University of the Virgin Islands

A study is the first to evaluate substrate recolonization by sponges in the U.S. Virgin Islands after two catastrophic storms using genetic analyses to understand how much clonality verses sexual recruitment occurs on coral reefs post-storms. Results show that populations of clonal marine species with low pelagic dispersion, such as A. cauliformis, may benefit from increased frequency and magnitude of hurricanes to maintain genetic diversity and combat inbreeding, enhancing the resilience of Caribbean sponge communities to extreme storm events. Named for its ropy-looking long branches, Aplysina cauliformis, a coral reef sponge, provides a critical 3D habitat for marine organisms and helps to stabilize the foundation of coral reefs. However, these upright branching sponges are highly susceptible to breaking during storms, which increases sponge fragmentation and contributes to population clonality and inbreeding. Many sponges can survive severe damage and undergo frequent fragmentation, which is considered a mechanism for asexual reproduction. While fragmentation is a commonly utilized reproductive strategy in rope sponges, they also can reproduce sexually by producing larvae. How and whether they recolonize following extreme weather events is critical for the restoration and resilience of coral reef ecosystems. Hurricanes Irma and Maria -- both in 2017 -- were two rapid succession storms that provided researchers from Florida Atlantic University's Harriet L. Wilkes Honors College and Harbor Branch Oceanographic Institute, and collaborators from the University of the Virgin Islands, the University of Mississippi and the University of Alabama, with a unique opportunity to address a priority concern -- the resilience of coral reef sponge populations after severe hurricanes. The researchers are the first to evaluate substrate recolonization by sponges in the U.S. Virgin Islands after these two catastrophic storms using genetic analyses to understand how much clonality verses sexual recruitment occurs on coral reefs post-storms. To date, studies of storm impacts have largely focused on scleractinian or stony corals. Results of the study, published in the journal Molecular Ecology, reveal that populations of clonal marine species with low pelagic dispersion, such as A. cauliformis, may benefit from increased frequency and magnitude of hurricanes to maintain genetic diversity and combat inbreeding, enhancing the resilience of Caribbean sponge communities to extreme storm events. The A. cauliformis population before the hurricanes was highly clonal but shifted to greater sexual reproduction for recolonization after the hurricanes, with 85 percent of sexual reproduction mainly due to local larval recruitment. Major storm events favored sponge larval recruitment but did not increase the genetic diversity. "Branching coral populations exposed to intermediate or low storm frequencies are known to have primarily sexual populations, whereas sites with the highest storm frequencies have mostly clonal populations," said Andia Chaves Fonnegra, Ph.D., principal investigator and an assistant professor of biology in FAU's Harriet L. Wilkes Honors College and Harbor Branch. "In contrast, our findings showed greater recruitment of sexually derived sponge larvae than clones arising from fragmentation/regeneration after these extreme events, maintaining genetic diversity. Because A. cauliformis sponges reproduce both asexually via fragmentation and sexually, interactions between these mechanisms may maximize their dispersal efficiency and their likelihood of successfully recolonizing habitats." Larval recruits (genets) and fragments (ramets) were detected at all St. Thomas sampling locations post-hurricane, indicating a potential for rapid population recovery for this species that was not affected by site physiography. At all sites combined, 65.8 percent of the pre-hurricane adult sponges were genets compared to 85.1 percent of the post-hurricane juveniles. This suggests that recolonization of A. cauliformis after the hurricanes was largely due to sexual reproduction, with gene flow across distances up to 60 kilometers, between St. Croix and Buck Island in St. Thomas, detected among the study sites. For the study, scuba divers collected small samples of the thin purple morphotype sponges 14 and 22 months after the two Category 5 hurricanes in St. Thomas. Researchers then extracted genomic DNA from the sponge samples using a genotyping method based on sequencing uniform fragments called 2b-RAD. This emerging method is used for mapping, population genetics, genetic mapping and estimating alleles. Genetic diversity was estimated for the pre-hurricane (adults) and post-hurricane (adults and juveniles) populations as expected (He) and observed (Ho) heterozygosities with inbreeding coefficient (FIS) and compared. "Over short time scales, intermittent disturbances such as hurricanes can alter the structure and function of the coral reef benthic community and impact recovery time," said Chaves Fonnegra. "However, as we have demonstrated in our study, storm events don't affect all reef species equally and can promote diversity by creating open substrate for larval attachment and recruitment." Given predictions of more frequent intense hurricanes as climate continues to change, it is likely that major disturbances such as the unprecedented landfall of the two Category 5 hurricanes in St. Thomas will continue to influence the population structure of coral reef species and their ecological interactions. Study co-authors are Iris Segura-Garcia, Ph.D., first author and a former postdoctoral fellow in the Chaves Fonnegra Lab; Julie B. Olsen, Ph.D., a professor of biological sciences, University of Alabama; Deborah J. Gochfeld, Ph.D., principal scientist, Department of Biomolecular Studies, the University of Mississippi; and Marilyn E. Brandt, Ph.D., research associate professor, University of the Virgin Islands. This research was funded by Chaves Fonnegra start-up funds and a National Science Foundation RAPID grant (OCE-1807807, Gochfeld, OCE-1808233, Olson and OCE1810616, Brandt).

