Tropical Conservation Biology and Environmental Science

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Life-stage–specific habitat associations and detection patterns of pākuʻikuʻi (Acanthurus achilles) on Hawaiʻi Island reefs
(University of Hawaii at Hilo, 2025-12) Larson, Annie Makaye; Tuttle-Raz, Lillian; Tropical Conservation Biology & Environmental Science
Monitoring coral reef fishes is essential for assessing ecosystem health and managing fisheries, yet it remains challenging due to imperfect detection, complex habitats, shifting environmental conditions, and life-stage-specific behaviors. Detection–occupancy models address these limitations by separating detection probability from true occupancy. This study applied a single-season, multi-method (diver vs. remotely operated vehicle, ROV) single- and two-species (juvenile vs. adult) detection–occupancy framework to pākuʻikuʻi (Achilles Tang, Acanthurus achilles), a culturally, ecologically, and economically important reef fish in both commercial and noncommercial fisheries experiencing population decline along the west coast of Hawaiʻi Island. Fifty-two sites around Hawai‘i Island were surveyed 3–4 times using combinations of SCUBA, snorkel, and ROV methods, and models incorporated environmental covariates representing human, oceanographic, and habitat conditions. Juveniles showed stronger associations with habitat conditions, including coral cover and relative slope, whereas adult occupancy was linked to broader oceanographic and human-based gradients. Adults were more likely to occur at sites where juveniles were present, suggesting habitat connectivity across life stages. Detection probabilities were comparable between survey methods, indicating that integrating ROV surveys may enhance monitoring efficiency and spatial coverage. Collectively, these findings demonstrate that accounting for imperfect detection improves inference about population status and habitat relationships for species with cryptic or ontogenetically shifting behavior. By modeling key habitat drivers and highlighting co-occurrence between life stages, this study provides actionable insight and a scalable framework to support recovery planning and adaptive management for an imperiled species on Hawaiʻi’s nearshore reefs.
Listening to hope: Using bioacoustics to monitor Hawaiian honeycreepers during the application of Incompatible Insect Technique
(University of Hawaii at Hilo, 2025-12) Smith, Lauren Kelsey; Hart, Patrick; Tropical Conservation Biology & Environmental Science
In Hawaiʻi, more than two-thirds of native bird species have gone extinct since the arrival of humans. The invasive mosquito Culex quinquefasciatus, as a vector for introduced avian disease, has contributed to approximately 50% of these extinctions, with four more species poised to disappear in as little as 10 years. To suppress C. quinquefasciatus and disease transmission, conservation partners are employing the Incompatible Insect Technique (IIT) on a landscape scale on the islands of Maui and Kaua'i. For my Master's thesis, I developed a novel technique to monitor the response of native Hawaiian honeycreepers to IIT in a relatively rapid and repeatable design. I deployed 54 autonomous recording units (ARUs) to record the sounds of honeycreepers during the 2024 and 2025 breeding seasons in The Nature Conservancy’s Waikamoi Preserve and bordering private lands owned by Mahi Pono on Maui. I placed ARUs 150m apart within and above the IIT treatment area (Treatment), as well as in an area to the west that did not receive IIT (Control), in a Control-Impact (CI) design. To process these acoustic data, I used the machine learning classifier Perch and a new analytical method co-developed by the UH Hilo Listening Observatory for Hawaiian Ecosystems (LOHE) lab and Google Research. Perch predicts whether species are vocalizing within acoustic data, which I used to calculate the proportion of detection windows containing the target species vocalizations, or call densities, through manual validation. I compared the maximum likelihood estimates of call densities for six native species within the 2024 and 2025 breeding seasons across our CI design. I also used these data to model the relationships between call density, forest structure, and elevation to understand the use of habitat across the study site. Models were fitted using generalized linear mixed models (GLMM) and a generalized additive modeling framework (GAM). I found increased call densities in 2025 across both the Control and Treatment sites (p < 0.05) for ʻapapane (Himatione sanguinea), Hawaiʻi ʻamakihi (Chlorodrepanis virens wilsoni), and ʻiʻiwi (Drepanis coccinea). ʻIʻiwi also showed a significant negative effect in the 2025*Treatment interaction term, showing that the increase in the Control site for ʻiʻiwi was greater than in the Treatment site (β = -0.484, p < 0.001). The elevation-smoothed GAMs revealed two different patterns: 'akohekohe (Palmeria dolei), Hawai'i 'amakihi, and 'i'iwi had curvilinear relationships with elevation, while 'apapane, kiwikiu (Pseudonestor xanthophrys), and Maui 'alauahio (Paroreomyza montana) had increasing relationships with elevation for all habitat types. I conclude that there has not been sufficient time to detect a change in call densities since IIT implementation, but my study design is sensitive enough to detect changes between years and can reveal important patterns for honeycreeper conservation.
