Galápagos Undergraduate Research Program

Permanent URI for this collectionhttps://hdl.handle.net/10125/111197

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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.
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.
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.
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.
Modeling the habitat suitability of Caulerpa sp. across the Galápagos Islands
(2024-08) Precourt, MeiLin
Globally, the number of invasive marine species has increased in recent years, posing a substantial risk both ecologically and economically. Throughout the Galápagos islands, two species of the green macroalgae Caulerpa, C. chemnitzia and C. racemosa, exhibit invasive tendencies, which may threaten native biodiversity. Characterized by fast growing species that reproduce asexually via fragmentation, the genus Caulerpa is known for successful invasion and establishment of populations outside of their natural range. We hypothesized that Caulerpa sp. are suitable for a broad geographic range in the Galápagos, with the potential to disperse beyond their current known ranges. Using R packages “terra” and “sdm”, we utilized an array of geospatial and presence/absence data to create a habitat suitability model for both species individually, and then ran a comparison of the two models. Findings indicate that the occurrence for both species is highly suitable in locations far beyond their current known range. For C. chemnitzia, the highest predictor for habitat suitability was sea surface temperature (AUC: 51.4%), and for C. racemosa was chlorophyll concentration (AUC: 44.5%). For both species, we also found that chlorophyll concentration was a high predictor of the model’s likelihood of occurrence (AUC: >35%). In addition, proximity to human population was found to be a strong predictor for C. racemosa suitability (AUC: >40%) which suggests anthropogenic activity is correlated with occurrence. Although model variable importance differed between species, results indicate that both species are highly suitable to occupy the same niche. This modeling approach serves as a cost-effective and efficient first step for prioritizing management efforts.
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.
Fly or die: Environmental conditions, not trap design, influence Philornis downsi capture rate in the Galapagos
(2024-08) Miranda, Rebecca
The avian vampire fly, Philornis downsi, is one of the greatest threats to the landbirds of the Galapagos. In its larval stages P. downsi parasitizes on many of the archipelago’s endemic and native birds, resulting in nestling death or lifelong deformities. Because P. downsi mating habits and biology are not well understood, live trapping wild flies is integral to growing a lab population. Currently, McPhail and tephri traps are used to capture flies, however, they are often able to escape. This study assessed the effectiveness of four trap designs over a two month period in the summer of 2024. We found that an insignificant numberof flies escaped from traps, and different trap types did not affect P. downsi daily catch rates. Additionally, an alternative trap that included an extended entrance aimed to minimize the number of escapees had lower catch rates compared to traps currently in use. Catch rates were positively correlated with temperatures and negatively correlated with humidity. Our results suggest the optimal strategy for live capture of P. downsi should focus on increasing the quantity of traps during periods of increased temperature and decreased humidity. Using McPhail and Tephri traps with mesh lining for capture of live vampire flies will further our scientific understanding of this threat.
Assessing plant diversity after giant tortoise reintroduction on Santa Fé Island, Galápagos
(2024-08) Kahokuloa, Matthew
Invasive species pose significant threats to island ecosystems, often leading to the loss of native biodiversity and altered ecosystem functions. On Santa Fé Island (SFI) in the Galápagos, the eradication of invasive goats has been followed by the introduction of the giant tortoise species Chelonoidis hoodensis from Española Island as an ecological replacement for the extinct native tortoise species. This study investigated the impact of this introduction on plant diversity since giant tortoise reintroduction in 2015. We established 20 permanent quadrats (PQs) along gradients of tortoise activity on SFI and conducted vegetation surveys using the line-intercept method, along with observations of tortoise presence and scat. We used Shannon's diversity index to measure plant diversity and performed non-metric multidimensional scaling (NMDS) with Bray-Curtis dissimilarity to compare plant diversity. An activity index was created from tortoise and scat counts to estimate tortoise activity in each plot. Our results, revealed no significant correlation between tortoise activity and plant diversity (r = 0.0406, p = 0.9). Our findings suggest that the introduction of C. hoodensis has not yet significantly influenced plant diversity on SFI. The lack of observed impact could be due to the relatively short timescale since introduction, the predominance of juvenile tortoises, and the prior recovery of vegetation post-goat eradication. This study highlights the complexity of ecological replacement strategies and underscores the need for long-term monitoring and adaptive management to fully understand and enhance their effectiveness in conservation efforts.
Exploring the impact of reintroduced Chelonoidis hoodensis on Opuntia echios on Santa Fé Island, Galápagos
(2024-08) Godbehere, Ashlyn
The ecological balance of Santa Fé Island, Galápagos, is determined, to a large degree, by the interplay between introduced giant tortoises (Chelonoidis hoodensis) and the native arboreal cactus (Opuntia echios var. barringtonensis). Historically heavily impacted by invasive feral goats, the island has undergone significant ecological restoration. Notably, the original giant tortoise population on Santa Fé Island went extinct, leading to the introduction of an ecologically similar species, C. hoodensis, in 2017. This study aimed to elucidate the impact of reintroduced tortoises on O. echios populations, recognizing their pivotal roles as ecosystem engineers and keystone species. The locations and sizes of tortoise carapaces encountered during the study indicate that since their release, they have continued to disperse throughout the island. Prior to this study, accurately distinguishing between Santa Fé land iguana and tortoise scat for density measurements was challenging due to limited field ID information. Through this research, new methodologies were developed and applied that facilitate accurate field identification of tortoise scat, thereby enhancing our ability to measure population densities effectively. These data suggest that the reintroduction of giant tortoises is likely to aid in the restoration of Santa Fé Island by increasing the dispersal of O. echios.
Understanding the developmental dynamics and temperature sensitivity of avian vampire fly (Philornis downsi) eggs: A dual-study approach
(2024-08) Buyukacar, Nicole
The Galápagos Islands, known for their unique and diverse ecosystems, face a significant threat from the invasive parasitic fly, Philornis downsi, which endangers 17 endemic passerine bird species. The introduction of P. downsi, likely via produce cargo from Ecuador, has resulted in substantial reductions in nesting success across the archipelago, prompting urgent research for effective control methods. This study aims to enhance the lab-rearing efficiency of P. downsi by investigating the effects of temperature on egg development and creating a developmental reference. Eggs were collected and subjected to various temperatures (20, 25, 32, and 36 °C) to monitor hatching times and developmental stages through manual and automatic imaging techniques. Results indicate that lower temperatures significantly prolong hatch times, with the 20 °C group exhibiting the longest mean hatch time of 195.65 hours. In turn, higher temperatures accelerated development, with the 32 °C group showing the shortest mean hatch time of 43.8 hours. Four main developmental phases were identified, contributing to a preliminary reference for future research. These findings support the hypothesis that higher temperatures correlate with faster egg development and suggest that temperature manipulation could improve captive rearing outcomes. Enhanced understanding of P. downsi egg development will aid in refining control strategies, crucial for protecting the Galápagos’ endemic avifauna. Further research should explore additional temperature ranges and their impact on the fitness and reproductive success of lab-reared P. downsi.

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