1. de Souza, J.N., F.L.D. Nunes, C. Zilberberg, J.A. Sanchez, A.E. Migotto, B.W. Hoeksema, X.M. Serrano, A.C. Baker, and A. Lindner. Contrasting patterns of connectivity among endemic and widespread fire coral species (Millepora spp.) in the tropical southwestern Atlantic. Coral Reefs, 36(3):701-716, doi:10.1007/s00338-017-1562-0 2017

    Abstract:

    Fire corals are the only branching corals in the South Atlantic and provide an important ecological role as habitat-builders in the region. With three endemic species (Millepora brazilensis, M. nitida and M. laboreli) and one amphi-Atlantic species (M. alcicornis), fire coral diversity in the Brazilian Province rivals that of the Caribbean Province. Phylogenetic relationships and patterns of population genetic structure and diversity were investigated in all four fire coral species occurring in the Brazilian Province to understand patterns of speciation and biogeography in the genus. A total of 273 colonies from the four species were collected from 17 locations spanning their geographic ranges. Sequences from the 16S ribosomal DNA (rDNA) were used to evaluate phylogenetic relationships. Patterns in genetic diversity and connectivity were inferred by measures of molecular diversity, analyses of molecular variance, pairwise differentiation, and by spatial analyses of molecular variance. Morphometrics of the endemic species M. braziliensis and M. nitida were evaluated by discriminant function analysis; macro-morphological characters were not sufficient to distinguish the two species. Genetic analyses showed that, although they are closely related, each species forms a well-supported clade. Furthermore, the endemic species characterized a distinct biogeographic barrier: M. braziliensis is restricted to the north of the São Francisco River, whereas M. nitida occurs only to the south. Millepora laboreli is restricted to a single location and has low genetic diversity. In contrast, the amphi-Atlantic species M. alcicornis shows high genetic connectivity within the Brazilian Province, and within the Caribbean Province (including Bermuda), despite low levels of gene flow between these populations and across the tropical Atlantic. These patterns reflect the importance of the Amazon–Orinoco Plume and the Mid-Atlantic Barrier as biogeographic barriers, and suggest that, while M. alcicornis is capable of long-distance dispersal, the three endemics have restricted ranges and more limited dispersal capabilities.

  2. Serrano, X.M., M.W. Miller, J.C. Hendee, B.A. Jensen, J.Z. Gapayao, C. Pasparakis, M. Grosell, and A.C. Baker. Effects of thermal stress and nitrate enrichment on the larval performance of two Caribbean reef corals. Coral Reefs, doi:10.1007/s00338-017-1645-y 2017

    Abstract:

    The effects of multiple stressors on the early life stages of reef-building corals are poorly understood. Elevated temperature is the main physiological driver of mass coral bleaching events, but increasing evidence suggests that other stressors, including elevated dissolved inorganic nitrogen (DIN), may exacerbate the negative effects of thermal stress. To test this hypothesis, we investigated the performance of larvae of Orbicella faveolata and Porites astreoides, two important Caribbean reef coral species with contrasting reproductive and algal transmission modes, under increased temperature and/or elevated DIN. We used a fluorescence-based microplate respirometer to measure the oxygen consumption of coral larvae from both species and also assessed the effects of these stressors on P. astreoides larval settlement and mortality. Overall, we found that (1) larvae increased their respiration in response to different factors (O. faveolata in response to elevated temperature and P. astreoides in response to elevated nitrate) and (2) P. astreoides larvae showed a significant increase in settlement as a result of elevated nitrate, but higher mortality under elevated temperature. This study shows how microplate respirometry can be successfully used to assess changes in respiration of coral larvae, and our findings suggest that the effects of thermal stress and nitrate enrichment in coral larvae may be species specific and are neither additive nor synergistic for O. faveolata or P. astreoides. These findings may have important consequences for the recruitment and community reassembly of corals to nutrient-polluted reefs that have been impacted by climate change.

  3. Serrano, X.M., I.B. Baums, T.B. Smith, R.J. Jones, T.L. Shearer, and A.C. Baker. Long-distance dispersal and vertical gene flow in the Caribbean brooding coral Porites astreoides. Nature Scientific Reports, 6:21619, doi:10.1038/srep21619 2016

    Abstract:

    To date, most assessments of coral connectivity have emphasized long-distance horizontal dispersal of propagules from one shallow reef to another. The extent of vertical connectivity, however, remains largely understudied. Here, we used newly-developed and existing DNA microsatellite loci for the brooding coral Porites astreoides to assess patterns of horizontal and vertical connectivity in 590 colonies collected from three depth zones (≤10 m, 15-20 m and ≥25 m) at sites in Florida, Bermuda, and the U.S. Virgin Islands (USVI). We also tested whether maternal transmission of algal symbionts (Symbiodinium spp.) might limit effective vertical connectivity. Overall, shallow P. astreoides exhibited high gene flow between Florida and USVI, but limited gene flow between these locations and Bermuda. In contrast, there was significant genetic differentiation by depth in Florida (Upper Keys, Lower Keys and Dry Tortugas), but not in Bermuda or USVI, despite strong patterns of depth zonation in algal symbionts at two of these locations. Together, these findings suggest that P. astreoides is effective at dispersing both horizontally and vertically despite its brooding reproductive mode and maternal transmission of algal symbionts. In addition, these findings might help explain the ecological success reported for P. astreoides in the Caribbean in recent decades.

  4. Serrano, X., I.B. Baums, K. O’Reilly, T.B. Smith, R.J. Jones, T.L. Shearer, F.L.D. Nunes, and A.C. Baker. Geographic differences in vertical connectivity in the Caribbean coral Montastraea cavernosa despite high levels of horizontal connectivity at shallow depths. Molecular Ecology, 23(17):4226-4240, doi:10.1111/mec.12861 2014

    Abstract:

    The deep reef refugia hypothesis proposes that deep reefs can act as local recruitment sources for shallow reefs following a disturbance. To test this hypothesis, nine polymorphic DNA microsatellite loci were developed and used to assess vertical connectivity in 583 coral colonies of the Caribbean depth-generalist coral Montastraea cavernosa. Samples were collected from three depth zones (≤10, 15–20, and ≥25 m) at sites in Florida (within the Upper Keys, Lower Keys, and Dry Tortugas), Bermuda, and the U.S. Virgin Islands. Migration rates were estimated to determine the probability of coral larval migration from shallow to deep and from deep to shallow. Finally, algal symbiont (Symbiodinium spp.) diversity and distribution were assessed in a subset of corals to test whether symbiont depth zonation might indicate limited vertical connectivity. Overall, analyses revealed significant genetic differentiation by depth in Florida, but not in Bermuda or the U.S. Virgin Islands, despite high levels of horizontal connectivity between these geographic locations at shallow depths. Within Florida, greater vertical connectivity was observed in the Dry Tortugas compared to the Lower or Upper Keys. However, at all sites, and regardless of the extent of vertical connectivity, migration occurred asymmetrically, with greater likelihood of migration from shallow to intermediate/deep habitats. Finally, most colonies hosted a single Symbiodinium type (C3), ruling out symbiont depth zonation of the dominant symbiont type as a structuring factor. Together, these findings suggest that the potential for shallow reefs to recover from deep-water refugia in M. cavernosa is location-specific, varying among and within geographic locations likely as a consequence of local hydrology.