Interactions between marine megafauna and plastic pollution in Southeast Asia.

Southeast (SE) Asia is a highly biodiverse region, yet it is also estimated to cumulatively contribute a third of the total global marine plastic pollution. This threat is known to have adverse impacts on marine megafauna, however, understanding of its impacts has recently been highlighted as a priority for research in the region. To address this knowledge gap, a structured literature review was conducted for species of cartilaginous fishes, marine mammals, marine reptiles, and seabirds present in SE Asia, collating cases on a global scale to allow for comparison, coupled with a regional expert elicitation to gather additional published and grey literature cases which would have been omitted during the structured literature review. Of the 380 marine megafauna species present in SE Asia, but also studied elsewhere, we found that 9.1 % and 4.5 % of all publications documenting plastic entanglement (n = 55) and ingestion (n = 291) were conducted in SE Asian countries. At the species level, published cases of entanglement from SE Asian countries were available for 10 % or less of species within each taxonomic group. Additionally, published ingestion cases were available primarily for marine mammals and were lacking entirely for seabirds in the region. The regional expert elicitation led to entanglement and ingestion cases from SE Asian countries being documented in 10 and 15 additional species respectively, highlighting the utility of a broader approach to data synthesis. While the scale of the plastic pollution in SE Asia is of particular concern for marine ecosystems, knowledge of its interactions and impacts on marine megafauna lags behind other areas of the world, even after the inclusion of a regional expert elicitation. Additional funding to help collate baseline data are critically needed to inform policy and solutions towards limiting the interactions of marine megafauna and plastic pollution in SE Asia.

Residency, movement patterns, behavior and demographics of reef manta rays in Komodo National Park.

Background: The reef manta ray (Mobula alfredi) is a globally threatened species and an iconic tourist attraction for visitors to Indonesia's Komodo National Park (NP). In 2013, manta ray fishing was banned in Komodo NP and its surroundings, preceding the nationwide manta ray protection in 2014. Over a decade ago, a previous acoustic telemetry study demonstrated that reef manta rays had high fidelity to sites within the park, while more recent photo-identification data indicated that some individuals move up to 450 km elsewhere. Characterization of manta ray demographics, behavior, and a focused assessment on site use of popular tourism locations within the park is vital to assist the Komodo NP Management Authority formulate appropriate manta ray conservation and management policies. Methods: This study uses a long-term library (MantaMatcher.org) of photo-identification data collected by researchers and citizen scientists to investigate manta ray demographics and habitat use within the park at four sites frequented by tour operators: Cauldron, Karang Makassar, Mawan, and Manta Alley. Residency and movements of manta rays were investigated with maximum likelihood analyses and Markov movement models. Results: A total of 1,085 individual manta rays were identified from photographs dating from 2013 to 2018. In general, individual manta rays displayed a higher affinity to specific sites than others. The highest re-sighting probabilities came from the remote southern site, Manta Alley. Karang Makassar and Mawan are only ~5 km apart; however, manta rays displayed distinct site affinities. Exchange of individuals between Manta Alley and the two central sites (~35.5 km apart) occurred, particularly seasonally. More manta rays were recorded traveling from the south to the central area than vice versa. Female manta rays were more mobile than males. Similar demographic groups used Karang Makassar, Mawan, and Manta Alley for foraging, cleaning, cruising, or courtship activities. Conversely, a higher proportion of immature manta rays used the northern site, Cauldron, where foraging was commonly observed. Fishing gear-related injuries were noted on 56 individuals (~5%), and predatory injuries were present on 32 individuals (~3%). Tourism within the park increased from 2014 to 2017, with 34% more dive boats per survey at Karang Makassar and Mawan. Discussion: The Komodo NP contains several distinct critical habitats for manta rays that encompass all demographics and accommodate seasonal manta ray movements. While the present study has not examined population trends, it does provide foundational data for such work. Continued research into manta ray abundance, long-range movements, and identifying and protecting other critical aggregation areas within the region is integral to securing the species' recovery. We provide management recommendations to limit undue pressure on manta rays and their critical habitats from tourism.

Microplastics in fecal samples of whale sharks (Rhincodon typus) and from surface water in the Philippines.

