Seventeen Students Earn Masters of Marine and Environmental Studies Degrees at UVI

This is an exciting time for the Center for Marine and Environmental Studies (CMES) at the University of the Virgin Islands (UVI) as seventeen students receive a Master of Marine and Environmental Studies (MMES) degree. 

“Given that we have had approximately 50 graduates in the first decade of the MMES program, for us to see 17 finish in a year after such devastation is remarkable. This accomplishment speaks to the perseverance of the MMES and CSM faculty who guided these new scientists towards completing their degree requirements while working without offices and lab space.  As for the graduating students, kudos to them as well and I’m particularly excited to see such relevant research emerge from their theses that can help inform territorial resource managers and scientists alike.” says Dr. Kim Waddell, Director of VI-EPSCoR.


To illustrate the range and complexity of the student's research topics and its relevance to the Territory, their abstracts are listed below. It is notable that much of the work relies on VI-EPSCoR-sponsored acoustic tracking technology, and is centered within Brewers Bay.  The work therefore draws from, and adds to, the wealth of information gathered within the Brewers Bay Ecosystem Analysis Project

One consistent theme of the work by these students is their interest in studying the relationship of marine organisms with their environment such as their habitat and food preferences. The use of new technology provides these new researchers unique insights in the behavior of these species that are otherwise virtually impossible to track in the sea. Their research findings are particularly important as scientists work to understand the effects of a changing environment on these important marine species.

We also see that VI-EPSCoR's investment in the acoustic tracking arrays within Brewers Bay is being used to support and inform the research. Acoustic telemetry uses tags surgically implanted into or onto marine animals. These tags emit unique pings every minute. The pings deliver information to strategically placed hydrophones or receivers which record the animal's identification code, date and time.  Scientists turn this information into maps of the animal's movements over weeks and months. Atlantic tarpon, lane and mutton snapper, and green and hawksbill sea turtles are some of the species tagged and tracked using this technology.  

Climate change and environmental disruptions in the form of marine debris, watershed runoff, and coral diseases, are also areas of focus. We see these as issues that affect the Territory as a whole and will help support the work of marine researchers and environmental decision makers. 

We are immensely proud of these graduates as they receive their Masters degrees in Marine and Environmental Science. Through their accomplishments we see the continued success of this program at the University of the Virgin Islands.



Seasonal Patterns Of Seagrass Species, With Relations To Herbivore Preference In A Small Caribbean Bay

Seagrass meadows provide marine ecosystems with numerous beneficial services but face many threats including the presence of non-native species. The seagrass Halophila stipulacea, native to the Red Sea, has recently spread throughout the Caribbean, including the U.S. island territories of Puerto Rico and Virgin Islands. Currently there is a lack of data on the ecological interactions between this non-native and local herbivorous species. This thesis sought to close knowledge gaps regarding the implications of H. stipulacea on herbivores by observing the feeding patterns of juvenile green turtles (Chelonia mydas) and long-spine urchins (Diadema antillarum) through behavioral surveys and multiple-choice feeding experiments. Seasonal leaf contents of three species (Thalassia testudinum, Syringodium filiforme, and H. stipulacea) found in Brewers Bay were also examined. Juvenile turtles counted in weekly belt transects were significantly more likely to graze over beds containing native species, while 30-minute observational surveys had no individuals graze in monotypic patches of H. stipulacea. In the multiple-choice feeding experiment D. antillarum displayed significant preference to consume S. filiforme over the other seagrasses. While variation was found across all nutrients and species, T. testudinum tended to have higher amounts of each nutrient compared to the other species both in wet and dry mass. Overall, these findings indicate that H. stipulacea will be eaten by two herbivores in Brewers Bay but there is potential preference towards native species. Further testing should be conducted throughout the Caribbean to establish a nutrient baseline for native and alien seagrasses and potential influences on herbivore-plant interactions.

"Doing research in the Caribbean was amazing. Most of the studies conducted at CMES occurred in the same study site (Brewers Bay), which allowed us graduate students to help one another obtain a masters this year. Thanks to the funding provided by UVI, my transformative thesis was successful. I look forward to working on future groundbreaking projects here in the Virgin Islands." John Cassell

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Assessing Impacts Of The Invasive Seagrass, Halophila stipulacea, On Juvenile Southern Stingray (Hypanus americanus) Habitat Preference And Delineation Of Diel Movement Patterns In Brewers Bay And Perseverance Bay, St. Thomas, USVI

