Marine top secrets: Ichthyoplankton in surface water uncover hidden knowledge on fish diversity and distribution

Most marine fish species exploit the upper water layers during their early life stages, thus accounting for a considerable component of neuston communities. During this period, the early life stages of fish are subjected to coastal or oceanic currents, and developed and dispersed to ultimate adult habitats according to their specific ecological requirements. Despite the ecological importance of these pelagic communities, knowledge about species assemblages of fish eggs and larvae, particularly in an oligotrophic sea is scarce. To overcome this knowledge gap and to evaluate the contribution of such communities to invasive biology, we collected neuston ichthyoplankton above the coastal, shelf and bathyal waters of the Eastern Mediterranean Sea (Israeli coast), an oligotrophic basin prone to a dynamic invasion of tropical biota. To obtain species-level knowledge of fish diversity, we used DNA-based methods that uncovered the presence of 137 species which is one third of the total local Osteichthyes fauna, evidencing that neuston ichthyoplankton can be significantly diverse. In addition, we showed that neuston communities can provide new knowledge regarding cryptic or rare species, and have a potential to contain new non-indigenous species, by documenting fish larvae of three unreported species for the Mediterranean Sea. Last, we posit that ichthyoplankton biomonitoring in surface water layer can provide a holistic perspective regarding fish biodiversity throughout the marine environment.

Automated summary

Most marine fish species, especially during their early life stages, inhabit the upper water layers and have a significant impact on neuston communities. However, knowledge about the composition of fish eggs and larvae, particularly in oligotrophic seas, is limited. Through DNA-based methods, we discovered the presence of 137 fish species in neuston communities, providing a more diverse understanding of fish diversity in the marine environment.