The coral reefs of the Pitcairn Islands are in one of the most remote areas of the Pacific Ocean, and yet they are exposed to the impacts of anthropogenic climate change. The Pitcairn Islands Marine Protected Area was designated in 2016 and is one of the largest in the world, but the marine environment around these highly isolated islands remains poorly documented. Evidence collated here indicates that while the Pitcairn Islands' reefs have thus far been relatively sheltered from the effect of warming sea temperatures, there is substantial risk of future coral decalcification due to ocean acidification. The projected acceleration in the rate of sea level rise, and the reefs' exposure to risks from distant ocean swells and cold-water intrusions, add further uncertainty as to whether these islands and their reefs will continue to adapt and persist into the future. Coordinated action within the context of the Pitcairn Islands Marine Protected Area can help enhance the resilience of the reefs in the Pitcairn Islands. Options include management of other human pressures, control of invasive species and active reef interventions. More research, however, is needed in order to better assess what are the most appropriate and feasible options to protect these reefs.

This report provides the first confirmed identifications of wahoo (Acanthocybium solandri) and striped marlin (Kajikia audax) in the Red Sea, expanding the known ranges of these species into the basin. Potential mechanisms responsible for the lack of regional documentation of the two species are further discussed. These findings illustrate the need for systematic biodiversity surveys of pelagic fish assemblages in the Red Sea.

Fisheries constitute a major threat to marine mammals globally. To evaluate the impact of small-scale fisheries (SSF) on regional under-studied marine mammal populations, we tested a novel and cost-effective approach at three data-limited locations of the central and eastern Mediterranean Sea. Using off-the-shelf GPS loggers to track SSF activities and systematic surveys to map the distribution of marine mammals, we assessed the probability of co-occurrence between SSF and marine mammals by reporting areas of spatial overlap. Spatial overlap between SSF and the core zones of marine mammal distribution (ranging between 21.85–35.4%) was observed in all three locations, indicating potential interaction hotspots. The probability of co-occurrence in those areas varied from 0.5–2.9% depending on the species. The resulting overlap between fishing activity and marine mammals may pose a threat in both directions: higher risk of species entanglement and economic burden on fishers due to gear damage. Despite the spatial and temporal limitations of this pilot study, the proposed approach can provide baseline information on SSF-marine mammal co-occurrence, particularly in financially limited regions. If applied on a larger scale, our method may be used to inform future conservation actions with the aim to reduce pressure on key populations.

Suckerfish attached to dolphin species have been extensively reported worldwide, yet such association has been rarely seen in the tropical and shallow waters of South America. In Brazil, the Guiana dolphin Sotalia guianensis is distributed along almost the entire extent of the coast and only one case of association with suckerfish has been published. Here we report on a sharksucker Echeneis naucrates associated with a young Guiana dolphin on the north-eastern coast of Brazil. The juvenile dolphin with an attached sharksucker was observed on two occasions separated by a 47-day period; we hypothesize the occurrence of host attachment fidelity. The present report adds information to better discuss the ecological interactions between echeneids and dolphins, and expands the baseline information on cetacean species serving as host to suckerfish.

The present study aims to investigate the reproductive biology of the small pelagic Sardinella aurita Valenciennes, 1847 in the Canary Islands, to enable its reliable assessment and advise on appropriate management measures for a fishing resource showing a declining trend in landings. Reproductive biology and sexual patterns of round sardinella were examined from monthly random samples of commercial catches landed by the artisanal purse-seine fleet. The landings' length frequencies, ranging between 9–32 cm (based on the total lengths, TL), were recorded from 2013–2019. The overall mean value of TL was 20.9 cm, with annual mean values between 20–22 cm, except in 2016 (TL = 19 cm). The overall sex ratio M:F was 1:0.92, with males significantly predominant. Sex ratios fluctuated as a function of size and month: females were more abundant in the larger length classes, as well as before and after spawning, whereas males were more abundant in the smaller length classes and during spawning. Based on gonad maturity stages and gonadosomatic index, round sardinella spawns during almost all the year, with a peak in January–February and a resting period during October–November. The length at first maturity was estimated at TL of 18.2 cm, notably smaller than the value obtained for the NW African coastal waters where the demographic structure in round sardinellas' landings is totally different.

