Use of Integrated Landscape Indicators to Evaluate the Health of Linked Watersheds and Coral Reef Environments in the Hawaiian Islands

Abstract

A linkage between the condition of watersheds and adjacent nearshore coral reef communities is an assumed paradigm in the concept of integrated coastal management. However, quantitative evidence for this "catchment to sea" or "ridge to reef" relationship on oceanic islands is lacking and would benefit from the use of appropriate marine and terrestrial landscape indicators to quantify and evaluate ecological status on a large spatial scale. To address this need, our study compared the Hawai'i Watershed Health Index (HI-WHI) and Reef Health Index (HI-RHI) derived independently of each other over the past decade. Comparisons were made across 170 coral reef stations at 52 reef sites adjacent to 42 watersheds throughout the main Hawaiian Islands. A significant positive relationship was shown between the health of watersheds and that of adjacent reef environments when all sites and depths were considered. This relationship was strongest for sites facing in a southerly direction, but diminished for north facing coasts exposed to persistent high surf. High surf conditions along the north shore increase local wave driven currents and flush watershed-derived materials away from nearshore waters. Consequently, reefs in these locales are less vulnerable to the deposition of land derived sediments, nutrients and pollutants transported from watersheds to ocean. Use of integrated landscape health indices can be applied to improve regional-scale conservation and resource management.

Place‐based management can reduce human impacts on coral reefs in a changing climate

“…The findings for Kaʻūpūlehu are consistent with past research conducted at the regional scale, which showed that wave‐sheltered shores of the Main Hawaiian Islands are more vulnerable to land‐based source pollution, while wave‐exposed shores are more resilient due to higher flushing (Rodgers et al. ). However, our spatially explicit models also revealed that coral reefs in these areas are also vulnerable at the local scale.…”

A fresh approach reveals how dispersal shapes metacommunity structure in a human‐altered landscape

“…Most indices of ecosystem 'health' are derived from variables measuring environmental condition, which are used as a surrogate for biological diversity (e.g. Kwok, Eldridge & Oliver 2011;Rodgers et al 2012;Dobbie & Cllifford 2015). The strength of the relations between environmental condition and species abundances can be tested using basic survey data (sites 9 species abundances 9 environmental variables: e.g.…”

Effects of reduced water quality on coral reefs in and out of no‐take marine reserves

“…However, in systems where development of coastal catchments has resulted in chronic, degraded coastal WQ, significant re‐structuring of near‐shore coral communities suggests a breakdown in the resistance of reefs against reduced WQ (Cramer et al. ; Rodgers et al ).…”

“…Although acute disturbances from extreme flood plumes can result in high coral mortality, in the absence of any additional disturbance, recovery is possible (Browne et al 2010;Graham et al 2015), depending on the inherent resilience of the system (Nyström et al 2008). However, in systems where development of coastal catchments has resulted in chronic, degraded coastal WQ, significant re-structuring of near-shore coral communities suggests a breakdown in the resistance of reefs against reduced WQ (Cramer et al 2012;Rodgers et al 2012).…”