Per Meyer Jepsen

Microplastic potentiates triclosan toxicity to the marine copepod Acartia tonsa (Dana)

ABSTRACT Microplastics (MP) are contaminants of environmental concern partly due to plastics ability to sorb and transport hydrophobic organic contaminants (HOC). The importance of this “vector effect” is currently being debated in the scientific community. This debate largely ignores that the co-exposures of MP and HOC are mixtures of hazardous agents, which can be addressed from a mixture toxicity perspective. In this study, mixture effects of polyethylene microbeads (MP) and triclosan (TCS) (a commonly used antibacterial agent in cosmetics) were assessed on the marine copepod Acartia tonsa. Data indicated that MP potentiate the toxicity of TCS, illustrating the importance of understanding the mixture interaction between plastics and HOC when addressing the environmental importance of the vector effect.

Effects of elevated pH on marine copepods in mass cultivation systems: practical implications

Female tolerance to pH (8.0–9.5) by six marine copepods, Oithona similis, Temora longicornis, Acartia spp., Centropages typicus, Pseudocalanus elongatus and Eurytemora affinis was investigated to identify robust species for live feed production. The species with the most oceanic-neritic distribution, O. similis, exhibited 72 h LC50 at pH 8.39 ± 0.11 (±95% CL) whereas the most estuarine E. affinis had LC50 at pH 9.51 ± 0.04. The rest had LC50 at intermediary pH’s. Egg hatching by a selection of species, Acartia spp., C. typicus and E. affinis, was unaffected by pH up to 9.0–9.5. Nauplii from both Acartia spp. and C. typicus had higher mortality at pH 9.5 than at the other pH regimes while E. affinis nauplii were not affected by pH. Wild Acartia spp. and A. tonsa from a culture showed some differences in response although of minor practical importance for aquaculture; both produced no eggs at pH 9.5, A. tonsa exhibited significantly higher egg production at all other pH’s than 9.5, both showed egg hatching invariant of pH, but gradually increasing nauplii mortality with pH. We suggest active/passive selection to obtain the most pH robust species able to cope with accidently, but frequently, elevated pH in aquaculture systems.

Environmental stress responses and experimental handling artifacts of a model organism, the copepod Acartia tonsa (Dana)

Handling animals during experiments potentially affects the differential expression of genes chosen as biomarkers of sub-lethal stress. RNA sequencing was used to examine whole-transcriptome responses caused by laboratory handling of the calanoid copepod, Acartia tonsa. Salinity shock (S=35 to S=5) was used as positive stress control; individuals not exposed to handling or other stressors served as negative stress control. All copepods were grown from eggs to adults without being handled or exposed to any stressors prior the experiment. Survival of nauplii and adults was estimated for up to 10 min of exposure to handling stress and salinity shock. Only adults exhibited decreased survival (44±7% with 10 min of exposure) in response to handling stress and were selected for definitive experiments for RNA sequencing. After 10 min of experimental exposures to handling stress or salinity shock, adults were incubated for 15 min or 24 h at normal culture conditions. A small number of significantly differentially expressed genes (DEGs) were observed 15 min after exposure to handling stress (2 DEGs) or salinity shock (7 DEGs). However, 24 h after exposure, handling stress resulted in 276 DEGs and salinity shock resulted in 573 DEGs, of which 174 DEGs were overlapping between the treatments. Among the DEGs observed 24 h after exposure to handling stress or salinity shock, some commonly-used stress biomarkers appeared at low levels. This suggests that a stress-response was induced at the transcriptional level for these genes between 15 min and 24 h following exposure. Since handling stress clearly affects transcriptional patterns, it is important to consider handling when designing experiments, by either including additional controls or avoiding focus on impacted genes. Not considering handling in gene expression studies can lead to inaccurate conclusions. The present study provides a baseline for studying handling stress in future studies using this model organism and others.