Ingestion and translocation of microplastics in tissues of deposit-feeding crabs (Grapsoidea, Ocypodoidea) in Kochi estuary, Japan.

Estuaries contain some of the highest concentrations of accumulated microplastics (MPs) that can be ingested by abundant deposit-feeding crabs. We investigate MPs in gill, hepatopancreatic, and gastrointestinal tissues of seven intertidal crab species in Kokubu River, Kochi, Japan. By applying a reliable method that considers limits of detection and quantification, we report MPs in 63 of 116 crabs (>50%), with a mean of 3.2 MPs individual-1. Concentrations are greatest in gastrointestinal tracts (62.15%), suggesting that feeding is the main route for MP uptake. PET is the dominant polymer (44%), and fragments are the dominant shape (50%-77%). A greater MPs burden g-1 body weight is reported for deposit-feeding small ocypodid crabs than for larger herbivorous/omnivorous grapsoid crabs. Factors possibly influencing MP uptake by crabs include feeding habit, crab size, and ambient MP composition.

Potential sources of microplastic contamination in laboratory analysis and a protocol for minimising contamination.

Measurements of microplastics in environmental and biological samples can be overestimated because of contaminants introduced during the analytical process. Knowledge of the potential sources and frequency of contamination during analysis is required to develop a protocol to prevent analytical errors. In this study, potential sources of contamination in the laboratory analysis of biological samples were evaluated, and reliable, inexpensive measures to prevent contamination were tested. Glass fibre filters, water samples, air samples, and chemicals [Fenton's reagent (H2O2 and FeSO4), and ZnCl2] were tested for the presence of contaminants. Particulate contamination, including microplastics, was found in all samples when tested before application of any preventative measures. The following measures were evaluated for preventing contamination: (1) filtration of the water and chemical solutions using a glass fibre filter, (2) pre-combustion of the glass fibre filters, and (3) use of a clean booth for experimental work. The preventative measures reduced the levels of microplastics in all samples by 70-100%. The dominant polymers identified by Fourier transform infrared spectroscopy were polyethylene terephthalate, cellulose fibre (rayon), polystyrene, polyacrylonitrile, and polyethylene. With the preventative measures, the number of microplastics in the laboratory blanks was low enough to set the limit of detection to < 1. This limit of detection would be suitable for examination of microplastics contamination at the individual organism level, even at trace levels. Preventative countermeasures are essential to reduce overestimation of microplastics in biological samples and can be implemented at low cost.

Microplastic distribution among estuarine sedimentary habitats utilized by intertidal crabs.

The high accumulation potential of estuaries for plastics, particularly microplastics, poses a threat to the high societal value and biodiversity they provide. To support a spatially refined evaluation of the risk that microplastic pollution poses to fauna utilizing estuarine sedimentary habitats, we investigated the distribution of microplastics (lower limit of quantification, LOQ = 62 µm) at the sediment surface of two dominant habitats, and subsequently compared microplastic burdens between two crabs species utilizing these habitats. Microplastics were dominated by low density polyolefins (45-50 %), comparable to the polymer composition of macroplastics. The vast majority (99 %) of microplastics were ≤1 mm, and increased exponentially (with an exponent of 2.7) in abundance at smaller sizes, hinting at three-dimensional fragmentation. Our results suggest that the presence of vegetation needs to be accounted for in risk assessments with small microplastics (≥62 µm and ≤1 mm) on average 2.6 times more prevalent within reed beds compared to mudflats. Additionally, sediment properties also play a role with an exponential decrease in small microplastic abundance at coarser sediments, increased organic matter content, and decreased water content. These results suggest that at specific locations, such as the study area, local sources can provide a substantial contribution to microplastic contamination. To translate these habitat- and site-specific differences into a risk assessment relevant for macroinvertebrates, ecological traits such as differences in feeding modes should be accounted for, as we found substantial differences in both size and abundance of microplastics in gastrointestinal tracts of two crab species, Chiromantes dehaani and Chasmagnathus convexus, with different feeding modes.

