Oceanic-Atmospheric Modes of Variability and Their Effect on River Flow and Blue Crab (\u3ci\u3eCallinectes sapidus\u3c/i\u3e) Abundance in the Northcentral Gulf of Mexico

Oceanic-atmospheric modes of variability occur on interdecadal, multidecadal, decadal, and interannual timescales and their influence on climate around the world has been confirmed. The present study investigates Mississippi River and Pascagoula River flows in response to the influence of one or more of the four oceanic-atmospheric modes of variability: the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), and the El Nino Southern Oscillation (ENSO). These modes of variability are present in phases: PDO warm (PDOw) and cold (PDOc), AMO warm (AMOw) and cold (AMOc), NAO positive (NAOp) and negative (NAOn), and ENSO warm (ENSOw), neutral (ENSOn), and cold (ENSOc). High Mississippi River mean flow was associated with the PDOw, AMOc, and NAOp phases, with low river flow linked to their opposite phases. High Pascagoula River mean flow was related to the AMOc and NAOp phases, with low river flow linked to their opposite phases. Pascagoula River flow was significantly higher during the ENSOw than ENSOc events, within PDOw/AMOw/NAOp and NAOn phase. Blue crab data on abundance were taken from fishery-independent trawl survey programs conducted by the Gulf Coast Research Laboratory, Ocean Springs, Mississippi and the Louisiana Department of Wildlife and Fisheries in coastal waters of Mississippi and Louisiana, respectively. Four long-term climatic phases (PDOc/AMOc/NAOn, PDOc/AMOc/NAOp, PDOw/AMOc/NAOp, and PDOw/AMOw/NAOp and NAOn) overlapped with four distinct periods of annual blue crab abundance that were identified using hierarchical agglomerative clustering and non-metric, non-parametric multidimensional scaling techniques. The following abundance periods were delineated: period I (1967-1970), period II (1971-1980), period III (1981-1998), and period IV (1999-2004). For all but three years (1991, 1995, 2005) the overall abundance of blue crabs fell into chronological sequences under climatic phases. A single year (1990) did not group with any of the four abundance periods. Periods II and III were characterized by high numbers of crabs and increased river flow, whereas Period IV was distinguished by low numbers of crabs and decreased river flow. Years of lowest abundance (period IV) occurred at a time of unprecedented change in habitat associated with catastrophic storms, the cumulative consequences of man-made alterations to coastal wetlands, and an unfavorable climatic regime. Whether a shift to a more favorable climatic regime would increase abundance is unknown. Blue crab abundance was related to long-term hydrological conditions across the Mississippi River and Pascagoula River basins with 23% of the variability explained by oceanic-atmospheric modes of variability (AMO, NAO), salinity, and frequency of southeast winds. These factors may favor blue crab productivity by increasing marsh edge habitat, decreasing predation, and facilitating shoreward transport of megalopae. The importance of biotic factors associated with quality of habitat as refuge has been emphasized by recent studies. Because climate operates on an ever-changing coastal environment and because of the inability to quantify sources of natural mortality of young crabs, prediction of blue crab abundance is difficult when current knowledge is coupled solely with the influence of climatic factors