Southern stingrays (Hypanus americanus) are marine ecosystem engineers that rely on food and safety within soft sediment habitats (i.e., seagrasses) in near coastal waters. Most aspects of southern stingray ecology and behavior are poorly understood and their populations are threatened due to overfishing and habitat degradation. The introduction of the invasive seagrass Halophila stipulacea to the Caribbean has changed the composition of seagrass habitats and may negatively affect southern stingrays. To understand the effect of H. stipulacea on habitat use, visual surveys and point count surveys were conducted in Brewers Bay, St. Thomas USVI. Visual surveys were carried out from 02/18/16 to 10/20/16, where 92 juveniles and 3 adults were observed (mean± SE) (7.08 ±0.71 per survey). Behavior and percent habitat (Syringodium filiforme (native), H. stipulacea, sand, macro algae, sponge, and coral) were recorded at every siting. There were significantly higher (p<0.05) stingray observations in H. stipulacea and S. filiforme than in all other habitat types. A habitat selection index (HSI) revealed that stingrays used S. filiforme more than H. stipulacea. Behavior across habitats showed stingrays foraged significantly (p<0.05) more in S. filiforme than H. stipulacea or sand. These results suggest that native seagrass foraging habitat of Southern stingrays may become limited if H. stipulacea continues to outcompete S. filiforme in the Caribbean. From 2015 to 2017, southern stingrays (10 juveniles and 2 mature females) were passively tracked using an acoustic array in Brewers and Perseverance bays, St. Thomas, USVI. Stingray position was calculated using weighted center of activities (COA) for every 30 minutes. From calculated positions, 95% and 50% home range utilization distributions were created using a lattice-based density estimator (LBDE). Total core home range area estimations (50% utilization distribution) for stingrays ranged from 0.05 to 0.17 km2 (0.09 ± 0.01), and day and night home range estimated areas were the same (p>0.05) from 0.04 to 0.13 km2 (0.08 ± 0.01). There was no significant difference (p>0.05) between day and night rate of movement (ROM) m/hr. However, there was a significant (p<0.05) multivariate response of 24-hour ROMs m/hr to 4 diel periods, (0400-0800, 1000-1400, 1600-2000, and 2200-0200). Size was positively related (p<0.05) to total and day home range estimates, as well as total and day ROM with only juveniles (p<0.05). Results from ROM and home range analyses suggest that further investigation of crepuscular movement of southern stingrays should be conducted, rather than solely day vs. night comparisons to understand diel movement patterns. This study contributes to a greater understanding of diel movement patterns of juvenile southern stingrays and the potential of an invasive seagrass to limit their foraging habitat throughout the Caribbean.

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Spatial-Temporal Movement Patterns of Atlantic Tarpon (Megalops atlanticus) And Lane Snapper (Lutjanus synagris) In The US Virgin Islands

Fish movement takes place across various spatial and temporal scales, which can range from small to large home ranges, diel movements between foraging and resting areas, ontogenetic habitat shifts, vertical movements or long migrations for spawning or other purposes. Atlantic tarpon (Megalops atlanticus) are highly mobile pelagic fish and important recreational fish species found across coastal areas along the Atlantic Ocean, especially along the Gulf of Mexico and the Caribbean Islands. Lane snapper (L. synagris) is a medium sized reef fish of commercial importance. This study describes the movement patterns of M. atlanticus and L. synagris across time and space using acoustic telemetry in Brewers Bay, St. Thomas, US Virgin Islands. Fourteen Atlantic tarpons and fifteen lane snappers were passively tracked in Brewer’s Bay to identify their general home range and changes in their diel, crepuscular and seasonal home ranges; as well as the vertical movement of tarpon. Home range size and location was calculated based on 50% and 95% kernel utilization distribution (KUD).  Only five tarpons and eleven lane snappers were present every day in Brewer Bay and showed greater than 80% residency time within the array. Both Atlantic tarpon and lane snappers showed significant higher rate of movement during the day compared to at night. The average KUD home range size for all Atlantic tarpon was 0.486 km2 and ranged between 0.082 km2 and 1.349km2. Atlantic tarpon primarily utilized the airport runway and the lagoon as their home range. Dawn and dusk home ranges overlapped with day and night home ranges. Monthly home range size varied significantly between tarpons for both 50% and 95% KUD (R2 0.4311, p=0.001). Home range expansion of Atlantic tarpon was primarily evident during the months of April, September and October, indicating they were following food sources and avoiding high fluctuations of water temperatures. Tarpon preferred shallow waters (<18m depth), but also moved to deeper waters up to 25m depth. We found that tarpon used larger ranges of the water column during the day and stayed at shallower depths at night. Although we found that tarpon stayed at similar average depth ranges throughout the year, we found that tarpon moved to deeper waters during the months of January and from July to October. The average KUD home range size for all lane snappers was 0.0316 km2 and ranged 0.009 km2 and 0.054 km2. Lane snapper showed home range site fidelity at four locations of Brewers Bay: Black Point reef, shallow Brewers Bay beach, mid Brewers Bay and Ratchford reef. Mean daytime activity space size was significantly larger than night activity space size of lane snapper for the 50% KUD (p-value = 0.0389). Lane snappers were primarily found in coral reefs (both aggregate and patch reef) during the day, while at night they were found in soft bottom habitats (seagrass beds and sand patches). Dawn and dusk home ranges overlapped with day and night home ranges. Home range sized varied significantly across months for both 50% and 95% KUD (R2=0.0238 and p=0.034). Home range expansion was evident in the spring and summer months (March-September), implying lane snappers moved to nearby areas within Brewers Bay to participate in spawning aggregations.


