ScholarSpace

ScholarSpace is an open-access, digital institutional repository for the University of Hawaiʻi at Mānoa community. ScholarSpace stores the intellectual works and unique collections of the UH at Mānoa academic community and also provides a permanent web location for those accessing these resources.

Request Access to Upload

Photo by @inspiredimages

Communities in ScholarSpace

Select a community to browse its collections.

Recent Submissions

From canopy to seedling: Exploring the potential role of nurse plants on Santa Fé Island, Galápagos
(2025-08) Westhelle, Stephanie
Island endemic species are highly susceptible to extinction by invasive species, which severely impact native plants and ecosystems. For over a century, feral goats (Capra hircus) on Santa Fé Island confined Scalesia helleri to cliff-sides and led to substantial decreases in Bursera graveolens juveniles prior to goat eradication in the 1970s. Ongoing restoration studies indicate that native species are slowly recovering, with anecdotal evidence suggesting that a nurse plant syndrome may be facilitating recovery of some native plants. Nurse plant syndrome facilitation occurs when an adult nurse plant creates a beneficial microhabitat that aids seedling survival and establishment, with little to no negative impact on the adult plant. To evaluate whether Opuntia echios, Bursera graveolens, and Scalesia helleri act as potential nurse plants on Santa Fé Island, data were collected on adult species, GPS coordinates, height, basal area, and canopy cover; juvenile species and height; and the distance between each juvenile and its associated adult. Results revealed a significant positive association between adult Opuntia and conspecific juveniles, while adult Bursera exhibited a significant positive association with heterospecific juveniles. Furthermore, Scalesia juveniles were found to be significantly closer to adults of any species than Opuntia juveniles. These results support nurse plant syndrome in Santa Fé’s recovery and may inform restoration efforts on other islands.
Assessing the impact of mangrove bark beetles (Coccotrypes rhizophorae) on red mangrove (Rhizophora mangle) propagule buoyancy and germination
(2025-08) Mitchell, Lana
Throughout the coastal tropics, mangroves are a widely beneficial tree because they contribute to the maintenance of coastal areas by protecting shorelines against erosion, including wildlife and habitats within these intertidal areas. In the Galápagos, there are four native mangrove species, with Rhizophora mangle (red mangrove) being the most prominent. Rhizophora mangle can most commonly be found on the islands of Santa Cruz, Fernandina and Isabela. Although mangroves have survived in the Galápagos, the Coccotrypes rhizophorae beetle impacts propagule (mangrove seedling) state (i.e. horizontal, vertical and sunk) and survival. C. rhizophorae was first detected in 1985 and was found to infest R. mangle propagules by boring into and causing decay from the inside out, proving to be fatal for some propagules. Because of this observation, this study aims to determine the level of damage caused by C. rhizophorae onto R. mangle propagules, its impact on propagule buoyancy (~2 weeks), and initial growth (~3 weeks) periods. Currently, the direct impacts of C. rhizophorae on R. mangle remains unknown. Additionally, taking into account that R. mangle propagules rely on nutrients for growth, the impacts of nitrogen, phosphorus and potassium-rich fertilizer were assessed on both C. rhizophorae-infested and non-infested R. mangle propagules. This study found that C. rhizophorae infestations led to shorter flotation times in propagules. Additionally, it was found that fertilizer did not have any impact on propagule growth. Future research could implement smaller doses, possibly giving way to new findings on propagules exposed to controlled fertilizer treatments. This study aims to provide researchers and environmentalists with a better understanding on R. mangle survival and endurance against C. rhizophorae. By extension, this can allow environmental collaborators to discover new solutions to maintaining mangrove forests in the Galápagos, aiding in the protection of the archipelago’s unique biodiversity.
Assessing the impact of the invasive bark beetle Coccotrypes rhizophorae on Rhizophorae mangle propagule growth
(2025-08) Lambert, Jackson
