Variation in the abundance of periphytic algae in marine biofilms on glass surfaces submerged in the sea off Shin-Nagasaki Port, Nagasaki, Japan

Abstract

Glass slips were submerged in the sea (1 m depth) off Taira-cho, Nagasaki, Japan for 1, 2, 3 and 4 weeks every month from Jul 2010 to Oct 2012, and the dry weights, chlorophyll contents and diatom community structures of the marine bio- films were investigated. Glass slips immersed in the sea acquired biofilms that consisted mainly of diatoms. Young thalli of Ulva compressa also occurred in the biofilms from Apr to Dec. Marine biofilms increased in mass with longer immersion periods, indicating that growth of marine biofilms should be looked into for up to a month. Colonization on glass slips by invertebrate macroorganisms occurred from Jul to Sep, consequently making the estimation of biofilm biomass inaccurate during this period. Dry weights of biofilms were linearly correlated with the amounts of chlorophylls-a and -c, indicating that these pigments can be used as indices to estimate biomass growth of marine biofilms, which primarily consist of peri- phytic microalgae. Chlorophyll-a contents and diatom densities of biofilms both showed temporal and seasonal variations, whereas chlorophyll-c contents of biofilms showed seasonal variation. Decrease in the chlorophyll (-a and -c) contents and diatom densities of biofilms in Jul to Sep may probably be due to the disturbance of biofilms caused by the attachment of invertebrate macroorganisms. Navicula almost always was the dominant diatom in established marine biofilms