Benthic cyanobacterial bloom impacts the reefs of South Florida (Broward County, USA)

Benthic cyanobacteria of the genus Lyngbya can form prominent mats and blooms in tropical and subtropical coral reef and seagrass habitats worldwide. A Lyngbya bloom on the reef tract offshore of Broward County, Florida, was first noted in 2002, and although it is seasonally variable in its distribution and abundance, it has persisted and spread over the past 3 years. In this study, the most abundant species of Lyngbya found in the blooms have been identified and compared to other species of Lyngbya by morphological and molecular methods. The most common species of Lyngbya is consistent with the properties of Lyngbya confervoides C. Agardh. The 16S ribosomal DNA sequence shares 88–92% identity with other known Lyngbya sequences, suggesting that this bloom consists primarily of a new, previously unsequenced species of Lyngbya. The second most common Lyngbya in the bloom is consistent with Lyngbya polychroa. This persistent bloom is a concern because it smothers octocorals and other invertebrates and negatively impacts these southeastern Florida reefs.     

Changes in coral reef communities among the Florida Keys, 1996–2003

Hard coral (Scleractinia and Milleporina) cover data were examined from 37 sites surveyed annually from 1996 to 2003 in the Florida reef tract, USA. Analyses of species numbers and total cover showed that site-to-site differences were generally very much greater than differences among times within sites. There were no significant differences among different geographical areas within the reef tract (Upper, Middle and Lower Keys). Large-scale changes documented included a reduction in species numbers and total cover on both deep and shallow offshore reefs between 1997 and 1999 followed by no recovery in cover, and only scant evidence of any recovery in species numbers by 2003. These changes coincided with bleaching events in 1997 and 1998, and the passage of Hurricane Georges through the Lower Keys in 1998. The lack of recovery among offshore reefs suggests that they were no longer resilient. Multivariate analyses revealed that some sites showed relatively little temporal variation in community composition, essentially random in direction, while others showed relatively large year-on-year changes. There was little evidence of any major region-wide changes affecting assemblage composition, or of any events that had impacted all of the sampling sites in any single year. Instead, different sites exhibited differing patterns of temporal variation, with certain sites displaying greater variation than others. Changes in community composition at some sites are interpreted in the light of knowledge of events at those sites and the relative sensitivities of species to various stressors, such as changes in cover of Acropora palmata and Millepora complanata at Sand Key following the bleaching events and hurricane in 1998, and declines in Montastraea annularis at Smith Shoal following a harmful algal bloom in 2002. For most sites, however, it is impossible to determine the causes of observed variation.     

NUTRIENT EFFECTS ON SEAGRASS EPIPHYTE COMMUNITY STRUCTURE IN FLORIDA BAY1

A field experiment was employed in Florida Bay investigating the response of seagrass epiphyte communities to nitrogen (N) and phosphorus (P) additions. While most of the variability in epiphyte community structure was related to uncontrolled temporal and spatial environmental heterogeneity, P additions increased the relative abundance of the red algae–cyanobacterial complex and green algae, with a concomitant decrease in diatoms. When N was added along with P, the observed changes to the diatoms and the red algae–cyanobacterial complex were in the same direction as P‐only treatments, but the responses were decreased in magnitude. Within the diatom community, species relative abundances, species richness, and diversity responded weakly to nutrient addition. P additions produced changes in diatom community structure that were limited to summer and were stronger in eastern Florida Bay than in the western bay. These changes were consistent with well‐established temporal and spatial patterns of P limitation. Despite the significant change in community structure resulting from P addition, diatom communities from the same site and time, regardless of nutrient treatment, remained more similar to one another than to the diatom communities subject to identical nutrient treatments from different sites and times. Overall, epiphyte communities exhibited responses to P addition that were most evident at the division level.     

