Harte Research Institute for Gulf of Mexico Studies
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Item Age, growth, and mortality of King Mackerel in the western Gulf of Mexico(Marine and Coastal Fisheries, 2023-11-07) Kesley G. Banks; Matthew K. Streich; Gregory W. StunzObjective Temporal and spatial variation in growth can have significant implications for the assessment and management of exploited populations. Therefore, the age and growth of King Mackerel Scomberomorus cavalla were estimated for the western Gulf of Mexico, where there are large gaps in the available data. Methods A total of 727 sagittal otoliths from 411 females, 248 males, and 68 individuals of unknown sex were collected from headboats, private recreational anglers, tournaments, and fishery-independent sampling and aged. Result Ages ranged from 0 to 17 years with lengths ranging from 13 to 147 cm fork length. The distribution of lengths and ages differed marginally for fishing sector (i.e., tournament vs. headboat vs. private). The fish that were collected from tournaments were larger than those collected from headboats and private anglers. The distribution of lengths and ages did vary by sex, with females obtaining larger sizes than males. However, there was no difference in mean age by sex. Using the multimodel approach, the Richards model improved the fit for both the youngest and oldest fish in the sample relative to the other growth models that were evaluated. Sex-specific differences in the Richards model were detected, with females growing larger than males but more slowly. Although peak catch was observed at age 5, King Mackerel were not fully recruited to the recreational fishery until age 6. The Chapman-Robson Peak Plus estimate of Z was 0.37. Conclusion These data provide a contemporary snapshot of size structure, age, growth, and mortality for King Mackerel from an undersampled region of the Gulf of Mexico and highlight several key considerations for upcoming stock assessments.Item Alkalinity distribution in the western North Atlantic Ocean margins(2010-08-13) Cai, Wei-Jun; Hu, Xinping; Huang, Wei-Jen; Jiang, Li-Qing; Wang, Yongchen; Peng, Tsung-Hung; Zhang, XinTotal alkalinity (TA) distribution and its relationship with salinity (S) along the western North Atlantic Ocean (wNAO) margins from the Labrador Sea to tropical areas are examined by this study. Based on the observed TA-S patterns, the mixing process that control alkalinity distribution in these areas can be categorized into a spectrum of patterns that are bracketed by two extreme mixing types, i.e., alongshore current dominated and river-dominated. Alongshore current-dominated mixing processes exhibit a segmented mixing line with a shared mid-salinity end-member. In such cases (i.e., Labrador Sea, Gulf of Maine, etc.), the y-intercept of the high salinity segment of the mixing line is generally higher than the local river alkalinity values, and it reflects the mixing history of the alongshore current. In contrast, in river-dominated mixing (Amazon River, Caribbean Sea, etc.), good linear relationships between alkalinity and salinity are generally observed, and the zero salinity intercepts of the TA-S regressions roughly match those of the regional river alkalinity values. TA-S mixing lines can be complicated by rapid changes in the river end-member value and by another river nearby with a different TA value (e.g., Mississippi-Atchafalaya/Gulf of Mexico). In the wNAO margins, regression intercepts and river end-member vale have a clear latitudinal distribution pattern, increasing from a low of ~300 mol kg-1 in the Amazon River plume to a high value between ~500-1100 mol kg-1 in the middle and high latitude margins. The highest value of ~2400 mol kg-1 is observed in the Mississippi River influenced areas. In addition to mixing control, biological processes such a calcification and benthic alkalinity production may also affect ocean margin alkalinity distribution. Therefore, deriving inorganic carbon system information in coastal oceans using alkalinity-salinity relationships, in particular, those of generic nature, may lead to significant errors.Item An Analysis of Artificial Reef Fish Community Structure along the Northwestern Gulf of Mexico Shelf: Potential Impacts of “Rigs-to-Reefs” Programs(PLoS ONE, 2015-05-08) Ajemian, Matthew J.; Wetz, Jennifer J.; Shipley-Lozano, Brooke; Shively, J. Dale; Stunz, Gregory W.Artificial structures are the dominant complex marine habitat type along the northwestern Gulf of Mexico (GOM) shelf. These habitats can consist of a variety of materials, but in this region are primarily comprised of active and reefed oil and gas platforms. Despite being established for several decades, the fish communities inhabiting these structures remain poorly investigated. Between 2012 and 2013 we assessed fish communities at 15 sites using remotely operated vehicles (ROVs). Fish assemblages were quantified from standing platforms and an array of artificial