Mangrove crab intestine and habitat sediment microbiomes cooperatively work on carbon and nitrogen cycling.

Mangrove ecosystems, where litter and organic components are degraded and converted into detrital materials, support rich coastal fisheries resources. Sesarmid (Grapsidae) crabs, which feed on mangrove litter, play a crucial role in material flow in carbon-rich and nitrogen-limited mangrove ecosystems; however, the process of assimilation and conversion into detritus has not been well studied. In this study, we performed microbiome analyses of intestinal bacteria from three species of mangrove crab and five sediment positions in the mud lobster mounds, including the crab burrow wall, to study the interactive roles of crabs and sediment in metabolism. Metagenome analysis revealed species-dependent intestinal profiles, especially in Neosarmatium smithi, while the sediment microbiome was similar in all positions, albeit with some regional dependency. The microbiome profiles of crab intestines and sediments were significantly different in the MDS analysis based on OTU similarity; however, 579 OTUs (about 70% of reads in the crab intestinal microbiome) were identical between the intestinal and sediment bacteria. In the phenotype prediction, cellulose degradation was observed in the crab intestine. Cellulase activity was detected in both crab intestine and sediment. This could be mainly ascribed to Demequinaceae, which was predominantly found in the crab intestines and burrow walls. Nitrogen fixation was also enriched in both the crab intestines and sediments, and was supported by the nitrogenase assay. Similar to earlier reports, sulfur-related families were highly enriched in the sediment, presumably degrading organic compounds as terminal electron acceptors under anaerobic conditions. These results suggest that mangrove crabs and habitat sediment both contribute to carbon and nitrogen cycling in the mangrove ecosystem via these two key reactions.

Sediment grain size determines microplastic exposure landscapes for sandy beach macroinfauna.

Despite the global occurrence of microplastic contamination on sandy beaches, evidence of microplastic distribution within beaches remains contradictory. When conflicting evidence is used to inform sampling surveys, it increases uncertainty in resulting data. Moreover, it hampers spatially explicit risk characterization of microplastic pollution to intertidal fauna. We aimed to guide sampling designs for microplastic monitoring on beaches, and to quantify macroinfauna exposure to microplastics. Microplastic abundance, quantified between 5 mm-66 µm, lacked a significant zonation across the top sediment layer of sub-terrestrial, upper and lower midlittoral, and swash zones at two sites with varying anthropogenic influence on a microtidal dissipative beach in Uruguay. Microplastic abundance decreased exponentially with increasing grain size, as revealed by Bayesian Poisson regression, although the decrease was less steep compared to prior knowledge regarding sediment - plastic interactions obtained for large (millimeter-sized) industrial pellets. Significant differences in microplastic contamination between the two sites with varying anthropogenic influence likely related to their proximity to a freshwater canal. Corresponding field measurements of body burdens of fibers and irregular particles were significantly lower for the polychaete Euzonus (Thoracophelia) furcifera, despite its preference for finer sediments with higher microplastic loads, compared to the isopods Excirolana braziliensis and Excirolana armata. Results provide critical insights toward representative sampling of microplastics within beach sites. Specifically, we caution against sampling limited to the drift line, and instead recommend: 1) reporting beach morphodynamic characteristics; 2) using clearly defined, ecologically-informed zonation schemes; and 3) accounting for sediment grain size as a covariate to normalize among reported contamination levels. The results contribute valuable baseline data toward realistic exposure landscapes relative to the sediment grain size preferences of macroinfauna, needed to inform laboratory experiments.

Identification of black microplastics using long-wavelength infrared hyperspectral imaging with imaging-type two-dimensional Fourier spectroscopy.

