Plastic fragments < 5 mm, known as microplastics (MPs), are ubiquitously present in the marine environment. Research on MPs pollution has gradually shifted from field investigations to laboratory studies. With the rapid growth of plastic consumption and the prevalence of aquaculture products, studies on marine MPs have focused on key marine species, such as mollusks. This review summarizes the recent knowledge including 77 important relevant literatures (from 2010 to 2021) on MPs contamination in mollusks with the objectives of (1) elucidating the current status of MPs pollution levels in mollusks, (2) highlighting the main methods and techniques for separation, extraction, and identification of MPs in soft tissues of bivalves and (3) presenting the current research progress and future directions. The review visually presents some of the important results in graphic form, which shows that the most common polymer plastics in bivalves are polypropylene, polystyrene, and polyethylene, and the shapes were mainly fiber and threadiness, mollusks are more likely to feed smaller MPs, most of the MPs in bivalves are less than 500 μm, and the abundance of MPs in seawater and the abundance of MPs in mollusks have a positive relationship, etc. This review will provide a comprehensive reference for studies of microplastics in marine organisms and the ecological pollution, and also has scientific guiding significance in the research method.
Bacteria are an integral component of their host. However, information about the microbiota living in and around many aquatic animals is lacking. In this study, multiplex bar-coded pyrosequencing of the 16S ribosomal RNA gene was used to monitor the dynamics of abalone, Haliotis discus hannai, bacterial communities in the intestine, water from cement culture ponds, and surrounding sea areas. Correlations between the bacterial communities and common aquaculture diseases were also evaluated. A total of 329,798 valid sequences and 15,277 operational taxonomic units (OTUs) from 32 samples were obtained by 454 tag amplicon pyrosequencing. The Shannon indices of the seawater samples ranged from 2.84 to 5.6 and the Shannon indices of the abalone intestine samples ranged from 1.2 to 5.12, which were much lower than those of seawater. The dominant phyla in seawater samples were Proteobacteria, Bacteroidetes, Fusobacteria, Cyanobacteria, etc. The dominant phyla in the abalone intestine varied greatly in different months. The dominant genera in the seawater of the cement culture ponds changed in different months, mainly Psychrilyobacter and Pseudoalteromonas. The dominant genera in seawater from the open sea vary considerably between months. The dominant genus of bacteria in the abalone intestine during the months when abalones are susceptible to disease is mainly Mycoplasma spp. Canonical correspondence analysis revealed that bacterial communities in seawater and the intestine responded differently to environmental variables, with similar microbiota in the same area. pH, dissolved oxygen concentration, and temperature were closely related to the samples from the sea area. Oxidation-reduction potential, salinity, phosphate, nitrate, and ammonia nitrogen concentrations were closely related to the water samples from the artificial pools. These findings may add significantly to our understanding of the complex interactions between microbiota and environmental variables in the abalone intestine as well as in the surrounding seawater.
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