reef types (Liberty Ships and partially removed or toppled platforms) distributed over the Texas continental shelf. The depth gradient covered by the surveys (30–84 m) and variability in structure density and relief also permitted analyses of the effects of these characteristics on fish richness, diversity, and assemblage composition. ROVs captured a variety of species inhabiting these reefs from large transient piscivores to small herbivorous reef fishes. While structure type and relief were shown to influence species richness and community structure, major trends in species composition were largely explained by the bottom depth where these structures occurred. We observed a shift in fish communities and relatively high diversity at approximately 60 m bottom depth, confirming trends observed in previous studies of standing platforms. This depth was also correlated with some of the largest Red Snapper captured on supplementary vertical longline surveys. Our work indicates that managers of artificial reefing programs (e.g., Rigs-to-Reefs) in the GOM should carefully consider the ambient environmental conditions when designing reef sites. For the Texas continental shelf, reefing materials at a 50–60 m bottom depth can serve a dual purpose of enhancing diving experiences and providing the best potential habitat for relatively large Red Snapper.Item Anthropogenic effects on the marine environment adjacent to Palmer Station, Antarctica(Antarctic Science, 2021-12-07) Palmer, Terence A.; Klein, Andrew G.; Sweet, Stephen T.; Montagna, Paul A.; Hyde, Larry J.; Wade, Terry L.; Pollack, Jennifer BeseresLocalized contamination from research-related activities and its effects on macrofauna communities in the marine environment were investigated at Palmer Station, a medium-sized Antarctic research station. Relatively low concentrations of polycyclic aromatic hydrocarbons (PAHs; 32–302 ng g-1) and total petroleum hydrocarbons (TPHs; 0.9–8.9 μg g-1) were detected in sediments adjacent to the sewage outfall and pier, where most human activities were expected to have occurred, and at even lower concentrations at two seemingly reference areas (PAHs 6–30 ng g-1, TPHs 0.03–5.1 μg g-1). Elevated concentrations of PAHs in one sample taken in one reference area (816 ng g-1) and polychlorinated biphenyls (353 ng g-1) and dichloro-diphenyl-trichloroethane (3.2 and 25.3 ng g-1) in two samples taken adjacent to the sewage outfall indicate spatial heterogeneity of localized sediment contamination. Limpet (Nacella concinna) tissues collected adjacent to Palmer Station had high concentrations of PAHs, copper, lead, zinc and several other metals relative to outlying islands. Sediment and limpet tissue contaminant concentrations have decreased since the early 1990s following the Bahía Paraíso spill. Natural sediment characteristics affected macrofaunal community composition more than contamination adjacent to Palmer Station, presumably because of the low overall contamination levels.Item Anthropogenic food in the diet of the Sacred Ibis, Threskiornis aethiopicus, a non-native wading bird in southeastern Florida, USA(Florida Field Naturalist, 2011-03) Calle, Leonardo; Gawlik, Dale E.The Sacred Ibis ( Threskiornis aethiopicus ), is native to sub-Saharan Africa. A small breeding population in southeastern Florida, USA, was established in 1992 and expanded to surrounding natural areas until 2008 when an eradication program was initiated. This study investigated the degree to which the population of Sacred Ibis in South Florida consumes food items derived from human activities which may have contributed to its population expansion. Body measurements, the first such data for this species in North America, were obtained for eight adult males and five adult females. The contents of the esophageal tract and gizzards were used to classify ibis diets (N = 22) as being of anthropogenic origin (derived from human activities) if they contained cheese, meat, paper pulp, and/or pellet meal. The diet of the Sacred Ibis was comprised of predominately anthropogenic food items (58% of the cumulative biomass). Ibises with anthropogenic food items found in their diet consumed more biomass (26.99g ± SE 5.35g) than did birds that contained only natural food items in their diet (8.74g ± SE 2.21g). Natural diets, on average, contained a significantly greater percent vegetative matter (63% ± SE 12%) than did anthropogenic diets (8% ± SE 3%). Novel organic and inorganic items found in anthropogenic diets included bacon, glass, hot dog, pellet meal, and plastic. A cluster analysis revealed that some ibises used anthropogenic food as a primary food source whereas others used it as a supplement to natural food items. This study suggests that human food resources, and the habitats that contain them, may have the ability to support this species’ establishment. Further investigation, of ecologically similar species, may elucidate linkages between human food resources in urbanized areas