Marine plastic abundance has increased over the past 60 years and microplastics (< 5 mm) constitute a primary component of such litter. Filter-feeding megafauna, such as the whale shark, might be particularly affected by microplastic pollution as their feeding mode requires filtration of up to thousands of cubic meters of water. In addition, the habitat range of whale sharks intersects with several recognized microplastic pollution hotspots, among which is the Coral Triangle. Direct evidence for microplastic ingestion in whale sharks however, has not yet been presented. Here we show that whale shark scat collected in the Philippines from 2012 to 2019 contained a mean of 2.8 microplastics g- 1. Contrary to our expectations, the microplastic concentration in the scat remained consistent from 2012 to 2019. Water samples from the study site in 2019 indicated that the local microplastic pollution (5.83 particles m- 3) was higher than in surface waters in other whale shark habitats, but well below other pollution hot-spots found in Southeast Asia and China (range: 100-4100 particles m- 3). With the predicted growth in plastic use, leading to increased plastic marine pollution, whale sharks are expected to become more exposed to this form of pollution. To what extent microplastic ingestion impacts the overall health status of this endangered species remains an open question. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s43591-021-00017-9.

What's in the soup? Visual characterization and polymer analysis of microplastics from an Indonesian manta ray feeding ground.

Plastics in marine environments vary in their physical and chemical properties, influencing their risk to biota once ingested. Manta rays are large filter-feeders that ingest plastics. To assess this risk, we characterized the plastics in a critical feeding habitat off Nusa Penida, Indonesia. We examined the color and polymer composition of sampled small-sized plastics (<30 mm). Plastics were mostly secondary microplastics and transparent (46%), white/off-white (24%), and blue/green (22%). Fourier transform infrared spectroscopy of plastics grouped according to type (films, fragments, foam, or lines) and color indicated that most plastics were polyethylene (PE) or polypropylene (PP) (99%), with the remainder polystyrene and polyester. Visual characterization aligned with single polymer composition in seven out of ten groups. Although PE and PP have relatively low toxicity compared to other plastics, their composing monomers and associated pollutants and microbes are of concern to manta rays and other marine biota.

It's not all black and white: investigating colour polymorphism in manta rays across Indo-Pacific populations.

Intraspecific colour polymorphisms have been the focus of numerous studies, yet processes affecting melanism in the marine environment remain poorly understood. Arguably, the most prominent example of melanism in marine species occurs in manta rays (Mobula birostris and Mobula alfredi). Here, we use long-term photo identification catalogues to document the frequency variation of melanism across Indo-Pacific manta ray populations and test for evidence of selection by predation acting on colour morph variants. We use mark-recapture modelling to compare survivorship of typical and melanistic colour morphs in three M. alfredi populations and assess the relationship between frequency variation and geographical distance. While there were large differences in melanism frequencies among populations of both species (0-40.70%), apparent survival estimates revealed no difference in survivorship between colour morphs. We found a significant association between phenotypic and geographical distance in M. birostris, but not in M. alfredi. Our results suggest that melanism is not under selection by predation in the tested M. alfredi populations, and that frequency differences across populations of both species are a consequence of neutral genetic processes. As genetic colour polymorphisms are often subjected to complex selection mechanisms, our findings only begin to elucidate the underlying evolutionary processes responsible for the maintenance and frequency variation of melanism in manta ray populations.

Microplastics: No Small Problem for Filter-Feeding Megafauna.

Microplastic pollution can impact filter-feeding marine megafauna, namely mobulid rays, filter-feeding sharks, and baleen whales. Emerging research on these flagship species highlights potential exposure to microplastic contamination and plastic-associated toxins. Research and its wide communication are needed to understand the magnitude of the issue and improve marine stewardship.

Running the gauntlet: regional movement patterns of Manta alfredi through a complex of parks and fisheries.

Manta rays (Genus Manta) are economically important for fisheries and tourism in Indonesia. These species have been listed by the International Union for the Conservation of Nature Red List as Vulnerable to extinction; therefore, human exploitation of manta rays must be regulated. A better understanding of the habitat use and movement patterns of manta rays in Indonesia is needed in order to employ effective conservation measures. To gain better insight into the movements of Manta alfredi we used 'Manta Matcher', an online database with an integrated automated matching algorithm, to compare photographs from 2,604 encounters of M. alfredi collected by recreational divers and dive operators throughout Indonesia over a nine-year period. This photographic comparison revealed that manta rays migrated between regional sanctuaries such as Nusa Penida, the Gili Islands, and the Komodo National Park (up to 450 km straight-line distance). The areas between these sanctuaries are heavily fished and trafficked by ships, and when manta rays travel through these regions they risk being fished and injured by ship strikes. These long-range manta ray movements suggest connectivity between M. alfredi populations in neighboring islands and raise concerns about the future management of regional populations. It is recommended that a national conservation strategy be developed to protect the remaining populations in the country.

Enhanced tumor metastasis in response to blockade of the chemokine receptor CXCR6 is overcome by NKT cell activation.