Kari Gerkhe

Home Range And Habitat Use Of Juvenile Green Sea Turtles (Chelonia mydas) In Brewers Bay, St. Thomas, USVI

Green turtles living in coastal foraging areas often occupy distinct home ranges within which they visit resting and foraging sites. Knowledge about the size of home ranges and movement patterns within these areas is important for sea turtle conservation. However, few data are available for the wider Caribbean. This study measured the movement pattern of five juvenile green sea turtles in Brewers Bay, St. Thomas, in the US Virgin Islands. Each turtle was fitted with a Vemco V13 acoustic transmitter and tracked from 90 to 214 days. Turtles were tracked with a fixed array of 30 acoustic receiving stations placed ~200-260 meters apart throughout Brewers Bay. Minimum convex polygon (MCP) and kernel density estimator (KDE) techniques were used to measure home range size. Home ranges were split into day vs. night times and compared by using utilization distributions (UD). Habitat classification was done in areas of high turtle activity and overlapped with home ranges. A general linear model was used to explore the relationship between the home range size (95% UD), core area size (50% UD), and potential predictors: mass. Average KDE day home range size was 63.3 Ha and average day core area was 6.9 Ha. Average KDE night home range size was 35.9 Ha and average night core area was 5.1 Ha. All five incremental area plots became asymptotic, indicating that the home range estimates are robust. There was a statistically significant relationship between core area size and predictor variable (P-value= 0.002; mass). Tracking results showed that all five turtles remained in Brewers Bay for 98% of the tracking duration. During the day turtles were located in seagrass beds and at night they moved to resting areas associated with natural and artificial coral reefs. Core areas for foraging overlapped with seagrass beds dominated by Syringodium filiforme; turtles occurred less frequently in seagrass beds with the invasive Halophila stipulacea. During the night there is less activity when compared to day time hours. Our data confirm that Brewers Bay is an important foraging and resting habitat for juvenile green sea turtles and that their foraging movements center on areas with S. filiforme. These areas in return should receive focused management for both seagrass and reefs to protect green sea turtles. With this management these areas should receive protection from recreational boaters and tourists to prevent the spread of the invasive H. stipulacea.

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Diel Patterns In Movements Of Mutton Snapper, Lutjanus analis, Within Home Ranges And On Spawning Grounds In The US Virgin Islands

Coral reefs are highly heterogeneous environments across which fish move in daily, seasonal, and ontogenetic patterns. Some larger reef fish participate in transient fish spawning aggregations (tFSAs), events at predictable times and locations during which fish migrate tens to hundreds of kilometers to spawn in large groups. The mutton snapper, Lutjanus analis, is a large, generally solitary species of reef fish that is of economic and ecological importance. This species shows diel movements across habitats within its home range as well as seasonal migrations to tFSA sites. This study describes movements of L. analis using acoustic telemetry at home ranges and spawning grounds in the US Virgin Islands (USVI). Six individuals were passively tracked within their home ranges in Brewers Bay, on the southwestern side of St. Thomas, to identify diel patterns in home range size and benthic habitat preferences. Separately, twenty-four individuals were passively tracked around a known spawning aggregation near the Mutton Snapper Seasonal Closed Area (MSSCA) along the southwest bank of St. Croix, in order to better understand how to manage the population. Specifically, the study sought to identify timing of aggregation formation, movement of the aggregation throughout the day, and the appropriateness of timing and boundaries of the MSSCA. Five of six tagged L. analis in Brewers Bay were present in the bay every day and showed residence times of greater than 90% within their home range. Home ranges were relatively small at an average of 0.112 ± 0.086 km2, variable in size and location, and characterized by distinct diel movement patterns. In St. Croix, spawning L. analis began to appear at the array around 2 days before the full moon, consistently from April through June in 2015-2017, when the MSSCA was closed to fishing. The number of individuals present at the southwest bank peaked at 5 days after the full moon (DAFM), and most left the bank by 10 DAFM each month. Diel movements of tagged fish were recorded along the bank, between the apparent spawning site at the western end of the shelf edge and an area farther east near the MSSCA. Tracked fish spent only 47% of total time detected within the MSSCA, but this occurred during nighttime, when they are most likely to be fished. The results of this study demonstrate direct connectivity between habitat types and across seascapes, highlighting the importance of ecosystem-level management strategies to protect species of interest. Determining the size and benthic composition of home ranges and spawning locations, as well as identification of migratory corridors, can inform the planning of marine protected areas that will best protect economically and ecologically important species like L. analis across all life stages.



