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.

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Vitamin B12 limitation of trace metal efficiency in a Southern Ocean diatom
(University of Hawaiʻi at Mānoa, 2026) Soriano, Micah; Hawco, Nicholas; Oceanography; Global Environmental Science
High-nutrient, low-chlorophyll regions, such as the Southern Ocean, are primarily limited by iron, and more recently evident, vitamin B12. This cobalt-containing trace metal is a cofactor involved in various cellular processes, but is not synthesized by phytoplankton. Consequently, its availability can significantly affect phytoplankton growth and negatively impact primary productivity. While previous studies have investigated the interactions between Vitamin B12 and other biogeochemical parameters, a study solely focused on the relationship between Vitamin B12 and zinc remains lacking. We conducted inoculation experiments using Fragilariopsis cylindrus CCMP1102, a cold-water-adapted diatom. Cultures were grown in separate media with and without Vitamin B12, at varying zinc concentrations. Vitamin B12 presence significantly enhanced the growth rates of Fragilariopsis cylindrus, with B12-replete cultures exhibiting up to 2.2x faster growth than B12-limited treatments at elevated zinc concentrations. Trace metal quotas normalized to phosphorus were generally higher under B12 limitation, indicating reduced metal use efficiency when the vitamin was scarce. Additionally. B12 dramatically improved trace metal net use efficiency (NUE), notably increasing iron efficiency by up to 15.2x and zinc efficiency by as much as 60x.
Dissolution dynamics and nutrient release from rice husks in sea water: Effects of surface coatings and biological activity
(University of Hawaiʻi at Mānoa, 2026) Velasquez, Emily; Björkman, Karin; Grabowski, Eric; Karl, David; Oceanography; Global Environmental Science
Rice husks are a globally abundant agricultural byproduct with high concentrations of amorphous biogenic silica whose dissolution behavior in seawater remains poorly characterized, limiting understanding of their potential as a controlled silica source, their nutrient release dynamics, and their suitability for ocean-based phytoplankton enrichment and carbon export applications. Two laboratory incubation experiments using seawater from Station ALOHA examined how surface coating chemistry and biological activity govern silica and phosphate release. In filtered seawater, bare husks dissolved approximately 30% faster than lignin-iron-coated husks during the initial linear phase (0.646 ± 0.121 and 0.496 ± 0.034 μmol husk-1 d-1, respectively), following surface-controlled kinetics over the first ~17 days, with release scaling linearly with husk mass. Mass balance confirmed that dissolved Si measured in solution plus particulate Si remaining in the leached husk accounted for ~95% of the theoretical Si yield assuming pure opaline silica. In unfiltered surface seawater, husk-derived Si was rapidly incorporated into diatom frustules rather than accumulating in solution, with chlorophyll a peaking near day 35 before declining, and epifluorescence microscopy suggesting community succession toward diazotrophic taxa. These results establish that rice husks are a chemically consistent, biologically responsive Si source, and that engineering a coating that co-delivers Si, Fe, and P in proportions tuned to the stoichiometric demands of each stage of the ecological cascade represents the central design challenge and most promising direction for future work.
Community-informed flood risk modeling for climate adaptation in Waihe'e - Waiehu, Maui
(University of Hawaiʻi at Mānoa, 2026) McGreevy, Flannery; Shuler, Christopher; Oceanography; Global Environmental Science
Flash flooding over the decades has repeatedly affected the community of Waiheʻe–Waiehu, Maui, damaging homes, farms, and periodically closing the area’s only access road. To improve community resilience amid increasing flood risks, this study developed high-resolution (10 m) flood maps for Waiheʻe–Waiehu by integrating local knowledge with physics-based modeling techniques. To accomplish this, Gridded Surface Subsurface Hydrological Analysis (GSSHA) models were developed in the Kalepa Gulch and Waiehu stream watersheds. Publicly available data, including a digital elevation model, a land use map, Manning's roughness coefficients, and precipitation data, were used to produce 2D flood models for a hypothetical 100-year precipitation event and a 2018 flood event. High-resolution physics-based GSSHA flood models show greater inundation under a hypothetical 100-year rainfall event than a 1 in 5-year storm that occurred on February 18, 2018. Results help identify flood-prone areas that are not fully represented in FEMA hazard maps, and demonstrate that community input improves the interpretation and evaluation of modeled flood patterns in Waiheʻe–Waiehu. Conversations with community members also helped identify areas of model overprediction and underprediction, resulting in a modeling project rooted in community-informed practices, strengthening the accuracy of the model itself and bridging gaps between science and the local community directly impacted.