Carbon Mineralization and Labile Organic Carbon Pools in the Sandy Soils of a North Florida Watershed

The large pool of actively cycling carbon (C) held in soils is susceptible to release due to changes in landuse, management, or climate. Yet, the amount and distribution of potentially mineralizable C present in soils of various types and the method by which this soil C fraction can best be quantified, are not well established. The distribution of total organic C (TOC), extractable C pools (hot-water-extractable and acid-hydrolyzable), and in vitro mineralizable C in 138 surface soils across a north Florida watershed was found to be quite heterogeneous. Thus, these C quality parameters could not statistically distinguish the eight landuses or four major soil orders represented. Only wetland and upland forest soils, with the largest and smallest C pool size, respectively, were consistently different from the soils of other landuse types. Variations in potential C mineralization were best explained by TOC (62%) and hot-water-extractable C (59%), whereas acid-hydrolyzable C (32%) and clay content (35%) were generally not adequate indicators of C bioavailability. Within certain landuse and soil orders (Alfisol, Wetland and Rangeland, all with >3% clay content), however, C mineralization and clay content were directly linearly correlated, indicating a possible stimulatory effect of clay on microbial processing of C. Generally, the sandy nature of these surface soils imparted a lack of protection against C mineralization and likely resulted in the lack of landuse/soil order differences in the soil C pools. If a single parameter is to be chosen to quantify the potential for soil C mineralization in southeastern U.S. coastal plain soils, we recommend TOC as the most efficient soil variable to measure. Author Contributions  Conceived of or designed study: Sabine Grunwald, Nick Comerford, and James Sickman—Performed research: Mi-Youn Ahn—Analyzed data: Mi-Youn Ahn, Andrew Zimmerman, and Nick Comerford—Contributed new methods or models: Andrew Zimmerman, Nick Comerford, and James Sickman—Wrote the paper: Mi-Youn Ahn, Andrew Zimmerman, and Nick Comerford.     

A genomic scan for divergent selection in a secondary contact zone between Atlantic and Gulf of Mexico oysters, Crassostrea virginica

The degree of population structure within species often varies considerably among loci. This makes it difficult to determine whether observed variance reflects neutral-drift stochasticity or locus-specific selection at one or more loci. This uncertainty is exacerbated when evolutionary equilibrium cannot be assumed and/or admixture potentially inflates genomic variance. Thus, the value of a 'genome scan', where locus-specific summary statistics are compared with a simulated neutral distribution among loci, may be limited in secondary contact zones if the null distribution is sensitive to the timing of secondary contact. Of particular interest here is the wide variance previously observed in locus-specific patterns of population structure between Atlantic and Gulf of Mexico populations of eastern oyster, Crassostrea virginica. To test the robustness of an equilibrium null model, we compared among-locus distributions of F(ST) simulated under migration-drift equilibrium and several nonequilibrium secondary contact histories. We then tested for evidence of divergent selection between two oyster populations on either side of a secondary contact zone using 215 amplified fragment length polymorphism (AFLP) loci. Constant-migration equilibrium and nonequilibrium secondary-contact simulations produced equivalent distributions of F(ST) when anchored by the global mean F(ST) observed in oysters, 0.0917. The 99th quantile of simulated neutral F(ST) encompassed most of the variation among oyster loci. Three AFLP loci exhibited F(ST) values higher than this threshold. Although no locus was significant after correcting for multiple tests, our results show in geographically clinal organisms: AFLPs can efficiently characterize the genomic distribution of F(ST); equilibrium models can be used to evaluate outliers; these procedures help focus research on genomic regions of interest.     

Hematological changes in Florida pompano (Trachinotus carolinus) supplemented with β-glucan and Pediococcus acidilactici synbiotic

