Effects of microplastics and attached heavy metals on growth, immunity, and heavy metal accumulation in the yellow seahorse, Hippocampus kuda Bleeker

Microplastics represent a new kind of environmental pollutant that has recently attracted extensive attention and become a research hotspot. Microplastics are similar in size to the food items of many marine organisms and are thus, often consumed by them, with potentially harmful and toxic effects. We examined the effects of microplastics on the growth of the yellow seahorse Hippocampus kuda. Seahorses were split into three groups fed Mysis + microplastics + heavy metals (group A), Mysis + microplastics (group B), and Mysis alone (group C). We analyzed and compared the accumulations of microplastics and heavy metals among the groups and monitored seahorse growth following the different treatments. Body length, body weight, condition factor, specific growth rate, and survival rate were all lower in group A compared with the other groups, but there was no significant difference in any of the parameters between groups B and C. The accumulation of microplastics was similar in groups A and B, and the accumulation of heavy metals was similar in groups B and C. These results suggest that the effect of microplastics on seahorse growth is caused by the accumulation of heavy metals, rather than by the microplastics themselves.