M.S. - Marine Biology

Permanent URI for this collectionhttps://hdl.handle.net/10125/50817

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Comparing the metabolic and behavioral resilience of a native mullet (Mugil cephalus) and invasive mullet (Osteomugil engeli) to marine heat waves
(University of Hawai'i at Manoa, 2025) Rosen, Jonathan Yoshio; Johansen, Jacob L.; Marine Biology
Marine heatwaves (MHWs) have increased in both frequency and intensity since pre-industrial times, with tropical ecosystems emerging amongst the most vulnerable. Rising temperatures cause thermal stress to many stenothermic (thermally specialized) ectotherms, while also increasing their cost of survival due to thermally driven rises in metabolic demand. Concurrently, MHWs is thought to facilitate the spread of eurythermic invasive species which exhibit broad ranges of thermal tolerance and a capacity to rapidly colonize vulnerable habitats. Here, we compare the impacts of moderate (+2 °C) and intense MHW conditions (+4 °C) on the juveniles of two Mugilid species found in Hawaiʻi, the native striped mullet (Mugil cephalus; ʻamaʻama) and the invasive Marquesan mullet (Osteomugil engeli; kanda). These species compete for habitat throughout their life cycle, with O. engeli increasingly dominating mullet assemblages across the Hawaiian Islands. Given its invasive status, O. engeli was hypothesized to exhibit a greater tolerance to MHW temperatures. Comparisons included seven metrics critical for ecological fitness, including five physiological traits spanning standard metabolic rate (i.e. metabolic cost of survival, SMR), Q10 of SMR (i.e. thermal sensitivity), maximum metabolic rate (MMR), aerobic scope (AS, i.e. maximum surplus capacity for aerobic activities), and critical thermal maximum (CTmax, i.e. upper thermal limit for survival). We also compared two behavioral responses: preferred temperature (Tpref and maximum avoidance temperature (Tavoid). Individuals (Mugil cephalus: 82, Osteomugil engeli: 95) were randomly assigned to a temperature treatment representing ambient temperatures and 5-day MHW conditions typical for Hawaiian reefs (ambient summer temperature 27.5±0.1°C, current moderate summer MHW 29.5±0.1 °C, intense summer MHW 31.5±0.1 °C). Contrary to expectations, native M. cephalus showed a 49.0% increase in aerobic scope (AS) at 31.5 °C, while invasive O. engeli experienced a 27.5% decrease from 29.5 °C to 31.5 °C, denoting strong thermal sensitivity in the capacity of physiological functions. Both species had CTmax values above intense MHW temperatures (40.6–41.2 °C for M. cephalus, 40.4–42.0 °C for O. engeli), with O. engeli showing significantly higher thermal tolerance (p < 0.005). Temperature preference (Tpref) did not differ across treatments for either species. Contrary to expectations, these results suggest M. cephalus may be more resilient to MHWs than its invasive competitor and highlight the importance of combining physiological and behavioral metrics when predicting MHW impacts on native and invasive species.
The role of submarine groundwater in shaping nearshore coral physiology
(University of Hawai'i at Manoa, 2025) Stephenson, Callie N.; Donahue, Megan J.; Marine Biology
Although coral reefs evolved in oligotrophic waters, corals are now distributed across a variety of biogeochemical environments that shape their physiology. Allochthonous sources of nutrients – such as coastal runoff, rivers, and submarine groundwater discharge (SGD) – increased nutrient availability and altered carbonate dynamics. To investigate the influence of SGD on coral physiology, we conducted a seven-week field experiment along an SGD gradient in Moorea, French Polynesia. This gradient was characterized by tidally-regulated pulses of cooler, less saline water with lower pH, higher alkalinity, and elevated macronutrient concentrations (phosphate, N+N, and silicate). We evaluated the physiological responses of two common fringing reef corals, Porites rus and Pocillopora acuta, by examining changes in the holobiont (percent change in buoyant weight), endosymbiont photopigmentation (total chlorophyll content), and nutrient partitioning (δ15NH-S and δ13CH-S) when exposed to SGD influence for 7-8 weeks across 20 stations on the exposed reef. In P. acuta, total chlorophyll content and δ15NH-S both displayed a significant relationship with SGD influence, highlighting the sensitivity of the symbiont physiology to SGD. There were no effects of SGD on any of the measured parameters for P. rus.Isotope analyses showed P. rus and P. acuta display different feeding strategies: P. acuta relied more on heterotrophy (67% overlap in isotopic niche between the host and symbiont) while P. rus relied more on autotrophy (93% overlap in isotopic niche between the host and symbiont). δ15N values of zooplankton and particulate organic matter within and outside the seep indicated heterotrophic contributions to corals were predominantly derived from non-seep sources outside the seep. These results indicate that the complex biogeochemical inputs from SGD drive contrasting physiological responses within coral holobionts. Our findings reveal that submarine groundwater discharge, an often-overlooked coastal input, can drive differential physiological responses that may ultimately influence species composition and trophic dynamics on coral reefs.
