Marine macrophyte composition during summer, southwest and northeast monsoons in Verde Island, Batangas City, Batangas, Philippines

Verde Island Passage is the world’s center of the center of marine shore fish biodiversity, located in southwestern Luzon Island in the Philippines. The passage is named after Verde Island, which is located at its middle. Although the island is located within a key biodiversity area, studies on its marine macrophyte biodiversity are scant. The present study was conducted to determine the composition, distribution, and dominance of marine macrophytes, specifically seaweeds and seagrass, during the northeast monsoon, summer, and southwest monsoon in four coastal areas in Verde Island using the line transect-quadrat method. Results revealed 63 macrophyte species, of which 92% were seaweeds and 8% were seagrass. The majority of the seaweeds were green (41%), followed by red (35%) and brown (16%) seaweeds. In most sites, the brown seaweed Padina sp. was dominant during summer and cover decreased during both monsoons. The green seaweed Neomeris annulata was present in all sites and seasons. The differences in cover across sites may be due to substratum type and topography where a relatively wider intertidal zone with different substratum such as rocky and sandy to muddy provides complex habitat promoting higher macrophyte cover. Temporal differences in marine macrophyte composition were more pronounced in macroalgae-dominated sites than in the seagrass-dominated site. Several important seaweeds that could be studied as bioindicators were recorded, such as Padina sp., which registered high cover especially in sites near populated areas and backyard pig pens. Ulva spp., which are known to form green tide blooms, and Caulerpa verticillata were also noted and should be monitored. Some red seaweeds with potential for cultivation were observed (i.e., Halymenia durvillei and Portieria hornemannii). Claudea sp., an uncommon red seaweed with limited distribution in the Philippines, was recorded and needs verification. This study is the first extensive marine macrophyte assessment at the heart of the Verde Island Passage. KEYWORDS: biodiversity, bioindicator, eutrophication, microbenthic algae, seagrass, Verde Island Passage