A Study on the Relationship between Habitats of Vargula hilgendorfii and Construction and Maintenance of the Sandy Beach in Southern Osaka

Abstract

In this study, we identified bottom environments suitable for habitation by Vargula hilgendorfii, or the sea-firefly, and the relationship between their habitats and the construction and maintenance of the sandy beach. The study areas included 7 observation lines at 5 sandy beaches in southern Osaka. The construction was assessed by the origin of sands and construction of artificial structures, and maintenance was assessed by leveling of sands and replenishment of sand. Bottom environments and the number of V. hilgendorfii were assessed using a Smith-McIntyre grab sampler. Statistical analysis of a classification and regression trees found the following suitable conditions for V. hilgendorfii inhabitation; oxidation-reduction potential of more than-5.5mV and sorting coefficient of less than 0.646. In addition, statistical analysis of a generalized linear model found habitats of V. hilgendorfii were created in the following places; places where without an artificial structure, places where water depth was shallow due to replenishment of sand. On the other hand, places where the bottom sediment was deoxidized due to offshore breakwaters and jetties hindering tidal currents were unsuitable for V. hilgendorfii. These results suggested that the difference of the construction and maintenance of the sandy beach influenced on the habitats of V. hilgendorfii.