Understanding amphidromy in HawaiModified Letter Turned Commai: Modified Letter Turned CommaOModified Letter Turned Commaopu nakea (Awaous stamineus)

HawaiModified Letter Turned Commai is home to Modified Letter Turned CommaoModified Letter Turned Commaopu nakea (Awaous stamineus), a culturally significant, endemic, goby that exhibits an amphidromous life cycle characterized by a marine larval stage followed by post-larval recruitment to streams, where they live to become reproductive adults. However, it was recently suggested that their migration to the ocean might not be obligatory, as originally thought. Despite their importance in Hawaiian traditions and the ecology of Hawaiian freshwater ecosystems, we still lack a full understanding of their migratory patterns and life history due to the difficulties in determining the environmental migratory cues that set the timing and location of their migratory paths. This study examined environmental factors, such as mean annual rainfall, streamflow, and water chemistry, to determine if they play a role in whether A. stamineus spend their larval period in the ocean or their entire life cycle in freshwater streams. We sampled A. stamineus (n = 90) from three streams (Kahana, KahaluModified Letter Turned Commau, and Waimanalo) on the island of OModified Letter Turned Commaahu, HawaiModified Letter Turned Commai that represented the range of hydroclimatic gradient in wet-habitat conditions on the windward side of the island and characterized their migratory pattern using elemental analysis of sagittae, the largest pair of otoliths (calcareous ear structures). Based on otolith strontium:calcium and barium:calcium ratios, we determined if individuals spent their larval period in the ocean or the stream. We found that 100% of individuals displayed clear evidence of marine residence during their larval phase, regardless of the environmental factors the fish experienced. This study highlights the necessity of stream-ocean connectivity for the survival of A. stamineus and emphasizes the importance of stream-mouth conservation and management as it is a critical transition zone in stream-ocean-stream migratory pathways.

Automated summary

The Hawaiian modified letter turned comma goby exhibits an amphidromous life cycle and spends its larval period in the ocean. This study demonstrates the importance of stream-ocean connectivity for the survival of this species.