Oxygen conditions affect the swimming behavior of sand dollar larvae

Abstract

Larval swimming behavior is not only critical to the survival and dispersal of marine invertebrates, but also has larger implications for population dynamics in species with planktonic larvae. However, little is known about these behaviors under variable oxygen conditions. Prior works present conflicting results, with marine invertebrate larvae demonstrating either increased or decreased swimming speeds under low-oxygen conditions when compared to normoxic conditions. Low-oxygen conditions, or hypoxia, can range from 2-5 mg of oxygen per liter of water depending on the group defining the standard (Gobler & Baumann, 2016). Normoxic conditions are anything over 7-8 mg of oxygen per liter of water. Hypoxic conditions are common among coastal zones and will expand with climate change (Gobler & Baumann, 2016). We used video techniques to track the vertical swimming speed of sand dollar Dendraster excentricus larvae in hypoxic, normoxic, and stratified conditions. Results demonstrated an increase in vertical swimming speed in hypoxic conditions, while swimming in stratified conditions showed no effect. This implies that larvae are capable of responding to hypoxic conditions by way of escaping lowoxygen environments. These results demonstrate that low-oxygen conditions could cause an escape behavior response and therefore should be considered when modeling larval survival and dispersal.