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.

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.

The shallow sandy marine subtidal ecosystem off Mar del Plata, Argentina, is the scene of multiple fisheries activities, in particular the prawn–shrimp Artemesia longinaris and Pleoticus muelleri grounds. We examined the δ13C vs δ15N isotope signatures of 22 species commonly found in the area in order to understand how this ecosystem supports the fishery, with special emphasis on imposex-affected gastropod populations. Our results indicate that the main food source for Olivancillaria urceus and Buccinanops monilifer were bivalves and crustaceans. Buccinanops duartei and Olivancillaria carcellesi feed on bivalves and also on macroalgae. These findings indicate, for the first time, a slight selectivity of some of the gastropods studied for local drifted algal sources and how gastropods may scavenge available food from by-catch returned to the sea. The fishes Urophysis brasiliensis and Callorhynchus callorhynchus appeared to be the top predators of this area with B. duartei and O. carcellesi constituting important components of their diet.

Basking sharks Cetorhinus maximus tend to aggregate in summer at favoured locations along Britain and Ireland's west coast. Sharks have been described approaching and close-following one another, often to one side. This has been interpreted as putative pre-mating behaviour. At aggregation sites around the Inner Hebrides we used boat-based observation and in-water and overhead drone video-photography to document behaviour and to determine the sex of individuals. It was confirmed that a shark will frequently move purposely towards another from a distance and swim to maintain a position either directly behind or closely to one side of a conspecific for short periods. Contrary to expectation, we found no relationship between the sex of a shark or its size and close-following. This suggests that following behaviours are not mainly related to courtship. Further, abrasions on the nose suspected to be related to male behaviour were found to occur on both sexes, although abrasions on pectoral fins, similarly suggestive of mating-related behaviour, were predominantly on females. Breaching by basking sharks has also been proposed as a means of attracting the opposite sex. We observed breaching by solitary sharks but commonly by sharks within aggregations, and at other times by more than one shark on the same day at the same time; but there was not any clear evidence to indicate that breaching is primarily related to mating. More likely individuals show close following chiefly for feeding-related hydrodynamic advantage. It remains plausible however that mature sharks make use of feeding aggregations to initiate pre-courtship behaviour.

Quantifying interconnected performances of the modules in a colonial organism (feeding, sexual reproduction, rejuvenation, dormancy) into an integral picture enables studying functional dynamics and resource allocation at different levels – from module to population. Testing this approach on the common boreal-Arctic bryozoan Cribrilina annulata in the White Sea, we describe its life history, comparing colonies on two algal substrates with contrasting size and lifespan. Colonies living on kelps were much larger and had a higher proportion of dormant zooids, whereas the percentage of reproducing, feeding and rejuvenating zooids was higher in colonies on red algae (with the colonies also exhibiting longer reproductive period). Colony lifespan was dependent both on substrate type and on time of colony establishment, lasting from 4–5 to up to 17 months on kelps and 14–18 months on red algae. During the reproductive season (May–September) the C. annulata population consisted of colonies of three cohorts on both substrata: overwintered and two summer generations that behaved differently. Whereas overwintered and summer colonies established in June–early August produced larvae, most of the colonies established after mid-summer were preparing for hibernation and postponed reproduction until next spring. Moreover, young reproducing colonies formed brooding hermaphrodite zooids of ordinary size, whereas overwintered colonies budded smaller-sized basal and frontal (dwarf) hermaphrodites. Finally, overall zooidal performance in co-existing colonies of the overwintered and young generations was different on kelps, but similar on red algae. Altogether our findings indicate that the life histories of colonial epibionts are much more complex and evolutionarily flexible than generally acknowledged.

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.

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).