Over the next century, global coastlines are projected to undergo profound transformations driven by accelerating climate change, including sea level rise, increased storm intensity, and shifting precipitation patterns. In this rapidly changing seascape, mangrove forests are an ecosystem intermediary. These intertidal ecosystems not only stabilize shorelines and reduce coastal erosion, but also create essential habitats for wildlife, and support fisheries vital to coastal livelihoods. Invasive species pose a major threat to mangrove trees and impact their role as keystone species in their environments. Their ecosystem integrity and ability to reproduce will become increasingly important, yet their survival depends on proactive conservation, adaptive management, and a deeper understanding of their ecological interactions between species. There is a species of beetle that has established itself in the Galápagos within the last 40 years, and its ecological effects are not yet understood. This project investigates the complex relationship between the invasive bark beetle Coccotrypes rhizophorae and Rhizophora mangle mangrove trees in the Galapágos Islands by focusing specifically on how varying levels of beetle infestation influence the development of mangrove propagules. It may be that beetle feeding changes mangrove seedling survival chances through compensatory growth responses. Coastal mangrove ecosystems are highly competitive, where the timing of propagule growth can be the difference between survival and death. By understanding these dynamics, this study aims to inform conservation strategies that protect these critical coastal systems and assess the impacts of the invasive bark beetle C. rhizophorae on juvenile red mangroves. The findings will contribute to a more nuanced understanding of invasive insect- native plant interactions in mangrove ecosystems.
Order up! Serving marine invasives on a plate: Comparing invasive species richness and percent cover at sites with differing maritime pressures around Santa Cruz Island, Galápagos
(2025-08) Kahrobaie, Cienna
Marine invasive species impact the biodiversity of island ecosystems, leading to negative effects on native species diversity and their environment. One pathway that facilitates this disruption is the unintentional transport of non-native species through human activities. Biofouling on boats accelerates the speed of dispersal and natural range of many marine invasives. Biofouling ships travelling from international waters can facilitate the initial colonization of invasive species while secondary spread can occur when smaller boats travel along the coast, picking up invaders at colonized ports. Native fouling communities can be impacted by these visiting biofouled boats. Can you insert a sentnece here that addresses the knowledge gap? That will set up your next sentence: To address this knowledge gap, settlement plates at docks in the Galápagos Marine Reserve were deployed for 2-3 months and analyzed for xyz with photoQuad software. Results indicated increased invasive species richness at sites with more boat traffic, but consistent measures of invasive species percent cover between sites. Native species richness was also consistent between sites. Docks also exhibited significant differences in community composition, consisting of a mix of strong and weak invasive competitors among sites. Implications of my results are discussed in the context of marine invader detection protocols and monitoring of sites with high maritime traffic or strong competitor presences. The relationship between marine invasive species and maritime traffic can help indicate which docks are at a higher risk to invasions, allowing managers to closely monitor these sites.
Desiccation resistance and survivorship of Caulerpa racemosa in Galápagos
(2025-08) Geise, Sydney
Algae are important components of marine ecosystems as they are primary producers and support the aquatic food chain. Invasive species impact ecosystem dynamics by outcompeting native organisms for resources, destroying habitats. These impacts can ultimately lead to a decline in an area's biodiversity. Caulerpa racemosa is a cryptogenic (species with an unknown origin) alga displaying invasive characteristics around the Galápagos Marine Reserve (GMR). This alga was first reported around Isabela Island and has since been observed in abundance near Fernandina and Santa Cruz islands, raising concerns about its impact on native reefs. Fragmentation is a key mechanism of spread in Caulerpa species, and boat anchors may mechanically fragment and transport C. racemosa. While fragmentation and desiccation tolerance are well studied in C. taxifolia, they remain understudied in C. racemosa. This study investigates the desiccation resistance of C. racemosa in Tortuga Bay, Santa Cruz Island, Galápagos, to understand the capabilities of fragments to travel via entanglement with boat anchors between bays and islands. Samples were collected and desiccated for up to three days, then measured daily to assess survivorship and growth. Here we show that desiccation time significantly impacts the growth and survivorship of C. racemosa. These results indicate that as desiccation time increases, growth and survivorship decrease. While this is the first time desiccation impacts of C. racemosa has been studied in the GMR, similar studies on C. taxifolia show these trends. We observed a significant difference in survivorship and mass loss between 0 or 12 hour desiccated fragments and 24 to 72 hour fragments. Our results suggest a potential for anchor spread of C. racemosa for short boat trips around the GMR. These results inform management and environmental boating regulations around the GMR. Understanding the desiccation limit and geographic spread potential is crucial for protecting these unique marine ecosystems.
Topographic heterogeneity and woody plant seedlings on Santa Fé Island, Galápagos