and impacts in nearby natural habitats.Item Application of watershed analyses and ecosystem modeling to investigate land–water nutrient coupling processes in the Guadalupe Estuary, Texas(Ecological Informatics, 2009-08-07) Arismendez, Sandra S.; Kim, Hae-Cheol; Brenner, JorgeEstuarine nutrient enrichment is thought to be controlled by land use patterns in coastal watersheds. Hence, the objective of this work was to conduct a watershed analysis in two adjacent river basins with different land use characteristics to determine their influence on estuarine ecosystem response in the Guadalupe Estuary, Texas, U.S.A. All data sources for this study were available electronically on the Internet; the data were mined, managed, analyzed and transformed to simulate the estuarine ecosystem response to watershed-derived nutrient loads. Between 1992 and 2001, developed land use/land cover increased the most while forest cover decreased the most in both basins. Two hydrologic units nearest the coast were responsible for the greatest change in land cover. Nutrient concentrations and loads were significantly higher in the San Antonio River Basin than in the Guadalupe River Basin. Both river basins exhibited the highest flows ever recorded in 1992, however the magnitude of difference in loads between the two coastal hydrologic units for a wet and dry year was much greater in the Guadalupe River Basin (GRB) than in the San Antonio River Basin (SARB); this difference supports the concept that the GRB is a nonpoint source dominated system and SARB is a point source dominated system. There was a strong correlation between developed land use and nutrient concentrations in river water; the GRB had less developed land use and lower nutrient concentrations while the SARB had more developed land use and higher nutrient concentrations. Estuarine ecosystem response differed in the timing, duration and magnitude of DIN, phytoplankton and zooplankton when nitrogen loads from the Lower Guadalupe River were used as opposed to the Lower San Antonio. The two basins studied differ in their fundamental characteristics, i.e. precipitation, flow, human population density, etc., resulting in different drivers of nitrogen loading, point sources in the San Antonio River Basin and nonpoint sources in the Guadalupe River Basin, therefore, differing estuarine ecosystem responses.Item Aquatic prey switching and urban foraging by the White Ibis Eudocimus albus are determined by wetland hydrological conditions(The Authors and The British Ornothologists' Union, 2011-02-22) Dorn, Nathan J.; Cook, Mark I.; Herring, Garth; Boyle, Robin A.; Nelson, Jennifer; Gawlik, Dale E.Prey availability is known to limit reproduction of some species of nesting birds, but identifying the primary prey types of a species with a flexible diet can be challenging. For the White Ibis Eudocimus albus, a tactile feeding, medium-sized wading bird, nestling prey composition is suggested to depend on landscape water depths⁄ availability of foraging habitat at the time of nesting and on historical drying events affecting prey production. We collected and compared inter- and intra-annual diet variation of White Ibis chicks reared in the Everglades over two years that were independently identified as being relatively good (2006) and poor (2007) nesting seasons. We collected 127 nestling boluses and analyzed the temporal variation in biomass of eight functional prey groups using multivariate techniques. The boluses from 2006 in the central Everglades were dominated by fish, but in 2007, after fish had been reduced by the previous year of drying, the boluses from the same region were more variable and dominated by garbage (i.e.scavenging). Analysis of five different collections taken from a different colony in the northern Everglades indicated that boluses were characterized by crayfish and had fewer fish or less garbage when landscape water depths were relatively higher and more preferred habitat was available. At lower landscape water depths in 2007 the bolus composition shifted away from crayfish towards small fish and urban food (terrestrial insects and garbage). Our results support the suggestion of depth-dependent diets; prey composition depends on the current landscape water levels around the colonies, and also suggests that previous drying events can lead to increased reliance on alternative food sources. White Ibis partially compensated for unavailable aquatic prey with alternative urban foods, but their nesting success appears to have sufferedItem Aragonite saturation states in estuaries along a climate gradient in the northwestern Gulf of Mexico(Frontiers in Environmental Science, 2022-10-10) Hu, Xinping; Yao, Hongming; McCutcheon, Melissa R.; Dias, Larissa; Staryk, Corey J.; Wetz, Michael S.; Montagna, Paul A.In the northwestern Gulf of Mexico (nwGOM), the coastal climate shifts abruptly from the humid northeast to the semiarid southwest within a narrow latitudinal range. The climate effect