Investigating forms of plasticity in three echinoid species from the tropical north Pacific
(University of Hawai'i at Manoa, 2025) Nash, Ethan G.; Moran, Amy L.; Marine Biology
Phenotypic plasticity allows marine invertebrate larvae to adjust morphology and development in response to environmental variability, but its expression across species and environmental gradients remains incompletely understood. We examined morphological plasticity in larvae of three tropical echinoids– Tripneustes gratilla, Echinometra mathaei, and Colobocentrotus atratus– reared under nine combinations of temperature (23, 26, 29 °C) and food concentration (200, 1000, 5500 algal cells mL⁻¹). Across seven experiments and six larval cohorts, we quantified post-oral arm length (POL), stomach length (SL), and median body length (MBL) to test for a morphological plastic response to these environmental variables. Tripneustes gratilla displayed consistent morphological plasticity across the three experiments, with low- and medium-food treatments producing the longest relative POL. Echinometra mathaei exhibited POL plasticity in both experiments, but in a nontraditional way that needs more observations to fully understand where this plasticity comes from. C. atratus showed a traditional plasticity trend (although not statistically significant) with the lowest food treatments producing the longest POL relative to body size in a single spawn. High-food treatments promoted longer SL across all species and experiments. For T. gratilla, we tracked time to metamorphic competence and beaker larval duration for and larval duration (PLD) in a single spawn in May of 2023. Developmental timing was plastic in T. gratilla: at 29 °C with high-food, larvae reached metamorphosis in ~25 days, while some medium-food larvae at 23 °C remained free-swimming after 366 days. Morphological plasticity was predominantly food-driven, with limited interaction effects from temperature. Larval duration was significantly affected by food availability, temperature, and their interaction in T. gratilla. These results show patterns of larval flexibility and suggest that morphology and larval duration is an environmentally responsive trait. Such plasticity may have important implications for dispersal, connectivity, and resilience under changing ocean conditions.
Nesting ecology of leatherback turtles (Dermochelys coriacea) on Buru island, Maluku, Indonesia
(University of Hawai'i at Manoa, 2025) Ningrum, Retno Kusuma; Honarvar, Shaya; Marine Biology
Leatherback turtles (Dermochelys coriacea) face significant conservation challengesdue to global population declines and their susceptibility to both environmental and anthropogenic pressures. Fine-scale, site-specific research is critical for understanding population characteristics and developing effective conservation strategies. This study uses beach monitoring data collected over eight years (2017-2024), along with beach characteristic survey data from 2024, to examine the nesting behavior of leatherback turtles, beach characteristics, hatchling production, impacts of seasonality, and threats to eggs at Fena Leisela beach, Buru Island, Indonesia. With over 1434 recorded nests and 178 unique individuals identified, findings show that leatherbacks typically lay five clutches per season, with internesting intervals ranging from 9 to 12 days and a remigration interval of approximately 2-4 years. Based on the number of nests and estimated clutches per female, it is estimated that approximately 36 females nest annually at Fena Leisela beach. Nesting occurs year-round, following a bimodal pattern with two peaks: June-July (dry season) and December-February (rainy season). Nesting activity has increased annually over the last eight years, likely due to the cessation of meat harvesting in 2017, which has allowed more turtles to complete their nesting cycles. However, a declining trend has been observed during the rainy season, suggesting increased pressures during this period. The combination of beach monitoring and beach characteristic data collection in 2024 reveals that artificial lighting, slopes, and beach width are important cues in selecting nest sites. Leatherbacks predominantly nest in areas with minimal artificial light, moderate beach widths (approximately 14.2-26.1 meters), moderate beach slopes (ranging from 11.32% to 15.48%), diggable sand, and sparse vegetation cover. These findings suggest that v leatherbacks exhibit specific preferences for nesting habitats. Interestingly, a few individuals were observed nesting in well-lit areas, indicating that some turtles may tolerate a degree of disturbance. Nevertheless, the presence of artificial light could disorient adults and hatchlings whose potential long-term conservation impact remains unclear. This study also highlights a significant reduction in egg harvesting and predation, largely due to active beach monitoring and increased community awareness efforts involving local citizens, government officials, and traditional and religious leaders. Nests in high-risk areas (“doomed nests”) were relocated, resulting in the successful release of approximately 5,674 hatchlings. However, the hatching and emergence success rates were lower in relocated nests (F(1,671)=3.364, P=0.06 and F(1,671)=4.187, P=0.04, respectively), possibly due to changes in nest conditions such as moisture and temperature. Despite this, seasonal variation did not appear to negatively impact relocated nests, suggesting that nest relocation may be most effective during the rainy season, when the risk to nests is the highest. These findings offer valuable insight into the nesting ecology of leatherback turtles at Fena Leisela beach and provide a strong foundation for future research and the development of site-specific conservation strategies.
