Status of seaweeds in San Miguel Island, Lagonoy Gulf, Philippines: a review related to the effects of changing environment and local issues

This contribution is a review on the results of three comprehensive studies previously done in 1994, 2004 and 2010 on the seaweed community in San Miguel Island, Lagonoy Gulf, Philippines. The status was evaluated with the aim of providing basis to sustain the resource along with local issues and the changing environmental factors. In 1994, twenty three (23) species were found and recorded mean biomass (B) of 112.72 g/m2. Only five (5) species had been found in 2004 with 35.22 g/m2 while eleven (11) species were determined in 2010 that registered to 159.45 g/m2. As depicted in the relative frequency (F) and cover (C) values, seaweeds in 1994 were diverse but have limited density compared in 2010 where most species have significant abundance rate. An implication of the decline in species composition was in fact altered by the individual productivity in the past 16 year. The predominant algae such as Sargassum spp. and Halimeda spp. have shared substantially to the standing crop. From the revealing status, several attributions were determined. The varying seaweed community structure has significant response with the seasonal variations in the environmental factors. The correlation indicator showed that the seaweed abundance was due to the gradual increase in sea surface temperature (SST) and the intensifying conditions of precipitation, wind speed and alternating wind direction. The effect of phenology was evident as the NE monsoon was pronounced more influential than SW monsoon. In the event of tremendous loss of seaweeds in 2004, severe climatic disturbances were depicted. The seaweed resource was indeed important to ecosystem and socio-economic aspect. The deposition of the calcareous Halimeda spp. to coral reef formation was reported in 1994. The seaweed involvement to fish and invertebrate aggregation influence local fisheries production. Assessment in 1994 has revealed 76 mollusk species, 30 echinoderms and 7 crustaceans associated with algal beds. Test fishing in 2004 recorded 54 finfishes and some invertebrates from various fishing gears used. The local Caulerpa sp. was highly utilized as food source, although species loss was noted in the recent survey. In the past studies cited herein mentioned that the production of siganids and commercially-important macro invertebrates were attributed to benefits from seaweeds association. The issues and problems in the resource involved anthropogenic and natural stressors. Human interventions i.e. through fishing and transportation apparently contributed to resource depletion. Whereas seaweeds pose a critical role to local economy and ecosystem though subjected to adverse natural and anthropogenic impacts, resilient conservation effort should be made. Management perspective must consider dual-pronged approaches, vis-à-vis seaweed stock protection and habitat interventions reduction.