In marine environments, exposure to microplastics threaten various organisms. A large portion of MPs may be bioavailable to copepods, and ingesting MPs has been reported to induce various adverse effects, including increased mortality, developmental retardation, and decreased reproduction. Adverse effects of MPs on these important processes of copepods may be induced by the obstructive effects of the ingested MPs on energy acquisition. However, few studies have explored the biological effects of MPs on copepods in terms of energy budgets. Therefore, we analyzed ATP (adenosine triphosphate) levels, enzyme activities, swimming distances, and excretion rates in marine copepods (Tigriopus koreanus) that have ingested polystyrene microplastics. Our results indicate that the ingestion of MPs may prevent adequate acquisition of nourishment and lead the copepods into a vicious circle in the respect to energetic burden. Our study provides biochemical evidence for a reduction in the energy budget of copepods due to MPs ingestion. Further, this study increases our understanding of the risks of microplastics, by providing advanced evidences of their effects on marine primary consumer.

The marine diatoms Thalassiosira proschkinae and T. spinulata are relatively small in size; their taxonomic identities have been debated owing to the diverse morphological variations. In the present study, we isolated both morphotypes from Korean coastal waters and examined their fine structures and conducted molecular sequence comparisons. The morphological and molecular analyses showed that T. proschkinae and T. spinulata were certainly distinct, and phenotypic plasticity of valve structure was not noted. Based on the morphological similarity and phylogenetic relationship, we transferred T. proschkinae and T. spinulata to another genus Minidiscus within Thalassiosirales that includes small-sized species and proposed new combination names, Minidiscus proschkinae (Makarova) Park & Lee comb. nov. and Minidiscus spinulatus (Takano) Park & Lee comb. nov., respectively. The genus description of Minidiscus was emended.