Abstract

Soil erosion is the main exacerbating threat to climate change impacts in tropical Pacific islands, particularly to steep and mountainous volcanic islands. The morphological features (steep and mountainous), short distance from ridge to reef, frequent storm events, extended raining season, and accelerating developments from growing populations pose serious threats to terrestrial and marine resources. Perhaps the most threatening part is the high dependency of their human populations on the land and ocean for food supplies, supporting national economies, and sustaining culture and human well-being. Locals, governments, and non-governmental organization projects are underway to improve protection and management of natural resources on islands like Hawai'i, Samoa, Fiji, Tahiti, and others. To enhance conservation efforts in sustaining natural resources, this dissertation focuses on first, establishing a spatial assessment of land cover to evaluate and predict erosion impact along the Faasaleleaga district in Savai'i, Samoa. Second, assessing coastal zone's physical features such as Moloka'i-Hawai'i fishponds and streams outlets in sediment retention and distribution. Third, assessing the impact of wave regime on reef topographic complexity, coral cover, and relationship of topographic complexity to coral cover and fish population in the Southern fringing reef of Moloka'i. Lastly, conducting a systematic review to determine whether the size of Marine Protected Areas (MPAs) enhances key ecological outcomes (review paper). First, we utilized WorldView-3 satellite imagery acquired on 06 January 2022, to map land and benthic cover in order to predict the cascading impact that erosion has on coral reefs. Our results show 77.2% of vegetation cover, 13.1% of agriculture, and 9.7% contribute to bare soil, urban areas, roads, and water bodies. Coral/algae covered 48% of benthic cover and decreased in cover near watershed outlets. Although vegetation in Faasaleleaga district is largely intact, land cultivation is expected to expand due to a growing population. Thus, our baseline land and benthic cover combined with the watershed risk model provide a valuable method for assessing impacts to the marine environment as a result of erosion and monitoring into the future. Second, our particle size analysis and elemental analysis indicate that fishponds retained a significant amount of terrigenous sediment relative to open areas. Further, the distribution of sediment in the inner reef is mainly influenced by input sources such as gulches (Kaunakakai, Kawela, and KamalÅ), Kaunakakai harbor, and the intensity of waves and swells. Third, after conducting reef surveys (photo-transect and surface vehicle survey), we found that reef topographic complexity and coral cover on the south east fringing reef is negatively influenced by the northeastern trade-wind waves and sedimentation accumulation by the Kaunakakai harbor. Additionally, we found that topographic complexity is positively associated with coral cover and fish richness. Lastly, our review on MPAs indicate significant increase of biological diversity and organismal density inside MPAs, driven primarily by studies focused on the fish community. Our results also demonstrated a negative correlation of MPAs size and fish diversity but positively correlated with fish density, coral cover, and algae cover. Further, we found medium (1-100 km2) and large MPAs (>100 km2) to be more effective than small-MPAs (< 1 km2), especially in increasing fish density and coral cover. In mitigating the impact of erosion in steep tropical Pacific islands, our findings provide important scientific information to enhance conservation management planning. This includes the use of remote sensing to identify areas with high risk to erosion and considering potential impact of coral reefs from sediment dynamics through wave regime and the structure of coastal zones. This can help determine the design, restoration, and management of MPAs and fishponds, projects that governments and other organizations such as United Nations Development Programme (UNDP), International Union for Conservation of Nature (IUCN), National Oceanic and Atmospheric Administration (NOAA), U.S Geological Survey (USGS), and others are invested for sustaining resources in small island nations of the Pacific.

Degree

PhD

College and Department

Life Sciences; Biology

Rights

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