Diel patterns of epifaunal macroinvertebrates associated with sea-grass beds are poorly investigated. This pattern indicated misconception in population and community dynamics, diel cycle, and overall functional activities in an ecosystem. A three-day diel sampling period was permanently established in four stations in Eastern Samar, Philippines, patterned of the same sites in an unpublished study by Pacoma, 2016. Collecting samples was done at 7:00-9:00 am and 7:00-9:00 pm, using a transect-quadrat method laid on seagrass beds perpendicular to the coastlines. Results show that there are 60 species identified throughout the collection period, composed of 9 species of echinoderms, 32 species molluscs, 5 species poriferans, 10 species arthropods, 3 species annelids, and; 1 species reptile. Dominated by mollusks Canarium sp., Pinna muricata, Nassarius margaritifer and Trochus sp. in all the sampling sites, some commercially important mollusks were also sampled, such as Gafrarium aequivocum, Callista erycina, and Fragum sp. Other notable species such as Clypeaster sp., Holothuria sp. and Euapta sp. were present in both nocturnal and diurnal sampling. Species richness compared to daytime collection of Pacoma, 2016 showed higher richness in the diel sampling. This shows that seagrass-associated epifaunal macroinvertebrate communities are more diverse at nocturnal than diurnal times. Diel diversity demonstrated a distinct community structure which indicates higher richness and abundance. Seagrass beds dispense several ecosystem functions, which makes them a preferred habitat in shallow waters. This suggests that patterns of the dynamics in seagrass beds, diurnal-diel cycle community structures shifts, and activities within this ecosystem are complex; thus, conservation mechanisms should be accorded within this pattern.