The strontium-to-calcium ratio (Sr/Ca) in aragonitic shells and statoliths often depends on temperature, and has been investigated for its potential availability as a sclerochronological record of the temperatures experienced during the life of the animal. Only a few cephalopod species have been subjected to rearing experiments to validate the temperature dependence of statolith Sr/Ca despite the strong demand for estimating their historical ecology, particularly of migratory squid populations. In this context, we examined the relationship between temperature and statolith Sr/Ca in the spear squid, Heterololigo bleekeri, by maintaining wild-caught immature individuals at one of three constant temperatures: 12, 14 or 16°C. A portion of statolith precipitated during the experiment was optically identified by daily increment analysis, and then subjected to Sr/Ca measurement using an electron probe micro-analyser. Regression analysis (N = 29) demonstrated the dependence of statolith Sr/Ca on temperature and the relationship was estimated as an equation Y = 9.93 (±0.29) − 0.11 (±0.02) X. However, ~90% of the total residual variance was accounted for by the among-individual variation of statolith Sr/Ca within each temperature group. Consequently, the 95% confidence interval ranged over ± 7.85°C when the temperature was estimated by inserting a Sr/Ca value into this equation. The statolith Sr/Ca values are unlikely to provide reliable estimates for absolute temperatures, but it may allow reconstruction of a time-series of relative temperatures experienced by a particular individual.

Monitoring the spread of non-indigenous species is fundamental to study global warming effects on marine biodiversity. A valuable tool is represented by the continuous updating of the geographic range expansion of non-indigenous species. Lamprohaminoea ovalis is a Lessepsian mollusc initially recorded in the Mediterranean Sea in 2001. This paper reports its range expansion over the last 20 years related to water warming. The first record of Lamprohaminoea ovalis from the Ligurian Sea (NW Mediterranean) is also reported. Two individuals (about 10 mm length) were observed on a sub-vertical rocky bottom at 26 m depth displaying potential trailing behaviour. This recent finding extends the currently known distributional range of Lamprohaminoea ovalis, representing the northernmost occurrence of this non-indigenous species in the western Mediterranean Sea.

Humpback whales (Megaptera novaeangliae) exhibit maternally driven fidelity to feeding grounds, and yet occasionally occupy new areas. Humpback whale sightings and mortalities in the New York Bight apex (NYBA) have been increasing over the last decade, providing an opportunity to study this phenomenon in an urban habitat. Whales in this area overlap with human activities, including busy shipping traffic leading into the Port of New York and New Jersey. The site fidelity, population composition and demographics of individual whales were analysed to better inform management in this high-risk area. Whale watching and other opportunistic data collections were used to identify 101 individual humpback whales in the NYBA from spring through autumn, 2012–2018. Although mean occurrence was low (2.5 days), mean occupancy was 37.6 days, and 31.3% of whales returned from one year to the next. Individuals compared with other regional and ocean-basin-wide photo-identification catalogues (N = 52) were primarily resighted at other sites along the US East Coast, including the Gulf of Maine feeding ground. Sightings of mother-calf pairs were rare in the NYBA, suggesting that maternally directed fidelity may not be responsible for the presence of young whales in this area. Other factors including shifts in prey species distribution or changes in population structure more broadly should be investigated.