Who are you calling a shrimp? Evaluating aggression, boldness, territoriality, and behavioral strategies in an invasive stomatopod (Gonodactylaceus falcatus)
(University of Hawai'i at Manoa, 2025) Hanscom, Sophia; Porter, Megan L.; Marine Biology
Biological surveys conducted on Oʻahu, Hawaiʻi have indicated the stomatopod (Order Stomatopoda), Gonodactylaceus falcatus, to be the most widely distributed invasive marine invertebrate in nearshore marine ecosystems. Similar to marine crustaceans around the world, G. falcatus was introduced to Hawaiʻi due to the combination of increased maritime activity following WWII and their planktonic larval phase. While this pathway has been documented for facilitating its introduction into the islands, it remains unclear what characteristics have supported the establishment and successful invasion of this species into this non-native environment. Previous work has focused on the role behavior can play in this scenario, suggesting that differences in specific behavioral traits between invasive and native species contribute to the invasion success and overall interactions between these species and their new environment. In particular, studies have identified behavioral syndromes (consistency of single behavior across contexts and/or correlation between two traits) as a behavioral strategy that has contributed to the invasion success of many taxa. I tested the boldness and aggression of G. falcatus (n = 101) to determine if a behavioral syndrome was present and to characterize the overall behavioral variation within these traits. Three syndrome analyses were conducted (mixed model, intraclass correlation coefficient, Spearman's correlation) and a lack of evidence for a behavioral syndrome in this species was identified. While a syndrome wasn't present, these behavioral traits may still be contributing to their success if as a species they are more bold and/or aggressive than the native stomatopod species. When analyzing the individual traits, boldness and aggression increased across trial number (replicate) and this study also found larger individuals to respond more aggressively than smaller counterparts. Some factors typically found to impact how bold or aggressive an individual is (e.g., sex) were not significant within this study.In addition to testing the boldness and aggression of G. falcatus, I also analyzed their territorial contests to determine the outcomes between size-matched individuals and what characteristics might drive these results. I conducted 86 size-matched contests that included three categories: intrasexual females, intrasexual males, and intersexual. The same individual won the majority (84%) of repeated trials but questions regarding what is driving these results, individual recognition or behavioral consistency, remain. Of the intrasexual contests (females and males), residents won the majority of contests supporting previous work that has identified a bias towards the resident in matched contests. On the other hand, during intersexual contests there was a substantial decrease in the proportion of contests won by residents. Further analysis determined that males were winning more frequently than females in intersexual contests. While it remains unknown why this shift has occurred, I hypothesize that sexual dimorphism in the weaponry of G. falcatus is impacting the resource holding potential and the perceived strength of their competitor. Overall, this thesis provides a behavioral characterization of G. falcatus and how their behavior may influence their success as invasive species, although additional studies should be performed to gain a deeper understanding of this invasion. This study also uncovered an interesting trend in the contest outcome during intersexual contests, which have rarely been included in previous work and proposes a hypothesis to explain what might be driving differences in context outcomes between females and males. Finally, this thesis has identified an overall lack of studies focused on the role of behavior in the invasions of marine crustaceans and how it may differ from other taxa (e.g., terrestrial vertebrates).
MICROBIAL COMMUNITY HERITABILITY IN LARVAE OF THE HAWAIIAN CORAL MONTIPORA CAPITATA
(University of Hawai'i at Manoa, 2024) Kuball, Kyleigh; Hunter, Cynthia; Marine Biology
Coral health depends on microbial interactions that support functions such as organic material cycling and disease resistance. Microbial communities in planulae and adult tissues of Montipora capitata were examined in factorial fertilization crosses to investigate the heritability of microbial community characteristics and specific microbial taxa in this common Hawaiian coral. I hypothesized that larval microbiomes would be predicted more by the dam (egg donor) than the sire (sperm donor), consistent with reports of egg-transmitted algal symbionts in M. capitata. A factorial cross of gametes from five parent colonies produced 18 viable sibling families after self-crosses and low viability crosses were removed. Amplicon sequencing of the 16S rRNA gene profiled the composition and diversity of Bacteria and Archaea among adults, seawater, and planulae, defining a consistent microbiome community characteristic of planulae. Taxa found in the seawater were rare to undetected in the larvae suggesting horizontal transmission was low. Significant differences were found among larvae when grouped by either parent, indicating both dam and sire influenced the microbiome of the planulae; siblings were also more similar than half-siblings or unrelated larvae, providing evidence of emergent effects of parental combinations. Results demonstrated parent-specific vertical transmission of specific microbial taxa, highlighting a previously unknown intergenerational effect in this coral species.
FEAR AND FLATTENING: REEF HABITAT COMPLEXITY ALTERS REEF FISH FORAGING BEHAVIORS
(University of Hawai'i at Manoa, 2024) Cook McNab, Aimee Arielle; Madin, Elizabeth; Marine Biology
A robust and diverse reef fish community is generally reflective of healthy, resilient reefs. Herbivorous fishes play a critical role in controlling algal populations on coral reefs, yet they are increasingly threatened by human pressures and other climate stressors. These fishes often concentrate their grazing near the protective refuge of coral reefs due to perceived predation risk. With increasing coral degradation due to bleaching and subsequent coral mortality, benthic complexity is lost, yet the impact of this loss on herbivore foraging behavior is unclear. This study employed a space-for-time substitution to assess how varying levels of reef structural complexity influence reef fish biodiversity and foraging behavior in Kāne‘ohe Bay, O‘ahu, Hawai‘i. Reef complexity was quantified using Structure-from-Motion (SfM) photogrammetry, while fish community structure (biodiversity, abundance) and foraging behaviors (foraging frequency, distance traveled from reef, and number of bites) were recorded through in-situ surveys. Results revealed that reef complexity significantly influenced species richness and foraging patterns. While fish species richness showed a positive association with reef height, reef fish abundance exhibited a more nuanced relationship which was influenced by site-specific variability. Herbivorous fish tended to concentrate foraging closer to reef margins as structural complexity decreased, whereas higher complexity reefs supported foraging further from the reef’s edge. This pattern was dominated by genera such as Acanthurus and Zebrasoma, which tended to forage farther from the reef margin, and Chlorurus, Ctenochaetus, and Scarus which foraged closer. Notably, this trend was consistent across complexity levels, as no significant differences in foraging behavior were observed for the herbivore species studied. These findings highlight the critical role of reef structural complexity in shaping fish community dynamics and behavior. The degradation of reef complexity may confine herbivore foraging to areas near remaining reef structures, potentially creating a feedback loop where reduced complexity promotes algal colonization, further diminishing reef health and resilience.