Implementing drone imagery as a tool for surveying vegetation in Hawaiʻi
(University of Hawaii at Hilo, 2025-08) Shiroma, Kalena; Price, Jonathan; Tropical Conservation Biology & Environmental Science
Hawaiʻi's forests, essential to its ecological balance and cultural heritage, are key to preserving biodiversity and sustaining water resources. Through thoughtful land management, these vital ecosystems continue to thrive, ensuring the enduring resilience of Hawaiʻi's landscapes. Forest monitoring is important in tracking the presence of threats and biological invasions that persist here. Here in Hawaiʻi, the United States Forest Service Forest Inventory and Analysis (FIA) Program completed its second forest inventory assessment between 2019–2022 using traditional on-ground surveys, providing forest estimates for land management. However, some sites were inaccessible due to the physical challenges faced by field crew members, particularly on sheer cliffs deemed “hazardous” and unsafe. This thesis’ analysis spans two methodological chapters, focusing on innovative methodologies and their applications. Chapter 2 first demonstrates the efficiency and consistency of data collected using drones compared to on-ground surveys, highlighting the practicality of modern technologies when conventional methods were not viable. Results show that there was no difference between the two survey methods for percent cover, vegetation structure, and species composition. Building on this foundation, Chapter 3 applied similar data collection strategies to investigate cliff forest ecosystems on the island of Kauaʻi without the need for a methodological comparison. This approach instead facilitated the safe exploration of inaccessible areas, addressing data gaps and enabling the study of percent cover, species composition, diversity, and their relationships to steep terrain. Results found that slope has a positive effect on native species richness as well as having an influence on the likelihood of locating rare and endangered plant species on areas with increased slope. Moisture also had a positive effect, with increased rainfall increasing the total percent cover of vegetation. Substrate type also had a positive effect on species richness, with rock and similar mixed compositions providing stable places for diverse vegetation to flourish. Finally, mesic forests were found to host higher rates of alpha and gamma diversity of plant species for these areas. Altogether, these methods and datasets establish a critical foundation for forest inventory and monitoring, integrating drone technology to support ongoing conservation efforts in Hawaiʻi and advance methodological innovation in ecological research.
Seed dispersal by wild pigs in Hawaiian forests
(University of Hawaii at Hilo, 2025-05) Aguirre, Kupono; Ostertag, Rebecca; Tropical Conservation Biology & Environmental Science
The introduction of novel species around the world can lead to dramatic shifts in native ecosystems. In Hawaiʻi, invasive species have drastically altered the composition and function of native systems. It is important to understand the effects that these species have in order to anticipate and mitigate any detrimental impacts. Pigs (Suidae) are a prevalent invasive species in many parts of the world and occur on all continents except Antarctica. Within their native range, pigs perform a variety of ecosystem services, especially in forests where they increase soil nutrients through rooting and act as seed dispersers. Pig introduction outside of their native range, however, has proven to be detrimental to native species across the globe. In Hawaiʻi, wild pigs decrease native plant regeneration and abundance, prey on native ground-nesting birds, alter soil composition, and disperse non-native seeds. Studies done on other islands in Oceania have shown that pigs disperse native seeds in addition to non-native seeds. To determine if pigs are dispersing native seeds in Hawaiʻi, my thesis focused on the question: How do the species richness and total abundance of germinants in the scat compare to the fruiting species at low and high elevation sites over time? To examine this question, three high and three low elevation forests on the east side of the Island of Hawaiʻi were chosen based on elevation, precipitation, and dominant vegetation type. Elevation and precipitation were consistent amongst the two sets of sites, while native vs. non-native vegetation dominance was the determining selection factor. Scat was collected and germinated during four time points over the course of 19 months from December 2022 to July 2024 to understand seasonal variability. A total of 346 scat samples were collected and of those 173 germinated with a total of 33,508 seedlings. No native seedlings germinated from any of these samples during any time points. There was a greater species richness in the forest compared to the scat, with some germinants that were completely absent in the vegetation and available fruit. Total abundance of seedlings was greater at low elevation sites, but did not differ over time points. The two dominant species that germinated from the samples, P. cattleyanum and C. obtusifolia, were present in low elevation scat from all time points. Overall, this study highlights the fact that pigs are not dispersing native seeds and are facilitating colonization of non-native plants in areas where these plant species were not present.
Movement patterns of juvenile blacktip sharks (Carcharhinus limbatus) within a tropical nursery habitat
(University of Hawaii at Hilo, 2025-05) Moe, Lauren; Turner, Jason; Tropical Conservation Biology & Environmental Science
Blacktip sharks (Carcharhinus limbatus) are a circumglobal species that rely on nearshorenursery habitats during their early years. Very little is known of the movement patterns and habitat usage of blacktip sharks in the Hawaiian Islands, and no nursery habitats have yet been designated for this species within Hawai‘i. For this study, juvenile blacktip sharks (n = 29) were caught and tagged in Hilo Bay, Hawai‘i, USA, using VEMCO V-13 PPM acoustic transmitters. Tracking occurred every 2-5 weeks between July 2022 and January 2024 at 44 stations throughout Hilo Bay using a VR-100 receiver and VH-165 omnidirectional hydrophone. Results showed that juvenile blacktip sharks were present in the Bay year-round with peak occurrence of tagged individuals (41.3-50.0%) between March and August, and more limited occurrence (24.1-30.1%) between October and January. Tagged sharks were detected within Hilo Bay more during the day than at night, likely due to excursions into deeper waters during heightened nocturnal foraging activity. Accordingly, blacktip sharks were detected more frequently in deeper waters at night. Detections were significantly higher in areas where the benthic composition was predominately mud as opposed to coral or rock. Temperature and salinity did not significantly vary among stations, and as such, were not influential factors in habitat use, though DO appeared to limit habitat use during the day when concentrations were lowest. Thus, juvenile blacktip sharks appear to preferentially utilize deeper habitats with mud substrates within Hilo Bay and are limited in these areas by DO. The lowest levels of DO were recorded during the months with the fewest sharks detected in the Bay, suggesting that oxygen requirements may be limiting both spatial and temporal habitat usage. The results presented here are the first to delineate Hilo Bay as a blacktip shark nursery habitat in Hawaiian waters and suggest that this population of blacktip sharks resides predominantly within Hilo Bay for the first few years of their life.