Reconstructing Male Hawksbill (E. imbricata) Genotypes in the Nesting Population of Buck Island Reef National Monument, St. Croix: An Assessment Of Multiple Paternity And The Breeding Sex Ratio

Recent advances in molecular genetics are playing a central role in the understanding of population genetics, including insight into the life of male sea turtles. One genetic technique in particular, microsatellite analysis, can be used to provide an in-depth look at mating patterns and the genetic dynamic of a given sea turtle population (Stewart and Dutton 2012). Microsatellites can valuable in finding evidence of multiple paternity (MP) and determining the breeding sex ratio (BSR). The National Park Service at Buck Island Reef National Monument (BIRNM) in St. Croix USVI has been conducting annual night time monitoring of the Critically Endangered Caribbean hawksbill (Eretmochelys imbricata) since the summer of 1988 when 12 nesters were observed. The program has had a major impact on the nesting population, seeing an average of 62.7 nesting females over the last 10 years. In 2016, during annual patrols tissue samples were collected from 28 female hawksbills and ten of their respective hatchlings. The genetic identity of maternal and hatchlings were compared using six polymorphic microsatellite markers, allowing for the identification of the male/s responsible for siring each clutch. This led to the identification of 29 breeding males from 28 nests, providing an estimated operational sex ratio of 1.11:1 adult males to females. The analysis also showed evidence of multiple paternity within 3 nests (10.7%) of the BIRNM population. This suggests that hawksbill MP rates may be less variable (0-20%; Joseph and Shaw 2011, Phillips et al. 2013, 2014 and Gonzalez-Garza 2015) than in other species of sea turtle. While the relatively balanced BSR suggests that the effect of female hatchling bias (Wibbels et al. 1999; and Wibbels 2003) observed in clutches has yet to be  seen in the BIRNM population.

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The Acclimatization Of The Caribbean Fused Staghorn Coral Acropora prolifera To Non-Natal Locations

Following the Caribbean wide population decline of Acropora palmata and A. cervicornis, there is a natural occurrence of a viable reproductive hybrid between these species, A. prolifera or fused staghorn coral. The natural occurrence of A. prolifera represents a significant evolutionary mechanism which may increase genetic diversity and subsequent resilience in remaining Acropora populations. With limited physiological data on this acroporid hybrid, the goal of this study was to provide baseline information on physiological differences between distinct hybrid populations and across multiple genotypes. The experimental design was intended to provide both comparable data with past studies on the parental species and recently developed coral restoration methodologies. Common garden experiments were conducted using A. prolifera fragments from two geographically distinct offshore islands Flat Cay and Inner Brass near St. Thomas, U.S. Virgin Islands. Among the sampled fragments, three genotypes from each location were identified using molecular analysis. Health metrics including growth rates across vertical, horizontal, and perpendicular axes and signs of ecological and environmental stressors including mortality, predation, temperature, and disease were compared between non-natal and natal genotypes. We hypothesized that natal fragments would have higher growth rates and lower signs of stress compared to non-natal fragments. Furthermore, we analyzed the linear relationship between growth rates and optimal thermal conditions in situ. Using linear mixed effects models, non-natal genotypes showed no detectable differences in growth rates for each axes or stress metrics when transplanted to a novel location. Non-natal fragments did however, show higher predation than natal fragments (generalized linear mixed effects model, family: binomial, z = 2.12, p = 0.033). Using multiple linear regressions we observed a positive linear relationship between vertical (β = 0.121, t(263) = 2.15, p = 0.02) and horizontal (β = 0.204, t(263) = 3.01, p < 0.01) growth axes with temperature but not for perpendicular growth rates. Overall, these results suggest site adaptation does not limit the acroporid hybrid’s ability to acclimate to non-natal locations. Furthermore, we also observed similar growth rate trends within optimal temperature ranges as seen with the parental species. This study provides baseline physiological data for the acroporid hybrid and supports the incorporation of A. prolifera in a controlled manner with current and future coral restoration efforts to re-establish Acropora populations throughout the Caribbean. 

"I'm grateful to have completed my masters at UVI. It was an honor to graduate at the same University as my mom. It was a pleasure working with so many talented people and I'm proud of the accomplishments we achieved. Creating awarding winning video content aimed at wider audiences, conducting vital and important research on Caribbean and USVI marine ecosystems, and most importantly forming lasting relationships with friends I can now call colleagues, just to name a few of my experiences. I had an unforgettable time." – Colin Howe

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Predictors Of And Variability In Seagrass Sediment Blue Carbon From St. Thomas, U.S. Virgin Islands