Uncovering the Long-Term Dynamics of Reef Manta Ray (Mobula alfredi) Aggregations in Kona, Hawai‘i Using Community-Sourced Data
(University of Hawai'i at Manoa, 2024) Nevels, Corey Rae; Holland, Kim; Marine Biology
Reef manta rays (Mobula alfredi) face conservation challenges due to global population declines and their susceptibility to anthropogenic pressures, particularly in tourism-driven settings. Fine-scale, site-specific studies are essential for understanding population characteristics and informing effective conservation measures. This study leverages citizen science data spanning 13 years (2010-2022) to elucidate the dynamics, residency patterns, and influence of prey availability of manta ray aggregations at two nighttime feeding sites, Garden Eel Cove (GEC) and Keauhou (KH), along the Kona coast of Hawai‘i Island. With over 23,000 recorded sightings of 167 unique individuals, the results reveal both similarities and site-specific distinctions between the two locations. For example, GEC consistently supports larger aggregations than KH, underscoring its role as a reliable feeding area. Both sites exhibited an overall balanced 1:1 sex ratio; however, while GEC showed similar visitation patterns for both sexes, KH was predominately frequented by females, suggesting that this area may serve other sex-specific ecological functions beyond nighttime feeding. The results also support previous indications that males are more mobile than females. Residency and movement patterns were analyzed using a modified maximum likelihood approach, confirming high site fidelity among females at KH and highlighting a degree of connectivity between the two sites. Fluctuations in seasonal and annual trends in aggregation size closely aligned with zooplankton density, emphasizing prey availability as a primary driver of manta presence and aggregation patterns. The relative stability of aggregations at both sites, despite increased tourism, suggests that current activity levels have not negatively impacted the viability of the local manta ray population and that they exhibit adaptable foraging strategies. These findings underscore the ecological significance of GEC and KH for Kona’s manta population and illustrate the potential of community-sourced data to capture long-term ecological patterns, providing a foundation for future research to inform conservation strategies tailored to these key aggregation sites.
Introducing a novel 28S rRNA marker for improved assessment of coral reef biodiversity
(University of Hawai'i at Manoa, 2024) Martineau, Gabrielle; Toonen, Robert RJT; Marine Biology
Biodiversity monitoring based on DNA metabarcoding depends on primer performance. Here, we develop a new metabarcoding primer pair that targets a ~ 318 bp fragment of the 28S rRNA gene. We validate the primer pair in assessing sponges, a notoriously challenging group for coral reef metabarcoding studies, by using mock and natural complex reef communities to examine its performance in species detection, amplification efficiency, and quantitative potential. Mock community experiments revealed a high number of sponge species (n = 94) spanning a broad taxonomic scope (15 orders), limited taxon-specific primer biases (only a single species exceeded a two-fold deviation from the expected number of reads), and its suitability for quantitative metabarcoding – there was a significant relationship between read abundance and visual percent coverage of sponge taxa (R = 0.76). In the natural complex coral reef community experiments, commonly used COI metabarcoding primers detected only 30.9% of sponge species, while the new 28S primer increased detection to 79.4%. These new 28S primers detect a broader taxonomic array of species across phyla and classes within the complex cryptobiome of coral reef communities than the Leray-Geller COI primers. As biodiversity assessments using metabarcoding tools are increasingly being leveraged for environmental monitoring and guide policymaking, these new 28S rRNA primers can improve biodiversity assessments for complex ecological coral reef communities.
BRIDGING THE GAP USING MORPHOLOGY AND PHYLOGENETICS TO DESCRIBE SIX NEW SPECIES OF TETRACTINELLID SPONGES AND REPORT THE FIRST RECORD OF GEODIA PAPYRACEA IN HAWAIʻI
(University of Hawai'i at Manoa, 2024) Nunley, Rachel; Toonen, Robert J.; Marine Biology
Kāneʻohe Bay has historically been known for the introduction of alien species from the Caribbean and the Western Indo-Pacific. Recent efforts that explore the reef cryptofauna have shown that in addition to the diversity of non-indigenous species, patch reef environments are rich with undescribed species. Here we integrate molecular phylogeny and systematics to distinguish introduced species from those that are potentially native or endemic. We focus on the order Tetractinellida and document the transoceanic dispersal of Geodia papyracea from the Caribbean to Hawaiʻi likely via the fouling of ship hauls navigating through the Panama Canal. Our integrative approach allowed us to describe new species of Stelletta, Stelletta kaluhiwa sp. nov., Stelletta cypheri sp. nov., Stelletta camvela sp. nov., Stelletta hewetta sp. nov., Stelletta brighti sp. nov., and one new species of Stryphnus, Stryphnus jonesi sp. nov; all collected from the reef cryptofauna. Specimens were barcoded using 28S and COI molecular markers, providing insights into the phenotypic plasticity of sponges and the phylogenetic placement of these new species based on morphological characters. Using both molecular phylogeny and traditional taxonomy enhances the accuracy of species identification and classification, contributing to a broader understanding of sponge biodiversity within the Hawaiian archipelago.
