Microplastic Consumption and Its Effect on Respiration Rate and Motility of Calanus helgolandicus From the Marmara Sea

Consumption rates of polystyrene microplastics (beads of 6, 12, and 26 μm diameter) and their effects on energy metabolism and motor activity of the copepod Calanus helgolandicus living in the Marmara Sea were investigated. All sizes of microplastic particles were actively consumed and excreted via fecal pellets, however, copepods displayed a significant preference for beads sized 6 μm. In a mixture of algae and microplastics beads of 6 μm, microplastics consumption rates linearly (r2 = 0.78, n = 154) increased 800 times from 50.8 ± 17.3 to 8,612 ± 5,972 beads ind–1 day–1 with an increase in bead concentration from 10 to 44,000 beads ml–1. The total and basal metabolic rates as well as time spent swimming for C. helgolandicus, decreased 1.7, 1.8 and about 3-fold, respectively after 7–8 days exposure to microplastic treatments, which was similar to the metabolism and activity of starving animals in filtered water. In copepods consuming microplastics, all vital parameters decreased on the first day of exposure, indicating either accelerated starvation, probably due to increased losses of energy and biological matter in the formation of fecal pellets and/or traumatic/toxic effects of the polystyrene beads on the copepods. Our data from laboratory experiments indicate that the presence of large concentrations of microplastics in water, even when mixed with algae, lowered energy metabolism levels of C. helgolandicus.

De Novo Transcriptome Assembly and Gene Expression Profiling of the Copepod Calanus helgolandicus Feeding on the PUA-Producing Diatom Skeletonema marinoi

Diatoms are the dominant component of the marine phytoplankton. Several diatoms produce secondary metabolites, namely oxylipins, with teratogenic effects on their main predators, crustacean copepods. Our study reports the de novo assembled transcriptome of the calanoid copepod Calanus helgolandicus feeding on the oxylipin-producing diatom Skeletonema marinoi. Differential expression analysis was also performed between copepod females exposed to the diatom and the control flagellate Prorocentrum minimum, which does not produce oxylipins. Our results showed that transcripts involved in carbohydrate, amino acid, folate and methionine metabolism, embryogenesis, and response to stimulus were differentially expressed in the two conditions. Expression of 27 selected genes belonging to these functional categories was also analyzed by RT-qPCR in C. helgolandicus females exposed to a mixed solution of the oxylipins heptadienal and octadienal at the concentration of 10 µM, 15 µM, and 20 µM. The results confirmed differential expression analysis, with up-regulation of genes involved in stress response and down-regulation of genes associated with folate and methionine metabolism, embryogenesis, and signaling. Overall, we offer new insights on the mechanism of action of oxylipins on maternally-induced embryo abnormality. Our results may also help identify biomarker genes associated with diatom-related reproductive failure in the natural copepod population at sea.