Crab Larval Abundance and Settlement Patterns in a Changing Chesapeake Bay

All estuarine crabs have two larval stages, the zoea and the megalopa. Zoeae are entirely planktonic, whereas megalopae begin as plankton before beginning to search for settlement substrates as late stage megalopae. At both stages, crab larvae are subject to environmental conditions of the estuary. With changing environmental conditions due to anthropogenic activities and climate change, an understanding of how these planktonic larvae respond to environmental conditions is necessary for understanding subsequent larval supply to benthic populations and implication for fisheries management and habitat restoration. For this dissertation, I: 1) analyzed long-term timeseries in the lower Chesapeake Bay for spatial and temporal change in zoeal abundance and to identify the environmental drivers of these changes; 2) examined effects of climate and environmental conditions on long-term change of dominant crab zoeae in the lower Chesapeake Bay; 3) investigated how warming temperatures in the Bay affect phenology of dominant crab zoeae; and 4) conducted a field experiment in the lower Bay to characterize settlement pattern of megalopae and determine environmental predictors of settlement. Zoeal assemblages of the lower Chesapeake Bay were characterized by distinct assemblages in the tributaries versus the mainstem Bay. Zoeae of the estuarine mud crab (Rithropanopeus harrisii) and fiddler crabs (Uca minax and Uca spp.) dominated in the tributaries, whereas a more diverse assemblage of crab zoeae, including larvae of the mud crab Hexapanopeus angustifrons, pea crab Pinnixa sayana, blue crab Callinectes sapidus, squatter pea crab Tumidotheres maculatus, and fiddler crabs Uca spp. were dominant taxa in the mainstem. Salinity was the single most important factor explaining patterns in the composition of zoeal assemblages in space and time. Variability in total zoeal abundance and richness in both regions was also significantly related to salinity. Abundance of four dominant species, Callinectes sapidus, Hexapanopeus angustifrons, Dyspanopeus sayi, and Pinnixa chaetopterana, in the mainstem significantly decreased from 1985-2002, while no significant trend was observed for dominant species in the tributaries. Variability in abundance of dominant zoeae was significantly related to the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO), which likely influenced zoeal abundance via streamflow into the Bay. From 1968 to 2002, I found no significant effect of warming on phenology of the zoeae of dominant species, except Rhithropanopeus harrisii, which had an earlier start of season (date of 10% of highest peak of abundance) as water temperature increased. in a field experiment, settlement of C. sapidus megalopae was episodic, beginning in mid-July and extending into November. in contrast, the settlement periods of R. harrisii and D. sayi were shorter than C. sapidus, begining in early-July and ending in early October. Local conditions, especially salinity and water temperature, were as important as factors associated with transport processes (e.g., tidal range, wind direction, lunar phases) in determining settlement of crab megalopae. This dissertation illustrated that zoeal assemblages and successful settlement of megalopal stage of crabs in the lower Chesapeake Bay were sensitive to changes in environment conditions. These changes in zoeal abundance and settlement success have important implications for adult populations of estuarine crabs

Larval dispersal in a changing ocean with an emphasis on upwelling regions

Dispersal of benthic species in the sea is mediated primarily through small, vulnerable larvae that must survive minutes to months as members of the plankton community while being transported by strong, dynamic currents. As climate change alters ocean conditions, the dispersal of these larvae will be affected, with pervasive ecological and evolutionary consequences. We review the impacts of oceanic changes on larval transport, physiology, and behavior. We then discuss the implications for population connectivity and recruitment and evaluate life history strategies that will affect susceptibility to the effects of climate change on their dispersal patterns, with implications for understanding selective regimes in a future ocean. We find that physical oceanographic changes will impact dispersal by transporting larvae in different directions or inhibiting their movements while changing environmental factors, such as temperature, pH, salinity, oxygen, ultraviolet radiation, and turbidity, will affect the survival of larvae and alter their behavior. Reduced dispersal distance may make local adaptation more likely in well-connected populations with high genetic variation while reduced dispersal success will lower recruitment with implications for fishery stocks. Increased dispersal may spur adaptation by increasing genetic diversity among previously disconnected populations as well as increasing the likelihood of range expansions. We hypothesize that species with planktotrophic (feeding), calcifying, or weakly swimming larvae with specialized adult habitats will be most affected by climate change. We also propose that the adaptive value of retentive larval behaviors may decrease where transport trajectories follow changing climate envelopes and increase where transport trajectories drive larvae toward increasingly unsuitable conditions. Our holistic framework, combined with knowledge of regional ocean conditions and larval traits, can be used to produce powerful predictions of expected impacts on larval dispersal as well as the consequences for connectivity, range expansion, or recruitment. Based on our findings, we recommend that future studies take a holistic view of dispersal incorporating biological and oceanographic impacts of climate change rather than solely focusing on oceanography or physiology. Genetic and paleontological techniques can be used to examine evolutionary impacts of altered dispersal in a future ocean, while museum collections and expedition records can inform modern-day range shifts

Gulf Estuarine Research Society 2014 Meeting

Table of Contents: Thank You to Our Sponsors! (p. 3) -- About the Gulf Estuarine Research Society (p. 4) -- Student Travel Award winners (p. 5) -- Abbreviated Schedule (p. 7) -- 2014 Plenary Speaker – Dr. Michael Osland (p. 8) -- 2014 Plenary Speaker – Dr. Maggie Walser (p. 9) -- Full Schedule (p. 10) -- Poster Session Directory (p. 17) -- Oral Presentation Abstracts (p. 21) -- Poster Presentation Abstracts (p. 38) -- Things to Do in Port Aransas (p. 52) -- Greening the Meeting (p. 53) -- Map of University of Texas Marine Science Institute (p. 54)Coastal and Estuarine Research Foundation, Port Aransas, Gulf of Mexico Foundation, Coastal Bend Bays & Estuaries Program, Lotek Wireless Fish & Wildlife Monitoring, Sea Grant Mississippi-Alabama, Sea Grant Louisiana, Sea Grant Texas, The University of Austin Marine Science Institute, Mission-Aransas National Estuarine Research ReserveMarine Scienc

