Selection of vertical zones in low oxygen water columns by larval Dendraster excentricus

Abstract

Decrease in dissolved oxygen levels is becoming more frequent in coastal marine environments. Causes may be of natural or anthropogenic origin, but human activities are having an impact on natural drivers. As organisms face many stressors in their environment, the need to understand how they respond to these increases. Most organisms have been studied at their adult life stage, while the embryo and larval stages are not considered. This study investigates the effect on marine invertebrate larvae of short-term exposure to hypoxia on selection of position in water column. It tests the hypothesis that larvae under oxygen-stress conditions will stay at the upper surfaces, where hypoxia is less likely to occur. An experimental setup was designed in which larvae could be placed in three columns, each filled with water a containing a different level of dissolved oxygen (DO) (three levels: 15 ± 1.71%, 36.7 ± 2.2% and 93.6 ± 0.97% DO). Larvae were then allowed to swim for 10 minutes, and their vertical positions in the experimental water columns were quantified. Three replicate swimming trials were conductued. . Larvae responded by choosing more the lower zones in hypoxic columns, while selection of upper zones was the most common in all treatments.