Using light traps to assess larval fish and octopus paralarvae diversity and ontogenetic structure around Santa Catalina Island, California

Monitoring planktonic larvae is important for understanding changes in recruitment, range shifts, and reproductive behavior. Here, we used light traps to examine the abundance, community diversity, and ontogenetic structure of ichthyoplankton and octopus paralarvae at three sites around Santa Catalina Island, California, USA across two seasons between 2018 and 2019. We identified 15,919 fish larvae and 205 octopus paralarvae using morphology supplemented by DNA barcoding. We found no differences in larval fish diversity or abundance between years or seasons. All octopus paralarvae were captured in the summer and were identified as Octopus bimaculatus . Cryptic substrate-associated fishes dominated samples, especially those from suborder Blennioidei and family Gobiidae. We conclude that light traps can be a valuable tool and useful supplement to other zooplankton sampling methods, especially in providing a more complete assessment of nearshore plankton communities and taxa that have been poorly represented in traditional, offshore monitoring programs. They may be particularly useful for studying cryptic and substrate-associated species whose larvae are often poorly described in the existing identification literature.