Spatial Patterns of Estuarine Habitat Type Use and Temporal Patterns in Abundance of Juvenile Permit, Trachinotus falcatus, in Charlotte Harbor, Florida

The life history of many marine fishes is a 2-phase cycle: juveniles and adults make up a demersal phase, whereas larvae are planktonic. Determining ontogenetic patterns of habitat type use of the demersal phase has important management and habitat conservation implications for species that use coastal habitat types as juveniles. Juvenile permit, Trachinotus falcatus, are presumed to be limited to beaches exposed to open ocean, but few studies have addressed juvenile permit use of estuarine habitat types. Ten years of fisheries-independent monitoring data from a subtropical estuary were analyzed to determine habitat type use patterns and seasonality of juvenile permit. Shallow (\u3c 2 m) habitat types in Charlotte Harbor, Florida, were sampled with 21 m and 183 m seines from 1991 through 2000. Juvenile permit were most abundant along sandy beaches in the lower estuary and were in densities similar to or higher than along exposed coastal beaches reported in other studies. Size of captured permit ranged from 15 to 360 mm standard length. Small juveniles (\u3c 100 mm) were present almost exclusively from June to December. Both small and large (∅ 100 mm) juveniles were most abundant over shallow bottom adjacent to unvegetated beach shorelines. These findings indicate that post-settlement permit recruit seasonally to specific estuarine habitat types. Then, as they grow, they shift to other habitat types, before migrating out of the estuary. Since identification of the suite of juvenile habitat types is prerequisite to determining their nursery value, and many estuarine habitat types are under anthropogenic stress, research on the relative importance of estuarine nurseries for juvenile permit is warranted

Temperature Variability in a Subtropical Estuary and Implications for Common Snook Centropomus undecimalis, a Cold-Sensitive Fish

Variability in winter water temperature was compared among three habitat types (estuary, river, canal) in a subtropical estuarine system to explore how it might affect site selection and survival of a cold-sensitive fish, Common Snook Centropomus undecimalis. The study was conducted during three winters (2008–2010); a rapid cooling event occurred during the first winter, mild temperatures the second, and an extreme cold event in the third (an 80-yr event). During the extreme cold event in January 2010, catastrophic fish mortality occurred throughout the region that resulted in the emergency closure of the Common Snook recreational fishery. Over the entire studied estuarine system, dead Common Snook were reported at 43 sites; 26 of the sites were large fish kills consisting of 100–2,000 individuals. The distribution of mortality sites was widespread, although most were located in the estuary proper (n = 39), with only several in rivers and canals (n = 4). Temperature loggers recorded similar water temperatures among habitat types (estuary, river, canal), except during short periods (~3 d; up to 2°C) after cold fronts; this indicates that fish have distinct time constraints if searching for warmer water sites. During the short periods after cold fronts, canal water temperatures were the warmest and most stable, whereas the river and estuary temperature rankings varied

The Effects of Season and Proximity to Fringing Mangroves on Seagrass-Associated Fish Communities in Charlotte Harbor, Florida

Little has been published on habitat use by fishes in Charlotte Harbor, one of Florida\u27s largest-and still relatively pristine-estuaries. Multivariate analyses of data from 21.3-m-seine samples (1996-2000) were used to examine spatiotemporal patterns of seagrass habitat use by Charlotte Harbor fishes. Two habitats (mangrove-associated seagrass shorelines and offshore seagrass flats) were examined. Throughout the year, the mangrove-seagrass habitat was distinguished by Menidia spp., Mugil gyrans, Eucinostomus harengulus, and Floridichthys carpio, and the offshore seagrass flats habitat was distinguished by Bairdiella chrysoura, Orthopristis chrysoptera, and Cynoscion nebulosus. The dry season (Dec.-May) was distinguished by Lagodon rhomboides, Leiostomus xanthurus, and O. chrysoptera in both habitats and by Mugil cephalus in the mangrove-seagrass habitat. The wet season (June-Nov.) was distinguished by Lucania parva, F. carpio, and Fundulus grandis in the mangrove-seagrass habitat and by Eucinostomus gula, Microgobius gulosus, C. nebulosus, and E. harengulus in the offshore seagrass flats habitat. Eucinostomus spp., Anchoa mitchilli, and Strongylura notata were abundant in both habitats during the wet season. In general, many species were collected in both habitats and were widely distributed in the estuary. Various combinations of four environmental variables (i.e., water temperature, salinity, dissolved oxygen, water depth) and their coefficients of variation were well correlated with the biotic community patterns. These results show that different fish communities use different seagrass habitats in Charlotte Harbor, depending on the season and the proximity of the seagrasses to fringing mangroves