The Effects of Sediment Runoff on the Foraging Behavior of Herbivorous Coral Reef Fishes
(University of Hawai'i at Manoa, 2024) Grellman, Katherine; Johansen, Jacob L.; Hunter, Cynthia L.; Marine Biology
Increased sediment and nutrient runoff – a consequence of localized and global anthropogenic impacts – is a primary threat to tropical coral reefs worldwide. Excessive sediment loads smother and kill coral, while algae flourish in the same nutrient-rich habitats. Herbivorous reef fishes are crucial for their role in top-down algal biomass control that maintains coral dominance. However, sediment-induced turbidity is known to affect fishes in a variety of ways, leaving questions about the ramifications of escalated sediment loads on herbivore foraging as an essential ecological function on impacted reefs. To assess broad foraging responses of herbivorous fishes to sediment-induced turbidity, foraging rates were quantified across herbivore functional traits, including reef fish that scrape algae off hard substrates (i.e., scrapers), turf croppers (i.e., grazers), and macroalgae consumers (i.e., browsers). Snorkel-based behavioral surveys focused on two scraper species (Chlorurus spilurus and Scarus psittacus), three grazer species (Acanthurus blochii, A. triostegus, and Zebrasoma flavescens) and three browser species (Naso lituratus, N. unicornis, and Z. velifer) along three independent turbidity gradients in Kāneʻohe Bay, Oʻahu Island, Hawaiʻi over the span of 13 months. Monthly surveys of benthic composition (i.e., branching coral, plate coral, macroalgae, turf, crustose coralline algae, sand, coral rubble, other) and water quality parameters (i.e., turbidity, salinity, dissolved oxygen, temperature, nitrate, visibility) were coupled with in situ behavioral observations of individual foraging rates, dietary choices, and consumption of substrates with or without settled sediment (SeS) across fish sizes (visually estimated total length). Subsequent in vivo foraging experiments were conducted with Z. velifer and inorganic sediment to tease apart the relative effects of sediment-induced turbidity versus SeS. My findings revealed a strong correlation between high macroalgae cover and turbid reefs, as well as clear functional trait- and species-specific foraging responses to turbidity gradients. Contrary to predictions, scrapers and grazers did not significantly alter foraging rates except for adult A. blochii, which showed a two-fold increase in foraging rate in response to turbidity. Despite high abundance on nearby clear-water reefs, Naso spp. and larger individuals of most scraper and grazer species were virtually absent from turbid reefs throughout the study. Zebrasoma velifer, which functions as a browser on clear-water Hawaiian reefs, avoided macroalgae relative to availability in high turbidity sites, instead showing a greater consumption of turf, denoting a high dietary plasticity in this species. There was also a significant difference in foraging responses between juvenile and adult Z. velifer, with juveniles tripling their foraging rate and adults slightly decreasing their rate across a turbidity gradient. While all species observed in the field preferred SeS-laden substrates, Z. velifer avoided inorganic SeS during in vivo foraging experiments, suggesting access to organic matter may be a driver for foraging on sedimented reefs. Overall, these results highlight divergence in tolerance to sediment-induced turbidity both within and between herbivorous fish guilds, indicating that sediment runoff causes a cascading effect whereby browsers and larger individuals disappear, and traditional top-down algal control by a variety of herbivores is diminished.
THE EFFECTS OF MICROPLASTIC INGESTION ON THE FEMALE REPRODUCTIVE SYSTEM OF THE CRYPTOBENTHIC GOBIID FISH, EVIOTA EPIPHANES, USING ARTIFICIAL TROPHIC TRANSFER
(University of Hawai'i at Manoa, 2024) Gaw, Isabella M.; Cole, Kathleen; Marine Biology
Plastic pollution is one of the most pervasive anthropogenic stressors faced today by aquatic fauna. One of the greatest threats that plastic pollution is associated with is ingestion, particularly microplastic (<5 mm) ingestion, which has been shown to lead to various pathologies associated with internal organ systems and physiological pathologies. The work reported on here attempts to better understand the relationship between microplastic ingestion and any subsequent morphological pathologies observed, and to take steps to develop more efficient methodologies to promote standardization across the study of microplastic effects on aquatic organisms. The first part of this thesis reports on an investigation to develop an effective artificial trophic transfer method using Artemia salina. Live A. salina nauplii were fed 6.10-μm polystyrene microplastic beads at three different time intervals (two-, four-, and six-hours) and in two treatment groups (aeration and no-aeration). Artemia salina had a significantly increased ingestion of microplastics in the aeration treatment (average of 20 to 24 microbeads per gut) when compared with no-aeration treatment (average of 1 to 10 microbeads per gut) but no significant difference of microplastic ingestion was observed across the time intervals in the aeration treatment group. The next experiment used these findings to implement indirect ingestion of 6.10-μm polystyrene microplastic beads to Eviota epiphanes, a small, cryptobenthic, Hawaiian reef fish. This study was designed to help elucidate if indirect ingestion of microplastic, through the consumption of microplastic-fed A. salina, resulted in accumulation and/or alteration of liver and gonadal morphology. Individual fish were maintained separately within a custom-made microplastic accommodating aquarium system, known as the Microplastic Experimental Aquarium System (MEAS). This system prevented microplastic cross-contamination between the treatment groups and inhibited microplastic pollution into the environment. In the MEAS, the experimental group of E. epiphanes were fed live A. salina that had in turn fed on microplastic beads. The control group of E. epiphanes were fed live A. salina that had not been exposed to the microplastic beads. Neither microplastic accumulation nor observable morphological differences were found in a detailed histological comparison of gonad and liver morphology between experimental and control fish. These findings suggest that E. epiphanes may not be particularly vulnerable to microplastics around the size range of 6.10-μm, at least over short periods of time. However, the possibility of deleterious effect(s) caused by the exposure of small-sized aquatic fauna to smaller-sized nanoplastics is currently unknown and may play an important role in trophic transfer through the lower end of aquatic ecosystem food chains.
