Net Phytoplankton of the Ala Wai Canal, O'ahu, Hawai'i

Abstract

The Ala Wai Canal currently possesses a diverse and differentially distributed phytoplankton community that includes a minimum of 20 diatom genera, four dinoflagellate genera, and one cyanophyte genus. The diatom populations of the canal may be characterized by two ecological components: (I) diatoms thought to be intolerant of the estuary's variable physical conditions, and (2) diatoms believed to be tolerant to most environmental conditions found in the canal. The phytoplankton in the region between the head of the Ala Wai Canal and the Manoa-Palolo Stream outfall are primarily dinoflagellates. These algae may be restricted to this part of the canal, in part, because the sediment berm formed adjacent to the Manoa-Palolo Stream outfall restricts water motion, thereby altering circulation patterns, water temperature, and oxygen concentration at the head of the canal, favoring a dinoflagellate dominated-community. Lyngbya (Cyanophyta) is found throughout the canal at low relative densities. The distribution of the dominant diatom Skeletonema costatum (Greville) Cleve as well as similarity of phytoplankton populations across sites indicated that migration of phytoplankton within the canal is tidally controlled. Flushing the canal by pumping in seawater at its head has the potential to substantially alter phytoplankton composition and distribution at points in this waterway and may eliminate an entire division of algae from the head of the canal.