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Marine canopies formed by seagrass and other coastal vegetated ecosystems could act as sinks of microplastics for being efficient particle traps. Here we investigated for the first time the occurrence of microplastic retention by marine canopies in a hydraulic flume under unidirectional flow velocities from 2 to 30 cm s-1. We used as model canopy-forming species the seagrass Zostera marina with four canopy shoot density (0, 50, 100, 200 shoots m-2), and we used as microplastic particles industrial pristine pellets with specific densities from 0.90 to 1.34 g cm-3 (polypropylene PP; polystyrene PS; polyamide 6 PA; and polyethylene terephthalate PET). Overall, microplastics particles transported with the flow were retained in the seagrass canopies but not in bare sand. While seagrass canopies retained floating microplastics (PP) only at low velocities (

Future ocean acidification (OA) and warming following climate change elicit pervasive stressors to the inhabitants of the sea. Previous experimental exposure to OA for 16 weeks at pH levels predicted for 2100 has shown to result in serious immune suppression of the Norway lobster, Nephrops norvegicus. The lobsters are currently affected by stressors such as periodical hypoxia inducing high levels of bioavailable manganese (Mn). Here, we aimed to investigate possible effects of interactions between OA and these stressors on total hemocyte counts (THCs) and on recovery of inoculated bacteria in the lobsters, measured as a proxy for bacteriostatic response. The effects were judged by following numbers of culturable Vibrio parahaemolyticus in hepatopancreas, 4 and 24h post inoculation in lobsters kept in replicate tanks with six different treatments: either ambient (pCO2∼500 μatm/pH∼8.1 U) or CO2-manipulated seawater (OA; pCO2∼1550 μatm/pH∼7.6 U) for 8 weeks. During the last 2 weeks, additional stress of either hypoxia (∼23% oxygen saturation) or Mn (∼9 mg L(-1)) was added except in control treatments. Our results showed clear effect on bacteriostatic response in Norway lobsters exposed to these stressors. In lobsters kept in ambient seawater without additional stressors, the number of culturable bacteria in hepatopancreas was reduced by ∼34%. In combined treatment of ambient seawater and hypoxia, the reduction was ∼23%, while in the Mn-exposed animals, there was no reduction at all. This was also the case in all OA treatments where mean numbers of culturable V. parahaemolyticus tended to increase. In lobsters from ambient seawater with or without hypoxia, the THC was not significantly different as was also the case in OA without additional stressors. However, in OA treatments combined with either hypoxia or Mn, THC was reduced by ∼35%. While the reduction of culturable V. parahaemolyticus in lobsters was clearly affected by these stressors, we found no notable effects on growth, survival or hemolytic properties of the bacteria itself. Thus, we conclude that this predicted stress scenario is beneficial for the pathogen in its interaction with the host. As OA proceeds, it may force the health of the ecologically and economically important N. norvegicus to a tipping point if exposed to more short-term stressors such as the periodical events of hypoxia and Mn. This could impact lobster condition and biomass and may as well increase the risk for bacterial transmission to consumers.

1. Aquatic chemical ecology is an important and growing field of research that involves understanding how organisms perceive and respond to chemical cues in their environment. Research assessing the preference or avoidance of a water source containing specific chemical cues has increased in popularity in recent years, and a variety of methods have been described in the scientific literature. Two-current choice flumes have seen the greatest increase in popularity, perhaps because of their potential to address the broadest range of research questions. 2. Here, we review the literature on two-current choice flumes and show that there is a clear absence of standardized methodologies that make comparisons across studies difficult. Some of the main issues include turbulent flows that cause mixing of cues, inappropriate size of choice arenas for the animals, short experiments with stressed animals, failure to report how experiment and researcher biases were eliminated, general underreporting of methodological details, underutilization of collected data and inappropriate data analyses. 3. In this review, we present best practice guidelines on how to build, test and use two-current choice flumes to measure the behavioural responses of aquatic animals to chemical cues, and provide blueprints for flume construction. The guidelines include steps that can be taken to avoid problems commonly encountered when using two-current choice flumes and analysing the resulting data. 4. This review provides a set of standards that should be followed to ensure data quality, transparency and replicability in future studies in this field. © 2016 The Authors. Methods in Ecology and Evolution © 2016 British Ecological Society

Many crustaceans communicate with pheromones during mating. In the infaunal amphipod Corophium volutator (Pallas), females release gender-specific waterborne pheromones that guide males in their search for receptive burrowed females. Pollutants that affect the pheromone release or impair the ability of males to detect and respond to chemosensory cues, could profoundly affect mating. C. volutator is commonly found on shallow soft sediments in estuaries and coastal waters, and their reproductive season coincides with intense traffic of leisure boats, which discharge high concentrations of fuel into the water and sediment of these areas. This study shows that sublethal exposure to naphthalene, a polycyclic aromatic hydrocarbon abundant in motor fuel, disturbs chemical communication in C. volutator. This was demonstrated in Y-maze bioassays, where males were allowed to follow female pheromones after separately exposing the males or females to naphthalene spiked sediments (0, 0.5, 5 or 50 microg g(-1) dw, nominal concentrations) for 3 days. The results show that exposure to naphthalene at the two lower concentrations significantly affects the males' response to female pheromones (p0.05 and p0.01, respectively). Male search activity was reduced by 27-45% and males could no longer find females by the use of the olfactory sense. Analysed sediment samples, however, indicate that the naphthalene concentrations causing this effect were 2-20 times lower than nominal concentrations. At the highest naphthalene treatment, no significant difference from the controls was found, probably explained by a different exposure regime for these amphipods since they seemingly avoided burrowing in sediments. Female C. volutator produce and release pheromones, despite naphthalene exposure. Disrupted chemical communication in C. volutator may affect the reproductive fitness of males and females with possible consequences for populations in contaminated areas.