Structural and functional properties of exoskeleton in moulting sea slaters Ligia pallasii from the Eastern Pacific coast were investigated with CT scanning and electron microscopy. Ultrastructure of preecdysial and postecdysial cuticular layers was described in premoult, intramoult and postmoult animals. Cuticle is a flexible extracellular matrix connected to the epidermal cells through pore channels. During premoult epicuticle and exocuticle are formed and during intramoult and postmoult endocuticular lamellae are deposited and the cuticle is progressively constructed by thickening and mineralization. Cuticle permeability, flexibility and waterproofing capacity change accordingly. Elaboration of epicuticular scales connected to an extensive network of nanotubules, establish its anti-adhesive and hydrophobic properties. Labelling with gold conjugated WGA lectins on Tokuyashu thawed cryosections exposes differences in chitin content between exocuticle and endocuticle. Histochemical staining of cuticle shows presence of acidic carbohydrates/glycoconjugates and lipoproteins in epicuticular layer. Chitin microfibrils are formed at the microvillar border of epidermal cells with abundant Golgi apparatus and secretory vesicles. Numerous spherules associated with nanotubules were observed in the ecdysial space in intramoult animals. The mineral component of the cuticle as visualized with CT scanning indicates progressive mineral resorption from the posterior to the anterior half of the body in premoult animals, its translocation from the anterior to posterior part during intramoult and its progressive deposition in the posterior and anterior exoskeleton during postmoult. Cuticle of sea slaters is a unique biocomposite and biodynamic material constantly reconstructed during frequent moults, and adapted to specific physical and biotic conditions of the high intertidal rocky zone.

Time-lapse photography was used to study the timing and duration of foraging activity of a population of the pulmonate gastropod Onchidella celtica on an exposed rocky shore in Cornwall, UK. The pulmonates spent most of their time in their home crevice, emerging onto open rock only during some ebb tides to forage for food and find a mate. Total duration and speed of foraging was highly variable and did not generally conform to a triphasic pattern. The number foraging was also highly variable and was not correlated significantly with the spring/neap tide cycle or weather (air temperature above 12°C, air pressure, solar radiation, precipitation, relative humidity and wind speed). There was a significant negative correlation between foraging and surf height. Although the pulmonates foraged during all hours of the day/night cycle, foraging activity tended to be highest during the afternoon and evening.

The stomach contents of thresher sharks (Alopias spp.; 162–385 cm total length) were collected from five landing points in northern Peru during 2015. A total of 128 thresher sharks were sampled, with 38 individuals identified as Alopias pelagicus and 90 aggregated to the genus level Alopias sp. to prevent any misidentification. The diet comprised 13 and 10 prey taxa for Alopias sp. and A. pelagicus, respectively. Humboldt squid Dosidicus gigas dominated the diet of both groups, with only minor differences in the diet in relation to size classes and location. The diet of Alopias shows a high degree of specialization and the average trophic positions were high for both groups, A. pelagicus (4.4 ± 0.13) and Alopias sp. (4.5 ± 0.14).

The effects of trampling are usually confounded by the diffuse impacts of the urbanization of sandy beaches. We performed a controlled experiment on a beach with low visitation rates to test the hypothesis that ghost crabs avoid building their burrows on impacted plots as a result of the compacted sediment, and they migrate to non-trampled areas. The sampling design encompassed 11 survey quadrats (6 × 6 m) above the strandline, including five trampled plots (100, 300, 900, 1500 and 3000 steps) and six non-trampled plots. The plots were sampled before and after 24, 48 and 72 h of experimental trampling. We found that the ghost crabs avoided building their burrows in only the 1500× and 3000× trampled plots after 24 h, but the avoidance was not related to sediment compactness. Additionally, the emersion time and escape distance from humans were significantly delayed in the most trampled plots, suggesting a lower surface activity and an avoidance of irregular (i.e. high micro-relief) sediment surfaces by ghost crabs, which might reduce their ability to perceive potential predators.

