Size-Dependent Effects of Micro Polystyrene Particles in the Marine Copepod <i>Tigriopus japonicus</i>

We investigated the effects of three sizes of polystyrene (PS) microbeads (0.05, 0.5, and 6-μm diameter) on the survival, development, and fecundity of the copepod <i>Tigriopus japonicus</i> using acute and chronic toxicity tests. <i>T. japonicus</i> ingested and egested all three sizes of PS beads used and exhibited no selective feeding when phytoplankton were added. The copepods (nauplius and adult females) survived all sizes of PS beads and the various concentrations tested in the acute toxicity test for 96 h. In the two-generation chronic toxicity test, 0.05-μm PS beads at a concentration greater than 12.5 μg/mL caused the mortality of nauplii and copepodites in the <i>F</i>₀ generation and even triggered mortality at a concentration of 1.25 μg/mL in the next generation. In the 0.5-μm PS bead treatment, despite there being no significant effect on the <i>F</i>₀ generation, the highest concentration (25 μg/mL) induced a significant decrease in survival compared with the control population in the <i>F</i>₁ generation. The 6-μm PS beads did not affect the survival of <i>T. japonicus</i> over two generations. The 0.5- and 6-μm PS beads caused a significant decrease in fecundity at all concentrations. These results suggest that microplastics such as micro- or nanosized PS beads may have negative impacts on marine copepods

External whole valve of <i>Thalassiosira proschkinae</i> SMDC305.

<p>(a–d) Heavily silicified valves. (e, f) Valve cleaned by acid treatment showing the external opening of rimoportula (rp, black arrow) and internal structure of strutted tube (st, white arrowheads) surrounded by satellite pores (slp, black arrowheads). Scale bars are 1 μm.</p

Literatures on <i>T</i>. <i>proschkinae/T</i>. <i>spinulata</i> and re-identification based on the morphological criteria and their distribution.

<p>Literatures on <i>T</i>. <i>proschkinae/T</i>. <i>spinulata</i> and re-identification based on the morphological criteria and their distribution.</p

Comparison of the morphological characters of two small <i>Thalassiosira</i> species and the thalassiosiroid taxa having the rimoportula on valve face (<i>Minidiscus</i>, <i>Livingstonia palatkaensis</i>, and <i>Shionodiscus</i>) and <i>Thalassiosira nordenskioeldii</i> as the representative of the genus <i>Thalassiosira</i>.

<p>Comparison of the morphological characters of two small <i>Thalassiosira</i> species and the thalassiosiroid taxa having the rimoportula on valve face (<i>Minidiscus</i>, <i>Livingstonia palatkaensis</i>, and <i>Shionodiscus</i>) and <i>Thalassiosira nordenskioeldii</i> as the representative of the genus <i>Thalassiosira</i>.</p

Light microscopy of <i>Thalassiosira proschkinae</i> SMDC305.

<p>(a, b) Aggregated cells. (c) Solitary cell. (d) Chain colony of two cells by mucilage thread (arrow) extruded from central fultoportula. Scale bars are 10 μm.</p

Light microscopy of <i>Thalassiosira spinulata</i> SMDC303.

<p>(a, b) Cells embedded by mucilage. Scale bars are 10 μm.</p

Diagram of two small <i>Thalassiosira</i> species.

<p>(a) <i>T</i>. <i>proschkinae</i>. (b) <i>T</i>. <i>spinulata</i>.</p

Intraspecific genetic distances between the two strains of <i>T</i>. <i>spinulata</i>, and interspecific genetic distances between <i>T</i>. <i>proschkinae</i> and <i>T</i>. <i>spinulata</i> for the two nuclear rRNA and two chloroplast genes.

<p>Intraspecific genetic distances between the two strains of <i>T</i>. <i>spinulata</i>, and interspecific genetic distances between <i>T</i>. <i>proschkinae</i> and <i>T</i>. <i>spinulata</i> for the two nuclear rRNA and two chloroplast genes.</p

A phylogenetic tree for Thalassiosirales inferred from the maximum likelihood (ML) by using RAxML.

<p>Bootstrap values of ≥50% are shown, and nodes supported by bootstrap values of ≥95% are marked with an asterisk (*).</p

External valve view of <i>Thalassiosira proschkinae</i> SMDC305.

<p>(a) External small tube of central fultoportula (cfp, white arrow) and elliptic opening of rimoportula (rp, black arrow). (b–d) Acid cleaned valves showing the elliptical opening of rimoportula (rp, black arrow) and the exposed internal structure of strutted tube (st, white arrowhead) surrounded by two to three satellite pores (slp, black arrowheads). (e, f) External small tube of marginal fultoportula (mfp, white arrows) at the junction of valve face and mantle. Scale bars are 1 μm.</p