(2025-08) Herron, Riley
In arid and disturbance-prone ecosystems like the Galápagos Islands, understanding seedling establishment at the microsite level is critical for effective conservation. Island systems are resource-limited and host highly endemic vegetation due to isolation, making them especially vulnerable to disturbances such as invasive species. Santa Fé Island, Galápagos, experienced centuries of habitat degradation following the introduction of feral goats (Capra hircus), leading to biodiversity loss and shifts in the abundance and distribution of dominant woody species, including Scalesia helleri, Bursera graveolens, and Opuntia echios var. barringtonensis. Although the goats have since been eradicated, vegetation recovery is ongoing, underscoring the global need to understand post-disturbance regeneration processes. Topographic heterogeneity plays a key role in shaping microtopography - defined as small-scale (<1 m) terrain variation - which in turn influences abiotic factors critical for seedling establishment. This study (1) describes microtopographic features on Santa Fé Island; (2) identifies relationships between abiotic variables and topography; and (3) compares environmental conditions associated with seedlings of the three dominant woody species. Measurements of soil depth, volumetric water content (VWC), rugosity, canopy cover, and elevation were collected at seedlings of each of the species across nine locations using GPS, soil probes, and image analysis. Results indicate Opuntia echios seedlings were associated with the lowest canopy cover, Scalesia helleri with the lowest soil VWC and highest canopy cover, and Bursera graveolens with higher soil VWC. Soil depth differed significantly among species, and principal component analysis identified soil moisture, depth, and elevation as the strongest contributors to variation in seedling microsite conditions. These patterns suggest species-specific spatial associations likely shaped by dispersal strategies and regeneration niches. Findings underscore the importance of topographic heterogeneity impacts on seedling establishment and understanding plant community recovery to inform restoration planning following the eradication of feral ungulates on degraded arid islands globally.
Effects of an ecological replacement herbivore on cactus recruitment on an arid island
(2025-08) Aviles, Raquel
Recognized for their high biodiversity and endemism, island ecosystems are particularly vulnerable to anthropogenic factors such as invasive species and extinction of endemic keystone species. The Galápagos Islands, with some of the highest endemism rates in the world, are an important case study of these challenges. Native herbivores are increasingly at risk of extinction worldwide, leading to the loss of vital ecological functions such as seed dispersal and nutrient cycling. On Santa Fé Island, human-driven extinction of the giant tortoise is a prime example of this, while the introduction of feral goats (Capra hircus) further degraded island plant communities. Together, these changes altered the distribution and regeneration of endemic species like Opuntia echios var. barringtonensis, a dominant species and keystone resource for native herbivores. Recent conservation efforts have eradicated goats and reintroduced a related tortoise species, Chelonoidis hoodensis, to restore ecological functions and support ecosystem recovery. This study aimed to examine the role of C. hoodensis introduction in influencing the distribution and density of O. echios seedlings and saplings on Santa Fé Island that is recovering from more than a century of heavy feral goat degradation. I hypothesized that the presence of C. hoodensis would positively correlate with higher densities of O. echios seedlings and saplings; I hypothesize this because giant tortoises were historically one of the primary seed dispersers of O. echios. To examine the relationship between tortoise activity and O. echios demographics on Santa Fé Island, nine 50 × 50 m plots were established across varying tortoise activity zones and subdivided into 25 10 × 10 m subplots. Adult cactus height and DBH were recorded in large plots, while seedling and sapling densities and tortoise activity (via direct observation and scat) were documented in smaller subplots. Higher tortoise activity correlated with higher seedling density, suggesting a positive effect of ecological replacements on Opuntia regeneration. Continued monitoring is needed to assess long-term vegetation impacts given that the island vegetation is still recovering from feral goats and tortoises are still expanding. Ecological replacements, like the introduction of C. hoodensis on Santa Fé Island, offer a promising strategy for restoring lost functions in degraded ecosystems.
Below the surface: Unveiling submarine groundwater discharge at Playa de la Estación
(2024-08) Thomas, Aaliyah