A groundbreaking three-year study in the South Pacific has found evidence that ocean warming can trigger outbreaks of 'dinoflagellate-infecting RNA viruses' that attack symbiotic algae inside corals. Coral reef viruses have gained greater attention since being implicated in 2021 as a possible cause of stony coral tissue loss disease that has decimated Florida and Caribbean reefs for almost a decade. A groundbreaking three-year study in the South Pacific has found evidence that ocean warming can trigger outbreaks of "dinoflagellate-infecting RNA viruses" that attack symbiotic algae inside corals. Coral reef viruses have gained greater attention since being implicated in 2021 as a possible cause of stony coral tissue loss disease that has decimated Florida and Caribbean reefs for almost a decade. The breathtaking colors of reef-building corals come from photosynthetic algae that live inside the corals. A groundbreaking three-year study has found that viruses may increase their attacks on these symbiotic algae during marine heat waves. Few studies have examined how heat and other forms of stress affect coral virus outbreaks, and fewer still have looked at the reef-scale dynamics of those outbreaks. The study published online today in ISME Communications does both. It is also the first study to analyze the reefwide prevalence, persistence, triggers and health impacts of "dinoflagellate-infecting RNA viruses" (dinoRNAVs), single-stranded RNA viruses that infect the symbiotic algae that live inside the corals. Lead author Lauren Howe-Kerr said coral and marine disease researchers are paying closer attention to coral viruses in the wake of studies in October 2021 and February 2022 that found evidence suggesting viral infections of symbiotic dinoflagellates might be responsible for stony coral tissue loss disease (SCTLD). One of the deadliest coral diseases ever recorded, SCTLD has been decimating reefs in Florida and the Caribbean since it was first identified in 2014. "While this study is not focused on SCLTD, it builds our understanding of coral viruses, and particularly RNA viruses that infect coral endosymbionts," said Howe-Kerr, a Rice postdoctoral researcher who co-authored the study with more than a dozen colleagues from Rice, Northeastern University, the University of Oregon, the University of the Virgin Islands, Rutgers University, Oregon State University, George Mason University, New Zealand's National Institute of Water and Atmospheric Research and the Mote Marine Laboratory's Coral Reef Research and Restoration Center in Summerland Key, Florida. "Our work provides the first empirical evidence that exposure to high temperatures on the reef triggers dinoRNAV infections within coral colonies, and we showed those infections are intensified in unhealthy coral colonies," Howe-Kerr said. The study was carried out at the Moorea Coral Reef Long-term Ecological Research station on the Pacific Ocean island of Moorea in French Polynesia. Moorea, which is about 20 miles from Tahiti, is ringed by coral reefs. Samples from 54 coral colonies around the island were collected twice a year between August 2018 and October 2020. The warmest water temperatures during that span were in March 2019. Reefs across the island suffered heat-related stress during this period, including widespread bleaching. The study sites were located in a variety of reef zones that were subject to different kinds of environmental stress. For example, ocean-facing forereefs are deeper, with cooler and more consistent water temperatures, while near-shore fringing reefs in lagoons are subjected to the highest temperatures and greatest temperature variability. Howe-Kerr earned her doctorate from Rice in 2022 and recently finished a yearlong Ocean Policy Fellowship at the National Science Foundation. The sampling and analysis were carried out during her doctoral studies in the Rice lab of marine biologist and study co-authorAdrienne Correa. "It was a huge team effort to go out and locate and sample the exact same coral colonies two times a year over this three-year period," Correa said. "That was further complicated by the pandemic, which prevented us from sampling in March 2020, but in the end it was all worth it. We learned a great deal about reef-wide viral dynamics." Correa said it was clear from previous studies that corals "harbor lots of diverse viruses," but it wasn't known how specific viral types were distributed across a reef. A 2022 study from her group that was lead-authored by another former student, Carsten Grupstra, had detailed findings from tank-based experiments that showed viral activity of a single viral group -- dinoRNAVs -- in corals increased under heat stress. "This three-year study builds off that and shows it can also happen in the ocean," Correa said. "We saw the same kind of heat-induced increases in viral production across reefs." Howe-Kerr said the new study also offers one of the first glimpses of how dinoRNAVs behave in time and space over reefs and reef zones. "We were able to characterize the diversity of dinoRNAVs and their prevalence in colonies across multiple years and reef environments," she said. "We detected dinoRNAV infections in over 90% of the sampled colonies at some point in the three years. And the composition and diversity of viruses we found in those infections differed among reef zones. That indicates environmental conditions play a role in the dynamics of these outbreaks." While all 54 colonies survived the three-year experiment, 50% suffered partial mortality. The hardest hit were ocean-facing forereefs, which were almost three