The Effects of Drought on the Abundance of the Blue Crab, \u3ci\u3eCallinectes sapidus\u3c/i\u3e, in the ACE Basin NERR in South Carolina

Blue crabs make up one of the most important commercial fisheries in the U.S. but there has been some concern over the health of blue crab populations due to large declines in landings seen in recent years. There is a significant positive correlation between river discharge and commercial landings suggesting that drought may be to blame for the recent decline in crab numbers. The work I completed for my dissertation tested multiple hypotheses examining the link between decreasing freshwater discharge, the subsequent rise in salinity, and the abundance of blue crabs in the ACE Basin National Estuarine Research Reserve. To address these hypotheses, a combination of laboratory studies, field observations, and field manipulations were performed over a four year time period from June 2008 through March 2012. Water quality, crab health, fishing effort, and Hematodinium sp. infection rates were measured quarterly at 27 stations. Field experiments were performed to estimate both blue crab post-larval abundance and survival. River discharge varied both seasonally and annually causing shifts in the salinity profiles of each river. Increasing salinity increased crab survival, but also increased infection by Hematodinium sp, a lethal dinoflagellate parasite. Post-larval abundance was not related to changes in salinity. Over the four years, crab abundances increased in the river with the highest freshwater input and decreased in the river with the lowest freshwater input. These results suggest that drought can have both positive and negative consequences for crab abundance and that further reductions in freshwater discharge would likely have a net negative impact on future crab landings

Population Genetics of the Blue Crab (Callinectes sapidus) in the Gulf of Mexico, Chesapeake Bay, and Western South Atlantic

The blue crab, Callinectes sapidus, is an important species in estuarine habitats, serving as both predator and prey to other species, and plays a pivotal ecological and economic role throughout its range. In recent years, however, its populations have been declining. Declining blue crab populations will negatively affect critically endangered organisms that depend on the blue crab, like Kemp’s Ridley sea turtles and whooping cranes, as well as commercially important fish species, such as red drum, Sciaenops ocellatus. Despite its importance, little is known about its genetic population structure, which can be affected by population reductions. Previous research provides conflicting evidence of genetic variation in the blue crab across its range. Some studies have identified significant population structure in blue crabs in the Gulf of Mexico, attributed to seasonality, catastrophic events, and post-larval selection, while others have found genetic homogeneity in the Texas coast, possibly due to gene flow by larval dispersal. The results from previous studies are being used to implement management strategies, despite their limitations. In this study, population structure of the blue crab was assessed throughout the Gulf of Mexico, in the Chesapeake Bay, and southern Brazil using sixteen microsatellite markers. The results show high levels of gene flow for the blue crabs in the United States (GST = 0.005; DST = 0.015), with no genetic differentiation identified by any of the analyses. There is evidence of strong genetic differentiation between the U.S. and Brazil (GST = 0.067; DST = 0.056). No signs of a recent bottleneck were detected in any of the populations. Estimated NE was very high for all populations. This information will aid management decisions for the blue crab and help preserve this important species by improving stock delineations and providing a baseline of genetic diversity

Addressing the land loss-fish production paradox

Saltmarsh loss is occurring at high rates in Louisiana (LA), but understanding the impacts that marsh degradation has had on historical abundance of estuarine nekton in Barataria Bay, LA is lacking. I first examined the differences between fishery independent and fishery dependent data as indices of relative abundance. Previous studies used landings data to evaluate the importance of marsh habitat (e.g. distance of marsh edge and area of intertidal marsh) to fisheries production, but for most species, landings and survey data showed differing patterns of abundance through time. These findings emphasize the importance of using survey data (not landings data) to conduct habitat-related analyses in Louisiana and elsewhere. Next, I investigated the influence of a suite of environmental and fishery related predictors on fishery independent catch-per-unit-effort (CPUE) and developed descriptive models for these relationships. The descriptive models show that abundance of estuarine nekton varied only marginally with marsh habitat related predictors. Using both parametric and non-parametric statistical analyses, I then tested previous hypotheses that explained the relationship between marsh habitat and fish abundance, in addition to exploring community level effects. Results indicated that marsh and marsh edge distance do not appear to be driving nekton abundance. However, differences were found when comparing the community structure of Barataria Bay from different time periods over the last 44 years. Finally, I developed an ecosystem model to test the influence of marsh loss on nekton abundance, while accounting for changes in salinity and trophic interactions. Results indicate that marsh edge accounted for only a small portion of historical variation in nekton abundance. While this study suggests the influence of marsh loss on fisheries may be less significant than once thought, the importance of protecting coastal saltmarshes remains vital to the health and prosperity of Louisiana’s deltaic ecosystem

