Roldan T. Echem1 and Ephrime B. Metillo2
1Department of Biological Sciences, Mindanao State University-Iligan Institute of Technology, A. Bonifacio Ave., Iligan City 9200
2Department of Biology, Western Mindanao State University, Zamboanga City 7000
Three green (Chlorophyta) macroalgal species (Ulva reticulata, U. intestinalis, Chaetomorpha crassa) have become a nuisance in many coastal zones and beaches in the Philippines. We studied the temporal variation in dry weight biomass of these three species on November, February, May, and August in three intertidal sites representing a highly urbanized and industrialized area, a densely populated suburban area, and a highly agriculturised area. We also sampled select physico-chemical conditions (water temperature, dissolved oxygen, water motion, insolation, pH, dissolved NO3-N and PO4-P, salinity, rainfall and total suspended solids) that were regressed with variations in biomass of the three species. Except U. intestinalis which was seen only in May and August in all sites, the other two species were observed throughout the sampling period and peaked in February. Ulva reticulata was consistently in the top 8 most abundant species in the Dalipuga site. It occupied top 13-18 in other sites, except during the rainy month of August when it became top 2 in the Northwestern Bay and top 9 in the Southern Bay coinciding with decreased species richness at these two sites. Constrained multivariate redundancy analysis revealed significant relationship between biomass peaks and high levels of PO4-P and water motion, and moderate light intensity. In conclusion, U. reticulata and C. crassa are opportunistic species in that they bloom under ideal conditions of nutrient (PO4-P), water motion and insolation, and may dominate the macroalgal community under stressed conditions (reduced salinity and high turbidity).
Keywords: Chlorophyta, Ulva, Chaeotomorpha, green tide, nutrient, tropical