Peter W. Swarzenski

Most atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding

Sea-level rise and wave-driven flooding will damage freshwater resources of most atolls and soon render them uninhabitable. Sea levels are rising, with the highest rates in the tropics, where thousands of low-lying coral atoll islands are located. Most studies on the resilience of these islands to sea-level rise have projected that they will experience minimal inundation impacts until at least the end of the 21st century. However, these have not taken into account the additional hazard of wave-driven overwash or its impact on freshwater availability. We project the impact of sea-level rise and wave-driven flooding on atoll infrastructure and freshwater availability under a variety of climate change scenarios. We show that, on the basis of current greenhouse gas emission rates, the nonlinear interactions between sea-level rise and wave dynamics over reefs will lead to the annual wave-driven overwash of most atoll islands by the mid-21st century. This annual flooding will result in the islands becoming uninhabitable because of frequent damage to infrastructure and the inability of their freshwater aquifers to recover between overwash events. This study provides critical information for understanding the timing and magnitude of climate change impacts on atoll islands that will result in significant, unavoidable geopolitical issues if it becomes necessary to abandon and relocate low-lying island states.

Trophic transfer of essential elements in the clownfish Amphiprion ocellaris in the context of ocean acidification

Little information exists on the effects of ocean acidification (OA) on the digestive and post-digestive processes in marine fish. Here, we investigated OA impacts (Δ pH = 0.5) on the trophic transfer of select trace elements in the clownfish Amphiprion ocellaris using radiotracer techniques. Assimilation efficiencies of three essential elements (Co, Mn and Zn) as well as their other short-term and long-term kinetic parameters in juvenile clownfish were not affected by this experimental pH change. In complement, their stomach pH during digestion were not affected by the variation in seawater pH. Such observations suggest that OA impacts do not affect element assimilation in these fish. This apparent pCO2 tolerance may imply that clownfish have the ability to self-regulate pH shifts in their digestive tract, or that they can metabolically accommodate such shifts. Such results are important to accurately assess future OA impacts on diverse marine biota, as such impacts are highly species specific, complex, and may be modulated by species-specific metabolic processes.

The role of salinity in the trophic transfer of 137 Cs in euryhaline fish

In order to better understand the influence of changing salinity conditions on the trophic transfer of 137Cs in marine fish that live in dynamic coastal environments, its depuration kinetics was investigated in controlled aquaria. The juvenile turbot Scophthalmus maximus was acclimated to three distinct salinity conditions (10, 25 and 38) and then single-fed with compounded pellets that were radiolabelled with 137Cs. At the end of a 21-d depuration period, assimilation efficiencies (i.e. AEsu202f=u202fproportion of 137Cs ingested that is actually assimilated by turbots) were determined from observational data acquired over the three weeks. Our results showed that AEs of 137Cs in the turbots acclimated to the highest salinity condition were significantly lower than for the other conditions (pu202f<u202f0.05). Osmoregulation likely explains the decreasing AE observed at the highest salinity condition. Indeed, observations indicate that fish depurate ingested 137Cs at a higher rate when they increase ion excretion, needed to counterbalance the elevated salinity. Such data confirm that ambient salinity plays an important role in trophic transfer of 137Cs in some fish species. Implications for such findings extend to seafood safety and climate change impact studies, where the salinity of coastal waters may shift in future years in response to changing weather patterns.

Experimental evidence of dietary ciguatoxin accumulation in an herbivorous coral reef fish

Ciguatoxins (CTXs) are potent algal toxins that cause widespread ciguatera poisoning and are found ubiquitously in coral reef food webs. Here we developed an environmentally-relevant, experimental model of CTX trophic transfer involving dietary exposure of herbivorous fish to the CTX-producing microalgae Gambierdiscus polynesiensis. Juvenile Naso brevirostris were fed a gel-food embedded with microalgae for 16 weeks (89 cells g-1 fish daily, 0.4u202fμg CTX3C equiv kg-1 fish). CTXs in muscle tissue were detectable after 2 weeks at levels above the threshold for human intoxication (1.2u202f±u202f0.2u202fμg CTX3C equiv kg-1). Although tissue CTX concentrations stabilized after 8 weeks (∼3u202f±u202f0.5u202fμg CTX3C equiv kg-1), muscle toxin burden (total μg CTX in muscle tissue) continued to increase linearly through the end of the experiment (16 weeks). Toxin accumulation was therefore continuous, yet masked by somatic growth dilution. The observed CTX concentrations, accumulation rates, and general absence of behavioural signs of intoxication are consistent with field observations and indicate that this method of dietary exposure may be used to develop predictive models of tissue-specific CTX uptake, metabolism and depuration. Results also imply that slow-growing fish may accumulate higher CTX flesh concentrations than fast-growing fish, which has important implications for global seafood safety.

