Abstract
In this study, we identified bottom environments suitable for habitation by Vargula hilgendorfii, or the sea-firefly, whose habitat is the sea floor in shallow water, and environmental conditions which may affect habitation. The study areas included 70 points at 17 sandy areas off the eastern coast of Osaka Bay, where environmental degradation has been a concern. The quality of water and sediment on the sea floor was assessed, and the number of sea-fireflies inhabiting the locations was evaluated using bait-traps. The results showed that no or only a few sea-fireflies survive in the following places; places where salinity and dissolved oxygen were reduced due to nearby rivers, places where the bottom sediment was deoxidized due to artificial structures hindering tidal currents, and places where there was an accumulation of fine sand due to its drifting along rapid currents. The majority of the sea-fireflies live at limited locations in the center of Osaka Bay. Statistical analysis of a generalized linear model found the following conditions necessary for sea-firefly inhabitation; dissolved oxygen (explained deviance; 27.2%), oxidation-reduction potential (18.3%), salinity (12.8%), and mud content (7.3%).
