Shell use by sympatric hermit crab species in a seasonally open coastal lagoon in Northeastern Brazil

There are gaps in what is known about the patterns of gastropod shell use by hermit crabs in Brazilian lagoon areas, especially in Northeastern Brazil. However, this is important because the understanding of selection patterns provides information on life history and eco‐evolutionary conceptions of paguroids. The present study investigated the use of gastropod shells occupied by Pagurus criniticornis and Clibanarius sclopetarius in a coastal lagoon seasonally connected to an estuary and to the sea, correlating eco‐evolutionary aspects and hydrodynamic characters. The study was carried out between February 2013 and January 2014. Hermit crabs and their shells were identified and measured (hermit crabs’ cephalothorax shield length and width, major propodus length and height, weight, shell total length and width, shell aperture length and width). Partial least squares regression was used to analyse the morphometric data. Additionally, a multinomial proportions test was performed to infer patterns (inter‐/intra‐specific) of shells’ occupation. Hermit crab species occupied a total of 13 types of shells, predominantly those of Neritina virginea (67.83%). The shell weight was the most important determinant of shell occupancy in the morphometric model (variable importance in projection >1). The proportions of N. virginea shells used were similar in both species of hermit crabs, except between the sexes of P. criniticornis. Presumably, the high utilization rate of N. virginea shells is related to its abundance and dispersal, and to the shells’ suitability for hermit crabs, which is reflected by the morphometric model, as well as by the hydrodynamics of the lagoon‐estuarine environment. The relative occupation of different types of shells for each species of hermit crabs studied appears to be associated with regulation by inter‐/intra‐specific competition, which fosters the co‐occurrence of those populations. These results endorse coastal lagoons as a refuge and recruitment area for aquatic fauna. In addition, it highlights a challenge in the management and conservation of paguroid species whose population dynamics depend on the resources coming from the Gastropoda community.     

Distribution of sea cucumbers in relation to sediment characteristics in coral reef lagoons and adjacent waters around Ishigaki Island,southern Japan

To elucidate which environmental factors affect lagoonal‐scale sea cucumber distributions in Ishigaki Island, Okinawa, Japan, intertidal and subtidal areas of three coral reef lagoons were classified into several ground divisions by bottom characteristics, and sea cucumber densities therein were compared with the composition of sediment cover, grain size and organic content, and coverage of macroalgae, seagrass, and massive corals. Holothuria atra, Holothuria leucospilota, Stichopus chloronotus, and Synapta maculata had highest densities in the nearshore areas but were rare in reef flats, probably because of wave disturbance and low areal cover of sand sediment as potential feeding environments. No relationship was observed between sea cucumber densities and sediment organic content or grain size. Thus, even if these sea cucumbers have selectivity for habitats with a high sediment organic content, the effect of such selectivity on the distribution seems to be limited to relatively small areas. The sea cucumber distributions can be classified by bottom sediment/biota composition into bedrock (H. leucospilota), sand (H. atra), and lagoonal types (St. chloronotus and Sy. maculata). These habitat selections were possibly related to various aspects of sea cucumber ecology such as refuge from predators or turbulence, or settlement and nursery place, which have implications for importance of the complexity of lagoonal‐scale topography and sediment/biota conditions for the coexistence of various holothurian species.     

Cryptic diversity and phylogeography of the island‐associated barnacle Chthamalus moro in Asia

Pleistocene glaciations were among the important historic events that shaped the population structures of marine organisms. Genetic studies of different marine fauna and flora have demonstrated the effect of Pleistocene glaciations on taxa that reside in marginal seas. However, how marine island species responded to Pleistocene glaciations remains relatively unstudied, especially in Asia. Genetic analyses based on the island‐associated barnacle Chthamalus moro collected from 14 sites in Asia reveal that C. moro comprises three distinct lineages, with COI divergence ranging from 3.9 to 8.3%. Population genetic analyses on respective lineages reveal signs of demographic expansion within the Pleistocene epoch at different times. The Ogasawara lineage, which has a more oceanic distribution, expanded the earliest, followed by the population expansion of the Ryukyu and Southern lineages that inhabit islands closer to the continent. The data suggest that the inhabitants of outer islands may have been less affected by Pleistocene glaciations than those that reside closer to the continent, as the former were able to maintain a large, stable, effective population size throughout the late Pleistocene.     