Investigating the impacts of herbicides and ditch return flows on recreational stream water quality in East Maui
(University of Hawaiʻi at Mānoa, 2026) McCarter, Autumn; Shuler, Christopher; Oceanography; Global Environmental Science
Streams on Maui serve as vital resources for cultural and recreational activities, the tourism economy, and supplying water to the County's drinking water plant. However, companies in East Maui have been spraying herbicides in irrigation ditches and along roads as part of routine maintenance, prompting heightened community concerns that runoff may contaminate local streams. The Haʻikū Community Association (HCA) frequently monitors select streams for nutrient and bacterial contamination, but has been unable to test for herbicides. Therefore, this research aims to evaluate the HCA’s current monitoring sites, as well as several additional streams and ditches, to provide spatial data on contamination to complement their existing time series. This is intended to alert the community to potential human health risks in their local streams and to identify any relationship between contamination and streamflow that may help provide future safety warnings.
Effects of artificial light on behavior of Hawaiʻi Deep 7 bottomfish species
(University of Hawaiʻi at Mānoa, 2026) Martin, Malia; Drazen, Jeffrey; Oceanography; Global Environmental Science
Fishing is vital to Moananuiākea communities, cultures and economies. Deepwater bottomfish, living between 100 and 400 meters, are a key target for both commercial and recreational fishers. This group of fishes are known as the ‘Deep 7’, are highly valued and constitute the second largest commercial fishery in Hawaiʻi. Key to their sustainable use is regular stock assessment. Researchers in the tropical Indo-Pacific have used baited cameras to survey their populations non-invasively but typical camera systems become ambient-light limited at depths of 250m, shallower than the maximum range of the stock. This limits effective surveys and thus sustainable management. A way forward is to use artificial light to enhance visibility in deep deployments but effects on the fishes are unknown. We used different wavelengths of light (Blue, Red, Green, Amber) on 39 baited camera deployments to evaluate how lights affect Deep 7 behavior and visibility. On average, abundance of fishes declines over time in Green and Blue wavelengths while Red and Amber reflect a more stable abundance through the duration of the videos. The most avoidance reactions were observed under Blue light, but it also had the most species observed. Conversely, Red light had the least avoidance reactions but only had three species observed. Fishes could be seen at further distances of 5m-6m under Blue and Green light. Species could be identified between 2m-4m under Red light but identifications were only at high taxonomic levels such as family or class further away, as far as 6m. Amber lights had species to class level identifications from 2m-4m. The results have proven that artificial lights expand the range of study to deeper waters. However, each wavelength of light used had tradeoffs. For example, Blue light has a 6 greater range of visibility and will see more fish but the fish negatively react to the light so their abundance may be underestimated.
Dissolved zinc distribution: Trace nutrients in the Southern Ocean and carbon cycle implications
(University of Hawaiʻi at Mānoa, 2026) Jessen, Ema; Hawco, Nicholas; Oceanography; Global Environmental Science
The Southern Ocean around Antarctica is a critical contributor to global carbon sequestration and biogeochemical cycling. Rapid atmospheric warming may alter seawater nutrient composition due to ice melt, with consequences for phytoplankton growth and productivity. Zinc is an important cofactor in the metalloenzyme carbonic anhydrase, key for the carbon concentration mechanism used in photosynthetic reactions. Many Southern Ocean diatom species utilize up to 5-15 times as much zinc as diatoms in other areas, underscoring Zn’s role as a relevant micronutrient in this region. Measurements of dissolved zinc (dZn) distribution and comparison with other macronutrient distributions provides insight into the physical and biological processes taking place in the Amundsen Sea. This study determined dZn via electrochemical voltammetry for GEOTRACES GP17 samples collected from the Amundsen Sea. dZn concentrations were relatively consistent throughout most stations, with a slight depletion near the Amundsen Sea Polynya (ASP) and in stations along the Dotson-Getz trough. Increased surface and subsurface coastal dZn near the ice melt of the Dotson and Getz ice sheets suggests an external input of dZn. Given that silicate is an important building block in diatom external cell walls, silicate distribution often correlates with dZn. However, near the ASP, the elevated dZn measurements were consistent with other macronutrient profiles but diverged from silicate, pointing towards alternative phytoplankton species growth. dZn availability affects the rate of carbon acquisition and therefore of photosynthesis. Knowledge of trace metal nutrient distributions contributes to improved predictions of how future carbon drawdown and phytoplankton dynamics may change with global warming.