Seagrass habitats capture and store carbon in the sediment, thus providing a key ecosystem service. This sediment carbon storage in coastal vegetated habitats is known as blue carbon and blue carbon habitats are known to store and sequester more organic carbon per unit area than most other terrestrial, vegetated ecosystems. In the U.S. Virgin Islands, no studies to-date quantify sediment carbon content of seagrass beds or test meadow properties (percent cover, shoot height, shoot density) as predictors of sediment carbon. This study measured sediment organic matter with loss-on-ignition (LOI) and sediment organic carbon with elemental analysis techniques, from 60 cores (20 cm long, 7.6 cm diameter) in native seagrasses (Thalassia testudinum, Syringodium filiforme), invasive seagrass (Halophila stipulacea), and un-vegetated sand, at three sites around St. Thomas (Brewers Bay, Frenchman Bay, St. Thomas East End Reserves). We hypothesized that sediment carbon density would decrease with decreasing seagrass canopy complexity and structure, such that: T. testudinum > H. stipulacea > S. filiforme > sand. Average sediment carbon density per core was low, 2.56-14.55 mg C cm3, and a three-way Analysis of Variance (ANOVA) showed a significant interaction between benthic habitat and site, which suggests that allochthonous sources of organic matter are playing a role in the variability of sediment carbon density. A multiple linear regression revealed seagrass percent cover and average shoot height as significant predictors of carbon density, implying aboveground morphology may contribute to deposition of allochthonous material and prevent re-suspension of sediment. Sediment organic carbon and organic matter were highly correlated (R2 = 0.77), yet different from published, global calibration curves for seagrass habitats, which may overestimate sediment organic carbon for these species and region. Results reveal that easily-measured seagrass characteristics can be used to estimate sediment carbon density, which may be useful for data-poor or resource-limited Caribbean locations.



Factors Influencing Activity Space Of Juvenile Hawksbill Sea Turtles

Hawksbill sea turtles (Eretmochelys imbricata) are an ecologically valuable but critically endangered species. Although activity area estimates of juvenile hawksbills have been quantified at specific sites, drivers of space use remain understudied. Using passive acoustic telemetry and morphometrics from captures, I analyzed factors that may influence the size of weekly activity areas (95% Kernel Density Estimations) of 19 juvenile hawksbill sea turtles (25.9-62.3 cm SCL) in and around Brewer’s Bay, St. Thomas, U.S. Virgin Islands. A linear mixed model was used to investigate whether habitat complexity, turtle size, body condition, and water temperature influenced the space use of 19 juvenile hawksbills, with individual turtle ID as a random effect. In the full model, water temperature (p = 0.11), body condition index (p = 0.12), and straight carapace length (p = 0.66) were non-significant factors, but average habitat rugosity (a measure of habitat complexity) was significant (p < 0.0001). The best fit model (AICc = -1039.04) included rugosity as the only fixed factor. Turtle ID accounted for 47-48% of the unexplained variance in the data, suggesting that there are additional, individual-specific variables that may explain the variation in space use such as territoriality, cost-effectiveness of activity, or foraging strategy. Understanding the space use of juvenile hawksbills during this coastal, benthic-feeding phase could be critical for better management of priority habitats, and lead to better protection for this critically endangered species.



Microplastic Abundance Influenced By Anthropogenic Activity In St. Thomas, USVI

As plastic waste is exposed to UV radiation, high temperatures, and mechanical weathering, it breaks down into smaller pieces. Microplastics are plastics that are less than 5 mm in size. Microplastics can enter the marine environments through waste water discharge and rain water run-off. They are often mistaken for food and ingested by sea birds, fish, and corals, causing physical harm. Additionally, chemical pollutants present in the environment tend to adsorb to plastic surfaces, providing the opportunity to bioaccumulate in the food web if ingested. Many studies have quantified microplastics in coastal environments around the world. However, very few studies have quantified them in the Caribbean, and only at regional scales. This study quantifies microplastics on beaches and surface waters in embayments around St. Thomas, USVI, and tests whether microplastics are more abundant in bays with greater anthropogenic activity in associated watersheds. Results show that microplastics and microfibers (between 0.3mm - 1mm) are present in beach sediment and surface waters on St. Thomas, and are more abundant in most embayments experiencing high anthropogenic activity in associated watersheds. Microplastics were most abundant in beach sediment, but appear to be not as abundant on beaches that provide waste receptacles and are regularly cleaned. Near shore surface water samples mostly consisted of microfibers which could be due to marine based activities (i.e. fishing and boating activity) and/ or waste water effluent discharge. These results provide a foundation for future research on microplastic sources and sinks within the USVI territory as well as their impacts on the environment and humans.