Response of three krill species to hypoxia and warming: an experimental approach to oxygen minimum zones expansion in coastal ecosystems

To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZs), respiratory response and stress experiments combining hypoxia‐reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current System (HCS, Chilean coast) and the Northern California Current System (NCCS, Oregon). Euphausia mucronata from the HCS showed oxyconforming pO₂‐dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a ‘high oxygen stress’ for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba, maintained respiration rates constant down to low critical pO₂ values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. The temperate krill species (E. pacifica) had higher superoxide dismutase (SOD) values in winter than in summer, which relates to a higher winter metabolic rate. In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7 °C above habitat temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4 °C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2 °C). In this season, experimental warming by +4 °C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.     

Comparative phylogeography and population genetic structure of three widespread mollusc species in the Mediterranean and near Atlantic

Although several studies have evaluated the genetic structure and phylogeographic patterns in many species of marine invertebrates, a general model that applies to all of them remains elusive. For example, some species present an admixture of populations with high gene flow, whereas others exhibit more complex patterns characterized by small‐scale unstructured genetic heterogeneity, even at a local scale. These differences are thought to be due to clear biological aspects such as direct versus indirect development, or the presence of lecithotrophic versus planktotrophic larvae, but few studies compare animals with similar distributions and life modes. Here, we explore the phylogeographic and genetic structure patterns in two chiton (Chiton olivaceus and Lepidopleurus cajetanus) and one abalone (Haliotis tuberculata) species co‐occurring in the same habitat. Samples were obtained from shallow rocky bottoms along the Iberian Peninsula (Atlantic and Mediterranean coasts), Italy, Croatia and Greece, and the mitochondrial markers COI and 16S rRNA gene were sequenced. Our data show evidence of admixture and population expansion in C. olivaceus and H. tuberculata, whereas L. cajetanus exhibited a ‘chaotic patchiness’ pattern defined by a high genetic variability with locality‐exclusive haplotypes, high genetic divergence, and a lack of geographic structure. Shared haplotypes were sampled in both coasts of Iberia (for H. tuberculata) and in the Western and Eastern Mediterranean (for C. olivaceus), potentially indicating high dispersal ability and a recent expansion. The processes underlying the fine‐scale structuring in L. cajetanus remain a mystery. These results are especially interesting because the reproductive mode of the two chitons is similar but differs from that of the abalone, with a veliger larva, while instead the genetic structure of C. olivaceus and H. tuberculata are similar, thus contrasting with predictions based on the life history of the three molluscs and showing that the genetic patterns of marine species may be shaped by many factors, including historical ones.     

Experimental assessment of Posidonia oceanica‐associated gastropods grazing on an early‐successional biofilm community: nutrient availability and species‐specific effects

Although grazing is considered an essential process controlling epiphyte biomass on seagrass leaves, there is still a lack of fundamental knowledge about the species‐specific consumption rates of the most common grazers in Mediterranean meadows. This study experimentally assessed the effect of Posidonia oceanica‐associated gastropod grazing on early successional biofilm and the species‐specific relationship between biofilm consumption rates and biofilm biomass. Two biofilms on artificial substrata, both developed in situ (in a P. oceanica meadow), one under ambient conditions and the other under nutrient‐enriched conditions, were offered in aquaria assays to nine species of grazers found in P. oceanica meadows. Biofilm consumption rates and their association with biofilm biomass were assessed. It was found that: (i) there was a positive association between biofilm consumption and biofilm biomass up to 20 mg Chl a·m^?2 for Bittium reticulatum, Gibbula ardens, Jujubinus exasperatus and Tricolia pullus; (ii) Alvania montagui, B. reticulatum and Jujubinus striatus showed the highest consumption rates and are thus expected to be amongst the leading consumers in early‐successional epiphytic communities; (iii) there was not an increase of consumption rate when a substratum colonized under nutrient‐enriched conditions was offered to any of the nine studied species. This study provides species‐specific consumption rates knowledge that is useful for the assessment of the strength of grazer–epiphyte interactions and trophic fluxes in P. oceanica meadows.     

