Spatial and temporal changes in macroalgal diversity of a Hawaiian stream with the return of previously diverted water
Sherwood, Alison R.; Coontz, Kristopher M.
This study is the first to examine the effects of return of previously diverted water on macroalgal diversity in a Hawaiian stream. Two sections of a stream (Lālākea and Hi'ilawe) on the northeast coast of Hawai'i Island were studied for a 10-month period prior to, and 20 months after removal of a stream diversion. The habitat and macroalgal taxonomic composition of Hi'ilawe and Lālākea Streams was characterized over the course of the study. A decrease in the proportion of dry sites was noted for both streams with the return of water. A greater proportion of bedrock was found in quadrat substrata in Lālākea Stream than Hi'ilawe Stream, but otherwise composition was similar, with boulders, cobble, and gravel all major components. Average maximum depth was both deepest and shallowest following diversion removal, indicating a greater variability of physical stream characteristics with pre-diversion flows. Average percent cover by macroalgae was variable (from 14-63 %) and did not consistently change with diversion removal. However, like Hi'ilawe Stream, Lālākea macroalgal diversity substantially increased with the return of water (114 % and 118 %, respectively). In total, 25 cyanobacterial, 30 green algal, 5 red algal, 1 yellow-green algal and 5 diatom taxa were identified as macroalgae, which is an outstanding diversity for a stream in any part of the world, including the tropics. These taxa include 19 new macroalgal records for the Hawaiian Islands as well as several undescribed, possibly endemic species. This study suggests an important relationship between stream flow and macroalgal diversity, which is consistent with literature reports for other stream biota.