Evaluating high-resolution remote sensing data and machine learning for detecting strawberry guava (Psidium cattleyanum) and its biocontrol on Hawai'i island
(University of Hawaii at Hilo, 2025-05) Jarvis, Olivia Maya; Perroy, Ryan; Tropical Conservation Biology & Environmental Science
Strawberry guava (Psidium cattleyanum) is the most abundant non-native tree species across the Hawaiian Islands. This invasive species can create nearly impenetrable, dense thickets across rugged terrain which makes it difficult to map its distribution. The Brazilian scale (Tectococcus ovatus) is a gall forming insect that is currently being deployed as the biological control to reduce the spread of strawberry guava. High resolution remote sensing technologies, including sensors attached to small unoccupied aircraft systems (sUAS) and helicopters, allow researchers to survey more land in a short amount of time with machine learning models to find invasive species and observe the effects of management actions. This project uses remote sensing data, including high resolution RGB aerial imagery, lidar data, and machine learning to detect strawberry guava and implements computer vision techniques to detect biocontrol spread. Helicopter and sUAS flights collected these data for a portion of ‘Ōla‘a Forest Reserve on Hawai‘i Island. Additionally, ground truth surveys were conducted over three 20 x 20 m plots where every tree was exhaustively surveyed. Images of strawberry guava in the canopy during different phenological stages and leaves with Brazilian scale galls present were annotated and used to train convolutional neural network (CNN)-based object detection models with the python library DeepForest. In parallel, forest structure metrics including canopy height, foliage height diversity, plant area index, and point density at z-values equal to four to six meters were derived from the lidar data and used to classify areas of strawberry guava via a random forest classification model. The CNN detector was able to detect strawberry guava in aerial imagery better during periods when the canopy underwent a red flush, or new leaf growth, (mAP = 0.85 (SD = 0.02), F1 score = 0.58 (SD = 0.03)) compared to a green leaf canopy (mAP = 0.79 (SD = 0.02), F1 score = 0.50 (SD = 0.02)). The random forest model using forest structural metrics derived from lidar performed better in terms of precision (F1 score=0.72) than both CNN models while the red phenology stage CNN had better recall. Plant area index closely followed by canopy height and foliage height diversity were the metrics in the model with the greatest mean decrease accuracy, or importance to the model’s performance. The models captured large stands of strawberry guava in both aerial imagery and lidar data, but struggled to capture individual strawberry guava tree stems. For the Brazilian scale, another CNN-based object detection model was developed and was able to detect galling on strawberry guava leaves (mAP = 0.57 (SD = 0.02), F1 score = 0.40 (SD = 0.02)), but low precision values indicated many false positive predictions due to rain, discoloration, blur, and lighting. Using these tools to identify strawberry guava is useful for selecting candidates for ongoing biocontrol deployments and could be applied at a larger scale to map the presence and absence strawberry guava in Hawai‘i. Monitoring the Brazilian scale progress in the canopy with aerial imagery and machine learning will help better determine whether its establishing in strawberry guava canopy and spreading over time to reduce tree spread into high elevation native forests.
Best agronomic practices for biomass accumulation and tissue quality of two sugarcane (Saccharum spp. hybrid) varieties grown for biofuel in the tropics.
(University of Hawaii at Hilo, 2025-05) Rule, Brian; Krueger, Nicholas; Tropical Conservation Biology & Environmental Science
In support of the United Nations Net Zero Coalition, which aims to reduce global greenhouse gas emissions to near zero, identifying sustainable alternatives to fossil-based jet fuel is a global priority. Aviation accounts for approximately 2% of global emissions, and Sustainable Aviation Fuel (SAF) production depends heavily on lipid-based feedstocks such as soybean and used cooking oils. These sources are limited by feedstock availability and supply chain constraints. As processing technologies advance, lignocellulosic biomass has emerged as a promising alternative. Sugarcane (Saccharum officinarum) cultivars bred for high fiber and low sugar content, called energycanes, are desirable due to their high yields, suitable tissue composition, and compatibility with tropical climates.In a multi-year factorial field experiment conducted in Hilo, Hawai'i, this study evaluated the agronomic and biochemical performance of two energycane cultivars, H68-1158 and H78-0292. Treatments included three harvest durations (18-month, a 10-month ratoon, and 28-month) and three nitrogen fertilization regimes (0 and 150 N ha-1 yr-1 and 300 kg N ha⁻¹). Measured variables included biomass yield, fiber composition, sucrose concentration, and theoretical ethanol yield. Cultivar H68-1158 outperformed H78-0292 in total biomass and theoretically recoverable sugar (TRS), resulting in significantly higher estimated ethanol yields. H78-0292, in contrast, exhibited lower TRS, Brix, and sucrose traits favorable for lignocellulosic conversion. Findings support the dual-purpose potential of established sugarcane germplasm for both sugar-based and cellulosic biofuel production. Long-duration growth cycles enhanced fermentable sugar output, and pre- and post-soil analyses confirmed no immediate nutrient depletion other than potassium. Overall, this study highlights energycane’s viability as a tropical biofuel feedstock and underscores the importance of agronomic optimization to balance yield and land use efficiency for SAF production.