Florida pompano (Trachinotus carolinus) are a species of growing interest for commercial aquaculture. Effective health monitoring is crucial to the successful growout of the species, and prophylactic and therapeutic use of chemicals and antibiotics has been the traditional strategy for promoting stock health. However, concerns about antimicrobial resistance, chemical residues in seafood products and the environment, and resultant immunosuppression have prompted the industry to identify alternative management strategies, including supplementation with prebiotics, probiotics, and combinations of both (synbiotics). The objectives of this study are to determine and compare hematological, plasma biochemical, and plasma protein electrophoresis data of synbiotic-supplemented (β-glucan and Pediococcus acidilactici) and non-supplemented Florida pompano. Reference intervals for blood analytes are provided for both groups and for subgroups (females, males, large, and small fish) where statistically significant results exist. There are no differences between the hematological and plasma biochemistry analytes between the supplemented and control groups, except for blood urea nitrogen and carbon dioxide, indicating a possible effect of synbiotic supplementation on gill function and osmoregulation. Sex-related and size-related differences are observed within each of the control and supplemented groups; however, biometric measurements do not strongly correlate with blood analytes. These data represent baseline hematological and plasma biochemical data in the Florida pompano and indicate the safety of synbiotic supplementation in this commercially important species. This study serves to further the commercialization of Florida pompano by providing blood analyte reference intervals for health monitoring in the aquaculture setting.     

Effects of Hurricanes on Rare Plant Demography in Fire‐Controlled Ecosystems

Hurricanes have dramatic effects on forest vegetation, but their effects on shrublands have rarely been studied. We analyzed the effects of three 2004 hurricanes—among the strongest on record in Florida—on vital rates of 12 rare plant species of pyrogenic interior Florida scrub and sandhill. Tree damage varied by vegetation type (being highest in areas with Pinus clausa) and was associated with debris deposition. Most rare species were minimally impacted by hurricanes. The two most frequently damaged species were the shrubs Prunus geniculata (11% of individuals) and Asimina obovata (7%); both were resilient to damage. Prunus geniculata had little mortality during the hurricane year but damaged plants had a temporary (1‐yr) reduction in relative growth rate. Prunus geniculata flowering was unaffected by hurricane damage. Hurricane damage had no effects on vital rates of A. obovata, Eriogonum longifolium var. gnaphalifolium, or Chrysopsis highlandsensis. Other species suffered little or no observable hurricane damage. Of 12 species analyzed, nine had similar annual survival in hurricane and nonhurricane years. Relatively low survival in the hurricane year (compared with other years) was linked to prehurricane drought or prescribed fire in two of three species. Thus, the 2004 hurricanes did not have important effects on populations of interior Florida scrub and sandhill plants, especially herbaceous species. This is in marked contrast to dramatic demographic responses to fire in central Florida and strong effects of hurricanes in coastal Florida, highlighting that these different disturbances may have divergent effects on vegetation and populations over short distances.     

Habitat and microsite influence demography of two herbs in intact and degraded scrub

Identifying environmental factors associated with vital rate variation is critical to predict population consequences of environmental perturbation. We used matrix models to explore effects of habitat and microsite on demography of two widespread herbs, Chamaecrista fasciculata (partridge pea) and Balduina angustifolia (yellow buttons). We evaluated models simulating population dynamics in common microsites (shrub, litter, bare sand) within two habitats (intact, degraded Florida scrub) using data on experimental populations initiated by sowing seeds, and natural seed production. Models included four stages (seed bank, small vegetative, large vegetative, reproductive) and three vital rates (survival, growth, fecundity), summarized in sixteen transitions. We conducted life table response experiments to assess contributions of each habitat and microsite to population growth rates. We found that (1) C. fasciculata had greatest population growth in degraded habitat and litter microsites, (2) B. angustifolia had similar population growth between habitats and greatest in bare sand microsites, (3) advancing growth transitions of C. fasciculata had greatest elasticity on population growth in degraded habitat, shrub, and litter, as did seed survival in intact habitat and bare sand, (4) seed survival and advancing growth transitions of B. angustifolia had greatest elasticity on population growth in both habitats, as did seed survival in shrub and litter, and advancing growth in bare sand. Greater population growth of C. fasciculata in degraded scrub is probably explained by release from belowground competition; B. angustifolia may be most affected by competition with shrubs. Microsites in intact scrub were not ecologically equivalent to those in degraded scrub emphasizing that intact scrub is ecologically complex and critical to preserve.