Feeding Habits of Common Snook, Centropomus undecimalis, in Charlotte Harbor, Florida

We examined the feeding habits, ontogenetic and seasonal diet variations, and predator size–prey size relationships of common snook, Centropomus undecimalis, in Charlotte Harbor, Florida, through stomach contents analysis. A total of 694 stomachs were extracted from common snook (300–882 mm standard length [SL]) during a 24-month period (March 2000–February 2002); 432 stomachs contained prey items. At least 37 prey taxa were identified, including 19 that had not been previously reported. Fishes made up 71% of the prey by number and 90% by weight. Three prey items made up almost 50% of the diet numerically—Lagodon rhomboides, Anchoa spp., and Farfantepenaeus duorarum. Seven species made up more than 60% of the diet by weight—L. rhomboides, Cynoscion nebulosus, Mugil gyrans, Bairdiella chrysoura, Synodus foetens, Orthopristis chrysoptera, and Mugil cephalus. An ontogenetic shift in prey preference was identified in adult common snook at around 550 mm SL. Smaller individuals (300–549 mm SL) ate more F. duorarum, palaemonid shrimp, cyprinodontids, and Eucinostomus spp. than did larger individuals (550–882 mm SL), which ate more S. foetens, ariids, and sciaenids. Significant, positive relationships between predator size and prey size were observed between common snook and L. rhomboides, O. chrysoptera, portunid crabs, and all fish prey combined. Prey size selection contributed to some seasonal differences in their diet. For example, in winter when L. rhomboides are abundant in the estuary and small in size (mean = 23 mm SL), common snook ate few individuals, but they consumed many during summer when larger L. rhomboides (mean = 51 mm SL) were available. In summary, common snook are opportunistic predators that feed on a wide variety of prey and exploit specific-sized prey that are abundant in their environment

Fishes of the Charlotte Harbor Estuarine System, Florida

To date, 255 fish species in 95 families have been reliably reported from the Charlotte Harbor estuarine system in southwest Florida. The species list was compiled from recent fishery-independent collections, a review of reports and peer-reviewed literature, and examination of cataloged specimens at the Florida Museum of Natural History. Thirty-nine species are new records for this estuarine system. Many of the newly documented species are common on the west Florida continental shelf and associated inshore habitats. Twenty-two previously reported species were not included in the species list presented herein on the basis of more recent research, doubtful original identifications, or questionable locality data

Mercury's low-reflectance material: Constraints from hollows

Unusually low reflectance material, within which depressions known as hollows appear to be actively forming by sublimation, is a major component of Mercury's surface geology. The observation that this material is exhumed from depth by large impacts has the intriguing implication that the planet's lower crust or upper mantle contains a significant volatile-rich, low-reflectance layer, the composition of which will be key for developing our understanding of Mercury's geochemical evolution and bulk composition. Hollows provide a means by which the composition of both the volatile and non-volatile components of the low-reflectance material (LRM) can be constrained, as they result from the loss of the volatile component, and any remaining lag can be expected to be formed of the non-volatile component. However, previous work has approached this by investigating the spectral character of hollows as a whole, including that of bright deposits surrounding the hollows, a unit of uncertain character. Here we use high-resolution multispectral images, obtained as the MESSENGER spacecraft approached Mercury at lower altitudes in the latter part of its mission, to investigate reflectance spectra of inactive hollow floors where sublimation appears to have ceased, and compare this to those of the bright surrounding products and the parent material. This analysis reveals that the final lag after hollow-formation has a flatter spectral slope than that of any other unit on the planet and reflectance approaching that of more space-weathered parent material. This indicates firstly that the volatile material lost has a steeper spectral slope and higher reflectance than the parent material, consistent with (Ca,Mg) sulfides, and secondly, that the low-reflectance component of LRM is non-volatile and may be graphite