Ecological assessments of the coral reef communities in the Eastern Caribbean and the effects of herbivory in influencing coral juvenile density and algal cover

Caribbean reefs have been unevenly surveyed, with many areas lacking baseline data. In this study, the current status of Orbicella reefs, a structurally complex forereef habitat, was quantified in an understudied region, the Eastern Caribbean. During 2011 the same observers surveyed benthic assemblages, coral juvenile density, herbivorous fishes, and invertebrates at 30 Orbicella reefs in four Eastern Caribbean areas: Antigua, Barbados, St Lucia, and St Vincent and the Grenadines (hereafter St Vincent). Not all Orbicella forereefs were functionally the same in the Eastern Caribbean. Benthic communities and herbivorous fishes varied greatly among islands. Hard coral had the highest overall percent cover on most reefs in this study, with an average cover of 22%, and was greater than fleshy macroalgal cover at 83% of the sites. Overall, coral juvenile density was low but was positively associated with higher densities of Diadema antillarum, highlighting the importance of herbivory on the reefs. Nearshore coral reefs in Barbados were in a better state than other areas, exhibiting higher coral cover dominated by spawning corals, higher densities of coral juveniles exhibiting higher coral cover dominated by spawning corals, higher densities of coral juveniles and D. antillarum. Low biomass of herbivorous fishes at a majority of the coral reef sites is of major concern for the functioning of these reefs. Conservation of parrotfishes and other herbivores is necessary given the abundance of algae on most of these reefs and the beneficial effect of their presence on coral juveniles. This is the first comprehensive study that compares the state of Orbicella reefs in the Eastern Caribbean, providing valuable information that will be useful in creating realistic targets for future management and conservation.     

Population dynamics of cryptogenic calcarean sponges (Porifera,Calcarea) in Southeastern Brazil

The calcarean sponge Paraleucilla magna is classified as being an invasive species on the Mediterranean Sea, where it causes economic damages to mollusc farms. On the Brazilian coast, this species is considered to be cryptogenic, and information on its ecology is scarce. The same is true for Sycettusa hastifera, another calcarean sponge with a worldwide distribution. Data on the ecology of these species could help in elucidating their potential to become a threat if they are found to be exotic species in Brazil. In the present work, we studied habitat selection, growth and mortality of early juveniles of P. magna and habitat selection of S. hastifera in a Marine Reserve from Southeastern Brazil, where these species are abundant in the benthic community. Granite plates were used for habitat selection analysis, varying in substrate inclination (vertical and horizontal) and exposure to light and hydrodynamism (exposed and sheltered). To analyse the growth and mortality rates, sponges were mapped and then measured once a week for 10 weeks. If a monitored sponge was not found in the following week, it was considered to be dead. Our results showed that, although P. magna and S. hastifera are capable of inhabiting substrates exposed to different environmental conditions, they showed habitat preferences. Growth of the juveniles of P. magna seemed not to have damaged any neighbouring invertebrates. The mortality of juveniles of this species was higher during the first 2 weeks of life but its causes could not be elucidated.     

Crustacean decapod assemblages associated with fragmented Posidonia oceanica meadows in the Alboran Sea (Western Mediterranean Sea): composition,temporal dynamics and influence of meadow structure

The decapod assemblage associated with a Posidonia oceanica meadow located near its western limit of biogeographic distribution was studied over an annual cycle. Fauna samples were taken seasonally over a year (five replicates per season) in two sites located 7 km apart, using a non‐destructive sampling method (airlift sampler) for the seagrass. The dominant species of the assemblage, Pisidia longimana, Pilumnus hirtellus and Athanas nitescens, were associated with the protective rhizome stratum, which is mainly used as a nursery. The correlations between decapod assemblage structure and some phenological parameters of the seagrass shoots and wave height were negative or null, which reflects that species associated with the rhizome had a higher importance than those associated with the leaf stratum. The abundance and composition of the decapod assemblage as well as the ecological indexes displayed a seasonality trend with maximum values in summer‐autumn and minimum in winter‐spring, which were related to the seawater temperature and the recruitment periods of the dominant species. The spatial differences found in the structure and dynamics of the assemblages may be due to variations in the recruitment of the dominant species, probably as a result of the influence of local factors (e.g. temperature, currents) and the high dispersal ability of decapods, together with the patchy configuration and the surrounding habitats. The studied meadows are fragmented and are integrated within a mosaic of habitats (Cymodocea nodosa patches, algal meadows, rocky and sandy bottoms), which promotes the movement of individuals and species among them, maintaining a high species richness and evenness.     