Sam Mitchell

The Recovery Of Seagrass And Chelonia Mydas (Green Sea Turtle) After Hurricane Earl In 2010 In Brewers Bay, St. Thomas

Green sea turtles (Chelonia mydas) are keystone megavores that mainly prefer to forage upon seagrass in the neritic stages of their life cycle, maintaining healthy seagrass meadows by cropping seagrass and preventing high biomass and states of anoxia. Little is known about green sea turtles’ response to disturbances such as large storms and subsequent damages to their foraging grounds. Here I studied the effect of Hurricane Earl on green sea turtle abundance and seagrass cover in Brewer’s Bay in 2010. My study began in 2013 and continued until 2016; I conducted swimmer surveys that counted green sea turtles, which followed previously established band transect methods from 2007 and 2008. These observations were recorded as green sea turtle/hectare and green sea turtle/swimmer/hour. These data were compared to historical data obtained from 2007/2008 and 2011. Additional surveys were conducted by University of the Virgin Islands masters students to estimate percent cover of seagrass and quantify shoot density. These data were compared to previously conducted surveys since 2009. The results show that the mean green sea turtle/ swimmer/hour dropped from 6 to 1.4 due to Hurricane Earl and then increased to 11.2 by 2016. The data before and after Hurricane Earl were shown to be statistically different. Mean green sea turtle/Hectare went from 6.4 in 2007/2008 down to 3.3 after the storm in 2011, and began to climb to a mean of 17.9 by 2016. Again, there was a statistical difference before and after the storm. The mean percent cover of seagrass followed a similar trend, where it was at 28.7 percent in 2009, dropped to just 2.2 percent after the storm in 2010, and rose to 67.6 percent cover by 2016. A large part of this increase is due to the introduction of H. stipulacea to Brewer’s Bay, which in 2016 accounted for 64.1 percent of the seagrass cover. There was a significant difference between pre-storm levels and post-storm levels of percent cover. My findings confirmed that seagrass coverage was reduced by the storm, and as a result green sea turtles left the bay. A few years later, seagrass was reestablished into the bay, and green sea turtles began to return. By 2016, both seagrass cover and green sea turtle abundance had exceeded pre-storm levels. This may be due to the large increase of percent cover of seagrass because of the invasion of H. stipulacea. The seagrass meadows of Brewer’s Bay are still a foraging ground for green sea turtles and should be protected from recreational activities and development, such as boating and construction in the meadows.  Monitoring should be continued to keep watch on the expansion of H. stipulacea and its potential effects on the bay.


Lauren Olinger

An Evaluation Of Local And Community-Scale Multispecies Competition Among Corals, Sponges, And Macroalgae On Reefs In The U.S. Virgin Islands

Benthic communities on Caribbean reefs are structured by competition among corals, sponges, and macroalgae, yet little is known about how these groups compete in a multispecies context. In this study, experimental and observational field research and a spatial simulation model were used to investigate multispecies competition on two reefs in the U.S. Virgin Islands. During a six-month field experiment, local multispecies and pairwise competitive interactions were simulated among corals (Porites astreoides), sponges (Desmapsamma anchorata, Aplysina cauliformis) and macroalgae (Lobophora variegata). High resolution 3D models were generated using photogrammetry to measure individual growth in each competitive scenario. A benthic survey of pairwise overgrowth and standoff interactions was conducted to calculate transitivity indices for 18 combinations of locally abundant species. Results from the experiment and survey suggest a competitive hierarchy among corals, sponges, and macroalgae, in which corals are the inferior competitors. In the experiment, D. anchorata overgrew P. astreoides more rapidly when the sponge was in contact with L. variegata, causing the coral to lose a greater percentage of surface area during local multispecies competition with L. variegata and D. anchorata. Intransitivity indices from benthic surveys indicated at least 10 competitive hierarchies at each reef site, zero competitive networks, and a scarcity of standoffs compared to previous studies employing similar methods. A spatially-explicit modelling framework was built and parameterized with experimental data. Once validated, the model will be used to assess emergent patterns resulting from individual-based behaviors observed during the experiment (e.g., macroalgae facilitation of sponge-coral overgrowth). Simulations may also clarify whether tradeoffs in competitive ability and life-history dynamics may promote coral coexistence despite proliferation of sponges and macroalgae. Better understanding of these complex competitive dynamics can help clarify the processes structuring benthic communities, the factors impairing coral resilience, and more effective means to mitigate loss of corals on Caribbean reefs.

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Tanya Ramseyer

The Effect Of Herbivory And Nutrient Addition On The Dynamics Of The Macroalgae, Dictyota spp. On Caribbean Coral Reefs In St. Thomas, U.S. Virgin Islands

