Hanalei Bay, Kaua`i marine benthic communities since 1992: spatial and and temporal trends in a dynamic Hawaiian coral reef ecosystem

Friedlander, Alan M.
Brown, Eric K.
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Hanalei Bay, Kaua‘i is situated in a dynamic and relatively harsh environment that at times includes high wave energy, heavy fresh water influx, and high turbidity. These conditions result in overall low coral cover (ca. 14%) that is dominated by encrustingforms adapted to high wave energy. The five most abundant coral species in 1993 were Montipora patula (7%), M. capitata (2%), Porites lobata (2%), P. compressa (1%), and Pocillopora meandrina (1%). Average percent coral cover increased non-linearly among 20 permanent transects in Hanalei Bay from 1993 to 2004. Between 1993 and 1999 there was an increase of 5% absolute (34% relative) in live coral cover from 14% to 19%. From 1999 to 2004 coral cover remained relatively stable. Much of the initial increase was attributed to Montipora patula which increased in percent cover from 7% in 1993 to 11% in 2004. Species composition patterns remained similar during that time period. Coral settlement in 2003 and 2004 was higher in the outer bay compared to locations in the inner bay. Coral recruits were dominated by the genus Montipora that typically has high recruitment rates but low survival compared to other coral genera. Coral larval settlement was observed to be higher in Hanalei Bay compared to other regions around the world and may help explain the increase in coral cover observed over the past decade. Temporal variability, artificial substrate type used, or observer biases, however, could all effect documented settlement patterns, therefore these patterns may not be directly influenced by increases in coral cover. Fish species richness, biomass, and diversity were higher in habitats with high spatial relief adjacent to reef-sand interfaces. Most measures of fish assemblage structure were lower during the winter months when large north Pacific swells and heavy rainfall, coupled with high river discharge, impacted the bay. Fish assemblage characteristics did not vary significantly between 1993 and 2004 although trends in biomass are suggestive of an increase over time. Three introduced fish species (bluestripe snapper, blacktail snapper, and peacock grouper) have become well established in Hanalei Bay and their contribution to total fish biomass has increased from 15% in 1993 to as high as 39% in 1999. Hanalei Bay is one of the few areas in Hawaii that has shown an increase in live coral cover over the past decade. Increases in total fish biomass since the early 1990s cannot be attributed solely to introduced species, as other elements of the fish assemblage have also increased over this time period. Natural factors such as large wave events are thought to be more important in structuring the coral reef community of Hanalei Bay than anthropogenic factors, and this may help to explain the trends observed in this study.
Coral reef ecology, fish biomass trends, fish species
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