Habitat modification in tidepools by bioeroding sea urchins and implications for fine‐scale community structure

By creating novel habitats, habitat‐modifying species can alter patterns of diversity and abundance in marine communities. Many sea urchins are important habitat modifiers in tropical and temperate systems. By eroding rocky substrata, urchins can create a mosaic of urchin‐sized cavities or pits separated by exposed, often flat surfaces. These microhabitats appear to harbor distinct assemblages of species. We investigated how a temperate rocky intertidal community uses three small‐scale (<100 cm²) microhabitats created by or adjacent to populations of the purple sea urchin (Strongylocentrotus purpuratus): pits occupied by urchins, unoccupied pits, and adjacent flat spaces. In tidepools, flat spaces harbored the highest percent cover of algae and sessile fauna, followed by empty pits and then occupied pits. The Shannon diversity and richness of these sessile taxa were significantly higher in flat spaces and empty pits than in occupied pits. The composition of these primary space holders in the microhabitats also varied. Unlike primary space holders, mobile fauna exhibited higher diversity and richness in empty pits than in flat spaces and occupied pits, although results were not significant. The protective empty pit microhabitat harbored the highest densities of most trophic functional groups. Herbivores, however, were densest in flat spaces, concordant with high algal coverage. These results suggest the habitats created by S. purpuratus in addition to its biological activities alter community structure at spatial scales finer than those typically considered for sea urchins.     

Metals in eggs and hatchlings of Dermochelys coriacea (testudines) in Espírito Santo,Brazil and their relation to hatching and emergence success

Certain concentration of metal may influence survival in embryonic stages, reducing the birthrate and hatching emergence. This study aimed to evaluate concentration of metal in eggs and hatchlings of Dermochelys coriacea and correlate metal concentrations in eggs with hatching and emergence success. The samples were collected at Biological Reserve Station, ES, Brazil. At the nests' opening, unhatched eggs and stillborn hatchlings were collected to survey the successful hatching and emergence of D. coriacea. The eggs shell, egg content, and dead hatchlings metal concentrations were compared to hatching and emergence success. A positive correlation was found between the concentration of copper (Cu) in the hatchlings and the success of the emergence (r² = .28, p < .05), and a moderate positive correlation between the concentrations of iron (Fe) and barium (Ba; r² = .44, p < .05) and success hatching. The concentrations of metals in eggs and hatchlings of D. coriacea in the Espírito Santo are below the levels that could be considered harmful to the species. In summary, there is a positive correlation between metals levels and hatching and emergence success.     

Hierarchical analysis of the population genetic structure in Concholepas concholepas,a marine mollusk with a long‐lived dispersive larva

For most marine invertebrate species, dispersal is achieved mainly or exclusively by pelagic larvae. When the duration of the pelagic larval stage is long, genetic homogeneity over large geographic scales is expected. However, genetic structure has often been reported over small spatial scales, suggesting that more complex processes occur than a simple positive relationship between pelagic larval duration and gene flow. Concholepas concholepas has a larval stage that can last up to 3 months in the water column with a wide distributional range covering from 6°S to 56°S. We used a hierarchical sampling technique to test if the genetic homogeneity of this highly dispersive species is maintained throughout its total geographic range in spite of environmental heterogeneity. In the three studied regions (Antofagasta Bay, Valdivia and Patagonia), a spatial pattern of isolation by distance in conjunction with a spatial genetic structure was observed. Within each region, different spatial genetic patterns were detected. In Antofagasta Bay and Valdivia there was evidence of substantial gene flow among populations, whereas in Patagonia, populations showed genetic structure and a unique, genetically isolated location was identified. These results revealed the existence of spatial differences in the genetic patterns among regions with different coastal topographies in C. concholepas, and give us new insights into the inter‐relationships of larval dispersal potential, actual larval dispersal and physical processes. Regarding the sustainable management of C. concholepas, two important issues are derived from this study: (i) to highlight the need for a regional context in the management of C. concholepas, (ii) to determine the distinctiveness of the most austral population and to focus on the conservation efforts due to the relevance of this area.     