Remote Sensing and Geologic Studies of the Schiller-Schickard Region of the Moon

Near-infrared reflectance spectra, multispectral images, and photogeologic data for the Schiller-Schickard (SS) region were obtained and analyzed in order to determine the composition and origin of a variety of geologic units. These include light plains deposits, Orientale-related deposits, mare units, and dark-haloed impact craters (DHCs). Spectral data indicate that the pre-Orientale highland surface was dominated by noritic anorthosite. Near-IR spectra show that DHCs in the region have excavated ancient (greater than 3.8 Ga) mare basalts from beneath highland-bearing material emplaced by the Orientale impact. Ancient mare basalts were widespread in the SS region prior to the Orientale event, and their distribution appears to have been controlled by the presence of several old impact basins, including the Schiller-Zucchius basin and a basin previously unrecognized. Both near-IR spectra and multispectral images indicate that light plains and other Orientale-related units in the SS region contain major amounts of local, pre-Orientale mare basalt. The amounts of local material in these deposits approach, but seldom exceed, the maximum values predicted by the local mixing hypothesis of Oberbeck and co-workers

Craters Hosting Radar-Bright Deposits in Mercury's North Polar Region: Areas of Persistent Shadow Determined from MESSENGER Images

Radar-bright features near Mercury's poles were discovered in Earth-based radar images and proposed to be water ice present in permanently shadowed areas. Images from MESSENGER's one-year primary orbital mission provide the first nearly complete view of Mercury’s north polar region, as well as multiple images of the surface under a range of illumination conditions. We find that radar-bright features near Mercury's north pole are associated with locations persistently shadowed in MESSENGER images. Within 10 degrees of the pole, almost all craters larger than 10 km in diameter host radar-bright deposits. There are several craters located near Mercury's north pole with sufficiently large diameters to enable long-lived water ice to be thermally stable at the surface within regions of permanent shadow. Craters located farther south also host radar-bright deposits and show a preference for cold-pole longitudes; thermal models suggest that a thin insulating layer is required to cover these deposits if the radar-bright material consists predominantly of longlived water ice. Many small (less than 10 km diameter) and low-latitude (extending southward to 66 degrees N) craters host radar-bright material, and water ice may not be thermally stable in these craters for ~1 Gy, even beneath an insulating layer. The correlation of radar-bright features with persistently shadowed areas is consistent with the deposits being composed of water ice, and future thermal modeling of small and low-latitude craters has the potential to further constrain the nature, source, and timing of emplacement of the radar-bright material

The Regolith of 4 Vesta: Perspectives from Howardite Meteorites and Dawn Mission Observations

4 Vesta is the largest asteroid with a basaltic surface, the only surviving differentiated asteroid recording igneous processes from the earliest phase of solar system history. The Dawn spacecraft is in orbit about Vesta pursuing a campaign of high resolution imaging and visible and infrared spectrometry of the surface; compositional mapping by gamma-ray and neutron spectrometry will follow. Vesta is heavily cratered with a surface covered by impact debris, a regolith. One important goal of the Dawn mission is to develop an understanding of regolith processes that are affecting this surface debris. Regolith characteristics are a record of interaction with the environment (e.g., impactors, dust, solar wind, galactic cosmic-rays) and give evidence of surface processes (down-gravity movement, etc.). Regolith mineralogy and composition reflect the local bedrock, with influences from regional and global mixing. Understanding regolith processes will aid in determining the lithology of underlying crust. Vesta is most likely the parent asteroid of the howardite, eucrite and diogenite meteorites. Eucrites are intrusive and extrusive mafic rocks composed mostly of ferroan low-Ca clinopyroxene and calcic plagioclase, while diogenites are cumulate magnesian orthopyroxenites. Magmatism occurred within a few million years of the formation of the solar system and then ceased. Impacts into the igneous crust produced the howardites - polymict breccias composed of mineral and lithic debris derived mostly from eucrites and diogenites. Some howardites are true regolith breccias formed by lithification of extensively impact-gardened surface debris. However, howardites have a number of significant petrologic and compositional differences from mature lunar regolith breccias and soils reflecting the different environment around Vesta compared to that at 1 AU. The most significant differences are the higher impactor flux with a lower mean impact velocity and the lower gravity. As a result, regolith processes on Vesta differ in detail from those on the Moon. Laboratory study of howardites and orbital investigation of Vesta will allow for development of robust models of regolith formation on hand sample to multi-kilometer scales