Philip W. Stevens

Short-term Effects of a Low Dissolved Oxygen Event on Estuarine Fish Assemblages Following the Passage of Hurricane Charley

Hurricane Charley, a category 4 storm, passed directly over the Charlotte Harbor estuary and Peace River watershed on August 13, 2004. Following the storms passage, dissolved oxygen in the Peace River fell below 1 mg l−1 and hypoxic conditions (<2mgl−1) extended into Charlotte Harbor. A long-term fisheries-independent monitoring program (1989 to present) was already in place in Charlotte Harbor, and sampling was intensified during the month after the storm. Changes in fish assemblages that resulted from the hypoxic event were determined using nonmetric multidimensional scaling and similarity percentages analysis. At the mouth of the Peace River and upper Charlotte Harbor, fish abundance decreased dramatically after the hurricane, and typical estuarine fish assemblages were replaced by those dominated by a few resilient estuarine and freshwater species, including the nonindigenous brown hoplo (Hoplosternum littorale) and sailfin catfish (Pterygoplichthys spp.). Fish assemblages in the estuarine portion of the Maykka River, located only a few kilometers west of the Peace River, were unaffected. The hypoxic event was short lived; dissolved oxygen and estuarine fish assemblages in the Peace River and upper Charlotte Harbor recovered within a month. The results of this study are consistent with other hurricane-related hypoxic events in the literature which have reported acute effects to estuarine systems in the short term, rapid recoveries, and long-term resilience.

Environmental influences on the spatial ecology of juvenile smalltooth sawfish (Pristis pectinata): results from acoustic monitoring

To aid recovery efforts of smalltooth sawfish (Pristis pectinata) populations in U.S. waters a research project was developed to assess how changes in environmental conditions within estuarine areas affected the presence, movements, and activity space of this endangered species. Forty juvenile P. pectinata were fitted with acoustic tags and monitored within the lower 27 km of the Caloosahatchee River estuary, Florida, between 2005 and 2007. Sawfish were monitored within the study site from 1 to 473 days, and the number of consecutive days present ranged from 1 to 125. Residency index values for individuals varied considerably, with annual means highest in 2005 (0.95) and lowest in 2007 (0.73) when several P. pectinata moved upriver beyond detection range during drier conditions. Mean daily activity space was 1.42 km of river distance. The distance between 30-minute centers of activity was typically <0.1 km, suggesting limited movement over short time scales. Salinity electivity analysis demonstrated an affinity for salinities between 18 and at least 24 psu, suggesting movements are likely made in part, to remain within this range. Thus, freshwater flow from Lake Okeechobee (and its effect on salinity) affects the location of individuals within the estuary, although it remains unclear whether or not these movements are threatening recovery.

Effects of the 2004 hurricanes on the fish assemblages in two proximate southwest Florida estuaries: Change in the context of interannual variability

We examined interannual differences in fish assemblage structure in Tampa Bay and Charlotte Harbor, Florida, from 1996 to 2005 to reveal the extent of hurricane-induced changes in relation to multiannual variability for five different assemblages in each estuary: small-bodied fishes (generally 100-mm standard length) along bay shorelines. Fish assemblages tended to differ, between estuaries, as did interannual variability in assemblage structure. In the lower portions of tributary rivers to Tampa Bay, the small-bodied shoreline fish assemblage during August 2004 to July 2005, i.e., during and after the multiple hurricanes, was different from assemblages of August to July in previous years. This may have been a result of physical displacement of fish or suboptimal salinities caused by increased freshwater inflow. The small-bodied shoreline fish assemblage in Charlotte Harbor also differed between prehurricane and hurricane periods, possibly because damage to vegetated shorelines affected fish survival through a decrease in feeding and refuge habitats. In the remaining habitats, fish assemblage structure from August 2004 to July 2005 were within the range of variability exhibited over the 9-yr study period. There were several unusual fish assemblages that appeared to be attributable to drought conditions (1996, 1999–2000), suggesting that other major environmental perturbations may be as important as hurricanes in influencing assemblage structure. We conclude that although the 2004 hurricane season affected some of the fish assemblages of Tampa Bay and charlotte Harbor, these assemblages generally appeared quite resilient to natural environmental perturbations from a decadal perspective.