Predicting sea level rise impacts to coastal wastewater infrastructures and water quality along the Kailua-Kona shoreline
(University of Hawaii at Hilo, 2024-12) Kamau, Ihilani kawaipunahele ʻo omokaʻa; Wiegner, Tracy; Tropical Conservation Biology & Environmental Science
Sea level rise (SLR) poses a serious threat to coastal infrastructures. On-site sewage disposal systems (OSDS) and wastewater infrastructure (WI) are vulnerable, and when inundated, will result in human and ecosystem health threats. This study focused on the Kailua-Kona shoreline, Hawai‘i Island, where these two sewage sources are potentially impacting water quality. Study goals were to: 1) document and identify sewage pollution hotspots by assessing current water quality conditions, 2) map out and assess predicted SLR to determine what OSDS and WI are at risk of inundation. Sewage pollution hotspots were assessed using a dye tracer test and monthly water quality sampling at 12 stations from August 2022 to September 2023. At Kahaluʻu, dye traveled at 278 m/d, reaching the shoreline in < 6 hours. While Enterococcus spp. concentrations occasionally exceed water quality standards, Clostridium perfringens did not. Staphylococcus aureus was also detected, but Methicillin-resistant S. aureus was not. Nutrient concentrations were variable. Macroalgal δ15N measurements, a stable isotope mixing model, and a sewage pollution score determined that groundwater is the dominant source of NO3- at our stations contributing 77%. However, the results did display a sewage influence on these stations. We examined six different SLR scenarios (2024 Mean higher high water (MHHW), 0.3, 0.6, 1, 1.5, 2 m) and at 0.3 m SLR, 58 OSDS will be at risk of inundation and at a 2 m SLR, this number doubles. We also found that the majority of WI is already being inundated during MHHW events (66 manholes, 79 mains). Our results show that Kailua-Kona is already impacted by sewage pollution and that this will continue to worsen with SLR if management actions are not taken. The entire shoreline from Kailua-Kona to Keauhou should be a Priority 1 area for cesspool conversion for Hawai‘i County, and sewer line setbacks are needed; our results can help guide this effort. Our findings illustrate that adaptive planning is needed to protect future water quality and increase coastal resilience in Hawai‘i, as well as elsewhere where coastal waters are impacted by OSDS and WI.
Coral Reefs in the Pacific: Habitat Complexity, Functional Traits, and Temporal Changes
(University of Hawaii at Hilo, 2024-12) Ferreira, Sofia; Burns, John; Tropical Conservation Biology & Environmental Science
Coral reefs are critical ecosystems facing increasing threats from global and local stressors, leading to significant declines in live coral cover and biodiversity. This thesis investigates coral reef ecological interactions and their functional implications across three studies in the Pacific. In Chapter 1, long-term monitoring data revealed spatial and temporal trends in coral assemblages across four national parks, with stable coral cover in Guam and American Samoa contrasted by declines in Hawaiʻi. Notably, temperature fluctuations exhibited minimal effects on coral cover, underscoring the need for ongoing monitoring to inform conservation strategies. Chapter 2 employs a trait-based approach to quantify habitat complexity on Guam's reefs, demonstrating that coral morphology significantly influences structural metrics essential for biodiversity. Larger columnar corals were identified as crucial contributors to habitat complexity, suggesting a paradigm shift in assessing reef health beyond traditional taxonomic metrics. Finally, Chapter 3 explores the interactions between 3D habitat complexity, coral traits, and reef fish functional structures within a protected marine park. Specific habitat features, particularly branching corals and higher slope values, were found to be strongly linked to fish abundance across various functional groups, highlighting the intricate dynamics between habitat complexity and fish assemblages. This thesis not only elucidates the complex interplay between corals, habitat complexity, and reef fish but also establishes a robust framework for future research that enhances our ability to predict and mitigate the impacts of environmental change on coral reef ecosystems, ultimately informing effective conservation strategies for these vital habitats.
AGROFORESTRY RESOURCES, GENDER AND LOCAL KNOWLEDGE IN HAWAIʻI
(University of Hawaii at Hilo, 2024-12) Ezzy, Anna Nalani; Besio, Kathryn; Tropical Conservation Biology & Environmental Science
Federal, state and local governments are increasingly investing resources into expanding agroforestry practices and systems for climate resiliency. Yet, Hawaiʻi producers face systemic barriers to equitably accessing institutional resources to practice agroforestry. Women farmers in Hawaiʻi, particularly those practicing non-conventional agriculture, must navigate unique tensions related to gendered power and social relations which affect their interactions with the environment and access to resources. In this thesis, I used a Feminist Political Ecology (FPE) approach and semi-structured interviews to understand the perceptions and experiences of diverse women practicing agroforestry in Hawaiʻi accessing supportive resources. I explored the following research questions: 1) how do women growers in Hawaiʻi define agroforestry; 2) how are women accessing support and resources for agroforestry; 3) what factors inhibit women’s access to resources and support for agroforestry? Through grounded theory analysis, themes emerged around differences in agroforestry definitions between the USDA and women interviewed, affecting how growers navigated institutional and community resources. Caregiving, as a gendered responsibility, constrained many women’s ability to develop agroforestry systems, intersecting with environmental caregiving for some Kanaka ʻŌiwi women. Based on these findings, I discuss policy recommendations to equitably expand agroforestry in Hawaiʻi, including federal legislation and State and County initiatives to uplift local agroforestry knowledge and recognize the impact of gendered responsibilities on growers. These findings support enhanced resource access for women-identifying farmers as well as provide insight into trends of larger social and political marginalization in Hawaiʻi.
