Vertical distribution of epiplanktonic Chaetognaths in the upper 100 m of the Hilutangan Channel, Cebu, The Philippines

A study was made on the vertical distribution of Chaetognatha in the Hilutangan Channel, based on analyses of 48 plankton samples. Thirty-min horizontal plankton tows were performed at depths of 1, 20, 50, 70 and 100 m in January 1972. Thirteen species of 3 genera of maturing and mature chaetognaths were identified and counted. Sagitta inflata was the most common and abundant species (63.0%), folloed by S. neglecta (9.7%), S. robusta (8.6%), S. regularis (5.4%), S. serratodentata (4.2%), Krohnitta pacifica (2.9%), S. bedoti (2.3%) and S. decipiens (2.0%). S. pulchra (0.7%), S. ferox (0.5%), K. subtilis (0.3%), Pterosagitta draco (0.2%) and S. hexaptera (0.2%) were represented by less than 1% each. Of these 13 species in the upper 100 m, 12 were epiplanktonic while one species, S. decipiens, is generally considered to be mesoplanktonic. Three species were classified as neritic, 3 as neritic-oceanic, and 6 as oceanic, indicating the dominant influence and strong influx of oceanic water into the Hilutangan Channel. Temperature, salinity and dissolved oxygen content did not seem to influence the vertical distribution. Examination of gut contents showed that copepods, followed by arrow worms, were most common in the guts of the chaetognaths studied.