Testing of Electrical and Magnetic Stimuli on Captive Juvenile Tiger Sharks
(University of Hawai'i at Manoa, 2024) Cardona, Edward William; Holland, Kim N.; Marine Biology
Tiger sharks (Galeocerdo cuvier) are both ecologically and culturally important in Hawaii. It is also one of the species most frequently involved in attacks on humans worldwide Deterring sharks from biting unintended items has importance in three spheres – human safety, reducing shark bycatch in fisheries and reducing depredation (sharks biting target species that have already been hooked). Because sharks can sense electromagnetic fields, artificial electrical and magnetic stimuli have been hypothesized as solutions to mitigate these interactions. Previous research has focused on testing a variety of putative deterrent devices in captivity but often suffers from low sample sizes or small test arenas. Results from experiments in the wild can be confounded by uncontrolled variables (e.g., level of hunger). To address these concerns, I tested captive juvenile tiger sharks in a large naturalistic enclosure where hunger could be controlled. This study is the first to test putative deterrents (two permanent magnets - weak and strong fields - and an electric field transmitter) on tiger sharks in a controlled experimental protocol. I hypothesized that the fields produced by these devices would be aversive to sharks, and stronger magnets would be more effective than weaker ones. Eleven captive juvenile tiger sharks were exposed to the three devices under both baited (food) and unbaited conditions. Results showed uneven responses to all three devices depending on whether bait was present. In some circumstances deterrence was observed but the tests also revealed attractive properties of artificial magnetic fields. All responses occurred <1 meter from the deterrent device. The strong magnet and the electrical transmitter were found to reduce the probability of sharks taking the bait. However, the weaker permanent magnet showed signs of being attractive. These stimuli were not 100% effective under all conditions and, as in previous studies, there was individual variability in responsiveness among sharks. These findings highlight the importance of context dependent and species-specific testing of putative magnetic and electric deterrents.
The Effects of Human Presence on Fish Behavior at the Hanauma Bay Nature Preserve, Hawaiʻi During and Immediately Following the COVID-19 Pandemic Closure
(University of Hawai'i at Manoa, 2024) Graham, Andrew T.; Hunter, Cynthia L.; Marine Biology
Flight Initiation Distance (FID) data can provide valuable information on the behavioral patterns of fishes. This data can be coupled with other quantitative data such as the direct minimum approach distance (dMAD), start distance, and body size measurements of marine fishes to provide a better understanding of how fishes respond to perceived threats. Diver-operated stereo video cameras were used to collect flight response data at the Hanauma Bay Nature Preserve (HBNP) which is the oldest and most popular Marine Life Conservation District in the State of Hawaiʻi. In March 2020, the COVID-19 global pandemic suspended travel and tourism due to health concerns leading to a complete halt in visitor numbers at the Bay. This unprecedented change provided the unique opportunity to assess the crowding effects of humans on fish behavior in the Bay. Surveys were divided into two time points: during the closure when visitor populations were zero, and immediately following the reopening of the Bay when visitor populations were approximately 750 people/day. A total of 1,114 flight responses were recorded across eight species. FIDs were significantly affected by fish size, species, and starting distance. Similarly, dMADs were significantly affected by fish size, species, starting distance, rugosity, and the number of people in the water. The greater number of significant variables observed for the dMAD suggests that fishes are comparatively less wary during an initial approach than a continuous follow.
LOW HERBIVORY INTENSITY FACILITATES INVASIVE MACROALGAL PROLIFERATION IN COASTAL NEARSHORE HABITATS OF O‘AHU, HAWAI‘I.
(University of Hawai'i at Manoa, 2024) Chulakote, Scott; Smith, Celia; Marine Biology
Dominance by invasive algae on coral reefs has well known impacts, impairs the health of many reef communities, and lessens biodiversity. Experimentally increased herbivory intensity or manual biomass removal have led to successful reduction of invasive algae in typical reef flat habitats, yet numerous shallow lagoon and back reef habitats are often overlooked and also remain perennially dominated by invasive algae. Previous feeding experiments conducted in the “Edge of the Reef” tank at the Waikīkī Aquarium, Hawaiʻi, suggested that invasive algae Acanthophora spicifera and Gracilaria salicornia were primarily consumed by acanthurid fishes. However, when results were tested against in situ feeding preference tests, patterns differed. Herbivory assays using in situ video were conducted in two marine life conservation districts, the Waikīkī MLCD, and Moku o loʻe MLCD, as well as areas open to fishing in Kāneʻohe Bay and Honolulu, O‘ahu. Herbivory experiments quantified intensity and species-specific feeding preferences of herbivorous coral reef fish in shallow reef habitats. Herbivory observations via replicate automated video were few despite over 100 hours of video observation; feeding preferences could not be detected during replicate multiple-choice trials. Māneoneo, Zebrasoma velifer, consumed the most macroalgae in Kāneʻohe Bay in terms of bites per hour, algal biomass lost in assays, and was the only species observed grazing in all years of the study. These results indicate that herbivorous fishes currently have limited ability to control invasive macroalgae that dominate nearshore reefs. Given the severely overfished status of herbivorous fishes around Oʻahu, consumption of native and non-native macroalgae appears to be limited to a few species of herbivores. Low observed herbivory intensity associated with shallow habitat strongly suggests that invasive algal shallow reefs are unregulated by herbivory and this state may contribute to the continued proliferation of invasive macroalgae.