Climate communication framing: Not all climate messages are equal
(University of Hawaiʻi at Mānoa, 2026) Hobert, Ethan; Winter, Jenifer; Oceanography; Global Environmental Science
Public concern about climate change remains inconsistent despite growing scientific consensus on the urgency for action. While research in climate communication has identified message framing as an important influence on public engagement, questions remain about which specific frames most effectively motivate behavioral change. Drawing on the Theory of Planned Behavior, this study investigates the way in which different climate change message frames affect individuals' behavioral intentions. A randomized pre-post survey experiment exposed participants to one of five framing conditions, with behavioral intentions measured before and after frame exposure using validated 7-point Likert-scale items across six pro-environmental behaviors. Results indicate that all four analyzable frames produced significant pre-to-post increases in behavioral intention, with the Moral Responsibility (Δ=+0.41, d=0.82) and Environmental frames (Δ=+0.45, d=0.55) producing the largest and most consistent shifts. The Economic frame yielded the weakest response (Δ=+0.24, p=0.059), and the Catastrophic Disaster condition was excluded from analysis due to insufficient sample size (n=4). Behavior-level analyses revealed that the intention to share climate resources shifted consistently across all frames, while community-oriented behaviors responded selectively to values-based and ecological framing. Secondary analyses found that female participants demonstrated significantly greater frame-induced change than male participants (H=5.33, p=0.021). By identifying which frames are most effective at promoting specific pro-climate behaviors, this research contributes empirical evidence to guide the development of public-facing climate communication strategies. Understanding how different frames shape motivation can help organizations, educators, and policymakers craft messages that foster engagement and action rather than apathy or avoidance.
Systematics and phylogeography of Microdictyon (Cladophorales, Chlorphyta) in Hawai'i
(University of Hawaiʻi at Mānoa, 2026) Geise, Sydney; Sherwood, Alison; Oceanography; Global Environmental Science
Algae play an important role in reef ecosystems by providing habitat and food for marine species. The green alga Microdictyon is common on reefs across the Hawaiian Islands and provides these ecological services to support Hawaiʻi’s marine life. To date, recorded data states M. umbilicatum and M. setchellianum as the two species found in Hawaiʻi. In addition, phylogeographic studies have not been completed for these species due to the limited availability of published reference data. DNA sequences from numerous locations globally are available for M. umbilicatum that can be used for comparison to samples from Hawaiʻi, but M. setchellianum does not have published sequences available, so reports of this taxon in Hawaiʻi are based on morphological identifications. This study compares sequences of Microdictyon samples from the Hawaiian Islands with those from Microdictyon and related species published elsewhere to determine taxonomy and distributional patterns. The partial nuclear Large Subunit (LSU) rDNA was amplified and sequenced for 18 specimens from the Hawaiian Islands. Phylogenetic analyses grouped Hawaiian specimens with three taxa M. umbilicatum, M. cf. boergesenii, and cf. Boodlea vanbosseae. Haplotype networks were constructed for each taxa and analyses revealed most haplotypes had low nucleotide diversity. Some geographic and depth patterns were observed among Hawaiian and globally distributed samples. Although this study was limited in terms of number of samples and reference data, baseline data was constructed. Further research is necessary for creating a full profile of Microdictyon around the Hawaiian Islands helping to understand geographic differences overall supporting efforts in conservation of these unique ecosystems.
