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Despite first being described from Virginia, the widely distributed brackish water hydrozoan Blackfordia virginica is often hypothesized to have been introduced from the Black Sea to the United States. However, the alternative view that B. virginica was introduced to the Black Sea also persists in the literature. This study investigates the population structure of B. virginica in the United States to assess the directionality and/or the number of introduction events. During 2009 and 2010, estuaries were sampled from Delaware to Louisiana for brackish water hydromedusae. Nineteen samples of Blackfordia virginica were collected from four localities, including a channel running between St. Catherines Island and Lake Pontchartrain, Louisiana, a region for which it had not been reported prior to this study. We PCR amplified and sequenced two mitochondrial markers (COI & 16S), and one nuclear marker (ITS1). We compared data from individuals collected on the east coast of the United States with individuals collected in California. This revealed low diversity (two haplotypes with a maximal p-difference of 0.03% for COI and just a single haplotype for 16S) and no unique haplotypes at any locality. Low genetic variability, shared haplotypes in disparate localities, and a lack of unique haplotypes in any population are consistent with a founder effect, suggesting a single introduction and subsequent spread throughout the United States. [ABSTRACT FROM AUTHOR]

During the last century, the global biogeochemical cycles of carbon (C) and nitrogen (N) have been drastically altered by human activities. A century of land-clearing and biomass burning, followed by fossil fuel combustion have increased the concentration of atmospheric CO2 by approximately 20%, and since the mid-1900s, the use of agricultural fertilizers has been the primary driver of an approximate 90% increase in bioavailable N. Geochemical records obtained through stable isotope analysis of terrestrial and marine biota effectively illustrate rising anthropogenic C inputs. However, there are fewer records of anthropogenic N, despite the enormous magnitude of change and the known negative effects of N on ecosystem health. We used stable isotope values from independent octocorals (gorgonians) sampled across the Western Atlantic over the last 143 years to document human perturbations of the marine C and N pools. Here, we demonstrate that in sea plumes δ13C values and in both sea plumes and sea fans δ15N values declined significantly from 1862 to 2005. Sea plume δ13C values were negatively correlated with increasing atmospheric CO2 concentrations and corroborate known rates of change resulting from global fossil fuel combustion, known as the Suess effect. We suggest that widespread input of agricultural fertilizers to near-shore coastal waters is the dominant driver for the decreasing δ15N trend, though multiple anthropogenic sources are likely affecting this trend. Given the interest in using δ15N as an indicator for N pollution in aquatic systems, we highlight the risk of underestimating contributions of pollutants as a result of source mixing as demonstrated by a simple isotope-mixing model. We conclude that signals of major human-induced perturbations of the C and N pools are detectable in specimens collected over wide geographic scales, and that archived materials are invaluable for establishing baselines against which we can assess environmental change. [ABSTRACT FROM AUTHOR]

Octocorals, like many other colonial benthic invertebrates, exhibit remarkable levels of morphological variability. The basis for this variability has been largely unexplored.Plexaura flexuosaLamouroux, a common Caribbean octocoral, is found in virtually all reef habitats, and exhibits habitat-related differences in growth rates and fecundity. Population genetic structure and morphological variability in branch and sclerite characters were examined in nine populations from back reef, shallow forereef, and forereef habitats in the Florida Keys. Discriminant analysis of morphological characters correctly classified 89, 88, and 100% of samples from back, shallow fore, and forereef habitats, respectively. Analysis of randomly amplified polymorphic DNA profiles (RAPDs) showed no evidence of genetic differentiation between shallow back, shallow fore, and the majority of forereef colonies. However, there were two distinct genetic groups of forereef colonies. Much of the habitat-related morphological variability amongPlexaura flexuosais due to plasticity, which is likely an important feature contributing to the broad distribution of this species. However, there may be two genetic subgroups on forereefs. [ABSTRACT FROM AUTHOR]

Drivers of disease cycles are poorly understood in marine ecosystems in spite of increasing outbreaks. We monitored a newly emerged fungal epizootic (aspergillosis) affecting sea fan corals (Gorgonia ventalina L.) in the Florida Keys to evaluate causes of its rise and fall over 6 years. Since August 1997, aspergillosis has nearly eradicated large sea fans at some sites. However, sea fan densities have remained relatively constant due to episodic recruitment replacing large fans with small. Recruitment itself was affected by infection and occurred only when prevalence of disease was low. This impact on recruitment occurred because the largest, potentially most fecund colonies had the highest prevalence of disease, and the pathogen significantly suppressed reproduction of infected fans. Moreover, high mortality among adults resulted in a demographic shift to smaller colonies. The most dramatic impact of aspergillosis was the Keys-wide loss of >50% of sea fan tissue from complete and partial mortality. Aspergillosis prevalence has declined steadily over the last 6 years, and we consider the following hypotheses for decline of the epizootic: change in environment, change in pathogen input, and increase in host resistance. We conclude that increasing host resistance is the most likely driver of the decline. However, a change in any of a number of factors, for example, recruitment of naïve hosts, rate of pathogen input, or environmental conditions (water quality and temperature), is likely to promote reemergence of the epizootic. [ABSTRACT FROM AUTHOR]