Antagonism among bacteria is widespread and plays an important role in structuring communities. Inhibitory compounds can confer competitive advantage, but energetic trade-offs can result in non-transitive (i.e. ‘rock-paper-scissors’) interactions, ultimately allowing co-existence and community stability. Competition in sedimentary habitats is especially keen given high densities and attachment to inorganic particles. Because measuring trade-offs between bacterial species is challenging, much of our understanding of competitive interactions is based on theoretical modelling and simplified in vitro experiments. Our objectives were to determine (1) if interference competition occurs in microcosms mimicking in situ conditions; (2) whether the presence of sediment influences antagonistic interactions; and (3) if more complex assemblages alleviate or synergize interactions. Four sedimentary isolates, including antibiotic-producing, resistant and susceptible strains were incubated in porewater microcosms in 1-, 2- and 3-species combinations, both with and without natural sediments. Microcosms were sampled over 72 h to generate growth curves using quantitative PCR. Multiple growth attributes (growth rate, maximum density, lag time) were used to assess effects of treatment (species combinations) and environment (sediment vs porewater alone). Antimicrobial producers were more effective at inhibiting target species in microcosms that included sediment, in agreement with theory. We observed growth inhibition by antimicrobial-producing bacteria in both 2- and 3-species microcosms. However, the expected protection of sensitive bacterial strains by resistant strains was observed in only one (of four) 3-species combinations, thus the ‘rock-paper-scissors’ prediction was not fully supported. These results reinforce the notion that interspecies interactions are context-dependent, reliant on environmental conditions and the species involved.

The aim of this study is to determine the phytoplankton species found on the shores of Burgaz Island and the basic ecological variables that affect their seasonal distribution between May 2013 and February 2014. Water samples were collected from four stations at six different depths and plankton samples were gathered horizontally and vertically. The analysis of phytoplankton community composition revealed 101 phytoplankton taxa belonging to five classes. As a result of the study, two taxa belonging to the Dinophyceae (Corythodinium frenguellii and Gonyaulax scrippsae) were new records for Turkish coastal waters. Additionally, a taxon belonging to Dinophyceae (Pronoctiluca pelagica) and a taxon belonging to Bacillariophyceae (Nitzschia reversa) were new records for the Sea of Marmara. Prorocentrum micans, was the dominant species throughout all sampling periods. During the study, the highest phytoplankton abundance was observed at 0.5 m depth in May 2013 (138,500 cells l−1) and February 2014 (52,620 cells l−1). Primary ecological variables, such as temperature (9.0–21.5 °C), salinity (15.23–37.22‰) and dissolved oxygen (4.89–15.84 mg l−1), were recorded on each sampling occasion. In addition, nitrite + nitrate–N (NO2 + NO3–N) (0.01–7.37 μg-at N l−1), phosphate (PO4–P) (0.05–51.95 μg-at P l−1) and silicate (SiO4–Si) (0.01–0.20 μg-at Si l−1) concentrations were measured. Chlorophyll a and suspended material values ranged between 0.01–3.17 μg l−1 and 10.0–61.5 mg l−1, respectively. Spearman's rank correlation was used to determine the relationship between phytoplankton species and ecological variables, and Bray–Curtis analysis and Euclidean distance were applied to bring out the similarity between stations.

This systematic review analysed scientific publications to identify relevant research about the impact of alien polychaete species around the world, using the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analysis) guide. The criterion for inclusion was studies published in English, with the key terms (e.g. ‘impact’, ‘alien species’, ‘polychaetes’) in the title, abstract and keywords. The literature search was conducted in Scopus and Web of Science from April to December 2020. The search resulted in 150 papers that included information about impact of alien polychaete species. Of these studies, 98% were published in the last 25 years, reporting on the impact of 40 species in 18 regions of the world. Sixty-one per cent of the research was conducted in the Baltic Sea, South-west Atlantic and Mediterranean Sea. The most frequent type of study was field surveys (46%) and the most studied system was open coast areas (36%). The species with the highest number of publications about their impacts were Ficopomatus enigmaticus, Marenzelleria viridis, Sabella spallanzanii and Boccardia proboscidea. Based on evidence of their most severe documented impacts in their introduced ranges, the impact mechanisms (IMos) of the alien polychaete species were strongly related to their biology and lifestyles. We found that species that build conspicuous reefs and tube-dwellers mainly showed physical and structural impact on ecosystems; shell-borers, mainly parasitism and infauna species, showed mainly chemical, physical and structural impacts on ecosystems. Some recommendations for the study of alien polychaete species are discussed.