SOCIAL LEARNING AND FORAGING PROFICIENCY OF PALILA (LOXIOIDES BAILLEUI) IN AN AVIARY SETTING
(University of Hawaii at Hilo, 2024-12) Kluzak, Christopher Zdenek; Hart, Patrick; Tropical Conservation Biology & Environmental Science
The Palila (Loxioides baiileui) is a critically endangered Hawaiian bird that relies on the unripe pods of Māmane (Sophora chrysophylla). Previous authors have shown that aviary-raised Palila drill directly into the seeds, while wild Palila peel the entire pod, and that after relocation within a wild population about one out of three aviary-raised birds begin to peel pods. In summer 2017, six aviary raised after second-year (ASY) adult birds were offered partially peeled pods to train them to fully peel pods. Tear lengths and other pod measurements were collected in 2017 and 2018. These were compared to other aviary-raised adults, second-year (SY) aviary-raised Palila, and a captive pair known to peel pods. While the training attempt was not successful, it was found that most birds can produce long tears even if the average tear length is low, and that ASY adults were far more proficient than SY adults. Depending on which measurement of foraging ability is used, females may be more proficient than males. Also, two birds that tended to create small tears survived the longest after the 2019 re-location to Puʻu Mali, a finding that has conservation implications. Some of the deaths of wild released birds were attributed to predatory birds, suggesting that predator avoidance training maybe more important for post-release survival than improving foraging proficiency.
Ridge-to-Reef Connectivity under a Changing Climate: Current and Future Nutrient Export Dynamics of the Wailuku River Watershed in Hawai'i Island, HI, USA
(University of Hawaii at Hilo, 2024-12) Colo, Christian; Wiegner, Tracy; Tropical Conservation Biology & Environmental Science
Rivers serve as critical links between terrestrial and marine ecosystems by exporting nitrogen and phosphorus to the coastal zone. However, projected changes to precipitation patterns as a result of climate change have the potential to alter river discharge and nutrient export dynamics. By analyzing the dissolved nutrient and particulate organic matter (POM) content of river water samples over a 3-yr period in the Wailuku River Watershed (WRW) in Hawai‘i Island, HI, USA, this study: (1) quantifies N and P export in the WRW using USGS load estimation (LOADEST) software, (2) models changes to nutrient export dynamics under six future climate scenarios, and (3) examines potential sources of riverine nutrient input through stable isotope analyses of nitrate (NO3-). Results indicate that dissolved organic N (DON) and P (DOP) yields exceeded those of dissolved inorganic N (DIN) and P (DIP). However, complex temporal export patterns in dissolved P forms resulted in periods when DIP exceeded DOP. Annual nutrient export stoichiometry indicated P-limitation throughout the study period, though high contributions of DOP to P-pools lowered mean (±1 SD) annual TDN:TDP (49.1 ± 34.5) relative to DIN:DIP (72.1 ± 64.3). Yields of most nutrient forms were greater during the wet (November - April) season than the dry season (May - October), though mean DIP yields were greater in the dry season. Stormflow-driven export of POM contributed 56.6% and 38.6% to annual watershed yields (kg km-2 yr-1) of total N (82.4 ± 49.2) and total P (4.7 ± 4.9), though the timing and magnitude of stormflow nutrient pulses were highly variable across years. Under future climate scenarios, maximum changes to total N (+27.7 ± 2.7%) and total P (+24.6 ± 0.6%) annual yields occurred as modeled changes to river discharge were allocated to stormflow conditions. While modeled DIN, DON, and DIP yields displayed little variation across climate scenarios, maximum changes to DOP yields (+37.1 ± 19.2%) occurred as discharge changes were allocated to baseflow conditions. Mixing models of δ15N and δ18O-NO3- indicated that soil and groundwater are the predominant sources of riverine NO3-, though sewage and/or manure may also contribute. Overall, this study suggests that climate change may impact N and P export dynamics differently in the WRW, and these changes could impact downstream food webs and ecosystems by adding to the existing seasonal and interannual variability in nutrient export patterns.