plays an important role in controlling freshwater discharge into the shallow estuaries in this region. In addition to diminishing freshwater runoff down the coast, evaporation also increases substantially. Hence, these estuaries show increasing salinity along the coastline due to the large difference in freshwater inflow balance (river runoff and precipitation minus evaporation and diversion). However, this spatial gradient can be disrupted by intense storm events as a copious amount of precipitation leads to river flooding, which can cause temporary freshening of these systems in extreme cases, in addition to freshwater-induced ephemeral stratification. We examined estuarine water aragonite saturation state (Ωarag) data collected between 2014 and 2018, covering a period of contrasting hydrological conditions, from the initial drought to multiple flooding events, including a brief period that was influenced by a category 4 hurricane. Based on freshwater availability, these estuaries exhibited a diminishing Ωarag fluctuation from the most freshwater enriched Guadalupe Estuary to the most freshwater-starved Nueces Estuary. While Ωarag values were usually much higher than the threshold level (Ωarag = 1), brief freshwater discharge events and subsequent low oxygen levels in the lower water column led to episodic corrosive conditions. Based on previously obtained Ωarag temporal trends and Ωarag values obtained in this study, we estimated the time of emergence (ToE) for Ωarag. Not only did estuaries show decreasing ToE with diminishing freshwater availability but the sub-embayments of individual estuaries that had a less freshwater influence also had shorter ToE. This spatial pattern suggests that planning coastal restoration efforts, especially for shellfish organisms, should emphasize areas with longer ToE.Item Aragonite saturation states in estuaries along a climate gradient in the northwestern Gulf of Mexico(Frontiers in Environmental Science, 2022-10-10) Hu, Xinping; Yao, Hongming; McCutcheon, Melissa; Dias, Larissa; Staryk, Cory; Wetz, Michael; Montagna, PaulIn the northwestern Gulf of Mexico (nwGOM), the coastal climate shifts abruptly from the humid northeast to the semiarid southwest within a narrow latitudinal range. The climate effect plays an important role in controlling freshwater discharge into the shallow estuaries in this region. In addition to diminishing freshwater runoff down the coast, evaporation also increases substantially. Hence, these estuaries show increasing salinity along the coastline due to the large difference in freshwater inflow balance (river runoff and precipitation minus evaporation and diversion). However, this spatial gradient can be disrupted by intense storm events as a copious amount of precipitation leads to river flooding, which can cause temporary freshening of these systems in extreme cases, in addition to freshwater-induced ephemeral stratification. We examined estuarine water aragonite saturation state (Ωarag) data collected between 2014 and 2018, covering a period of contrasting hydrological conditions, from the initial drought to multiple flooding events, including a brief period that was influenced by a category 4 hurricane. Based on freshwater availability, these estuaries exhibited a diminishing Ωarag fluctuation from the most freshwater enriched Guadalupe Estuary to the most freshwaterstarved Nueces Estuary. While Ωarag values were usually much higher than the threshold level (Ωarag = 1), brief freshwater discharge events and subsequent low oxygen levels in the lower water column led to episodic corrosive conditions. Based on previously obtained Ωarag temporal trends and Ωarag values obtained in this study, we estimated the time of emergence (ToE) for Ωarag. Not only did estuaries show decreasing ToE with diminishing freshwater availability but the sub-embayments of individual estuaries that had a less freshwater influence also had shorter ToE. This spatial pattern suggests that planning coastal restoration efforts, especially for shellfish organisms, should emphasize areas with longer ToE.Item Assessing drought-related ecological risk in the Florida Everglades(Elsevier, 2003-04-28) Smith, Stephen M.; Gawlik, Dale E.; Rutchey, Ken; Crozier, Gaea E.; Gray, SusanIn the winter-spring of 2001, South Florida experienced one of the worst droughts in its recorded history. Out of a myriad of ecological concerns identified during this time, the potential for catastrophic peat fire and negative impacts to wading bird reproduction emerged as critical issues. Water managers attempted to strike a balance between the environment and protection of water supplies for agriculture and urban interests. It became evident, however, that a broad-scale, integrated way to portray and prioritise ecological stress was lacking in the Florida Everglades, despite this being considered a necessary tool for addressing issues of environmental protection. In order to provide a framework for evaluating various