Endemism in Freshwater Ecosystems in Hawai‘i

Trade winds and rainfall patterns in Hawai’i

• Windward vs. Leeward – most streams are on windward sides of islands

• Elevational differences – most rain at high elevations

• Types of flow

Interaction of flowing water and Hawaiian basalts

• Orographic rainfall

• Channel cutting

– headward extension of watersheds – deepening of valleys

– widening of stream valleys – amphitheater headed valleys

• Watershed types

Windward

Leeward

• Differences in stream mouths

Across sandy beach

Across bolder beach

Waterfall

Open/closed

Origin of Pacific High Island Freshwater Macrofauna

• Ecological

– The dominant fishes, gastropods and crustaceans are marine in origin

– Most retain their marine heritage with the amphidromous life history pattern

– Insects and microfauna show different patterns

• Biogeographic

– The amphidromous macrofauna all show strong Indo-Pacific connections

– Others tend to be cosmopolitan

Survey of the native stream fauna from mouth to headwaters

Eleotris sandwicensis ‘O‘opu akupa

Stenogobius hawaiiensis ‘O‘opu naniha

Awaous guamensis ‘O‘opu nakea

Sicyoptrus stimpsoni ‘O‘opu nopili

Lentipes concolor ‘O‘opu alamo‘o

Atyoida bisulcata ‘Opai Kala‘ole

Neritina granosa Hihiwai

Neritina vespertina Hapawai

The amphidromous life history pattern

• Adults live in freshwater habitats

– Species differences in elevation

– Adults spend entire life in one stream

• Mating and egg laying occurs in freshwater

– Sometimes in the adult habitat sometimes a downstream breeding migration

– Eggs hatch and tiny fry drift downstream

• Planktonic period in the ocean

• Post-larvae find and return to freshwater

• Upstream migration to the adult habitat

Threats to Hawaiian streams and their biota

• Dewaterment

• Channelization

• Alien species