Investigating drivers of coastal flooding to enhance the resiliency of loko iʻa along the Hilo Hanakahi coastline, Hawaiʻi
(University of Hawaii at Hilo, 2024-12) Ninomoto, Brianna K.; Burns, John H.; Tropical Conservation Biology & Environmental Science
Coastal ecosystem environments are undergoing stresses due to climate change, particularly in Hawaiʻi. Loko iʻa, traditional Hawaiian fishponds, require a balance of ocean and freshwater to sustain the ecosystem that lives within. With an increase in sea level, these sites become susceptible to higher water levels, salinity, and the introduction of invasive species. This study examines the environmental drivers of the water level variability experienced within the loko iʻa along the Keaukaha coastline during the summer 2023 and winter 2023-24 King Tide events. Given that Hawaii island only has two tidal stations for nearly 290 miles of coastline, water levels recorded by in-situ sensors were compared to the National Oceanic and Atmospheric Administration (NOAA) Hilo tide station to evaluate the accuracy of NOAA predictions in reflecting local conditions. Environmental variables like rainfall, wave height, wave period and direction, wind speed and direction, and water and air temperature were analyzed to determine their influence on the water level departures between the loko iʻa and NOAA. Results revealed that water levels measured at most loko iʻa were double or more than NOAA predicted values. In the summer, water levels departures were influenced by wave height (0.44%) and water temperature (0.89%), while in the winter, departures were influenced by wave height (2.27%) and by wave period (0.40%) and wind speed (0.35%). Wave action variables emerged as the dominant environmental factor influencing the loko iʻa water levels. This community-based research provides insight into how dynamic the coastlines of Keaukaha are and validates the observations of the loko iʻa kiaʻi, but also provides guidance into other environmental variables to assist in managing their sites for future sea levels.
INTRASPECIFIC VARIATION IN HOME RANGE SIZE, OVERLAP, AND MOVEMENT BEHAVIORS OF ‘IO - THE HAWAIIAN HAWK (BUTEO SOLITARIUS)
(University of Hawaii at Hilo, 2024-05) Durham, Amy; Ostertag, Rebecca; Tropical Conservation Biology & Environmental Science
‘Io (Buteo solitarius) is the only endemic hawk species across the Hawaiian archipelago and their range is restricted to Hawai‘i Island. Their federal delisting in 2020, alongside their cultural and ecological significance, emphasizes the importance of sustained long-term population monitoring efforts. However, existing home range estimates for the species are outdated, and research on their spatial behaviors remains deficient. This study aimed to update ‘io home range estimates while providing insights into their movement strategies and space-use sharing patterns. From June 2022 to October 2023, solar GPS-GSM transmitters tracked 43 ‘io on the east side of Hawai‘i Island. Using continuous-time stochastic process (CTSP) models and an autocorrelated kernel density estimator (ADKE), the estimated median home range size for the population was 616 hectares, which is larger than previous estimates obtained using traditional tracking and analysis methods. Although no significant difference in home range size existed across sex and age groups, it varied based on movement strategy. Birds whose movement patterns remained within a distinct range had smaller home ranges overall than those engaging in an occasional foray or commuting between multiple ranges. Additionally, all individuals within the population shared on average 10% of space, with up to 97% observed between presumed breeding pairs. A high likelihood of pairwise encounters was predicted to occur not only along home range boundaries but also within core areas, indicating a high potential for intraspecies interactions. This study provides new insights into ‘io spatial behaviors and highlights the importance of advanced technology and analytical tools to aid species conservation.
ʻAmakihi kaulana i ka hoʻōla maʻi: Assessing the long-term impacts of chronic infection with avian malaria in Hawai‘i ‘amakihi
(University of Hawaii at Hilo, 2024-05) Stierhoff, Emma; Hart, Patrick; Tropical Conservation Biology & Environmental Science
The introduction of avian malaria (Plasmodium relictum) to Hawai‘i has decimated native forest bird populations, driving many species to extinction, and threatening those that remain. However, one native honeycreeper, the Hawaiʻi ‘amakihi (Chlorodrepanis virens, hereafter referred to as ‘amakihi), has shown resilience against acute infection with avian malaria. ‘Amakihi who survive the acute stage remain chronically infected with low parasitemia levels. Although immediate costs of acute malarial infection have been closely studied, the long-term costs of chronic infection are poorly understood in this species. I assessed the impact of chronic infection on the physiological condition of ‘amakihi near ‘Ᾱinahou Ranch in Hawai‘i Volcanoes National Park. During biweekly banding sessions from May 2022 to August 2023, ‘amakihi were banded, measured for tarsus and wing chord, and weighed, and a blood sample was collected for each bird. Using the blood samples, I measured hematocrit, triglycerides, and reactive oxygen metabolites (ROMs) to assess physiological condition, and I determined disease status (undetermined or positive) using qPCR. There were no detectable differences in hematocrit, triglycerides, nor ROMs based on disease status. Body condition was slightly higher in birds that could be confirmed chronically infected than those that were undetermined, but this difference did not persist when accounting for all infected birds. Although acute infection with avian malaria has been shown to have significant costs, this study suggests that ‘amakihi surviving acute infection may not have negative long-term fitness impacts. These results further demonstrate the resilience ‘amakihi have against avian malaria and set the foundation for future research to determine factors facilitating this resilience and how that knowledge might be applied to protect more threatened honeycreeper populations.
