Hypoxia delays mating in the broad-nosed pipefish

Courtship is an important part of the reproductive process, ensuring reproductive compatibility and conveying individual quality. One factor in aquatic environments that has the potential to influence courtship behaviours and mating propensity is the level of dissolved oxygen. Furthermore, hypoxic areas are currently spreading due to anthropogenic disturbance, such as eutrophication. In marine environments, hypoxia often occurs in shallow coastal regions that are particularly important areas for reproduction. Here, we investigated how types of reproductive behaviour were affected by mild hypoxia using the well-studied broad-nosed pipefish, Syngnathus typhle. More precisely, we investigated the impact of acute hypoxia on the reproductive behaviour preceding mating, and on the probability of mating, as well as on the latency until these occurred. We found that the latency period to courting and copulation occurring was prolonged in the low-oxygen environment. However, the total time spent courting as well as the probability of mating was unaffected by hypoxia. Other types of reproductive behaviour found in this species, such as dancing, and the unique male pouch-flap behaviour, were also unaffected by the low-oxygen treatment. We conclude that although latency to courting and copulating was prolonged in the hypoxic environment, most reproductive behaviour investigated was unaffected by hypoxia. Thus, hypoxia commonly occurring in shallow coastal regions has the potential to delay certain components of reproduction, but overall the broad-nosed pipefish shows robustness to hypoxic conditions.