Influences of wind-wave exposure on the distribution and density of recruit reef fishes at Kure and Pearl and Hermes Atolls, Northwestern Hawaiian Islands

Abstract

This paper describes the results of a field survey designed to test the prediction that the density of benthic juveniles of shallow-reef fishes is greater on wind-wave "exposed" sectors of a pair of isolated oceanic atolls (Kure, Pearl and Hermes) at the far northwestern end of the Hawaiian Islands, an archipelago in which east-northeasterly trade winds dominate onshore water flow and transport by surface currents. The densities of recruits (juveniles ≤5 cm total length) were higher overall on windward versus leeward sectors of carbonate rock-rubble back reefs at both atolls, and the pattern was stronger for smaller (likely younger, more recently settled) recruits of four of the five most abundant species and the remainder pooled as an "Other" taxon. The windward-leeward disparity was four-fold greater at Pearl Hermes (the atoll with a three-fold longer perimeter) than at Kure. Resident predator biomass also was correlated with recruit densities, but habitat (benthic substratum) effects were generally weak. The distribution and abundance of recruits and juveniles of the primarily endemic reef fishes on shallow back reefs at these atolls appear partly influenced by relative rates of water flow over windward vs. leeward sectors of barrier reef and by the size, shape, and orientation of habitat parcels that filter out postlarval fishes with relatively weak swimming capabilities like labroids. Whole-reef geomorphology as well as fine-scale habitat heterogeneity and rugosity should be considered among the suite of many factors used to interpret observed spatial patterns of post-settlement juvenile fish distribution at atolls and perhaps some other tropical reefs.

Persistent spatial patterns of recruitment in a guild of Hawaiian coral reef fishes

“…Likewise, many additional factors such as the productivity of benthic prey and intra-and interspecific competition and predation on benthic young-of-year (YOY) can affect the settlement of larvae and their subsequent recruitment to benthic populations on tropical coral as well as temperate reefs (Jones 1991). Included among the many physical and biological factors potentially involved prior to settlement are the dynamics of planktonic nutrient availability and the influences of primary and secondary planktonic production and predation on larval growth and mortality (Hixon & Webster 2002); tidal and ocean currents and wind-generated waves that transport and disperse larvae as plankton (Cowen & Sponaugle 2009, DeMartini et al 2009); and ontogenetic changes in the swimming capabilities of larvae as they affect dispersion and transport (Leis 2006(Leis , 2010. Habitat geomorphology as the cause of localized retention versus enhanced dispersion and transport of larvae by currents remains among the most complex and least understood factors influencing larval settlement on coral reefs (Sponaugle et al 2002).…”

Management implications of juvenile reef fish habitat preferences and coral susceptibility to stressors

“…All sites were surveyed during June-July periods of 2006 and 2007 and during late May-early August 2008. The recruitment of most fish species on shallow Hawaiian reefs occurs during late spring-summer (Walsh 1987;DeMartini 2004;DeMartini et al 2009).…”

“…In general, the rugose corals of Hawai'i tend to be more susceptible to bleaching and sedimentation stressors as well as wind-swell disturbance than encrusting and mounding growth forms (Dollar 1982;Dollar and Grigg 2004). The recruits of many species of Hawaiian reef fishes primarily inhabit shallow wave-protected habitats where coral cover is often sparse, particularly in the NWHI (Vroom et al 2006;DeMartini et al 2009). Although relatively few species of Hawaiian reef fishes use corals either for food or shelter as adults, greater proportions of these species inhabit living corals as juveniles v. adults (E. DeMartini et al, unpubl.…”

“…Even the north-western Hawaiian Islands (NWHI), a high-latitude coral reef ecosystem once considered one of the most resilient to anthropogenic stressors like bleaching (Friedlander et al 2005), has experienced bleaching (Aeby et al 2003;Kenyon et al 2006b). Although coral development (Vroom et al 2006) and the structural complexity (DeMartini et al 2009) of habitat is generally low at the scale of entire reefs in the NWHI, locally high coral cover exists at wave-sheltered back reefs and some patch reefs in the lagoons of far NWHI atolls. Heating as a response to reduced water circulation (ponding) within lagoons at these atolls has resulted in moderate to strong bleaching during summertime doldrums in some years (Aeby et al 2003;Kenyon et al 2006b;Kenyon and Brainard 2006).…”