Exploring seasonal dynamics in Palythoa caribaeorum-dominated habitats using photogrammetry

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Abstract Ocean warming in subtropical waters of the Canary Islands is promoting the proliferation of thermophilic organisms, including zoantharians, which now dominate some shallow rocky reefs and induce community-level changes through their mat-forming growth. Advanced methodologies, such as photogrammetry, enable precise monitoring of spatiotemporal changes and population dynamics in sessile benthic species. In this study, a Palythoa caribaeorum -dominated area in Tenerife Island was surveyed biannually over 2 yr using structure-from-motion photogrammetry. Seasonal variations in benthic community coverages, P. caribaeorum growth rates, and zoantharian-algae interactions were assessed. Colony growth exhibited a strong correlation with seawater temperature, showing a significant coverage expansion during warm seasons (0.43 ± 0.33 cm 2 /month) and contraction during colder periods (− 0.36 ± 0.29 to − 0.49 ± 0.44 cm 2 /month). The 2nd year, which was 1.03 °C warmer on average, exhibited enhanced colony growth during the warm season, resulting in a 15.14% increase in total colony area compared to the previous warm season. Macroalgal interactions affected growth rates of the zoantharian: Lobophora spp. and turf algae slowed colonies growth compared to crustose coralline and Dictyoteae algae. However, temperature remained as the primary driver of colony dynamics, suggesting that ocean warming may facilitate zoantharian population outbreaks. This study provides the first quantitative data on P. caribaeorum natural growth rates in a subtropical region and demonstrates the effectiveness of photogrammetry for monitoring zoantharian-dominated communities, offering the first 3D digital documentation to evaluate the expansion of P. caribaeorum -dominated areas under warming conditions.

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