Ontogenetic social behavior and seasonal abundance of the subtropical krill Nyctiphanes simplex in northwestern Mexican waters

Nyctiphanes simplex (Euphausiidae) is the key prey for numerous pelagic predators because it is the most abundant of the 12 krill species present in the Gulf of California, forming dense and complex ontogenetic social interactions throughout its life cycle. We describe the diverse social behaviors of N. simplex and estimate its seasonal abundance in the Gulf of California accounting on average 74% of the krill assemblage. N. simplex exhibited complex and dynamic social repertoires of intraspecific behavioral interactions as early as Calyptopis 1 to adult phase, showing all possible ranges of social behavior known for pelagic invertebrates (aggregations, swarms, schools, shoals). We conclude that N. simplex displays different degrees of social behavior that concentrate abundance throughout their life cycle in epibenthic, pelagic and near surface habitats being highly adaptive behavior for feeding and reproduction. However, social interactions also pose a negative effect, facilitating parasite and disease transmission among conspecifics and facilitate predation for diverse visual predators adapted to find and prey on N. simplex aggregations and swarms. We report the most complete integrated evidence of social behavior and dataset of abundance data of any krill species in tropical and subtropical regions that have remained overlooked using traditional zooplankton net sampling methods.