Dietary analysis of harbour seals (Phoca vitulina) from faecal samples and overlap with fisheries in Erimo,Japan

The number of harbour seals in Japan has been rebounding since protection began in the mid‐1980s. With the increase in seal numbers, increased conflict with fisheries has occurred through depredation and the belief that seals compete with fisheries for prey. However, competition can only be determined if the prey species and quantities seals consume over time are known. We studied the diet of harbour seals in Erimo, site of the largest population of harbour seals in Japan, from 2011 to 2012 and assessed the degree of prey overlap with local fisheries. We used both hard parts and DNA techniques to identify prey items in seal scats, and compared these results to local fisheries data. A total of 46 prey occurrences was detected by both methods, of which 17 matched between techniques at least to the family level. Hard parts methods identified five incidences of prey undetected by DNA methods in five scats (one incidence per scat). DNA methods identified 24 additional prey occurrences in 13 scats, for which no hard part evidence for that prey had been found. This more than doubled the total number of prey occurrences across the 15 scats compared. Overall, the most frequently occurring harbour seal prey were walleye pollock (Theragra chalcogramma), sculpins and snailfishes. In contrast, the top three groups targeted by fisheries were codfishes, salmon and invertebrates. Many species common in the harbour seal's diet such as snailfishes and blennies were not targeted by fisheries. Fishes such as greenlings, sculpins, rockfishes and Japanese anchovy (Engraulis japonicus) were common in the diet of harbour seals, but made up a very small proportion of fisheries catches in Erimo. The importance of other prey species varied between seasons. Sculpins, greenlings and forage fishes were the top three prey groups for harbour seals in spring by percent modified frequency of occurrence, whereas the most important target groups by percentage mass caught by fisheries were codfishes, cephalopods and other invertebrates. Sculpins and rockfishes remained as important prey items for harbour seals in summer and autumn, in addition to codfishes, snailfishes and blennies. In contrast, the main groups caught by fisheries in summer were other fishes, particularly Japanese amberjack (Seriola quinqueradiata) and various species of sharks and eels, and invertebrates. By autumn, Erimo fisheries had focussed on catching salmon. Salmon were taken by harbour seals as well during this period, but at a relatively lower frequency compared to other prey groups. The results of our study show that although harbour seals consumed several of the prey species targeted by fisheries, the relative importance of these species to seals and fisheries and the seasons in which they were targeted were different.     

First reports of a mass mortality event across multiple life stages in a mesopelagic jellyfish in high latitude coastal waters

Mass mortality events can occur naturally and may have important ecological impacts on local populations. The abundance and stage structure of the coronate scyphozoan Periphylla periphylla in a Northern Norwegian fjord were studied between October 2010 and August 2011. Developmental stage composition varied for the duration of the study, with early developmental stages only present in the autumn and winter. Records of large number of dead P. periphylla across multiple life stages revealed that a mass mortality event occurred towards the end of the study period. The abundance of live medusa increased from 27 to 39 individuals (ind.)·1,000 m^–3 from October 2010 to February 2011, then fell to <10 ind.·1,000 m^–3 in August 2011. The estimated abundance of dead jellyfish increased from slightly >1 ind.·1,000 m^–3 in October 2010 to >34 ind.·1,000 m^–3 in August 2011, corresponding to an estimated population mortality of >80% on the last sampling date. Mortality increased as the length of high solar irradiance periods increased. Based on previous published evidence that strong light is harmful to P. periphylla, we speculate whether the light climate of this high latitude location may have contributed to the mass mortality of P. periphylla.     