Submarine groundwater discharge (SGD) is the outflow of an aquifer into the coastal ocean and is affected by oceanic, geologic, and anthropogenic processes. The basal aquifer of Santa Cruz Island, Galápagos, Ecuador has been over-pumped and poorly managed, resulting in saltwater intrusion, a brackish aquifer, and contamination of recreational sites such as Las Ninfas Lagoon. Further exploitation and contamination of the aquifer may harm coastal ecosystems and increase the potential for invasive species to establish and flourish. This study identifies the salinity gradient associated with SGD at Playa de la Estación, one of the few beach accesses on Santa Cruz Island. We consistently found low salinity near the shoreline ranging from 8-18 ppt. Although low salinity output was consistently observed, rainfall varied over the course of the study and was ruled out as a potential cause for the low salinity measured. There appears to be three main points of SGD seepage that also consistently had the lowest dissolved oxygen content averaging at 4.2 (mg/L) while the overall average was approximately 7.8 (mg/L). The island was thought to be waterless and lacking SGD, thus the existence and impacts of this phenomenon have been historically overlooked and underestimated. Uncontaminated SGD is beneficial and a preferred environment for native marine life in other regions of the Pacific Ocean, and anthropogenic alteration and contamination of the aquifer can change an ecosystem drastically. By identifying SGD seepage points, the water quality of the aquifer can be better understood and managed. Due to its scarcity, the groundwater of Santa Cruz must be studied in terms of aquifer health and SGD. Because SGD is seeping into the Galapagos Marine Reserve, further investigation can provide valuable foresight to those responsible for its protection.
Assessing the impacts of Caulerpa racemosa on sand dwelling benthic invertebrates in the Galápagos
(2024-08) Velasquez, Emily
The introduction of invasive marine algae has resulted in significant losses of native benthic fauna and incurred substantial costs for monitoring and management efforts. Isolated volcanic archipelagos, such as the Galápagos, are especially vulnerable to the introduction of nonnative species due to high levels of tourism, marine traffic, and ENSO events. Currently, the cryptogenic alga Caulerpa racemosa exhibits invasive behavior and rapid spread, posing a severe threat to the native ecosystems. This study examines the impact of Caulerpa racemosa on benthic invertebrate populations in the Galápagos Islands' shallow sandy habitats. Selected sampling locations included Cerro Dragon, Playa Estación, Tortuga Bay, Garrapatero, Concha Perla, and Venecia. Each site was analyzed for invertebrate diversity, richness, and abundance in areas with and without C. racemosa with the use of transects to collect sediment samples and percent cover quadrat images. Sediment samples were sieved and stored in preservatives, and the number of invertebrates identified to class were counted using microscopy. The dry weights of each sediment sample were taken to calculate diversity per gram. Kruskal-Wallis and Pairwise Wilcoxon tests was used to assess intergroup differences. Results showed no significant correlation between C. racemosa presence and invertebrate diversity, richness, or abundance. Findings suggest that the percent cover of C. racemosa was not correlated to the benthic invertebrate diversity of sampled locations as hypothesized. Inter-site differences in species richness and abundance were evident. The variability in results highlights the need for further monitoring to understand the ecological impacts of invasive algae and inform management strategies.
Evaluating the plant composition and abundance of Santa Fé, Galápagos, 50 years after the eradication of feral goats
(2024-08) Suzuki, Colby
Invasive species detrimentally impact island ecosystems, particularly native species that evolved in their absence. From the early 1800’s to 1971, feral goats heavily grazed on the native vegetation of Santa Fé Island, Galápagos. Feral goats were eradicated from Santa Fé in 1971, allowing native plant populations to begin to recover. However, the long term effects of feral goat eradication from this island are not well understood, which is particularly important in the context of the recovery of slow-growing arboreal plants like Opuntia echios and Bursera graveolens. This project assessed the recovery of woody plant species on Santa Fé 50 years after the eradication of feral goats, an building on vegetation monitoring previously done from 1971 to 2003. Since the last assessments in 2003, the slower-growing woody species such as Opuntia echios and Bursera graveolens did not increase notably in density over time, but their population demographies shifted to a higher concentration of younger individuals. There was also a marked increase in the density of fast-growing woody species such as Cordia lutea, Encelia hispida, and Lantana peduncularis. Overall, results for both slow- and fast-growing plants demonstrate that this system is still recovering from feral goat removal some 50 years later. This vegetation assessment provides increased clarity on how plant populations in island ecosystems recover over long time periods after the eradication of an invasive ungulate.