Temperature and salinity variation in oscular tubes of the branching sponge Haliclona sp. inhabiting a tidal pool influenced by fresh groundwater discharge in Taiwan

This study recorded temperature and salinity in oscular tubes of the branching sponge (Haliclona sp.) living in an intertidal coral reef with fresh groundwater inflow on Green Island, Taiwan. During the ebb tide period, seawater temperature and salinity around the sponges ranged from 30.6 to 34.1°C and 17 to 27‰, respectively. The temperature and salinity within sponge oscular tubes were 30.8 - 34.5°C and 23 - 27‰, respectively. The oscular openings usually had higher salinity than ambient waters near the fresh groundwater inflow. Some of the largest differences in salinity between the sponge oscular tube and ambient seawater were in the range of 6 - 8‰. The sponges regularly experienced wide fluctuations in salinity (4 - 28‰) and temperature (23.2 - 34.8°C) for at least 3 hours during ebb tide periods. Whether the ostia play a role in actively maintaining the internal salinity of the branching Haliclona sponges needs further investigation.