times more likely to experience partial mortality than were corals in the fringing reefs, which may be more used to dealing with the high temperatures of the shallower waters close to shore, Correa said. She said a wider variety of RNA viruses were found in heat-stressed colonies in 2019, which suggests viral production had increased. And the pattern proved strongest in colonies that suffered partial mortality, which points to specific host-virus interactions that could drive ecosystem impacts, she said. "Viral productivity will likely increase as ocean temperatures continue to rise," Correa said. "It's important to learn as much as we can about host-virus interactions, because they have the potential to alter the foundational symbiosis that underpins coral reef ecosystems." This research was funded by the National Science Foundation (2224354, 1933165, 1635913, 1635798, 2145472), an Early-Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences (2000009651), the Gordon and Betty Moore Foundation, Rice University, the Texas Branch of the American Society for Microbiology's Eugene and Millicent Goldschmidt Graduate Student Award fund, the American Philosophical Society's Lewis and Clark Fund for Exploration and Field Research, and Rice University's Wagoner Foreign Study Scholarship Program.

A more than 30-year marine conservation effort in the U.S. Virgin Islands helped aid the recovery of a fish species important in commercial, recreational and subsistence fisheries, a new study found. A more than 30-year marine conservation effort in the U.S. Virgin Islands helped aid the recovery of a fish species important in commercial, recreational and subsistence fisheries, a new Oregon State University study found. Red hind, a species of grouper in the Caribbean, historically experienced intense fishing pressure, which led managers to implement progressively restrictive fishing closures in the U.S. Virgin Islands. In a study just published in Frontiers in Marine Science, researchers at Oregon State and the University of the Virgin Islands found that the fishing restrictions at the location they studied helped lead to a more than 35% increase in average fish size and the recovery of the population to a benchmark considered sustainable for many fish species. "This is a management and conservation success," said Claire Rosemond, an Oregon State doctoral student and lead author of the study. "The recovery of the red hind population at the spawning aggregation tracks management decisions, so it appears that fishing restrictions are helping to accomplish the intended goal of recovering the red hind population and fishery." Globally, more than 200 species of marine fishes, including red hind, reproduce by forming spawning aggregations at specific times and locations. The predictability of these mass spawning events makes the aggregations susceptible to intense fishing pressure. Locations of many fish spawning aggregations in the Caribbean have been known and fished for decades. This has led to population collapse of several important species, including red hind, which are an important source of income and food for local people. By the late 1980s, the red hind population at a spawning site near St. Thomas, U.S. Virgin Islands showed signs of decline with a decrease in average fish length and an extremely skewed ratio of females to males because fishing disproportionately removed the larger males. This led fisheries managers in 1990 to establish the Red Hind Bank Marine Conservation District to protect the fish spawning site by seasonally closing the area to fishing during the months of peak spawning activity (December through February). In 1999, the district was permanently closed to fishing. The just-published research focused on that spawning site. The scientists used historical data collected by other researchers between 1988 and 2009 and gathered their own data during several trips to the U.S. Virgin Islands between 2018 and 2020. During those trips the resarchers caught, measured, and released 1,203 red hind. The mean size of the fish they caught was almost 16 inches, more than four inches longer than the mean size reported from data from 1988-89. Meanwhile, the female to male ratio at the spawning aggregation became less skewed over time. By a measure known as spawning potential ratio, the red hind are now at a benchmark considered sustainable for many fisheries, the researchers note, but that does not mean that continued recovery is guaranteed. "To me the take home message is this management measure worked, but it also means this management measure is currently working, so at this point in time let's keep it the way it is," said Scott Heppell, a co-author of the paper who is a professor in the Department of Fisheries, Wildlife, and Conservation Sciences at Oregon State in Oregon State's College of Agricultural Sciences. The recovery of the red hind population at the spawning aggregation site is due in part to management decisions, fishers adhering to closures and long-term monitoring. "The Marine Conservation District is a conservation success due to the participation of people from many different sectors," Rosemond said. "I think management agencies and fishers would be excited to know that their work and potential sacrifices, like not fishing in closed areas, have paid off." Richard Nemeth of the University of the Virgin Islands is also a co-author of this paper. The National Oceanic and Atmospheric Administration, the Puerto Rico Sea Grant College Program, and the Department of Fisheries, Wildlife, and Conservation Sciences funded this research.