Abiotic affinities and spatiotemporal distribution of the endangered smalltooth sawfish, Pristis pectinata, in a south-western Florida nursery

Understanding how endangered marine species rely on coastal habitats is vital for population recovery planning.Thesmalltoothsawfish(Pristispectinata)isoneofseveralcriticallyendangeredsawfishesworldwideknownto use estuaries and rivers during their early life history. In a Florida estuary designated as critical habitat by the USA government, juveniles were monitored to characterise seasonality, recruitment, and habitat use. Stretched total length ranged from 671 to 2172mm (n ¼137, mean ¼1248mm). Sawfish were captured year round. Captures of neonates with embryonic rostral sheaths allowed refinement of the size at birth (671-812mm) and confirmed a protracted timing of parturition(November-July), whichpeakedbetweenAprilandMay. Althoughsamplingoccurredthroughoutthe estuary, five locations had the greatest catch rates. Most juvenile sawfish had an affinity for water ,1m deep, water .308C, dissolved oxygen.6mgL � 1 ,and salinitybetween18 and30.Greater catch rates forsawfish.1yearold wereassociated with shoreline habitats with overhanging vegetation such as mangroves. These results detail habitat use within a recognised nursery that can be used for conservation of the first endangered marine fish species in the USA.

Species and condition specific adaptation of the transcriptional landscapes in Candida albicans and Candida dubliniensis.

BackgroundAlthough Candida albicans and Candida dubliniensis are most closely related, both species behave significantly different with respect to morphogenesis and virulence. In order to gain further insight into the divergent routes for morphogenetic adaptation in both species, we investigated qualitative along with quantitative differences in the transcriptomes of both organisms by cDNA deep sequencing.ResultsFollowing genome-associated assembly of sequence reads we were able to generate experimentally verified databases containing 6016 and 5972 genes for C. albicans and C. dubliniensis, respectively. About 95% of the transcriptionally active regions (TARs) contain open reading frames while the remaining TARs most likely represent non-coding RNAs. Comparison of our annotations with publically available gene models for C. albicans and C. dubliniensis confirmed approximately 95% of already predicted genes, but also revealed so far unknown novel TARs in both species. Qualitative cross-species analysis of these databases revealed in addition to 5802 orthologs also 399 and 49 species-specific protein coding genes for C. albicans and C. dubliniensis, respectively. Furthermore, quantitative transcriptional profiling using RNA-Seq revealed significant differences in the expression of orthologs across both species. We defined a core subset of 84 hyphal-specific genes required for both species, as well as a set of 42 genes that seem to be specifically induced during hyphal morphogenesis in C. albicans.ConclusionsSpecies-specific adaptation in C. albicans and C. dubliniensis is governed by individual genetic repertoires but also by altered regulation of conserved orthologs on the transcriptional level.

The transcriptomic profile of Pseudozyma aphidis during production of mannosylerythritol lipids.

The basidiomycetous fungus Pseudozyma aphidis is able to convert vegetable oils to abundant amounts of the biosurfactant mannosylerythritol lipid (MEL) with a unique product pattern of MEL-A, MEL-B, MEL-C, and MEL-D. To investigate the metabolism of MEL production, we analyzed the transcriptome of P. aphidis DSM 70725 under MEL-inducing and non-inducing conditions using deep sequencing. Following manual curation of the previously described in silico gene models based on RNA-Seq data, we were able to generate an experimentally verified gene annotation containing 6347 genes. Using this database, our expression analysis revealed that only four of the five cluster genes required for MEL synthesis were clearly induced by the presence of soybean oil. The acetyltransferase encoding gene PaGMAT1 was expressed on a much lower level, which may explain the secretion of MEL with different degrees of acetylation in P. aphidis. In parallel to MEL synthesis, microscopic observations showed morphological changes accompanied by expression of genes responsible for cell development, indicative of a coregulation between MEL synthesis and cell morphology. In addition a set of transcription factors was identified which may be responsible for regulation of MEL synthesis and cell development. The upregulation of genes required for nitrogen metabolism and other assimilation processes indicate additional metabolic pathways required under the MEL-inducing conditions used. We also searched for a conserved gene cluster for cellobiose lipids (CL) but only found seven genes with limited homology distributed over the genome. However, we detected characteristic TLC spots in fermentations using P. aphidis DSM 70725, indicative of CL secretion.