Marine ectotherms have evolved a range of physiological strategies to cope with temperature changes that persist across generations. For example, metabolic rates are expected to increase following an acute exposure to temperature, with potential detrimental impacts for fitness. However, they may be downregulated in the following generation if offspring experience the thermal conditions of their parents, with a resulting decrease in maintenance costs and fitness maximization. Yet, trans-generational studies on metabolic rates are few in marine ectotherms, thus limiting our ability to accurately predict longer-term implications of ocean warming on organisms' performance, metabolic rates being the fundamental pacemaker for all biological processes. This is particularly true for small-size organisms, for which the determination of individual metabolic rates has been historically challenging, and for many groups of marine invertebrates, such as annelids, which are under-represented in physiological investigations. Here, we exposed the subtidal annelid Ophryotrocha labronica (body length: ~4 mm) to a thermal gradient (21, 24, 26, 29°C) and measured, for the first time in this species, the temperature dependence of metabolic rates across two generations. We found that metabolic rates were positively related to temperature, but this relationship did not differ between generations. Our study provides additional evidence for the diversity of temperature-associated physiological responses of marine ectotherms and offers a number of methodological recommendations for unveiling the mechanisms underpinning the observed trans-generational responses of metabolic rates in marine annelid species.

The present study enhances knowledge of the biodiversity of diatoms in Chuuk, Micronesia following our 2018 study on the seaweed-associated diatoms. We collected planktonic samples of diatoms from five sites of reef flats using a 20 μm mesh net, and two samples of seaweeds with epiphytes by hand from an islet on the barrier reef. In addition, the seaweed-associated diatoms from our 2018 study were analysed using scanning electron microscopy. A total of 109 diatom taxa are documented in the present study. Of these, 70 species were from net samples, and 39 species from the seaweed-associated diatoms. Thirty-one species are newly recorded from Micronesian waters. Most taxa are benthic or tychoplanktonic; euplanktonic diatoms were rare. The occurrence of benthic diatoms from the water column might be related to the Chuuk environmental conditions which include shallow water, strong light intensity and high grazing pressure, to which benthic diatoms seem to be able to better adapt than planktonic diatoms.

The Patagonian longfin squid Doryteuthis gahi has an annual life cycle with two seasonal cohorts (autumn and spring spawners). Earlier studies on the Patagonian shelf found a predominance of Euphausiacea in the D. gahi diet, but no studies to date have investigated differences between feeding spectra of the two cohorts or decadal diet shifts. The present study investigated differences in diet of D. gahi on the Patagonian shelf sampled two decades apart, and differences between seasonal cohorts. Classical stomach content analysis and generalized additive models were used to investigate and model the influence of mantle length, sampling period and spawning cohort on the diet. Results revealed an ontogenetic diet change from ~70% Frequency of Occurrence of Euphausiacea in small squid to more than 60% FO of fish and Cephalopoda at larger sizes. Cannibalism was also frequently observed. Euphausiacea were ingested more frequently and in higher amounts during the austral summer and therefore were consumed more by the autumn spawning cohort, whereas fish was more frequently fed upon during austral winter and also by the spring spawning cohort. Cannibalism was also recorded more in austral winter months but, contrary to feeding on fish, was more prevalent in the autumn spawning cohort. Increased predation of Munida gregaria was observed in 2020 compared with 2001. This study is an important step towards improving the knowledge of D. gahi's two seasonal cohorts, providing data that can be used for future ecosystem modelling.

