Recovery of the neptune whelk, Neptunea arthritica, from imposex in Saroma Lagoon [Japan]
2002
Fujinaga, K. (Dohto Univ., Monbetsu, Hokkaido (Japan). Faculty of Social Welfare) | Ilano, A.S. | Nakao, S.
The extent and influence of imposex in the Neptune whelk, Neptunea arthritica, in Saroma Lagoon, northeastern Hokkaido, were investigated from 1997 until 2001 (excluding 2000), based on three criteria: relative penis size index (RPSI(, frequency of imposex, and sex ratio (mal/female). The condition of imposexi n female whelks in the lagoon turned into better year by year. The RPSI value of 13.7 in 1997, declined every year, and dropped very low to 0.1 in 2001. The frequency of imposex in adult whelks was 100% in both 1997 and 1998, but lowered to 76.9% in 1999 and 50.0% in 2001. The sex ratio in the adults was very high with values of more than 2.0 in 1997 and 1998. However, subsequently it sharply decreased to 1.62 in 1999, and furthermore to 0.81 in 2001. From these results, it was considered that the Neptune whelks in Saroma Lagoon have recovered from imposex. In addition, based on the yearly change in penis index (PI) distribution, the relation between shell height and penis weight, and simple anatomical observations on reproductive organs and digestive gland in female whelks, it was supposed that individuals suffered from imposex might recover at a very slow rate.
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