Caribbean coral reefs are experiencing an unwanted shift from coral to algal domination. A major question in coral reef ecology and management concerns understanding the factors that are leading to algal phase shifts and controlling macroalgal dynamics. Determining which factors, is extremely important for the resilience and survival of Caribbean coral reefs. The most abundant type of macroalgae on shallow coral reefs in St. Thomas, U.S. Virgin Islands is the opportunistic, brown algae, Dictyota spp. In this study two factors, herbivory and nutrient addition, were manipulated during three experiments at three sites south of St. Thomas. During experiment 1, herbivore reduction cages and plant fertilizer (OsmocoteTM) were used to explore how nutrient addition and herbivory affect thallus heights and percent cover over 4 months. At two shallower sites (11 and 14 m), growth was only changed (reduced) in uncaged-enriched plots, potentially reflecting targeting of enriched thalli by herbivores, but also generally demonstrating that Dictyota in ambient conditions was not vulnerable to herbivory and was nutrient replete. A deeper third site (20 m) with lower Dictyota abundance showed little response to any manipulation. To ensure the results reflected true impacts of herbivory and nutrients, experiment 2 used the same treatments to explore Dictyota biomass at one site (14 m) exclusively, for 21 days. The results of experiment 2 suggested, unexpectedly, that nutrient addition inhibited Dictyota growth, but also that herbivory had an equally reducing effect on growth, with no interaction. A third experiment was conducted across four levels of fertilizer addition (0, 5, 10, 20 g) and showed that over 21 days ambient conditions without herbivory resulted in no growth, whereas 5 g of nutrient addition reduced biomass by half, with concentrations above 5 g resulting in almost total thallus breakdown. The results suggest that Dictyota was not nutrient limited at any of the study sites, even though water column nutrient levels were often near detection limits, and was only weakly controlled by the herbivore population. Factors responsible for Dictyota abundance on modern Caribbean reefs may reflect changes in herbivore communities that have occurred on reefs altered by fishing and a reduction in coral cover. This study reinforces the need for essential management protecting herbivorous fishes, reducing coral reef stressors, and conducting further research on how nutrient addition affects Caribbean macroalgal growth.

"My experience at UVI has been educational, challenging and exciting. I am so grateful for the opportunity to research beautiful coral reefs, gain hands-on experience and make life-long friendships while in the MMES program at UVI. This multi-faceted program is truly one-of-a-kind and I encourage others to apply so they can experience it also!" – Tanya Ramsayer



Identifying Pathogen Sources And Vectors: A spatiotemporal RidgeTo-Reef Valuation Of A Gorgoinia ventalina Aspergillosis Epizootic in St. Thomas USVI

Although much is known about the Gorgonia ventalina Aspergillus sydowii pathosystem, the population source(s) and vector(s) for the fungal pathogen, A. sydowii, are unknown. Determining pathogen sources and vectors is one of the five priorities in coral disease research and is necessary for future epizootic mitigation and management. We investigate the longstanding, yet unexplored, hypothesis that neighboring land is a population source of A. sydowii, and sediment laden terrigenous runoff is a vector for the pathogen’s transport from land to marine waterways; resulting in disease of the common Caribbean sea-fan Gorgonia ventalina. On St. Thomas (United States Virgin Islands), within four north-side bays, in four permanently established quadrats, individually tagged fans were assessed using SCUBA. Each site was surveyed 10 times, on approximately 37-day intervals between August 2013 and August 2014. G. ventalina densities, heights, size class distributions, abrasion prevalence, prevalence of the predatory snail Cyphoma gibbosum and their lesions, and prevalence of two hypothesized forms of aspergillosis are presented herein as a baseline dataset for St. Thomas’s north-side near-shore G. ventalina communities. Moreover, we examined frequencies of abrasion and C. gibbosum predation lesions in fans with and without aspergillosis to determine if abrasion or predation was associated with disease. We also examined the relationship between aspergillosis and fan size. Additionally, the watersheds associated with each survey site bay were assessed for acreages, land cover, and slope severities to determine if slope severity or development was positively associated with prevalence and abundance of aspergillosis lesions. Furthermore, precipitation, total and dissolved marine nutrients, sediment accumulation and fractions, and ocean temperature were collected concurrently with in-situ G. ventalina surveys. 

Remarkably, we captured the onset of a localized aspergillosis epizootic. The epizootic occurred without the purple hyperpigmentation and necrotic tissue loss, exposing the axial skeleton, that has classically been associated with G. ventalina aspergillosis. Rapid loss of anastomosing gorgonin and tissues, causing the formation of holes, without intensified purpling at the lesion margin, was repeatedly observed. These observations, and re-examination of historical literature figures and lesion descriptions prompted us to categorize aspergillosis into two types: aspergillosis I- chronic purpling of tissues, often surrounding necrotic lesions, and aspergillosis II- recent loss of tissue and skeletal structure without purpling. 

A seasonal upswing in marine temperature coincided with the significant increase in prevalence and abundance of aspergillosis II lesions at Hendrik Bay. Yet, the same increase in disease was not observed at the other three sites, despite a similar increase in temperature. Hendrik Bay was associated with the greatest coverage of bare land and very steep slopes, and sediment data revealed greater percentages of terrigenous sediment collected after rain events at this site compared with the other three sites; where disease prevalence remained constant. G. ventalina densities were highest at Hendrik and Tutu Bays, and sea fan sizes were largest at Hendrik and Dorothea Bays. Aspergillosis II tended to affect larger sea fans but was not associated with abrasion or predation. These results suggest that land cover and runoff played a role in a spatially localized epizootic of aspergillosis.