Thermal perception is crucial for the fitness of marine invertebrates in intertidal and shallow waters. TRPA1 is a non-selective cation channel that belongs to the TRP family with pivotal roles in initiating signal transduction of thermal perception. We investigated expression patterns of SiTRPA1 in different tissues (tube feet, coelomocytes, gonads and gut) of the sea urchin Strongylocentrotus intermedius. SiTRPA1 expression patterns under acute and long-term temperature stimuli were investigated in tube feet of sea urchins. In the present study, the highest expression of SiTRPA1 was detected in tube feet of S. intermedius. The SiTRPA1 expression level in tube feet were significantly 235.7-fold, 450.0-fold and 3299.7-fold higher than those in the coelomocytes, gonads and gut (df = 3, F = 47.382, P < 0.001). Expression levels of SiTRPA1 in the other tissues (coelomocytes, gonads and gut) were not significantly different (df = 3, F = 47.382, P = 0.972). There was no significant difference of SiTRPA1 expression among all groups in the acute temperature increase experiment (df = 4, F = 0.25, P = 0.902). In the acute temperature decrease experiment, the expression of SiTRPA1 showed no significant difference among all groups (df = 4, F = 1.802, P = 0.205). With long-term exposure (6 weeks) to different temperatures, SiTRPA1 expression in the low temperature group (10°C) was significantly higher than those in the high temperature (20°C) and the control groups (15°C) (df = 2, F = 9.57, P = 0.014). There was no significant difference of SiTRPA1 expression between the high temperature (20°C) and the control temperature (15°C) groups (df = 2, F = 9.57, P = 0.808). These results indicate that SiTRPA1 expression significantly responds to long-term low temperature but not to acute temperature decrease. The present study provides new insights on the distribution and temporal expression of TRPA1 in marine invertebrates after acute and long-term temperature stimuli.

The present study investigated the population dynamics of Hepatus pudibundus in the Cananéia region, in southern São Paulo state, Brazil, focusing on population structure, growth parameters, longevity, sex ratio, reproduction and recruitment juvenile period. Sampling was performed monthly at seven stations from July 2012 to June 2014, using a shrimp fishing boat. A total of 1650 specimens were collected: 551 males and 1099 females. The males were larger than females. Reproductive females were captured throughout the study period and juveniles were captured in most months. Both of these demographic categories were positively correlated with temperature. Growth parameters showed differences between sexes: CW∞ = 78.91 mm, k = 0.0066 day−1, t0 = 0.0965 for males and CW∞ = 69.71 mm, k = 0.0053 day−1, t0 = −0.2404 for females. Longevity was estimated at 1.91 and 2.40 years for males and females, respectively. The findings provide a greater understanding of the life cycle in this species. Additionally, since trawl nets are not selective, this study also provides information for better trawl fishery management, addressing not only the target shrimp but also the by-catch species.

The coastal waters of east Lewis from the Butt of Lewis to Loch Erisort are a proposed Marine Protected Area (MPA) for Risso's dolphins (Grampus griseus). A total of 100.4 h (2006.4 km) of active search effort (Beaufort sea states ≤3) was collected during 72 dedicated boat surveys between 2010 and 2017 (primarily in August and September) in the southern part of the MPA and south to the Shiant Isles. Forty Risso's dolphin sightings and 24.1 h of encounter effort were recorded, predominantly along the southern and eastern Eye Peninsula in 20–40 m water depths and at distances <1 km from shore. Group size ranged from one to 50 animals (mean = 11.8 dolphins) and calves occurred in 37.5% of sightings. A total of 2404 shore-based scans (Beaufort sea states ≤3) carried out from Tiumpan Head between September 2011 and December 2017 resulted in 271 (11.3%) ‘dolphin-present’ scans. Dolphins were present year-round, with a seasonal increase between May and October. ‘Calf-present’ scans only occurred between April and October. Photo-identification images from 28 boat surveys produced a minimum population size of 117 animals. There was evidence of high inter- and intra-annual site fidelity, with individual dolphins photographically captured in up to six of the eight survey years, and between two and seven capture dates being recorded for over 45% of individuals within most years. The combined datasets support the importance of east Lewis for Risso's dolphins, and recommendations are made for ongoing monitoring of dolphin occurrence throughout the wider MPA.

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.

An array of nano-scale protrusions, called the nipple array, is found on the body surface of various invertebrates, and this structure is believed to decrease light reflectance and water wettability on the surface in the terrestrial environment. However, its potential functions have not been well studied in aquatic environments. Clavelina spp. are colonial ascidians that have the nipple array on their integumentary matrix (i.e. tunic). We examined the physical properties on the surface of the tunic of C. cyclus and C. obesa, such as hardness, wettability and refractive indices, to evaluate the functional importance of this structure. The tunic cuticle of both species was covered with the nipple array, and the cuticle of C. cyclus was bent into folds forming parallel plications. The Clavelina tunic was very soft and had high bubble- and oil-repellency. The refractive-index deviation between the tunic and seawater was 0.07–0.095 for 589-nm light (D-line). Rigorous coupled wave analysis (RCWA) showed that the nipple array slightly reduced reflectance on the surface and the parallel plications reduced the reflectance still more. The nanoimprinted plates imitating the parallel plications have higher bubble repellency and lower reflectance than the flat plates. These findings support the functional importance of the plications as well as the nipple array.