Fish Assemblages in the Oligohaline Stretch of a Southwest Florida River during Periods of Extreme Freshwater Inflow Variation

Abstract Maintenance or restoration of the oligohaline stretch (i.e., salinity 0.5–5 psu) of coastal rivers is becoming an increasingly important goal of water managers striving to balance human consumption of water with the ecological integrity of estuaries. The objectives of this study were to compare fish assemblage structure and species abundance of the oligohaline stretch to those of the lower river mouth during periods of varying freshwater inflow (wet and dry periods) in one of southwest Floridas largest rivers, the Peace River. The abundance of several estuarine residents and estuarine transients captured in 21.3-m seines—Sand Seatrout Cynoscion arenarius, Tidewater Mojarra Eucinostomus harengulus, Red Drum Sciaenops ocellatus, and Spot Leiostomus xanthurus—were similar between river sections, which is consistent with the premise that the oligohaline stretch is an extension of the juvenile habitat known to be important for fish in lower rivers. Estuarine residents known to have affinities for mar...

Preservation Effects on Stable Isotope Values of Archived Elasmobranch Fin Tissue: Comparisons between Frozen and Ethanol-Stored Samples

AbstractElasmobranch fin tissue has been sampled and archived for decades to support genetics research. However, these collections have the potential to provide additional information on the trophic ecology of and habitat use by elasmobranch species. The use of fin tissue is especially attractive considering the threatened status of many elasmobranchs and the call for limiting mortalities. Yet, the use of fin samples for stable isotope analysis requires either that (1) storage methods do not alter tissue isotope values or (2) any alterations in isotope composition that occur during storage are predictable. In this study, paired fin tissues sampled from Smalltooth Sawfish Pristis pectinata and cownose rays Rhinoptera spp. were stored frozen and in ethanol and were subsequently analyzed for carbon (δ13C) and nitrogen (δ15N) isotope ratios. Fin δ13C and δ15N values were highly correlated between treatments for both taxa (r2 ≥ 0.80). For Smalltooth Sawfish, ethanol storage significantly increased fin δ13C val...

Antifungal defense of probiotic Lactobacillus rhamnosus GG is mediated by blocking adhesion and nutrient depletion

Candida albicans is an inhabitant of mucosal surfaces in healthy individuals but also the most common cause of fungal nosocomial blood stream infections, associated with high morbidity and mortality. As such life-threatening infections often disseminate from superficial mucosal infections we aimed to study the use of probiotic Lactobacillus rhamnosus GG (LGG) in prevention of mucosal C. albicans infections. Here, we demonstrate that LGG protects oral epithelial tissue from damage caused by C. albicans in our in vitro model of oral candidiasis. Furthermore, we provide insights into the mechanisms behind this protection and dissect direct and indirect effects of LGG on C. albicans pathogenicity. C. albicans viability was not affected by LGG. Instead, transcriptional profiling using RNA-Seq indicated dramatic metabolic reprogramming of C. albicans. Additionally, LGG had a significant impact on major virulence attributes, including adhesion, invasion, and hyphal extension, whose reduction, consequently, prevented epithelial damage. This was accompanied by glucose depletion and repression of ergosterol synthesis, caused by LGG, but also due to blocked adhesion sites. Therefore, LGG protects oral epithelia against C. albicans infection by preventing fungal adhesion, invasion and damage, driven, at least in parts, by metabolic reprogramming due to nutrient limitation caused by LGG.

Loss of seasonal variability in nekton community structure in a tidal river: evidence for homogenization in a flow-altered system

Modifications to riverine systems that alter freshwater inflow to downstream estuarine habitats have resulted in altered patterns of nekton distribution and abundance. To examine how nekton assemblages respond to variable hydrologic patterns, we used trawl and seine survey data to compare the seasonal trends (dry vs. wet season) expected of a natural system to those of a river with regulated flow discharges that often magnify high flow events. Nekton assemblages differed between seasons in a representative natural system, similar to other estuaries of the region. For example, assemblage differences were characterized by significantly higher abundance and richness in trawl surveys, and significantly higher richness in seine surveys in the wet relative to the dry season. These seasonal trends were dampened in the altered system. Species important in defining seasonal dissimilarities in both systems were characterized as estuarine resident species, including Anchoa mitchilli, Menidia spp., Cynoscion arenarius, and Trinectes maculatus, yet were observed largely to have opposing seasonal trends in abundance between the two rivers. Our comparison provides evidence that flow modifications result in a loss of natural seasonal variability in estuarine nekton assemblages, but additional investigations of flow-altered systems are needed to confirm these findings.