EVIDENCE OF A MARINE LARVAL STAGE IN ENDEMIC HAWAIIAN STREAM GOBIES FROM ISOLATED HIGH-ELEVATION LOCATIONS

Tropical streams on high oceanic islands are characterized by populati ons of amphidromous gobioid fishes. Adult fish live and breed in fresh water and many spawn at high (>300 m) elevations. Newly hatched fry ar e swept down to the sea where they develop for a period of time before recruiting to a stream. In analogous habitats in other geographic are as, amphidromous populations have further evolved into landlocked form s (i.e., populations that spend their entire life cycle in freshwater) . We analyzed depositional patterns of trace elements in the otoliths of adult Lentipes concolor, an amphidromous goby endemic to Hawaii, to determine whether landlocked forms occurred. Otoliths were obtained f rom fish collected from the Hawaiian stream habitats most likely to ha rbor landlocked populations-upper elevations of interrupted streams an d sections of streams above high waterfalls. A transition from a marin e phase to freshwater existence was demonstrated as a decrease from hi gh to low strontium : calcium ratios in the otolith with increasing di stance from the otolith's core. In every case, otoliths from these gob ies showed evidence of a marine planktonic larval stage, suggesting th at even in habitats physically isolated from the sea, these freshwater fish require a marine larval phase.