Invariant NKT (iNKT) cells can induce potent antitumor responses in vivo. However, the mechanisms that regulate the effects of iNKT cells are unclear. The chemokine receptor CXCR6, and its ligand CXCL16, have been shown to play critical roles in iNKT cell homeostasis and activation. Thus we investigated the role of CXCR6 in protection against experimental metastasis of B16-F10 melanoma (B16) and Lewis lung carcinoma (LLC) cells to the liver and lungs. Wild-type and CXCR6(-/-) mice exhibited no differences in tumor cell metastasis to the lungs. However, metastasis of LLC and B16 tumor cells to the liver was enhanced in CXCR6(-/-) mice. Liver metastasis was also increased in wild-type mice treated with a CXCL16 neutralizing Ab. As Ab treatments did not alter iNKT cell numbers, this implicates a direct role for CXCR6/CXCL16 in regulating antitumor immunity. Cytokine induction was significantly attenuated in CXCR6(-/-) mice upon systemic iNKT cell activation with the glycolipid Ags alpha-galactosylceramide (alpha-GalCer), alpha-C-GalCer (a Th1 polarizing derivative), or OCH (a Th2 polarizing derivative). Despite differences in the levels of cytokine production, liver and lung metastasis were inhibited significantly in both wild-type and CXCR6(-/-) mice treated with glycolipids. Single doses of alpha-GalCer, alpha-C-GalCer, or OCH were sufficient to prevent liver metastasis and subsequent doses failed to elicit optimal cytokine responses. Our findings implicate a role for CXCR6 in natural immunosurveillance against liver metastasis. However, CXCR6 deficiency could be overcome by systemic iNKT cell activation, demonstrating that even suboptimal iNKT cell activation can protect against metastasis.

Critical role for the chemokine receptor CXCR6 in homeostasis and activation of CD1d-restricted NKT cells.

NK T (NKT) cells play important roles in the regulation of diverse immune responses. However, little is known about the mechanisms that regulate homeostasis and activation of these cells. Thymic NKT cells up-regulated the chemokine receptor CXCR6 following positive selection and migrated toward CXCL16 in vitro. However, CXCR6 was not essential for thymic development or maturation. In contrast, liver and lung NKT cells were depleted in CXCR6+/- and CXCR6-/- mice. The reduction in liver and lung NKT cells coincided with an increase in bone marrow NKT cells, suggesting a redistribution of NKT cells in CXCR6-/- animals. In wild-type mice, CXCL16 neutralization reduced accumulation of mature NK1.1+, but not immature NK1.1- NKT cell recent thymic emigrants in the liver. Given that thymic NKT cells are preferentially exported as NK1.1- cells, this suggests an additional role for CXCR6/CXCL16 in maturation or survival of immature liver NKT cells. CXCL16 blockade did not deplete resident NK1.1+ NKT cells, indicating that CXCR6/CXCL16 are not required to retain mature NKT cells in the liver. Cytokine production by liver and spleen NKT cells was impaired in CXCR6-/- mice following in vivo stimulation with alpha-galactosylceramide, implicating a novel role for CXCR6 in NKT cell activation. Reduced IFN-gamma production was not due to an intrinsic defect as production was normal following PMA and ionomycin stimulation. Preformed transcripts for IL-4, but not IFN-gamma, were reduced in CXCR6-/- liver NKT cells. These data identify critical roles for CXCR6/CXCL16 in NKT cell activation and the regulation of NKT cell homeostasis.

Current and future approaches for the therapeutic targeting of metastasis (review).

Metastasis is the process whereby cancer cells disseminate and establish secondary tumors at distant sites from the primary tumor and is estimated to be responsible for approximately 90% of all cancer deaths. Cancers with metastatic spread are frequently resistant to conventional chemotherapeutic approaches, underlining the urgent need for novel treatments in these diseases. Recent advances in understanding the mechanisms underlining both the intrinsic cellular and extrinsic micro-environmental factors contributing to the metastatic process have resulted in the identification of a number of molecular targets for the development of specific anti-metastatic therapeutic strategies. These targets include intracellular enzymes such as the protein tyrosine kinases, cell surface receptors and their ligands, and elements of the extracellular matrix such as pro-angiogenic factors, protease enzymes and cytokines. Many of these pathways interact with each other, with the possibility of multiple downstream antineoplastic consequences as well as the potential for synergistic effects by targeting more than one of these factors. This review outlines several of the promising targets, and provides examples, of how these targets are being exploited as anti-metastatic therapies in conjunction with conventional treatments.