Spatial and tidal profiles of seawater properties, and their relation to coral cover of selected reefs in Iligan City, Lanao Del Norte, Philippines

A hydrographic investigation was conducted in coral reefs along the coast of Iligan bay to evaluate the influence of tides to the spatial distribution of water parameters and determine the relation of the water parameters to the coral cover in the area. Water samples were collected at 0m, 5m and 8m using 1.5L Niskin bottle and water parameters were immediately measured using calibrated handheld meters on board. Coral assessment was done using Photo-transect technique and estimation of hard coral cover was done using Coral Point Count with Excel Extensions (CPCe). Salinity increased with depth and values were higher at high tide. The observed suboptimal salinity may account for the poor cover of hard corals. Temperature was highest at the surface and decreases with depth in both tides. Reef1 had the coldest waters in both tides, warmest at the farthest reefs 3 and 4 from the estuary. Dissolved oxygen decreases with depth in both tides and higher during high tide. At low tide, pH was highest at surface; at high tide pH highest at 5m. At low tide pH was highest at reef1, and lowest at reef4. During high tide pH was uniform at 8.1 in all four reefs. Temperature, pH and dissolved oxygen were within the ideal range for optimum growth and coral reef development. Therefore, the observed poor coral cover was not associated with the status of these parameters.