water management operations using real-time information, we developed GIS-based indices of peat-fire risk and wading bird habitat suitability. These indices, based on real physical, chemical, and biological data, describe two ecological conditions that help define the physical and biological integrity of the Everglades. In addition to providing continuous, updated assessments throughout the drought period, we incorporated predictive models of water levels to evaluate how various water management alternatives might exacerbate or alleviate ecological stress during this time.Item Assessing drought-related ecological risk in the Florida Everglades(Elsevier, 2003-04-28) Pierce, Rachael L.; Gawlik, Dale E.To determine how habitat structural complexity, which affects prey vulnerability, influences foraging habitat selection by wading birds, a habitat use versus availability study was conducted throughout the Florida Eve glades in 2005 and 2006. Also, an experiment was conducted where structural complexity was manipulated and effect on wading bird foraging efficiency quantified. Among-year differences in habitat selection were found, which corresponded to disparate hydrological conditions. In 2005, a poor hydrological year in terms of the seasonal r cession, wading birds chose foraging sites that had less emergent vegetation, a thicker flocculent layer and higher prey density relative to random sites. In 2006, an optimal hydrological year, wading bird foraging locations we similar to random sites in all aspects. Submerged vegetation did not affect wading bird site selection in either yea The study indicated that hydrological conditions that affect prey density were more important to wading bird foraging success than fine scale variation in habitat characteristics. However, in years of poor hydrology factors that affect prey vulnerability may become increasingly important because the penalty for choosing low quality foraging habitat is greater than in years of more optimal conditions. Elucidating habitat characteristics which create high quality foraging sites will be beneficial in planning wetland restoration projects and gauging future restoration progress. Received 2 October 2009, accepted 18 May 2010.Item Assessing ecological connectivity of blacktip sharks (Carcharhinus limbatus) in the Gulf of Mexico using stable isotope analysis of multiple tissues(Fisheries Research, 2023-08-30) Addie L. Binstock; Travis M. Richards; Kesley Gibson-Banks; J. Marcus Drymon; R.J. David Wells; John A. MohanEffective management of blacktip sharks relies on a comprehensive understanding of population distribution and stock structure. Previous stock separations and the implementation of regional quotas have proven successful in maintaining the sustainable harvest of blacktip sharks in both the Western North Atlantic and United States Gulf of Mexico (US GoM), in commercial and recreational fisheries. Within the US GoM, finer scale biological separation between blacktips in western and eastern regions has been supported through tagging, genetic, and diet data. This study provides additional evidence of unique ecological isotopic niche areas and δ15N and δ13C values for blacktip sharks from the western, central, and eastern US GoM across muscle and vertebral tissues that reflect different isotope turnover rates. Blacktip sharks from western and central regions exhibited isotope values and niches that were significantly smaller compared to eastern sharks, with enriched δ13C and depleted δ15N west of 88ºN. Ontogenetic shifts were noted for most regions and there was no crossover or overlap in average isotope values from early to recent life between regions. These spatiotemporal patterns suggest that in the year following birth and prior to the time of capture, blacktip sharks on the central and western shelves have separated ecologically from blacktips on the eastern US GoM Florida shelf.Item Assessing the Effectiveness of Large‑Scale Environmental Restoration: Challenges and Opportunities(Estuaries and Coasts, 2022-11-21) Greening, Holly; Heck, Kenneth; McKinney, Larry; Diefenderfer, Heida; Boynton, Walter; Kleiss, Barbara; Mishra, Deepak; George II, Albert; Carl Kraft, Bethany; Kling, Cathy; Windecker, LauraA recent National Academies consensus report addresses monitoring and assessment of cumulative effects of large-scale and multiple restoration projects within the context of long-term environmental change. Fines and penalties from the Deepwater Horizon oil spill in the Gulf of Mexico (GoM) have supported hundreds of restoration projects at spatial scales not often possible in the past. Here, the report committee members and staff provide personal reflections from our time working on the study. We found that gaps in data collection, issues with data accessibility, and a lack of synthesis and analysis are hindering the ability to answer a basic question: What are the impacts of these many restoration efforts on improving ecosystem health and