Abstract
Harmful algal blooms (HABs) constitute an emerging ecological and public health concern in tropical coastal ecosystems, particularly where high biodiversity intersects with increasing anthropogenic pressures. This study provides the first multi-habitat assessment of toxic and potentially harmful microalgae across contrasting Pacific and Caribbean waters of Panama. Phytoplankton communities were surveyed monthly from June to October 2024, complemented by exploratory HAB observations from 2023, integrating taxonomic profiling with in situ environmental characterization. A total of 234 taxa were identified across three representative coastal systems, including toxin-associated genera linked to diarrhetic shellfish poisoning (DSP), paralytic shellfish poisoning (PSP), ciguatera poisoning (CP), amnesic shellfish poisoning (ASP), and yessotoxin-related syndromes (YTX). Redundancy Analysis (RDA) revealed significant environmental structuring of assemblages, with DSP-associated genera (e.g., Prorocentrum , Dinophysis ) related to higher temperature and lower dissolved oxygen, whereas ASP-associated Pseudo-nitzschia aligned with higher salinity. The coexistence of multiple toxin syndromes, combined with recurrent bloom events of Noctiluca scintillans and Prorocentrum lima , underscores the need for site-specific early warning monitoring. These findings provide an ecological baseline for HAB risk mitigation and support the development of targeted monitoring strategies aligned with Sustainable Development Goal 14 (Life Below Water).