Widely distributed species such as Arbacia stellata adjust patterns of their life history according to local conditions. In the present study the reproductive cycle of this species was analysed throughout a sampling year. Gonadal development cycle, sex ratio, actual fecundity and oocyte size distribution were characterized and the relationship of these reproductive characteristics with environmental variables such as sea surface temperature, photoperiod, chlorophyll a and net primary production evaluated. Our results showed that A. stellata is a gonochoric sea urchin. Gametogenesis was classified into six stages for both sexes (immature, growth, pre-maturity I, pre-maturity II, mature and spawning) and no synchrony was observed for the gonads between individuals. The female to male ratio was close to 1:1 in most months. The gonadosomatic index (GSI) showed significant differences between sexes or months; however, the highest values were observed during spring, with positive correlation with chlorophyll a. No significant differences were observed in the maturity index (MI) between sexes, with a positive correlation with temperature but negative with chlorophyll. Actual fecundity showed wide variations throughout the year and correlation with chlorophyll a and temperature. Oocyte size distribution was unimodal and the predominant frequency was that of mature oocytes. The reproductive cycle of A. stellata has a semi-continuous pattern for both sexes and partial spawning throughout the year in the sampling site. We observed nutrient assimilation in the gonads during spring and a larger reproductive activity from late summer to early winter.

After the recent detection, by both morphology and DNA barcodes, of the larval stages of an unknown species of pea crab (Pinnotheres sp.) in European waters, adults of this crab are herein reported and described as a new species. The current known geographic distribution of the species comprises the Gulf of Cádiz in the eastern Atlantic and the adjacent Mediterranean waters of the south of the Iberian Peninsula (Alboran Sea), where this crab is well-established inside the anomiid bivalve Anomia ephippium. In the Gulf of Cádiz, the species displayed a relatively high prevalence: on average, 55.6–77.7%, in A. ephippium samples. The dominant demographic categories of the new species were soft females (61.8–77.0%) with fewer males (17.7–21.10%). Most of the host bivalves carried only one crab; in bivalves harbouring two crabs, heterosexual pairs were collected more frequently than expected by chance, which suggests that they could be mated pairs. A strong correlation between host size and soft female size was found (r = 0.73, P < 0.01) indicating that space availability within hosts seems to be relevant in determining the size of the sedentary phase of the new crab species.

The potential use of fatty acid (FA) profile as a dietary tracer in juvenile Chinese horseshoe crab Tachypleus tridentatus was assessed in a feeding experiment. Selected feed was provided to the juveniles at various growth stages according to their food sources in the wild: larval and adult brine shrimp Artemia salina for the first six months, followed by a mixture of short-neck clam Ruditapes philippinarum and greasyback shrimp Metapenaeus ensis for a further six months. Juvenile horseshoe crab haemolymph and tissues of book gill, opisthosomal spine, chelicera and swimming leg were sampled after the feeding experiment. The FA profiles revealed that the juvenile haemolymph and various tissues had a total of 23–24 FA components. The major FA components consisted of saturated (palmitic and stearic) at 22–34%, monosaturated (oleic) at 7–34% and polyunsaturated (eicosapentaenoic and arachidonic) FAs at 9–27%. According to principal component analysis, the FA signatures of juvenile haemolymph were greatly influenced by the shift of food sources from brine shrimp to clam and shrimp meat, whereas the FA profiles of different tissues were more resistant to the nutrient alteration. The present findings confirmed that the FA profile of both juvenile haemolymph and different tissues reflected the FA composition of recent and previous diets, respectively; and thus may be useful in indicating the foraging information of juvenile horseshoe crabs in the field.

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.