Life history characteristics of the native Hawaiian stream snail Neritina granosa (hihiwai)
Brasher AM. 1997. Life history characteristics of the native Hawaiian stream snail Neritina granosa (hihiwai). Technical Report 114. University of Hawai`i at Manoa. Honolulu, HI
Amphidromous neritid snails are an important component of island stream ecosystems in the tropics. In Hawaii, where Neritina granosa requires relatively pristine conditions, stream alteration and water diversion are a major threat. During a two-year monitoring study conducted in Waikolu Stream on the Island of Molokai, the number of N. granosa found at each station showed wide variation. However, the mean number of snails was consistent between seasons and during the two years. Substantially fewer N. granosa were found in and above areas of stream diversion. Peaks in reproduction (egg capsule production) occurred in the fall and summer. Recruitment (return of post-larvae from the ocean to the stream) was highest in the spring with a second, smaller peak in the late fall. Consistent with the amphidromous lifecycle, tagging studies showed smaller, younger snails migrateupstream while the majority of adults (snails > 14 mm) stay within 20 m of their original release site. Dewatered sections not only reduce habitat for N. granosa but inhibit downstream dispersal of larvae and upstream migration of post-larvae.