Recruitment ecology of pelagic-broadcast spawning minnows: paradigms from the ocean advance science and conservation of an imperilled freshwater fauna

Pelagic-broadcast spawning is a dominant mode of fish reproduction in the oceans and is associated with Fundamental Triad (i.e. nutrient enrichment, nutrient concentration, propagule retention) and Loophole (i.e. disruption of larval competition and predation) processes that are mediated by water currents. Pelagic-broadcast spawning is uncommon in freshwater, but is employed by an evolutionarily convergent spawning guild in rivers on the Great Plains, North America. We reviewed ecological studies of pelagic-broadcast spawning minnows to evaluate whether Fundamental Triad and Loophole concepts explain the adaptive significance of this behaviour. Pelagic-broadcast spawning minnows exhibit spawning periodicity dependent on floods. Nutrient enrichment, nutrient concentration and propagule retention are enhanced during flood recession. Retention is also enhanced by high fecundity and rapid development of pelagic-broadcast propagules. Predation and competition threats are relatively low in temporary, patchily distributed nurseries present during flood recession. Extended spawning periods and diffusive spread of juveniles and adults ensure annual recruitment despite the unpredictable and often harsh conditions in rivers on the plains. Over the last century, pelagic-broadcast spawners have suffered declines due to dewatering, flood control and sediment deprivation that disrupt natural Fundamental Triad and Loophole processes. We propose that restoration of conditions necessary for Fundamental Triad and Loophole processes to operate will be most successful at stopping decline and extinction of pelagic-broadcast spawning minnows of the Great Plains.