productivity in the GoM at the regional and Gulf wide scale? Restoration efforts are occurring in environments where many trends are changing and exhibiting higher variability than in the past, suggesting that previously successful restoration practices may no longer be adequate to compensate for the effects of environmental changes and variability. Our proposed approach to these challenges includes employing emerging monitoring technologies; using conceptual models; devising an adaptive management framework; rethinking restoration outcome goals; assessing cumulative effects; and undertaking rigorous synthesis and analysis of existing information on long-term environmental trends and restoration efforts. Restoration scientists and practitioners working in the GoM have an unprecedented opportunity to demonstrate large-scale environmental recovery if advances in monitoring, synthesis, assessment, and action are taken quickly. We are cautiously optimistic that, with mid-course adjustments, continued progress toward large-scale environmental recovery is possible.Item Assessment of a brown tide impact on microalgal benthic communities in Baffin Bay (Texas) in 1990 using a primary production simulation model(Oceanolgica ACTA, 1995) Montagna, Paul A.; Blanchard, Gerard F.A primary production simulation mode! was used to assess the effect of a brown tide (Chrysophytes) on benthic microalgal photosynthesis. This model is based on the assumption that photosynthesis of microphytobenthos is primarily determined by irradiance at the sediment-water interface and by the photophysiological response of microalgae to changes of this irradiance. So, irradiance recordings at the sediment-water interface were used as the forcing variable. The simulation indicates that before the introduction of the brown tide, primary production of microphytobenthos was physically controlled. Light levels, bence primary production rates, were very variable (<1-132 mg C m-2 d-1, CV= 80 %) because wind-induced resuspension generates turbidity within the water column. During the chrysophyte bloom, the mean production rate of microphytobenthos dramatically decreased by two orders of magnitude (0.25-1.31 mg C m-2 d-1, CV = 46 %) due to shading by the planktonic compartment. Simulations further indicate that the indirect effects of this light reduction (decrease of P-1 parameters and biomass) bad a higher impact on microphytobenthic production rates than its direct effect (reduction of light energy at the surface of the sediment). As a result, the collapse of rnicrophytobenthic productivity could partially explain the observed decrease of macrofaunal abundance in Baffin Bay, since microphytobenthos is an important food source for benthic invertebrates.Item An assessment of ocean margin anaerobic processes on oceanic alkalinity budget(Global Biogeochem, 2011-07-08) Hu, Xinping; Cai, Wei-JunRecent interest in the ocean’s capacity to absorb atmospheric CO2 and buffer the accompanying “ocean acidification” has prompted discussions on the magnitude of ocean margin alkalinity production via anaerobic processes. However, available estimates are largely based on gross reaction rates or misconceptions regarding reaction stoichiometry. In this paper, we argue that net alkalinity gain does not result from the internal cycling of nitrogen and sulfur species or from the reduction of metal oxides. Instead, only the processes that involve permanent loss of anaerobic remineralization products, i.e., nitrogen gas from net denitrification and reduced sulfur (i.e., pyrite burial) from net sulfate reduction, could contribute to this anaerobic alkalinity production. Our revised estimate of net alkalinity production from anaerobic processes is on the order of 4–5 Tmol yr−1 in global ocean margins that include both continental shelves and oxygen minimum zones, significantly smaller than the previously estimated rate of 16–31 Tmol yr−1 . In addition, pyrite burial in coastal habitats (salt marshes, mangroves, and seagrass meadows) may contribute another 0.1–1.1 Tmol yr−1 , although their long‐term effect is not yet clear under current changing climate conditions and rising sea levels. Finally, we propose that these alkalinity production reactions can be viewed as “charge transfer” processes, in which negative charges of nitrate and sulfate ions are converted to those of bicarbonate along with a net loss of these oxidative anions.Item An assessment of trends in the frequency and duration of Karenia brevis red tide blooms on the South Texas coast (western Gulf of Mexico)(PlosOne, 2020-09-18) Tominack, Sarah A.; Coffey, Kara Z.; Yoskowitz, David; Sutton, Gail; Wetz, Michael S.Limited data coverage on harmful algal blooms (HABs) in some regions makes assessment of long-term trends difficult, and also impedes understanding of bloom ecology. Here, observations reported in a local newspaper were combined with cell count and environmental data from resource management agencies to assess trends in Karenia