Baseline assessments for coral reef community structure and demographics on West Maui
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Resource Abstract:
<p>The coastal and upslope terrains of West Maui have had a long history of impacts owing to more than a century of human
activities. Resource extraction, agriculture, as well as residential and resort development have caused land-based pollution
that impairs water quality and adversely impact the adjacent marine ecosystem. Today, West Maui s coral reefs are chronically
impacted by the effects of land-based pollution, mainly sedimentation and nutrients, with documented losses of 30 75% in coral
cover over the last 20 years. Nonetheless, despite their current status and levels of environmental impact, these coral reef
communities represent a key local resource and a counterpoint to the overall low coral reef development levels both island-
and state-wide. This is of high relevance because the occurrence of coral-rich assemblages and accreted reef complexes statewide
is sparse. Only limited segments along the coastlines of Maui, Hawai i, Lana i, Moloka i, and Kaho olawe, harbor mature, fringing
coral reefs; and unfortunately, many of them are seriously threatened by terrestrial runoff. </p><p>This report describes
the results of baseline assessment surveys of coral reef benthic structure, coral community demographics, and coral condition.
These surveys are intended to provide benchmarks for continued monitoring efforts and provide a gauge for comparing and evaluating
the effectiveness of management actions to reduce land-based sources of pollution in priority watersheds on West Maui. Within
this context, 12 permanent, long-term monitoring sites were strategically established adjacent to the 7 primary stream drainages
(Wahikuli, Honokwai, Mahinahina, Kahana/Ka opala, Honokeana, Honokahua, and Honolua) within the five priority watersheds (Wahikuli,
Honokwai, Kahana, Honokahua, and Honolua). Herein, benthic cover and composition, coral demographics, and coral condition
of the monitoring sites are described and contrasted in the Benthic Characterization and Synthesis and Discussion sections
of this report. </p><p>The baseline assessments revealed that although some areas harbor prominent coral reef structures with
high live coral cover and multispecies assemblages, others are characterized by sediment-impacted corals in impoverished and
species-poor communities. Mean coral cover varied widely, from 49% at Wahikuli-shallow to 4.6% at Mahinahina-shallow. Similarly,
coralline algal cover averaged 12.7% at Ka opala and Honokeana-north, but was altogether absent at the Mahinahina sites. Macroalgae
was a minor component of the benthos across all study sites, representing only up to 2.3% at Mahinahina-south, while turf
algae varied considerably, from 41% at Honokeana-north to 84% at the Honokahua site. Consequently, the Benthic Substrate Ratio
(BSR) also varied considerably region wide, with the highest values ( 1), suggesting a healthier reef condition reported for
the Wahikuli, Honokeana, and Honokwai sites; and the lowest ( 0.5), suggesting impairment in structure and function, recorded
at the Honolua and Honokahua sites. Adult colony densities were the highest at the Wahikuli (27 col/m<sup>2</sup>) but lowest
at the Ka opala (7 col/m2 ) site. And, colony partial mortality peaked at the Ka opala (33%) and was the lowest at the Honokeana
Bay (12%). Moreover, in-situ and derived estimates of water turbidity and sediment loading revealed that the Ka opala and
Wahikuli stream sites ranked the highest for turbidity, whereas the Honokwai and Ka opala sites ranked highest for sediment
loading. </p><p>Chronic and episodic terrestrial sediment stress has resulted in coral reef community demise, clearly illustrated
at the Honolua, Honokahua, and Ka opala sites, where coral benthic cover and colony abundances ranked the lowest and levels
of turf algae ranked among the highest. Left unattended, land-based pollution impacts will continue to negatively affect the
coral reef communities of West Maui. And, under the current turbidity and sediment loading conditions, the coral-rich habitats
in the Wahikuli and Honkowai Watersheds are probably at greatest risk, given they harbor the most prominent and well-developed
reefs in the region, characterized by the highest coral cover, colony densities, and structural complexity. </p>
Citation
Title Baseline assessments for coral reef community structure and demographics on West Maui