Characterizing aggregating behavior in hā'uke'uke (Colobocentrotus atratus) in Hawai'i
(University of Hawaiʻi at Mānoa, 2026) Deatherage, Amy; Rivera, Malia; Keliipuleole, Kekuʻiapōiula; Oceanography; Global Environmental Science
The intertidal zone is an extreme environment where organisms face alternating air and water exposure, temperature shifts, and wave impacts. While most sea urchins seek shelter in burrows or subtidal regions to survive these conditions, Colobocentrotus atratus (hāʻukeʻuke, or helmet urchins) thrive openly on the rocky surfaces of Hawaiʻi, likely due to their uniquely flattened spines and strong suction abilities. Further, it has been observed that unlike most other urchins in Hawaiʻi, C. atratus tend to form aggregations, or clusters. This study seeks to explore this poorly understood grouping behavior, and addresses the research question: when and why do C. atratus exhibit aggregating behavior? Through this research, two hypotheses were tested: 1) aggregation is correlated to chlorophyll levels as a reflection of feeding behavior, and 2) aggregation is more common during spawning seasons to increase the likelihood of fertilization. Field surveys were conducted at Kaʻalawai Point, Honolulu, Oʻahu during low tides, approximately monthly for one year. Fieldwork entailed aerial imaging using a drone, close-up videography using a GoPro, and water quality/chlorophyll sampling using a YSI ProDSS to provide in-situ environmental data. While overall population size remained relatively stable across months, clustering frequency varied markedly, with a pronounced decline during winter months despite high abundance. Chlorophyll concentrations showed a weak, non-significant correlation with clustering, suggesting that suspended food availability is not a primary driver of aggregation. These findings provide the first systematic assessment of aggregation behavior in C. atratus and establish a methodological foundation for future studies examining the ecological and reproductive influences on this uniquely adapted rocky intertidal species.
Effects of an ecological replacement herbivore on cactus recruitment on an arid island
(University of Hawaiʻi at Mānoa, 2026) Aviles, Raquel; Litton, Creighton; Oceanography; Global Environmental Science
Island ecosystems, recognized for high levels of endemism, are particularly vulnerable to disturbance and the loss of native species. The extinction of endemic keystone herbivores can disrupt essential ecological functions such as seed dispersal, nutrient cycling, and habitat structuring. In addition, invasive species exacerbate these impacts worldwide. Feral goats (Capra hircus), for example, have caused extensive habitat degradation through overgrazing, trampling, and soil erosion. On Santa Fé Island, Galapagos, the historical extinction of giant tortoises (Chelonoidis sp.) in the mid-to-late 19th century and the introduction of feral goats dramatically altered plant communities and the distribution of key endemic species, including the tree cactus Opuntia echios var. barringtonensis. Feral goats were eradicated in 1978, and in 2015 a related giant tortoise species (Chelonoidis hoodensis) was introduced as an ecological replacement to restore lost ecosystem functions. Over the course of 10 years, ~700 juvenile tortoises were released in the center of the island, from where they have dispersed to create a gradient of tortoise activity on the island. This study aimed to examine the following on Sante Fé Island: (1) tortoise activity defined as tortoises per square meter, (2) O. echios height distribution and density, and (3) the relationship between tortoise activity and seedling and sapling densities of O. echios. To address these objectives, nine 50 × 50 m plots, subdivided into 25 10 × 10 m subplots, were established across varying tortoise activity zones. Results indicated that tortoise activity was greatest in the center of the island, near the release zone. The O. echios height distribution reflected a reverse-J pattern, indicating a healthy population. O. echios seedling and sapling densities peaked in areas with moderate tortoise activity, although the interaction was not significant. While the effects of tortoise reintroduction on the overall Opuntia population were not yet clearly detectable, the findings suggest that tortoises may influence Opuntia regeneration patterns, particularly at moderate tortoise densities. These results provide preliminary evidence that ecological replacement herbivores such as Chelonoidis hoodensis may affect vegetation dynamics on Santa Fe Island, although the small sample size and limited sampling duration mean that additional long-term research is needed. Because vegetation responses to large herbivores may take decades to fully manifest, continued monitoring will be important for understanding the long-term ecological impacts of tortoise reintroduction in island ecosystems.