Effects of dredging-related sedimentation on larval settlement in Harbor Porites coral
(University of Hawai'i at Manoa, 2024) Thomas, Samantha Kiara; Hunter, Cynthia; Marine Biology
Dredging of ports and harbors is crucial to the maintenance of shipping operations in coastal economies. Resuspension and subsequent deposition of sediment associated with dredging activity have been shown to adversely affect coral health and require strict science- based regulation. While previous work has tested the effects of sediment in adult corals, earlier life history stages are generally more vulnerable to environmental changes, yet few studies have quantified these effects. Harbor Porites, an undescribed coral of the Porites species complex, grows abundantly in Honolulu Harbor, Oʻahu, and produces brooded planulae year round. This study measured the effects of deposited silt-sized sediments (<63 μm) at dredging-related concentrations (0, 0.5, 1, 10, 25, and 50 mg/cm2) on Harbor Porites larval settlement, partial metamorphosis, swimming, and mortality. Larval settlement decreased with increasing sediment concentrations and was inhibited on upward-facing surfaces exposed to concentrations exceeding 1 mg/cm2, which is lower than reported sensitivity measures for adult corals. At higher concentrations, settlement was restricted to downward facing and vertical surfaces, where sediment did not accumulate. Partial metamorphosis of Harbor Porites planulae into a planktonic polyp increased at higher sediment loads. Partial metamorphosis is a rare phenomenon that likely provides an advantage to Harbor Porites by increasing planktonic duration, allowing more time for suitable habitat selection. There were no significant effects of sediment on larval swimming or mortality. The results of this study suggest the need for greater consideration of the effects of dredging on early life stages of corals, which are crucial to recovery after dredging and the persistence of healthy reefs in the future.
Abundance and demographic parameters of spinner dolphins (Stenella longirostris subsp.) off Oʻahu's Waiʻanae Coast
(University of Hawai'i at Manoa, 2023) McPherson, Liah Laila; Bejder, Lars; Marine Biology
The occurrence and behavior of spinner dolphins (Stenella longirostris subsp.) off Waiʻanae, Oʻahu are well-described, yet a data deficit on their abundance and trajectory hinders effective conservation. This study employed multi-state open robust design (MSORD) modelling to estimate seasonal dolphin abundance, apparent survival, and temporary emigration, and further-developed a method for age-structure quantification via unoccupied aerial system (UAS; drone) photogrammetry. Dolphin photo-identification and UAS data were collected between April 2021 and January 2023 off the Waiʻanae Coast. Abundance varied seasonally, ranging from 140 (± 36.8 SE) to 373 (± 60.0) individuals and was lowest during Winter. Apparent survival was high and constant (0.95 ± 0.02 SE) and temporary emigration was Markovian. Seasonal environmental variability and spinner dolphin reproductive biology may drive patterns of abundance and temporary emigration. A crude estimate of total abundance for spinner dolphins documented off Waiʻanae (N = 550) is comparable to a recent island-wide abundance estimate, suggesting that the Waiʻanae Coast is a candidate site for long-term monitoring of Oʻahu spinner dolphins. UAS data analysis showed that the total length of spinner dolphins can be effectively estimated by measurements of the blowhole to dorsal fin distance. As age-length growth curves do not exist for the subspecies of spinner dolphin in Hawaiʻi, age was estimated using a growth curve for a related subspecies. Additional life-history information about Hawaiian spinner dolphins will allow both the use of a more accurate growth curve, and an assessment of population health. This work provides the first systematic estimates of abundance and demographic parameters for spinner dolphins off Waiʻanae, imparting valuable information for monitoring and management decisions.
HETEROTROPHIC EUKARYOTIC PLANKTON COMMUNITY DIVERSITY IN AN INDIGENOUS HAWAIIAN MARICULTURE SYSTEM
(University of Hawai'i at Manoa, 2023) Thomas, William Hoakaokalani; Alegado, Rosanna A.; Marine Biology
Marine microorganisms are the engine that drive the global cycling of carbon, nitrogen, and many other elements by carrying out key ecosystem functions and are exquisitely responsive to environmental changes and perturbations of the food web. Subtropical coastal ecosystems are ecologically dynamic systems and susceptible to environmental perturbations caused by human activities such as pollution, development and changes in land usage; yet, microbial dynamics within coastal ecosystems in Hawaiʻi are understudied. Loko iʻa (Indigenous Hawaiian mariculture) practices use the ambient dynamic environment of estuaries to facilitate the growth of phytoplankton and macroalgae for the husbandry of herbivorous fish. The long term operation of loko iʻa are reliant on healthy and well described microbial food web systems. The Heʻeia Fishpond is situated at the ocean terminus of the Heʻeia watershed valley. This constructed tidal estuary provides an opportune place to describe fundamental ecological aspects of heterotrophic plankton communities such as mesozooplankton and the ecologically important yet understudied choanoflagellates. My research utilized microscopic identification and amplicon sequencing to describe fundamental ecological aspects of the mesozooplankton and choanoflagellate communities residing in Heʻeia Fishpond. With our community partners at Paepae o Heʻeia, we found that zooplankton abundance varied spatially and tidally. During high tides when salinity is at its relative peak, zooplankton at mākāhā (sluice gates) correlate with tidal amplitude and potential summer spawning events. I also developed and evaluated molecular primers specific to the choanoflagellate 18S rRNA gene to describe the overall diversity of choanoflagellates in Heʻeia Fishpond and inferred environmental drivers that influence choanoflagellate diversity. We found that choanoflagellate diversity within the fishpond is higher than initial descriptions and influenced primarily by tidal forcing. These results are the first ecological studies to specifically quantify choanoflagellate amplicon sequence abundance from environmental samples. My thesis demonstrates the importance of conducting microbial community surveys of the heterotrophic plankton community as they are critical to fishpond stability and productivity. Our results also highlight the need for additional research on estuarine zooplankton communities, choanoflagellate community ecology and further research on potential diseases that can destabilize the trophic structure of this extensive coastal habitat.