Age, Growth, And Reproduction Of The Queen Triggerfish, Balistes vetula, From The U.S. Virgin Islands

The queen triggerfish, Balistes vetula, is a commercially important, data- deficient Caribbean and Atlantic reef fish. We analyzed age, growth, and reproduction for this species from fisheries-dependent samples in the U.S. Virgin Islands (USVI). This is the first comprehensive study of the Balistes species to include age and reproduction life history information together. From 2015 to 2017, 1,019 samples were collected, ranging from 150 to 466 mm FL in size. Queen triggerfish from St. Croix were significantly smaller in size and weight than those in St. Thomas. We found that males from both islands were significantly larger than females. Based on reproductive histology, the spawning season is from December-August. Female size at 50% maturity was 287 mm FL in St. Thomas and 265 mm FL in St. Croix. Only one immature male was observed in our study. Our observed sex ratios did not significantly differ from 1:1 on either island. Age and growth analysis in St. Thomas found this species to be relatively long lived, ranging from 1 to 14 years, and slower growing, resulting in an overall growth coefficient of k = 0.33. Sex-specific growth curves were fitted, resulting in the following von Bertalanffy equations: FLt = 426[1 – e-0.42(t + 0.65)] for males and FLt = 430[1 – e-0.28(t + 0.34)] for females. Females were significantly older and exhibited a slower growth rate than males. Ninety-four percent of samples were between 3 and 10 years. The differences in the commercial fisheries and life history parameters between the two distinct island shelves of the USVI suggest that this species may require more tailored management by island; the queen triggerfish fishery is currently managed within the triggerfish and filefish unit across the territory. Local and regional management have a need for long-term fisheries-dependent studies such as this to collect relevant data for optimally designed fishery management plans.



Evaluating The Abundance And Size Distribution Of Indo-Pacific Lionfish (Pterois spp.) In The US Virgin Islands

The Indo-Pacific lionfishes, Pterois volitans and Pterois miles, are predatory marine fishes that have successfully established populations in the western North Atlantic, Caribbean Sea, and Gulf of Mexico.  Their rapid spread and distribution can be attributed to unique life history and behavioral traits.  In their invaded range, lionfish have higher densities and reach larger maximum sizes across a multitude of habitats and depths compared to their native range.   In the United States Virgin Islands, the first lionfish sighting occurred in 2008, and since then the lionfish population can be seen increasing over 100% in the first two years of the invasion.  In the present study, lionfish were found to be larger in St. Thomas/St. John (mean ± SD: 21.6 ± 7.7 SD cm) than in St. Croix (17.5 ± 6.0 SD cm; p < 0.001).  Lionfish were found occupying a variety of habitat types, including high-profile reef (n = 138), hard bottom (n = 4), patch reef (n = 74), rocky reef (n = 6), reef wall (n = 29), seagrass (n = 7), and unconsolidated habitats (n = 14), and depths ranging from <1 m to 64 m.  On high-profile reefs, a positive, but weak, relationship was found between lionfish length and depth (r2 = 0.09, p <0.001).  Moreover, lionfish were found occupying coral reefs primarily dominated by Orbicella spp., formerly Montastraea (p = 0.029) and with a higher density of prey (p <0.012), suggesting lionfish habitat selection may be associated with structurally complex reef habitats and prey availability.  There was no evidence of lionfish affecting native fish assemblages and benthic communities, but their impacts could change as the population continues to grow.  This study provides managers with vital information that would aid in their control of the lionfish population by identifying areas with the highest abundance of adult and juvenile lionfish and to identifying characteristics that may be driving lionfish habitat selection.

Logan Williams

The Impact of Coral Species Diversity on White Plague Disease Transmission

Within the past fifty years, coral diseases have devastated coral communities throughout the Caribbean. One particularly virulent disease that has been shown to cause widespread mortality as well as decreasing coral cover is white plague. The coral disease white plague (WP) has been shown to affect approximately 31 coral species, however the role species susceptibility plays in the initiation and propagation of WP is mostly unknown. In particular, species from the Orbicella genus, have suffered substantial losses in coral cover as a result of white plague outbreaks and are considered susceptible to numerous other coral disease. However, the dynamics behind species susceptibility to disease are poorly understood. Disease prevalence may be higher in abundant species since there are more hosts for infectious agents to occupy. Conversely, prevalence may be higher in species that lack morphological and immunological defenses against disease. This study quantified WP disease transmission from Orbicella annularis  to three susceptible and abundant coral species in the USVI (Orbicella annularis, Siderastrea siderea and Porites astreoides). We found WP primarily affects  Orbicella annularis and Siderastrea siderea, which may be as a result of species specific traits and not overall host abundance.