Many crustaceans use pheromones to find mates and induce mating behaviours. If pollutants impair the ability to detect chemosensory cues and respond to pheromone signals, they could profoundly affect mating. In a series of laboratory experiments, the effect of copper (0, 0.1 or 0.5 mg Cu(II) per litre for 5 days) on specific components of the mating behaviour of male shore crab Carcinus maenas was investigated, as well as differences in sensitivity between red and green colour morphs. The results show that copper exposure clearly altered the response of C. maenas males to a pheromone stimulus (pre-moult female urine) presented alone, together with a dummy female (a sponge injected with pre-moult female urine) or with a real female. Crabs exposed to the highest copper treatment took more than twice as long to initiate search activity after pheromone introduction and their search behaviour was less directed. When offered a dummy female, male crabs showed decreased pheromone discrimination in both copper treatments. Stroking was the only mating behaviour significantly affected, with a 90% reduction in red crabs in the highest copper treatment. Additionally, crabs of the highest copper treatment more often pinched the dummy female (non-mating behaviour). Finally, male crabs exposed to copper more often pinched pre-moult females and it took about three times longer to establish cradle-carrying. Thus, copper affects the ability of males to detect female pheromones, perform specific mating behaviours and to form pairs.

The decapod Norway lobster, Nephrops norvegicus (L.), lives on muddy sediments rich in manganese (Mn). In hypoxic conditions, manganese is reduced and released from the sediment, so increased concentrations of dissolved Mn(2+) become bioavailable. In excess, manganese acts as a neurotoxin and may inhibit vital functions of benthic organisms, such as muscle contraction. We investigated in a laboratory flume experiment, the effect of environmentally realistic concentrations of manganese (0.1 and 0.2mM for 12 days) on the food search behaviour of N. norvegicus. We found that lobsters exposed to manganese had a more than doubled reaction time to food odour stimuli compared to the controls (p

The amphipod Corophium volutator (Pallas) is a tube-dwelling species that only occasionally leaves its burrow. Animals that do crawl on the sediment are mainly males, apparently in search of females. This study was designed to determine whether C. volutator males and females release chemical signals that attract con-specifics, and if so, whether these signals are gender specific. Laboratory experiments were conducted on the over-wintering generation during their reproductive season, using a Y-maze choice test apparatus. The results show that C. volutator females release chemical signals that attract males. In the field, the attractant may guide males in search of burrowed females. In addition, male odour tends to attract males, while females do not follow chemical signals from con-specifics. We thereby show on gender-specific chemical attraction of this species.

The ability to identify chemical cues in the environment is essential to most animals. Apart from marine larval stages, anomuran land hermit crabs (Coenobita) have evolved different degrees of terrestriality, and thus represent an excellent opportunity to investigate adaptations of the olfactory system needed for a successful transition from aquatic to terrestrial life. Although superb processing capacities of the central olfactory system have been indicated inCoenobitaand their olfactory system evidently is functional on land, virtually nothing was known about what type of odourants are detected. Here, we used electroantennogram (EAG) recordings inCoenobita clypeatusand established the olfactory response spectrum. Interestingly, different chemical groups elicited EAG responses of opposite polarity, which also appeared forCoenobita compressusand the closely related marine hermit crabPagurus bernhardus.Furthermore, in a two-choice bioassay withC. clypeatus,we found that water vapour was critical for natural and synthetic odourants to induce attraction or repulsion. Strikingly, also the physiological response was found much greater at higher humidity inC. clypeatus, whereas no such effect appeared in the terrestrial vinegar flyDrosophila melanogaster. In conclusion, our results reveal that theCoenobitaolfactory system is restricted to a limited number of water-soluble odourants, and that high humidity is most critical for its function.

Environmental hazards associated with traditional, toxic antifouling coatings based on heavy metals calls for the development of alternative, environmentally acceptable antifouling compounds. Medetomidine ((±)-4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole) is a candidate antifouling biocide which impedes settlement of barnacles in the nanomolar range. Prior to introducing novel biocides it is of great importance to consider potential effects on non-target organisms. This study is the first to investigate the effects of medetomidine on the amphipod Corophium volutator, specifically effects on male mate search behaviour. In a laboratory, Y-maze bioassay, C. volutator males were allowed to follow female pheromones after 24 h exposure to 0 (control), 0.01 and 0.1 μg mL−1 medetomidine. We found that exposure to medetomidine at both concentrations significantly reduced pheromone induced mate search (by 42–71%), with fewer males crawling towards female odour. The results obtained indicate that medetomidine may impair the reproductive fitness of non-target crustaceans, an aspect that needs to be considered before further commercialisation.