Coral Restoration: Roles Of Shelter For Herbivores And Reef Health In Early Recruitment Success
(University of Hawaii at Manoa, 2023) Dilley, Eric Ryan; Hixon, Mark A.; Marine Biology
Survival and growth of new coral recruits is crucial for reef restoration, yet few details are known about coral demography during the first several years post-settlement. We experimentally tested how reef health and shelter availability for fishes and sea urchins affect juvenile coral demographic rates on coral-restoration platforms. On the island of O‘ahu, Hawai‘i, we deployed cubic-meter concrete modules in both low- and high-shelter configurations at the relatively degraded reef off Waikīkī Beach and the relatively healthy reef at Hanauma Bay. Naturally settling corals, especially of the genera Pocillopora, Montipora, and Porites, were mapped and sized quarterly to track individual colony recruitment, survival, and growth for nearly the first four years post-deployment. We predicted that demographic metrics would be enhanced on high-shelter modules at both sites by providing refugia for herbivores (Shelter Hypothesis), and on all modules in the relatively healthy reefscape at Hanauma Bay (Reefscape Hypothesis). Across experimental modules, overgrowth of coral by benthic algae was negatively correlated with herbivore biomass, which was greater on high-shelter modules, and in turn, total coral cover often benefited from reduced algal abundance. However, the shelter effect was evident only for recruitment of the genus Pocillopora, as well as for survival of Porites. We hypothesize that this weak trend was due to very low recruitment of herbivores, except for a single pulse of sea urchins at Hanauma Bay. Significant patterns for Montipora and Pocillopora were more consistent with the benefits of a healthy reefscape. Compared to Waikīkī, corals at Hanauma Bay experienced higher recruitment (Montipora only), survival (Pocillopora only), and growth (Montipora only), with none of the predicted patterns occurring for Porites. We conclude that determinants of coral recruitment success in this Hawaiian system are idiosyncratic at small scales, due to fine-scale variation in larval settlement and environment, as well as differences in biology and life history among genera. Nonetheless, on average, herbivores benefitted corals by reducing competition with benthic algae, and the context of a healthy reefscape did enhance two common corals. We recommend that reef managers implement policies fostering herbivory, especially on coral restoration structures in degraded habitat and where patches of healthy reef occur nearby, to facilitate coral recruitment, survival, and growth.
Age, Growth, Reproduction, And Mortality Of The Lined Surgeonfish (acanthurus Lineatus) From Saipan, Northern Marianas
(University of Hawaii at Manoa, 2023) Leon Guerrero, Keena; Franklin, Erik C.; Marine Biology
Fisheries in the Commonwealth of the Northern Mariana Islands (CNMI) consist of shore‐based and boat‐based catches of coral reef species. Surgeonfish (Family Acanthuridae), especially Lined Surgeonfish Acanthurus lineatus, contribute significantly to total landings in the nearshore coral reef fishery of the CNMI. Despite being an important component of the nearshore fishery, there is very little known about the biology and life history of the Lined Surgeonfish in the CNMI. The objective of this study was to investigate the age-based demography and reproductive biology of Acanthurus lineatus from Saipan, CNMI to enhance our understanding of their life history. To determine age and growth, longevity, mortality rates, age- and length-at-maturity, and spawning seasonality, fishery-dependent specimens collected during May 2017 to October 2019 were examined. There were no significant mean length differences between the distribution of male and female specimens. The combined length-weight relationship for all specimens across all years was ?=0.031×10−5^2.957. Growth model parameters were a mean asymptotic length (? ∞) of 20.5 cm FL, a growth coefficient (K) of 0.24 ?−1 and a ?0 of -3.2 years. The maximum recorded age was 20 years. Otolith weight was a good predictor of age for both males and females. Estimated total mortality was 0.495 ?−1, natural mortality (M) was 0.315 ?−1, and fishing mortality was 0.18 ? −1. The overall sex ratio was male to female = 1:1.81. For females, the length at 50% sexual maturity (? 50) was 18.8 cm fork length and age at 50% maturity (?50) was 6.2 years. Maturity for males was not estimated due to an insufficient number of immature males. Spawning capable and active A. lineatus females and males were observed during all months with sample collection, potentially supporting a year-round spawning cycle. The outcomes of the work could be used to inform length-based fishery regulations and indicator-based single species stock assessment approaches to support the sustainable fishery management of A. lineatus in the CNMI.

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