brevis “red tide” frequency and duration in the Nueces Estuary (Texas) and adjacent coastal waters, and to determine relationships with environmental factors. Based on these analyses, the Coastal Bend region of the Texas coast has experienced a significant increase in the frequency of red tide blooms since the mid-1990s. Salinity was positively correlated with red tide occurrence in the Nueces Estuary, and a documented long-term increase in salinity of the Nueces Estuary may be a major factor in the long-term increase in bloom frequency. This suggests that freshwater inflow management efforts in Texas should consider impacts on red tide habitat suitability (i.e., salinity regime) in downstream estuaries. Natural climate variability such as the El Niño-Southern Oscillation, which is strongly related to rainfall and salinity in Central and South Texas, was also an influential predictor of red tide presence/absence. Though no significant change in the duration of blooms was detected, there was a negative correlation between duration and temperature. Specifically, summer-like temperatures were not favorable to K. brevis bloom development. The relationships found here between red tide frequency/duration and environmental drivers present a new avenue of research that will aid in refining monitoring and forecasting efforts for red tides on the Texas coast and elsewhere. Findings also highlight the importance of factors (i.e., salinity, temperature) that are likely to be altered in the future due to both population growth in coastal watersheds and anthropogenic climate change.Item An assessment of two visual survey methods for documenting fish community structure on artificial platform reefs in the Gulf of Mexico(Elsevier B.V., 2020-01-07) J. Wetz, Jennifer; J. Ajemian, Matthew; Shipley, Brooke; W. Stunz, GregoryNon-extractive visual survey methods are commonly used to assess a variety of marine habitats. The use of Underwater Visual Census (UVC) by SCUBA divers is predominant; however, remotely acquired video data (e.g., cameras systems, remotely operated vehicles (ROVs), submersibles) are becoming more frequently used to acquire community data. Both remote and diver-based surveys are currently used to survey artificial reef habitat in the Northwestern Gulf of Mexico (GOM) and have associated error due to inherent method bias. Because survey methods that most accurately document the occurrence and estimated abundance of several important fisheries species are greatly needed in the GOM, we compared data collected on the same days and sites from both Roving Diver Surveys (RDS) and micro-ROV surveys conducted on reefed oil and gas platforms. The combined datasets identified a total of 56 species from 22 families, and there was no significant difference in measured species richness between a comprehensive 30 min ROV survey and RDS. Five species of federally managed fish in the GOM were more frequently detected by ROV, as were the majority of species in the Lutjanid and Carangid families. However, abundance estimates from RDS surveys were up to an order of magnitude greater. Multivariate analyses indicated that method choice affected community composition, with Lutjanids and Carangids driving the differences. These two fish families in particular are subject to method bias, probably due to inflated abundance estimates with RDS, or alternatively, deflated estimates from ROV. Although our ROV surveys more frequently detected important fisheries species and produced conservative abundance estimates, a further examination of species distributions on these high-relief platform reefs is needed to fully determine the most accurate survey method. In addition, the attraction and/or gear avoidance of certain species to underwater vehicles deserves further investigation. Overall, our data indicate these methods are viable but the choice of survey method can have implications for the management of certain species, and that careful consideration of methodology is necessary to most accurately document species of interest.Item Avian Communities in Bayheads, Willowheads, and Sawgrass Marshes of the Central Everglades(Wilson Bulletin, 1997-10-03) Rocque, Deborah A.; Gawlik, Dale E.We compared avian community composition, species richness, and total bird abundance among three vegetation types (bayheads, willowheads and marshes), and between a reduced-hydroperiod and relatively unimpacted landscape in the central Everglades during July-August, 1996. Our results showed that the collective Everglades bird community contained a substantial number of forest birds as well as marsh species. Red-winged Blackbirds (Agelaius phoeniceus), Common Yellowthroats (Geothlypis trichas), and White-eyed Vireos (Vireo griseus) accounted for 65% of total individual birds during the period of study. Wading birds accounted for a relatively small proportion of the total avian community. White-eyed Vireo was the most abundant bird species in bayheads and was closely associated