A new visual index for assessing zooplankton biomass and its utility in assessing prey availability for megaplanktivores’

Zooplankton are vital links in marine food webs, yet their biomass remains challenging to quantify across broad spatial and temporal scales.
This study introduces the Zooplankton Visual Index–a simple, rapid and scalable semi-quantitative method for evaluating zooplankton biomass
through underwater observations. Following the establishment of a standardized protocol, validation against in situ net samples demonstrated
that indexlevels increased consistently with measured biomass and predictable shifts in community composition. We then applied the validated
indexto a 9-year dataset of reef manta ray (Mobula alfredi) sightings in the Maldives. Increased M. alfredi abundance significantly correlated with
higher index levels, confirming that the index effectively captures the food environment as an important predictor of behavior and habitat use.
Thus, the Zooplankton Visual Index provides an accessible and validated tool for assessing prey availability, enabling researchers, non-specialist
field staff and citizen science programs to contribute to broad-scale ecological research and conservation efforts for marine megaplanktivores.