First distribution record of the invasive copepod Oithona davisae Ferrari and Orsi, 1984, in the coastal waters of the Aegean Sea

The occurrence of the invasive nonindigenous copepod Oithona davisae Ferrari and Orsi, 1984, is reported for the first time in the Aegean Sea. The data we collected in August 2017 from 14 stations along the Turkish coast of the Aegean Sea reveal the spatial distribution of O. davisae between the openning of the Dardanelles Strait in the north and the Izmir Bay in the south. The O. davisae individuals, in seven mesozooplankton samples collected from a single station, were consistently found in the inner part of the Izmir Bay from April 2015‐October 2016. The abundance of female O. davisae ranged from 4 ind./m³ in April 2015 to 31,524 ind./m³ in July 2016 and contributed to the total oithonid female population by 10.8% in April 2015 and 92.8% in September 2016. Our results show that this species is well established in the inner part of Izmir Bay and that it has become a permanent component of the copepod community in the area.     

Long‐term temporal and spatial patterns in bioeroding sponge distribution at the Abrolhos Bank,Brazil, Southwestern Atlantic

Bioeroding sponges belong to the most dominant bioeroders, significantly contributing to the erosion of coral reefs. Some species are tolerant or even benefit from environmental conditions such as ocean warming, acidification, and eutrophication. In consequence, increases in sponge bioerosion have been observed on some coral reefs over the last decades. The Abrolhos Bank is the largest coral reef system in the South Atlantic. It has been affected by sedimentation, eutrophication, overfishing, and climate change, mainly affecting coastal reefs, and at lesser intensity outer ones as well. This study aimed to describe spatial and temporal patterns in bioeroding sponge distribution in carbonate substrates in the Abrolhos Bank. Photo‐quadrats were used to compare bioeroding sponge abundance between two shallow reefs: a coastal, Pedra de Leste (PL), and an outer reef, Parcel dos Abrolhos (PAB). Each individual was delimitated over the substrate by determining the sponge surface through a line connecting the outermost papillae. The study was conducted over 6 years in 2008–2009 and 2013–2016. Four species of bioeroding sponges were identified: Cliona carteri Ridley, 1881, C. delitrix Pang, 1973, C. cf. schmidtii Ridley, 1881, and Siphonodictyon coralliphagum Rützler, 1971. The distribution and abundance of species varied between the inner and outer reefs and across the years, and displayed certain selectivity for the calcareous substrates recorded. Crustose coralline algae (CCA) were the main substrate excavated by the most abundant bioeroding species, C. carteri, and represented 70% of the substrate types occupied by this sponge (CCA, coral overgrown by CCA and plain coral). The highest abundance of bioeroding sponges observed in photo‐quadrats was 21.3 individuals/m² at the outer reefs (PAB) in 2014. The abundances or areal extents of bioeroding sponges were up to 10 times greater on the outer reefs than on the coastal ones, where sedimentation is higher and more strongly influenced by siliciclastic material. Moreover, a higher herbivorous fish biomass has been reported on outer reefs which could also influence the higher abundance of bioeroding sponges in outer reefs. During the study period of 6 years, an increase in bioeroding sponge abundance was observed at the outer reefs (PAB), with the sea surface temperature increase. As CCA have an important role in reefal cementation and carbonate production in the Abrolhos reefs, a bioerosion impact might be expected, in particular, on the outer reefs.     

Influence of habitat and host morphology on macrofaunal assemblages associated with the sponge Halichondria melanadocia in an estuarine system of the southern Gulf of Mexico