Targeting Infection at the Source: evaluating the efficacy of semiochemical repellent compounds in the management of rapid ʻōhiʻa death-associated ambrosia beetles
(University of Hawaii at Hilo, 2024-05) Mikros, Dan; Hart, Patrick J.; Tropical Conservation Biology & Environmental Science
Rapid ʻōhiʻa death (ROD) is a highly virulent and aggressive fungal disease that has been devastating ʻōhiʻa forests on Hawai‘i Island since the mid 2010s. ʻŌhiʻa (Metrosideros polymorpha) is the dominant keystone tree species in native Hawaiian wet forests and its decimation could lead to an ecological collapse. . Therefore, management strategies for preventing ROD transmission are crucial. Ambrosia beetles have been implicated as the primary dissemination agents of environmental inoculum and have the capacity to directly transmit the pathogens as well. Currently, the only widely endorsed management recommendation is to fell and tarp infected trees, thereby physically isolating beetles and inoculum from the environment. But this is often neither practical nor does it offer a preventative strategy for inoculum production. Alternatively, non-toxic semiochemical repellents, which exploit the beetles’ chemical communication system, have been shown to be effective against similar ambrosia beetle species, and may be useful in regards to ROD. I tested the efficacy of two semiochemical repellents, SPLAT Verb® (10% verbenone) and SPLAT Beetle Guard® (10% verbenone + 10% methyl salicylate) for their ability to reduce beetle attack, colonization, and frass production when applied to felled ROD-Ceratocystis infested ʻōhiʻa wood in order to examine the products’ utility as an alternative post-felling management solution. Verbenone alone displayed the capacity to reduce new beetle gallery formations and frass production, but not beetle emergence. Verbenone + MeSA also exhibited the ability to reduce galleries, more so than verbenone in one of the trials, and reduced beetle emergence and frass production. As beetle attack and frass production are the primary concern to inoculum dissemination, both products show a strong potential for use as an active ROD management treatment. After felling trees, new beetle attacks subsided to near zero across all treatments by week 10 in both trials, suggesting a single application of repellent is suitable to protect target trees for the extent of their host-suitability period post-felling. Semiochemical beetle repellents will play a pivotal role in the multifaceted management approach that is needed to manage the disease, and the findings from this project support the growing body of evidence surrounding their use within the ROD pathosystem. Due to the products’ accessibility and ease of use, they offer a comparatively simple management strategy which can be widely employed by land managers and the general public to reduce infectious material in the environment and restrict ROD transmission.
High-Resolution Satellite Imagery: An Alternative Method for the Detection and Monitoring of Rapid ‘Ōhi‘a Death in Hawai‘i
(University of Hawaii at Hilo, 2024-05) Odachi, Nai'a; Perroy, Ryan; Tropical Conservation Biology & Environmental Science
Rapid ‘Ōhi‘a Death has caused extensive mortality of endemic ‘ōhi‘a (Metrosideros polymorpha) across the Hawaiian Islands. First detected on Hawai‘i Island, the responsible Ceratocystis pathogens have now spread to Kaua‘i, O‘ahu, and Maui. Multiple remote sensing efforts such as RGB aerial imagery, laser spectroscopy, and Digital Mobile Sketch Mapping have been successful in identifying mortality outbreaks, although each method has temporal, spatial, or fiscal limitations. In this thesis I explore the utilization of high-resolution satellite imagery with a spatial resolution of £ 0.5 m for individual symptomatic tree identification for field sampling and laboratory testing of the Ceratocystis pathogen. I also analyze landscape scale annual patterns of mortality across East Hawai‘i and compare my findings to annual helicopter- based Digital Mobile Sketch Mapping (DMSM) surveys. Lastly, I created an object detection model using NV5’s ENVI Deep Learning for suspect tree identification and compared the results to DeepForest object detection using the same datasets for training. Results showed that of the individual suspect trees visited in the field (n = 55), 94.5% were successfully located with imagery. Of the trees located (n = 52) using satellite imagery suspects, 98.1% were correctly identified as ‘ōhi‘a. From the subset sampled (n = 35), 40% resulted in a Ceratocystis lukuohia detection. Annual patterns of mortality were found to be similar between satellite-identified and DMSM survey datasets and showed rapid increases in mortality patterns in initial infection years. Temporal and spatial differences between datasets limit direct comparisons due to the short duration of the red phase that strongly signifies ROD-related mortality. Used jointly, these two datasets provide a comprehensive picture of annual mortality trends across East Hawai‘i. Finally, DeepForest models (F1-score = 0.32 and mAP = 0.73) were significantly better overall compared to ENVI models (F1-score = 0.04 and mAP = 0.017) and were promising for automatically identifying tree mortality in new satellite imagery. These results indicate that high-resolution satellite imagery complements existing remote sensing efforts and can help to create a robust and comprehensive monitoring system. This research documents the utilization of high-resolution satellite imagery for landscape-scale ecological monitoring of forest pathogens in Hawai‘i. These results provide annual mortality trends of Hawai‘i Island and share a pathway for future automated identification of new outbreaks which can be inform land management decisions and be implemented on other islands.
FOREST RESTORATION TECHNIQUES IN A SUB-ALPINE FOREST ON HAWAIʻI ISLAND, KANAKALEONUI, MAUNA KEA.
