Environmental DNA (eDNA) metabarcoding can greatly enhance our understanding of global biodiversity and our ability to detect rare or cryptic species. However, sampling effort must be considered when interpreting results from these surveys. We explored how sampling effort influenced biodiversity patterns and nonindigenous species (NIS) detection in an eDNA metabarcoding survey of four commercial ports. Overall, we captured sequences from 18 metazoan phyla with minimal differences in taxonomic coverage between 18 S and COI primer sets. While community dissimilarity patterns were consistent across primers and sampling effort, richness patterns were not, suggesting that richness estimates are extremely sensitive to primer choice and sampling effort. The survey detected 64 potential NIS, with COI identifying more known NIS from port checklists but 18 S identifying more operational taxonomic units shared between three or more ports that represent un-recorded potential NIS. Overall, we conclude that eDNA metabarcoding surveys can reveal global similarity patterns among ports across a broad array of taxa and can also detect potential NIS in these key habitats. However, richness estimates and species assignments require caution. Based on results of this study, we make several recommendations for port eDNA sampling design and suggest several areas for future research.

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Analyses of the mitochondrial cox1, the nuclear-encoded large subunit (LSU), and the internal transcribed spacer 2 (ITS2) RNA coding region of Pseudo-nitzschia revealed that the P. pseudodelicatissima complex can be phylogenetically grouped into three distinct clades (Groups I-III), while the P. delicatissima complex forms another distinct clade (Group IV) in both the LSU and ITS2 phylogenetic trees. It was elucidated that comprehensive taxon sampling (sampling of sequences), selection of appropriate target genes and outgroup, and alignment strategies influenced the phylogenetic accuracy. Based on the genetic divergence, ITS2 resulted in the most resolved trees, followed by cox1 and LSU. The morphological characters available for Pseudo-nitzschia, although limited in number, were overall in agreement with the phylogenies when mapped onto the ITS2 tree. Information on the presence/absence of a central nodule, number of rows of poroids in each stria, and of sectors dividing the poroids mapped onto the ITS2 tree revealed the evolution of the recently diverged species. The morphologically based species complexes showed evolutionary relevance in agreement with molecular phylogeny inferred from ITS2 sequence-structure data. The data set of the hypervariable region of ITS2 improved the phylogenetic inference compared to the cox1 and LSU data sets. The taxonomic status of P. cuspidata and P. pseudodelicatissima requires further elucidation.

Microplastic pollution is a global issue that has a detrimental impact on food safety. In marine environments, microplastics are a threat to marine organisms, as they are often the same size range as prey and are mistaken as food. Consumption of microplastics has led to the damage of digestive organs and a reduction in growth and reproductive output. In this study, microplastic pollution was assessed across three commercially available shrimp species that were obtained from the supermarkets of Singapore. A total of 93 individuals were studied from the Pacific white leg shrimp, Litopenaeus vannamei, the Argentine red shrimp Pleoticus muelleri and the Indian white shrimp Fenneropenaeus indicus. Microplastic fibers, fragments, film and spheres were identified from the digestive tract of these organisms. Microplastic abundance ranged from 13.4 to 7050 items. F. indicus exhibited the highest number of microplastics. Microplastic film was the most abundant in L. vannamei individuals (93–97%) and spheres were the most abundant in P. muelleri (70%) and F. indicus (61%) individuals. This study demonstrates that microplastic contamination is evident in commonly consumed shrimp and highlights the role of shrimp in the trophic transfer and accumulation of microplastics in seafood. The consumption of microplastic-containing seafood is a route of exposure to humans and has implications on human health and food security. Capsule: Microplastics were examined in three shrimp species from the supermarkets of Singapore. Microplastics ranged from 13.4 to 7050 items of shrimp.