The introduction of Pacific oysters to the sedimentary south-eastern North Sea coast and their establishment on intertidal native blue mussel beds has caused the development of mixed reefs of mussels and oysters with extensive tidepools. Tidepools have been intensively studied at rocky shores where they show community structures, which usually differ from that of the surrounding emerging substrates. Tidepools at sedimentary coasts, however, have received less attention. We compared the community structure and species interactions inside and outside tidepools in oyster reefs by determining densities of snails, barnacles and amphipods. Snail densities were similar in and outside tidepools. Barnacle coverage on bivalve shells, however, was lower inside tidepools, which may be caused by higher predation pressure and increased snail grazing under permanently submerged conditions, as was revealed by field and laboratory experiments. Additionally, we studied the occurrence of copepod and trematode parasites in blue mussels inside and outside tidepools. Prevalence and intensity of parasitic copepods was higher in mussels inside tidepools. Trematode parasites, by contrast, showed a lower intensity in mussels inside tidepools. This can be explained by high amphipod densities found inside tidepools because trematode larvae represent a food source of amphipods. Our study suggests that the community structure of oyster reefs within tidepools is not a submerged equivalent to that of intertidal reefs. As their counterparts at rocky shores, they show their own species distribution patterns with particular species interactions and only provide refuge for specific species such as parasitic copepods.

This paper presents the first records of the brittle star Ophiactis abyssicola in Canadian waters and range extensions of up to 1900 km in the Northwest Atlantic from previously known locations. Samples were collected off northern Labrador and the northern portion of insular Newfoundland (eastern Canada) at 433 and 1097 m depths, respectively. This newly recorded species of brittle star from the bathyal zone off Newfoundland and Labrador adds to the marine biodiversity of Canada and to the general distribution knowledge of O. abyssicola.

There is ever-greater need for information about changing marine biodiversity, but such information is sparse at large spatial or temporal scales. Records about distributions of species collected by volunteers can fill gaps in knowledge that cannot yet be addressed by more structured sampling. Bayesian occupancy models show great promise for estimating trends in occurrence of species through time. This study uses the Sparta occupancy model with records from the Seasearch programme from coastal waters of Britain and Ireland during the period 2000–2020, focussing on three species of Crustacea (Cancer pagurus, Homarus gammarus and Palinurus elephas). Populations of P. elephas crashed in the 1970s, but now appear to be re-establishing in south-west England. The Sparta model provides evidence about recovery that is more robust than anecdotal reports or simple counts of records. Estimates of occupancy are made at different spatial scales and compared among species and areas. Trends in occupancy are compared qualitatively with patterns in fisheries landings data. Occupancy by P. elephas has increased drastically since 2014, a pattern not seen in the other two species. For each species, occupancy varied among areas and in some areas, patterns in estimates of occupancy were similar to trends in landings from fisheries. Citizen science records are increasingly recognized to have value which has not yet been fully exploited. Greater use should be made of the Seasearch dataset in order to provide population trends for benthic marine taxa. Such analyses will broaden our understanding of and taxonomic coverage of changes in biodiversity.

The ocean quahog, Arctica islandica, is a commercially important bivalve in the eastern USA but very little is known about the recruitment frequency and rebuilding capacity of this species. As the longest-living bivalve on Earth, A. islandica can achieve lifespans in excess of 200 y; however, age determinations are difficult to estimate and age variability at size is extreme. Objectives for this study included the creation of an extremely large age-composition dataset to constrain age at length variability, development of reliable age-length keys (ALK), and descriptions of sex-based population dynamics for the quasi-virgin A. islandica population at Georges Bank (GB) within the greater US Mid-Atlantic stock. Sexually dimorphic characteristics are clearly present, as females are larger than males within age classes and males tend to dominate the oldest age classes. A male represented the maximum age of 261 years and is older than the maximum age previously documented for this region. Sex-specific ALKs were robust and reliable but not interchangeable. This population had higher estimated natural mortality rates than presumed for other regions in the Mid-Atlantic, and females have the highest mortality rate. However, recruitment expansion was also occurring which would affect the age-frequency data used to derive mortality estimates and result in higher mortality. Age frequencies at GB suggest effective recruitment to the population each year since 1867 CE. Reduced recruitment periods are documented and likely attributed to fluctuating environmental conditions. Sex-based demographics are clearly divergent in regard to growth rate, maximum size, longevity and mortality rates.