Environmental variables structuring the stream gobioid assemblages in the three protected areas in Southern Luzon, Philippines

Three estuarine-linked streams (Bulusan, Iyam, and Pansipit rivers) in different protected areas were investigated to evaluate the influence of environmental and habitat variables on gobioid assemblages (Gobiidae and Eleotridae). The study collected a total of 1,071 specimens belonging to 19 species, and 17 genera. Twelve gobiids and seven eleotrids were recorded from the three rivers. Four gobioid species comprised 57.17% of the total abundance. These were Giuris margaritacea (Eleotridae), Glossogobius celebius (Gobiidae) Bostrychus sinensis (Eleotridae) and G. giuris (Gobiidae) (in order of importance). Log(10)-transformed abundance data were used in indirect (detrended correspondence analysis, DCA), and direct (canonical correspondence analysis, CCA) gradient ordination analysis. DCA (50.76% variability on the first and second ordination axes) revealed the gobioid assemblage variability as a response of species abundance to stream gradients. Species variation along the longitudinal stream gradient profile (upstream and downstream dwellers) was also emphasised. From the 19 environmental variables, CCA (71.49% variability on the first and second ordination axes) recognised substratum types, distance to sea, and land use pattern as the most weighted causative environmental parameters influencing the gobioid assemblages (within and between stream variations). Bray-Curtis similarity analysis using species and abundance data registered low similarity percentages (18-40%) between the three rivers, validating the high beta diversity estimated in DCA1 axis.