Despite recent progress in focal plane array Fourier transform infrared spectroscopy (FPA-FT-IR) for automatic microplastic (MP) discrimination, the analysis time is still too long (e.g., 9 h for a sample with a diameter of 47 mm) and the equipment is expensive. As a solution, a hyperspectral camera restricted to the near-infrared or short-wavelength infrared band could be applied. However, with these bands, the minimum discriminable size is only about 100 µm, and discrimination among darkly colored plastics is difficult. The long-wavelength infrared (LWIR) band is reportedly effective for discrimination among darkly colored plastics. In this study, we constructed a palm-sized LWIR hyperspectral camera (105 mm × 90 mm × 50 mm, 1.25 kg) for imaging-type two-dimensional Fourier spectroscopy. Our system used a general-purpose, inexpensive, and compact microbolometer for the LWIR band. This system could record the absorbance of black MPs (polystyrene, polyethylene, and polypropylene) in a 3.8 mm × 3.0 mm area in 36 s, which was less than 1/6th of the time required for FPA-FT-IR. Additionally, our system could obtain spectra for a 12 µm × 12 µm area. Because our device is cheaper and more compact than a FPA-FT-IR, it will be easier to take out in the field or on a research vessel.

Sources and sinks of plastic debris in estuaries: A conceptual model integrating biological, physical and chemical distribution mechanisms.

Micro- and macroplastic accumulation threatens estuaries worldwide because of the often dense human populations, diverse plastic inputs and high potential for plastic degradation and storage in these ecosystems. Nonetheless, our understanding of plastic sources and sinks remains limited. We designed conceptual models of the local and estuary-wide transport of plastics. We identify processes affecting the position of plastics in the water column; processes related to the mixing of fresh and salt water; and processes resulting from the influences of wind, topography, and organism-plastic interactions. The models identify gaps in the spatial context of plastic-organisms interactions, the chemical behavior of plastics in estuaries, effects of wind on plastic suspension-deposition cycles, and the relative importance of processes affecting the position in the water column. When interpreted in the context of current understanding, sinks with high management potential can be identified. However, source-sink patterns vary among estuary types and with local scale processes.

LuxA gene of light organ symbionts of the bioluminescent fish Acropoma japonicum (Acropomatidae) and Siphamia versicolor (Apogonidae) forms a lineage closely related to that of Photobacterium leiognathi ssp. mandapamensis.

A molecular phylogenetic analysis of luxA gene sequences of light organ symbionts of the fish Acropoma japonicum (Acropomatidae) and Siphamia versicolor (Apogonidae) revealed that the sequences were related to those of Photobacterium leiognathi ssp. mandapamensis, which is not known to occur as a light organ symbiont among bioluminescent P. leiognathi clades. The presence of another lux gene element, luxF, coding for nonfluorescent protein, provided additional support for the identity of the light organ symbionts of the fish. Cladogenesis of the light organ symbiont P. leiognathi may be influenced by the radiation of host fishes.

Molecular phylogeny and possible scenario of ponyfish (Perciformes:Leiognathidae) evolution.

The family Leiognathidae, commonly known as ponyfish or slip mouth, comprises three genera, each being characterized mainly by mouth morphology. To date, however, neither the phylogenetic relationships within the family nor monophyly of the genera has been tested. The phylogenetic relationships among 14 species of Leiognathidae, inferred from two protein coding mitochondrial genes (ND4 and 5), indicated monophyly of the studied species form genera Gazza and Secutor, and paraphyly of the genus Leiognathus, with L. equulus occupying a basal branch of the family. The relationships allowed phylogenetic analyses of mouthpart structures and light organ systems. The results suggested that the morphology of the upwardly and forwardly protractile mouth types (latter with canine-like teeth) are phylogenetically informative, and the downwardly protractile mouth type being ancestral in the family. The results also suggested that internal sexual dimorphism of the light organ system was present in the common ancestor of a sister clade to L. equulus, whereas external sexual dimorphism seems to have evolved subsequently in two monophyletic subgroups.