A double-tracer radioisotope approach to assess simultaneous bioaccumulation of caesium in the olive flounder Paralichthys olivaceus

To better understand bioaccumulation of radiocaesium in the commercially important Japanese flatfish, Paralichthys olivaceus, the uptake and depuration kinetics of caesium via both seawater and food were assessed simultaneously using controlled aquaria. The pre-conditioned fish were exposed to radionuclides via the two different pathways (aqueous versus dietary) concurrently using two isotopes of caesium, 137Cs and 134Cs, respectively. Dissolved caesium uptake was linear and did not reach a steady state over the course of the 8-day exposure period. Consumption of 134Cs-labelled food led to higher bioaccumulation rates of radioactive Cs than via seawater exposure of 137Cs during uptake and following depuration, though the model-derived long-lived biological half-lives of both pathways was approximately 66u202fd. Further development of this method for assessing multiple radiocaesium bioaccumulation pathways simultaneously could lead to a promising new approach for studying Cs contamination in marine organisms.

Application of nuclear techniques to environmental plastics research

Plastic pollution is ubiquitous in aquatic environments and its potential impacts to wildlife and humans present a growing global concern. Despite recent efforts in understanding environmental impacts associated with plastic pollution, considerable uncertainties still exist regarding the true risks of nano- and micro-sized plastics (<5u202fmm). The challenges faced in this field largely relate to the methodological and analytical limitations associated with studying plastic debris at low (environmentally relevant) concentrations. The present paper highlights how radiotracing techniques that are commonly applied to trace the fate and behaviour of chemicals and particles in various systems, can contribute towards addressing several important and outstanding questions in environmental plastic pollution research. Specifically, we discuss the use of radiolabeled microplastics and/or chemicals for 1) determining sorption/desorption kinetics of a range of contaminants to different types of plastics under varying conditions, 2) understanding the influence of microplastics on contaminant and nutrient bioaccumulation in aquatic organisms, and 3) assessing biokinetics, biodistribution, trophic transfer and potential biological impacts of microplastic at realistic concentrations. Radiotracer techniques are uniquely suited for this research because of their sensitivity, accuracy and capacity to measure relevant parameters over time. Obtaining precise and timely information on the fate of plastic particles and co-contaminants in wildlife has widespread applications towards effective monitoring programmes and environmental management strategies.

Using the radioligand-receptor binding assay for paralytic shellfish toxins: A case study on shellfish from Morocco

Paralytic shellfish poisoning (PSP) events occur regularly along the Mediterranean and Atlantic coast of Morocco, and have been responsible for several severe cases of human intoxication. Along the southern Atlantic coast of Morocco, aquaculture and intensive artisanal fishing practices have recently been particularly heavily impacted, and toxic species have been observed in increasing intensity and frequency. In the 1990s a regulatory monitoring program was established for the coastal waters off Morocco by the National Institute of Fisheries Research (INRH), to reduce the risk of intoxication with biotoxins. The regulatory monitoring is conducted weekly and includes toxic phytoplankton enumeration and identification, as well as saxitoxin (STX) analysis in seafood using the mouse bioassay (MBA). Animal testing remains the most widely used screening method for PSP toxin detection, yet its use is being reconsidered for animal-related ethical issues, as well as for practical considerations. To be able to better evaluate alternatives to animal testing, the performance of a nuclear-based radioligand-receptor binding assay (RBA) for paralytic shellfish toxins was assessed and compared with the MBA using four commercially important shellfish matrices, including cockles Cerastoderma edule, razor shells Solen marginatus, oysters Crassostrea gigas, and mussels Perna perna. Over 50 samples were collected and analysed as part of the regulatory monitoring framework including a suite of monthly samples from 2017 and all samples identified as toxic by MBA since 2011. Testing of reference material and evaluation of assay-critical parameters (e.g. slope of calibration curve, internal quality control QC and IC50) confirmed the robustness of the RBA methodology. With this RBA method, STX-like activity detected in shellfish samples ranged from 33 to 8500u202fμg STX equivalents per kg. RBA data were significantly correlated (Pu202f<u202f0.0001, Pearson ru202f=u202f0.96) with the MBA-derived dataset. Importantly, the RBA method allowed for the detection and quantification of PSP toxins at levels not detectable by using the mouse bioassay. The limits of quantification of the RBA was calculated and found to be 10-fold lower than that of the MBA, respectively 35.24u202f±u202f5.99 and 325u202fμg STX equivalents per kg of tissue. In addition, the RBA was easier to use and produced reliable results more rapidly than the MBA and without use of live animals. Considering the increasing risks associated with harmful algal blooms, globally and in Morocco, together with the increased development of aquaculture production and seafood consumption and the difficulties of live animal testing, these findings indicate that the RBA method is a reliable and effective alternative to the MBA method.