Sponges are inhabited by a wide variety of organisms and have been regarded as one of the richest biotopes in tropical seas. The aim of this study was to assess the influence of the host morphology and selected environmental conditions on macrofaunal assemblages associated with the sponge Halichondria melanadocia in an estuarine system of the southern Gulf of Mexico. This sponge exhibits different growth forms when it inhabits mangrove prop roots of Rhizophora mangle (thickly encrusting form) and adjacent seagrass beds (massive, amorphous or ramose form). From a total of 50 sponge specimens collected in each habitat, a total of eight taxa (of epi‐ and endobionts) was found associated with this sponge, with polychaetes, echinoderms and crustaceans the most abundant groups. In both morphotypes (thickly‐encrusting and massive‐ramose forms), taxon richness was positively related to sponge volume and oscular diameter. The overall mean abundance of associated fauna was also positively related to sponge volume in both morphotypes and with the oscular diameter (in the seagrass morphotype only). These findings suggest that H. melanadocia constitutes an important microhabitat for a wide variety of fauna, independent of its morphology and habitat type. However, when comparing the two morphotypes, the mangrove individuals, despite having smaller sizes, smaller oscular diameter and less structural complexity, displayed an overall mean abundance of fauna 17 times higher [0.36 ± 0.18 individuals (ind.)·ml·sponge^?1] than that recorded in the seagrass individuals (0.021 ± 0.01 ind.·ml·sponge^?1). There were also marked differences in the proportions of the major taxonomic groups; in fact, some of them were found exclusively in one morphotype. The variability recorded in the composition and abundance of associated fauna between the morphotypes seems to be influenced by differences in sponge morphology, environmental conditions (e.g. sedimentation rate and light intensity), substrate orientation and the fauna inhabiting the surrounding area.     

Vertical zonation and aggregated distribution of the Manila clam on subtidal sand flats in a coastal brackish lagoon along the Sea of Japan

The Manila clam, Ruditapes philippinarum, has maintained small‐sized populations in a semi‐enclosed brackish lake along the Sea of Japan, the Honjo area of Lake Nakaumi, although the environment and biota of this area have changed dramatically due to a large‐scale reclamation project. There should be underlying processes that enable the restoration of this species from small‐sized populations, such as the existence of source (i.e. reproductive) populations in other areas and depth zones of the lake. However, there has been no robust, properly designed evaluation of the distribution of the Manila clam in the subtidal sand flats. In order to elucidate the possible mechanisms that allow for the persistence of populations of the Manila clam, we examined the spatiotemporal and vertical variation in distributions of 0‐age clams in the subtidal zone of sand flats. Seasonal effects on population variations showed erratic changes among depth zones without a decreasing trend along the depth gradient. Further, many local populations became extinct even in the shallower zones due to seasonal (summer) hypoxia at deeper zones and hypoxia by the accumulation of key benthic species (Asian mussel and decaying macroalgae) in mats at shallower zones. A few surviving local populations were stable with a spatial‐fragmental (patchy) distribution, associated with fragmented accumulations of Asian mussels and macroalgae. Efforts to maintain stable populations and to restore this species in the subtidal area may depend on these small, restricted, patchy local populations. These findings suggest that high fertility and productivity of the Manila clam as well as patchy distribution of small populations may contribute to the maintenance of the population and the avoidance of extinction (by spatially diffusing the risk of extinction) in harsh environments resulting from the reclamation project.     

Sexual reproduction and early life‐history traits of the Mediterranean soft coral Alcyonium acaule

Understanding processes that contribute to a better comprehension of the population dynamics of long‐lived species is critical for the maintenance and potential recovery of such species. Despite the abundance of soft corals in Mediterranean rocky reefs, little information exists on their life histories and reproductive patterns. In this study, we assessed the main reproductive characteristics and early life‐history traits of the long‐lived soft coral Alcyonium acaule. The sex ratio was 1:1; the smallest fertile colonies were one finger in size (2.1 ± 0.6 cm in height), and both colony and polyp fertility increased with colony size. Likewise, the number of eggs and spermary sacs per polyp increased significantly with colony size, whereas the diameter of the female and male sexual products did not. Over 6 years of observations (2007–2012), spawning occurred primarily in July, after the seawater reached 20 °C, in a single spawning episode per year. Approximately 80% of female colonies released eggs, which were retained on the surface of the mother colony by mucous strings for up to a few days. High fertilization rates were observed during spawning in 2008 and 2009 (94.9% and 87.0%, respectively). The timing of development was ~24 h for the blastulae, ~48–72 h for the planulae and 8–22 days for metamorphosis into primary polyps. Survivorship of planulae was relatively high (~50% at 45 days after release), but only 24% of larvae metamorphosed into primary polyps, and their survivorship was moderate after 2 months (65% in 2008 and 74% in 2009). Asexual reproduction was negligible, indicating that sexual reproduction is the main mechanism supporting the maintenance and recovery of populations.