with that habitat. Red-winged Blackbird and Common Yellowthroat were the most abundant species in both willowheads and marsh vegetation. We found no significant difference in bird abundance among vegetation types (P > 0.05) nor between landscapes (P > 0.05). We also found no difference in species richness between landscapes (P > 0.05). A significant (P = 0.02) interaction between vegetation and landscape indicated that species richness differed among vegetation types in the unimpacted landscape, but not in the reduced-hydroperiod landscape. In the unimpacted landscape we detected significantly more species in bayheads than the other two vegetation types (both tests, P ' 0.004). An ordination revealed that in the unimpacted landscape, bird communities were more specific to vegetation types than in the reduced- hydroperiod landscape. Our study demonstrates that two characteristics of a relatively unimpacted landscape in the central Everglades are higher avian species richness and a more distinct avian community in bayheads than in willowheads or marshes. The Everglades restoration process will promote the conservation of avian diversity by restoring the landscape matrix of both marsh and bayhead vegetation.Item Avian Radio-transmitter Harness Wear and Failure(Eagle Hill Institute, 2010) Herring, Garth; Gawlik, Dale E.Although investigators have compared radio-transmitter attachment devices and their likelihood of failure before the end of a study, few have directly evaluated the harness materials and fastening methods that are to be shed by a bird after the research period is over. We compared the likelihood of effective detachment after transmitter life of four harness materials (7-mm- and 9-mm-wide polyester rib- bon tape and polyester-coated rubber elastic) and three fastening methods (polyester thread, cotton thread, and Gorilla Super Glue™) using dummy transmitters exposed to the elements for >1.5 years. Both polyester ribbon and polyester-coated rubber elastic materials resulted in similar physical wear and remained intact for longer than a typical field seasonal, but fastening harnesses using Gorilla Super Glue™ resulted in the earliest and most consistent harness failure. Polyester ribbon material and glue fastening resulted in the earliest failure; mean failure time for 7-mm- and 9-mm-wide polyester ribbon tape with glue fastening was 408 days ±30 SE, and 249 days ± 29 SE, respectively. Failure times for both 7-mm- and 9-mm-wide polyester- coated rubber elastic and Gorilla Super Glue™ fastening treatments were in excess of one year (438 days ± 14 SE and 438 days ± 13 SE, respectively). All harnesses with sewn thread fastening treatments lasted a minimum mean of 456 days, and i the case of both 7-mm-wide polyester ribbon and polyester-coated rubber elastic neither treatment ever failed over the period of study. Results suggest that using Gorilla Super Glue™ as a fastener maximized the likelihood of eventual harness failure, whereas transmitters fastened via sewing showed minimal signs of wear an were unlikely to be shed by a bird during a period of time less than two years. Additional experimental studies are warranted to examine alternative harness material types, fastening methods, and harness styles to maximize the potential of successful radio transmitter shedding.Item Avian response to nutrient loading in an oligotrophic wetland(The Condor, 2002-08-01) Gawlik, Dale E.; Crozier, Gaea E.We studied the effects of nutrient enrichment on the bird community in an oligotrophic wetland, the Florida Everglades. Among the non-wading birds surveyed in 1996 and 1997, Boat-tailed Grackles (Quiscalus major) and Common Moorhens (Gallinula chloropus) were consistently more abundant in enriched sites, whereas Common Yellowthroats (Geothlypis trichas) were consistently more abundant in unenriched sites. The abundance of Red-winged Blackbird (Agelaius phoeniceus) was not significantly different between enriched and unenriched sites. Among wading birds, Wood Storks (Mycteria americana) and Great Egrets (Ardea alba) were significantly more abundant in enriched than unenriched areas in a dry year, 1991. Great Egrets and all wading species combined were significantly more abundant in enriched than unenriched areas in the wet year, 1995. Great Blue Herons (Ardea herodias) and White Ibises (Eudocimus albus) did not differ in abundance between enriched and unenriched areas in the dry or wet year. A significant interaction between water depth and nutrient status in the wet year indicated that wading bird abundance increased with water depth only in nutrient-enriched areas presumably because the enriched areas had greater food availability than unenriched areas at the same water depth. Bird abundance appeared to increase in nutrient-enriched areas; however, this increase was accompanied by a shift in species composition typically found in the unenriched Everglades and was a fundamental change in the Everglades' distinctive structure.