimates was associated with the method and number of parameters, their uncertainty, theoretical background and probability distribution. M estimates are not comparable, raising the need to propagate the uncertainty of M into the stock assessment of Chilean squat lobsters.

The food composition of whiting, Merlangius merlangus, caught around the sea-cage fish farms off the coast of Perşembe, was analysed and compared with the diet of whiting from a control site off the coast of Fatsa (Ordu Province, south-eastern Black Sea). A total of 815 stomach samples were collected during the study, and of these, 195 (23.9%) were empty. According to the percentage of relative importance index (IRI%), pellet food (47.8%) and Annelida (25%) were the main prey groups of whiting in the sea-cage fish farms area, while unidentified teleost (85.3%) and Engraulis encrasicolus (8.2%) were dominant in the control site. The other prey groups in both areas were Crustaceans (Mysidae, Amphipoda, Upogebia sp.), Sprattus sprattus and Gobius spp. Seasonally, pellet food was the most consumed food in all seasons, but Mysidae was the first preference of whiting around the sea-cage fish farms in spring. In the control site, unidentified teleost was the first preference in all seasons, except winter, where E. encrasicolus was the first choice, followed by crustaceans and S. sprattus in winter. Bray–Curtis analysis shows that seasonally, there is no significant difference in the sea-cage fish farms, while there is significant difference in the control site, and two-dimensional nMDS of IRI% revealed a clear separation between both sites. SIMPER analysis revealed that the most contributing factors to the differences between seasons were pellet food in the sea-cage fish farms, and E. encrasicolus in the control site.

Rhinoptera steindachneri is a commercially important, medium-sized, pelagic migratory batoid fish with benthic feeding habits. It has been considered a specialized predator that feeds on molluscs as well as benthic ophiurids and arthropods off the Mexican Pacific coast. Most biological aspects of this species in La Paz Bay are unknown, despite its being a commercially important species of conservation interest. Therefore, the aim of this study was to characterize the feeding habits of R. steindachneri based on specimens caught in artisanal fisheries. The stomach contents of 310 specimens (146 females and 164 males) were analysed, all captured from 2013 to 2015. The vacuity index was 97.1%, and the most important prey species were Mysidium spp. and Cylichna spp. Because of the high frequency of empty stomachs recorded, it was not possible to describe with precision the general diet of the species. Three hypotheses were developed to try to explain why this characteristic occurred in this species, ranging from eating habits to physiology and prey digestion and geographic location of the study. However, considering the mechanical process of prey handling of R. steindachneri, several hypotheses were formulated, with the hour of capture, chemical processes and physiology and prey digestion being the most probable to explain this high vacuity index reported in this study.

In this study, we examine how the Guri catfish Genidens genidens uses estuarine and freshwater habitats along the largest South American coastal lagoon, through the chemical analysis of otoliths and microscopic analysis of gonads. Chemical composition (Sr:Ca) of otolith edges allowed distinguishing between individuals who used the estuarine or freshwater compartments of the lagoon. The analysis of core-to-edge chemical profiles of each individual otolith revealed that the population may present two different patterns of habitat use along the lagoon. The ‘type 1’ pattern (89.5%) includes fish who appear to have been born in estuarine waters, whereas ‘type 2’ (9.5%) includes those fish born in fresh water. Nevertheless, juveniles from both patterns appear to migrate to estuarine waters. The gonad analysis shows G. genidens may reproduce in fresh water, as nearly 57% of all sampled fish were found to spawn in the freshwater portion of the lagoon. Also, the otolith core of many adult fish presented freshwater signatures, thus suggesting consistent fresh water use during early life. Our findings based on otolith and gonadal analyses challenge the previous classification of G. genidens as an estuarine resident. Rather, our results allow the suggestion that this species should be placed in the ‘estuarine and fresh water’ guild, which includes both fish completing their life cycles within the estuary and fish who consistently use freshwater habitats.

The aim of this study was to test the effective separation of shape indices of otoliths of three species belonging to the family Sciaenidae before and after in vitro digestion. We measured 328 sagittal otoliths and applied six shape indices. Before the experiment, the aspect ratio (otolith height/otolith length%), circularity, ellipticity and relative surface of the sulcus acusticus were suitable for differentiating the species of genera Paralonchurus and Stellifer. Among the species of Stellifer, the aspect ratio and rectangularity were suitable. Otoliths exposed to in vitro digestion showed no significant differences in their morphometry before and after the experiment. After in vitro digestion, the aspect ratio and circularity were effective in separating Paralonchurus and Stellifer. However, none of the indices used in the present study were efficient to separate otoliths of congeneric species after in vitro digestion.