No abstract

The impacts of microplastics on some individual organisms have been well studied but what is less clear is what impacts microplastics have on wider ecosystem processes. Using salps as model organisms, we studied the effect of microplastic ingestion on the downward flux of high-density particulate organic matter in the form of salp faecal pellets. While to date most microplastic studies used virgin microplastics at unrealistic environmental concentrations here we exposed Salpa fusiformis to fractured and UV exposed polyethylene and polystyrene microplastics possessing a biofilm. It was found that when exposed to environmentally relevant concentrations, reported for the Mediterranean and the South Pacific Gyre, only few faecal pellets had microplastics incorporated within them. Under potential future scenarios, however, up to 46% of faecal pellets contained microplastics. Incorporated microplastics significantly altered the size, density and sinking rates of salp faecal pellets (p-value < 0.05 in each instance). Sinking rates decreased by 1.35-fold (95% CI = 1.18, 1.56) for faecal pellets with polyethylene microplastics and 1.47-fold (95% CI = 1.34, 1.61) for polystyrene. These results suggest that today, microplastic ingestion by salps has minimal impact on the biological pump. However, under future microplastic concentrations (or in areas such as convergent zones), microplastics may have the potential to lower the efficiency of the biological pump.

the extent to which commercially important Nephrops norvegicus lobsters feed on particulates in the wild is unknown, even though this could be an important way for burrow-dwelling females to avoid starvation during the long breeding season. this was investigated using δ 13 c and δ 15 n isotopic signatures in tissues with long and short turnover rates to provide diet discrimination and compare this between males and females. Secondary objectives examined size-related differences and calculated the trophic position based on the new results. Almost half the diet (47%) was made up of suspended particulate organic matter (poM susp) alone. Fish was another important item in the diet, with plankton and invertebrate sources coming much lower down in dietary importance. Significantly more suspension feeding was observed in small or medium sized individuals than large ones in both sexes. However, there were no sex-related patterns, despite females being restricted to burrows for part of the analysis period. female diet was almost identical to males and poM susp comprised a large component of the diet in both sexes. The trophic position was estimated at 2.94 ± 0.16 (mean ± SD), which was at the lower end of the range reported in previous studies (2.60 to 4.32). Dublin Bay prawn, Nephrops norvegicus, is a decapod crustacean and an important economic resource in Europe: global production of this fishery was 59,033 tons in 2016 of which the United Kingdom and Republic of Ireland were the main producers, capturing up to 32,708 and 10,379 tons per annum respectively during 2012-2016 1. Nephrops populations are distributed on semi-isolated mud patches which are assessed by ICES as separate Functional Units (FU), however this resource is not 'managed' via fishing quotas, and some FUs periodically display signs of over-exploitation 2,3. The Marine Strategy Framework Directive and reformed Common Fisheries Policy (CFP) require ecosystem-based fisheries management which observes interactions among all components of the ecosystem, including trophic interactions 4-6. Although not currently managed under the CFP, key gaps and ambiguities exist in knowledge of Nephrops' diet and feeding ecology which should be addressed, given their economic importance and occasional over-exploitation. Nephrops individuals are known to be opportunistic predators and scavengers, which seem to have a diet driven by prey abundance rather than prey preference 7-10. Diet from stomach contents analyses seems to be similar across a wide geographical range in the northeastern Atlantic and Mediterranean, composed mainly of crustaceans, polychaetes, molluscs and echinoderms 8,9. A considerable contribution to the diet is also made by fish in southern Atlantic and Mediterranean samples 11,12. However, some mystery surrounds the extent of feeding on particulates in Nephrops. In the absence of alternative food sources, such as in the aquarium, Nephrops was demonstrated to feed on planktonic items larger than 300-500 µm, which were later recovered from the stomach and...

Stock enhancement activities provide an opportunity to examine density-dependent suppression of population biomass which is a fundamental issue for resource management and design of no-take-zones. We document ‘catch-and-wait’ fisheries enhancement where all but the largest lobsters are thrown back, recapturing them later after they have grown to a larger size. The residency, rate of return, and potential negative density-dependent effects of this activity are described using a combination of tagging and v-notching and by relating spatial growth patterns to population density defined with Catch Per Unit Effort. The results successfully demonstrated the concept of catch-and-wait practices. However, a density-dependent suppression of growth (in body size) was observed in male lobsters. This demonstrates a mechanism to explain differences in lobster sizes previously observed across EU fishing grounds with different stock densities. This negative effect of density could also affect individual biomass production in marine reserve or no-take zones.Electronic supplementary materialThe online version of this article (10.1007/s13280-019-01158-1) contains supplementary material, which is available to authorized users.

This study examines the diet of lesser spotted dogfish Scyliorhinus canicula, one of the most ubiquitous predators of European coastal waters. This species is of increasing ecological significance as other large predatory fish decline as it has known interactions with fisheries. Scyliorhinus canicula diet was investigated in Irish coastal waters during June and July 2014 using both stomach-content analysis and δ C and δ N stable-isotope ratios. Prey contribution to the diet from dual stable-isotope data was estimated using Bayesian mixing models. It was found that only stable-isotope analysis provided a time-integrated picture of the diet of S. canicula and allowed for a new estimation of their trophic position. Trophic positions from stomach-content analysis within the present study and previous studies were found to be higher than revealed by isotopes. Stomach-content analysis could not reveal the importance of soft-bodied animals in the diet of these fish, however this approach remains a valuable tool to understand the potential prey spectrum in advance of isotope analysis and allows for a better resolution down to species level. The results highlight a greater variety in the diet of this important predator and the benefit of taking a multidisciplinary approach in dietary studies.