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Abstract

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 biomassthrough underwater observations. Following the establishment of a standardized protocol, validation against in situ net samples demonstratedthat indexlevels increased consistently with measured biomass and predictable shifts in community composition. We then applied the validatedindexto a 9-year dataset of reef manta ray (Mobula alfredi) sightings in the Maldives. Increased M. alfredi abundance significantly correlated withhigher 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-specialistfield staff and citizen science programs to contribute to broad-scale ecological research and conservation efforts for marine megaplanktivores.

Publication Date

2026-05-27

Publication Title

Journal of Plankton Research

Volume

48

Issue

3

ISSN

0142-7873

Acceptance Date

2026-04-07

Deposit Date

2026-05-29

Funding

Hannah M. Moloney was funded by the University of the Sunshine Coast Research Training Program scholarship. This study was made possible due to funding from the Save Our Seas Foundation, Carl F. Bucherer and the logistical support and funding from the Four Seasons Resort at Landaa Giraavaru, Maldives. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors acknowledge the logistical, field and laboratory assistance from the team at theMaldives Manta Conservation ProgramandThe Manta Trust, with specific thanks to Tam Sawers, Beth Falkner, Elspeth Strike, Yaniu Rauf Mohamed, Catherine Cushenon, Henry Gould, Katie Sweeney, Dua Abdulla, Tiff Bond, Hussain Rasheed and Yoosuf Abdul Haadhee. Thanks to the team at Reefscapers Maldives, especially Simon Dixon, Akbar Ahmed and Koan Hughes, for the use of their laboratory facilities and assistance. We thank Enas Mohamed Riyaz from the Environmental Regulatory Authority for their continued support of this zooplankton work. We thank the Four Seasons Resort team based at Landaa Giravaru for providing ongoing support to this research project, particularly the General Manager, Armando Kraenzlin. We extend our gratitude to the Plankton Ecology Lab in Brisbane at CSIRO for their expert assistance, namely Frank Coman, Anita Slotwinski, Julian Uribe Palomino and Sarah Pausina. Approval for the research was received from the Maldives Ministry of Fisheries [Permit No. (OTHR)30-D/PRIV/2017/280, 30-D/PRIV/2023/263] and the Maldives Environmental Protection Agency [Permit Nos.EPA/2016/PSR-M02, EPA/2017/RP-01, EPA/2021/PSR-M06, EPA/2022/PSR-M04, EPA/2023/PSR-M08], and in accordance with the University of the Sunshine Coast Animal Ethics [ANS23101].Thank you to the editors and reviewers for their constructive comments and very helpful revisions, which significantly improved the quality of this manuscript. Hannah M. Moloney was funded by the University of the Sunshine Coast Research Training Program scholarship. This study was made possible due to funding from the Save Our Seas Foundation, Carl F. Bucherer and the logistical support and funding from the Four Seasons Resort at Landaa Giraavaru, Maldives. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Keywords

blooms, marine, planktivores, plankton, prey abundance

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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