(University of Hawaii at Hilo, 2023-12) Pigao, Amberly K.; Price, Jonthan P.; Tropical Conservation Biology & Environmental Science
Climate change in Hawaiʻi stands to alter forest succession with native bird populations being threatened by mosquito-borne avian disease, forested corridors may create a path to higher elevation habitats with less disease threat. Areas with an abundance of fog may be key in forest self-regeneration but because many of these areas have turned into degraded grasslands, water capture by trees and subsequent regeneration is not occurring. An enclosed 514 acre (208 ha) area, Kanakaleonui Bird Corridor (KBC), located on the east slope of Mauna Kea, is a unique transition zone from a Tropical Montane Cloud Forest (TMCF) to a colder, drier subalpine forest. We conducted two separate experiments at two elevation zones (a lower site at 2,200 m; 7,150 ft. and an upper site at 2,400 m; 7,900 ft.) to understand how fog water capture may facilitate seedling growth. For the first experiment Acacia koa and Sophora chrysophylla were used as nurse trees to both capture fog and buffer seedlings from high and low temperatures. For the second experiment synthetic fog structures were built along existing fence lines to capture moisture as fog passes through. Experimental plantings involved seedlings of five species: māmane (Sophora chrysophylla) naʻenaʻe (Dubautia arborea), ʻaʻaliʻi (Dodonaea viscosa), pāwale (Rumex giganteus), and ʻāweoweo (Chenopodium oahuense). These were planted under nurse trees, along a fence with 40% and 63% shade cloth, along a fence without shade cloth, and in control plots away from nurse trees and fences. ZENTRA soil moisture probes and HOBO temperature gauges were installed at each experiment. Species survival and growth responses to each treatment were generally higher in fence and nurse designs than in control plots (although survival was significant and growth was not significant). Seedings in the lower site still survived in control plots, but seedlings in the upper site, which is drier, had a high mortality rate in control plots. The results indicate that shade cloth and nurse trees facilitate fog water capture at KBC where fog is frequent. Future restoration efforts can benefit from fog capture strategies to successfully restore native Hawaiian forest.
Signal Interactions Between Native and Introduced Forest Birds of Hawaiʻi Island and Predicting Distance of Signals from Their Energy
(University of Hawaii at Hilo, 2023-12) Hunt, Noah James; Hart, Patrick J.; Tropical Conservation Biology & Environmental Science
Passive acoustic monitoring using autonomous recording units (ARUs) offers uniqueopportunities to investigate both theoretical and applied ecological questions. I used Song Meter SM4s to answer: (1) whether native and introduced birds in Hawaiʻi are dividing acoustic space in time and frequency, and (2) whether wildlife managers can improve their density estimates of bird species by achieving unbiased distance measurements from ARUs. First, using recordings I collected from a diversity of vegetation types, I compared the observed overlap between introduced and native bird vocalizations from what was expected under a null model of 500 vocalization randomizations. I found that overlap did not differ from the null distribution and was unaffected by community composition nor vegetation type, suggesting that introduced birds are not having a strong impact on native forest bird communication. Second, using field recordings collected while observing vocalizing birds, I modeled distances between birds and the ARUs, measured from range finders as a function of the random effects of maximum power level (amplitude) of bird vocalizations, the orientation of the bird to the microphone, and wind and rain levels, with the species and call type as fixed effects. Overall, there was no strong relationship between distance and any of the random effects. However, when modeling within individual call types, I found four call types among four species showing relationships between distance and sound power level, suggesting that while this method has potential for wildlife monitoring, it requires further refinement.
EFFECTS OF CLIMATE CHANGE AND FISHING PRESSURE ON CIGUATERA PREVALENCE IN HAWAIIAN REEF FISHES: IMPLICATIONS TO PUBLIC HEALTH IN A CHANGING CLIMATE
(University of Hawaii at Hilo, 2024-01) Rodriguez, Nikola Deborah; Grabowski, Timothy B.; Tropical Conservation Biology & Environmental Science
Ciguatera fish poisoning (CFP) is caused by consuming reef fishes containing toxins produced by epiphytic dinoflagellates in the genus Gambierdiscus. Changing reefscapes due to climate change and altered reef fish assemblages from overfishing may increase the range of and habitat available to Gambierdiscus spp. while altering how ciguatoxins (CTX) move through coral reef food webs. However, it is not clear how these factors may interact to influence the probability of ciguatoxic fishes and thus the risk of CFP to local communities dependent upon these fisheries. Therefore, the objectives of this study are to 1) evaluate the relationship between a suite of habitat characteristics at multiple spatial scales, including those related to changing temperature regimes and fishing pressure on the probability of fish testing positive for CTX; 2) evaluate the relationship of the same habitat characteristics on the concentration of CTX; and 3) assess the degree to which local fishing communities practices and beliefs that are used to limit risk of CFP agree with the findings of the first two objectives. I evaluated the presence and concentration of ciguatoxins in two common reef fish species: the high-level predator, Peacock Grouper (Cephalopholis argus), hereafter referred to by its Tahitian name – Roi, and a frequently sought-after herbivore, Goldring Bristletooth (Ctenochaetus strigosus), known as Kole in Hawaiian, sampled bi-annually across four sites along west Hawaiʻi Island. For Roi, both the probability of testing positive for CTX and CTX concentration exhibited a positive relationship to length and negative relationship to the number of days under a coral bleaching alert and fishing pressure. For Kole, the probability of testing positive for CTX was negatively related to length, the number of coral bleaching alert days, effluent, fishing pressure. The concentration of CTX in Kole was also negatively related to length, effluent, fishing pressure, and mean percent live coral cover. Most anglers and spearfishers are unlikely to restrict their fishing activity in response to CFP risk, instead tending to avoid species, size classes, or fishing areas perceived as high risk. However, my results suggest that fish behaviors are likely to become less effective as changing temperature regimes, loss of live coral cover, and human fishing pressure may be altering the prevalence and distribution of ciguatoxic fishes. The results of the study will allow resource managers to better communicate the risk of CFP to anglers and spearfishers so they can mitigate the dangers of ciguatera fish poisoning in a fast-changing climate.

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