Patterns of Habitat Use and Trophic Structure in Turtle Grass (Thalassia testudinum)-Dominated Systems Across the Northern Gulf of Mexico

Seagrass structural complexity is a primary driver of nekton recruitment and faunal community structure. Few studies, however, have quantified the role of seagrass complexity on habitat use and trophic structures over large spatial scales. A large-scale simultaneous survey was conducted to assess relationships of multiple seagrass morphological complexity metrics to nekton habitat use, trophic dynamics, and blue crab (Callinectes sapidus) growth and mortality across the Northern Gulf of Mexico. Seagrass morphological and nekton community characteristics depended on site and season, and regional variation in seagrass morphology was an important driver of juvenile nekton abundance, species richness, beta diversity, assemblage structure, and functional diversity across the Northern GOM. Results from a stable isotope survey indicate that food web structures across turtle grass (Thalassia testudinum)-dominated ecosystems are similar, although there was a clear trend of more depleted carbon isotopes in primary producers, fish, shrimp, and crabs at sites in the Eastern GOM and more enriched isotopes at sites in the Western GOM, which may be associated with site-specific differences in environmental conditions, such as freshwater inflow and nutrient inputs. Blue crab growth and mortality experiments revealed that growth and mortality rates varied across the six sites, but overall mortality rate declined with increasing seagrass leaf area index and crab size. Blue crab growth rates, however, had no measurable relationship with seagrass complexity metrics. Results from this work indicate that habitat complexity metrics such as shoot density, canopy height, and leaf area index are important factors that define the nursery functions of seagrass habitats and should be incorporated into monitoring programs, conservation initiatives, and fishery models. This study also demonstrates the utility of conducting large-scale comparative studies to reveal regional differences and similarities in trophic structures. Finally, this study highlights the need for additional regional and species-specific studies of environmental drivers of nekton community production throughout the GOM, and our results suggest that models of nekton production in seagrass habitats should be created at regional, as well as local, scales to identify broad patterns but also to account for site-specific differences in nekton responses to environmental and habitat characteristics

Spatiotemporal Abundance Patterns and Ecological Drivers of A Nearshore U.S. Atlantic Fish and Invertebrate Assemblage

Taking an ecosystem approach to fisheries requires the consideration of relevant ecological processes within research and assessment frameworks. Processes affecting ecosystem productivity can be categorized as biophysical (climate variability, primary production), exploitative (fishing), or trophodynamic (food web interactions). This dissertation incorporates these three governing processes to characterize spatiotemporal diversity and population abundance trends for multiple demersal fish and invertebrate species that inhabit the nearshore zone (15-30 ft. depth) along portions of the U.S. Atlantic east coast. Two large marine ecosystems (LMEs) encompass the U.S. East coast – the Southeast and Northeast U.S. Continental Shelf LMEs. The level of connectivity within and between these two ecosystems is well understood for some individual species, but not generally for the nearshore assemblage. The first research chapter of this dissertation is a spatial diversity analysis of 141 fish and invertebrate species that inhabit nearshore waters from Florida to New York. Latitudinal diversity patterns revealed multiple biotic ecotones, or areas of high species turnover. An ecotone was evident in northern spring near the Cape Hatteras border of the two LMEs, but this barrier dissipated as water temperatures homogenized and assemblage connectivity between ecosystems increased throughout the year. Multiple other biotic ecotones were evident within the Southeast U.S. LME and were explained by seasonality and the proximity and area of adjacent estuarine habitat. The second and third research chapters of this dissertation focus on explaining temporal abundance trends for multiple nearshore fish and invertebrate species within the Southeast U.S. LME. For the second research chapter, abundance trends for 71 species were analyzed during 1990-2013 within a univariate time series modeling framework with the goal of determining the relative importance of climate variability and fishing pressure as governing influences on abundance. A decrease in bycatch mortality explained changes for multiple species, while climate variability governed the dynamics for others. Multivariate ordination revealed similar trends for groups of taxonomically related species, indicating governing processes act on species with similar life histories. An extension of results from the second research chapter, research chapter three explores trophic interactions between the bonnethead shark (Sphyrna tiburo) and five of its prey species within Southeast U.S. LME nearshore waters. Multivariate time series modeling supports a negative effect of bycatch on bonnetheads, and population-level predation effects of larger sharks on multiple prey species. Abundance trends for most prey species were also explained by environmental variability associated with the Pacific Decadal Oscillation, although trophic effects were stronger. This body of work incorporates relevant ecological factors in characterizing diversity and abundance trends for fish and invertebrate species comprising the nearshore demersal assemblage within Southeast and Northeast U.S. LMEs. Results indicate seasonal connectivity between LMEs that require further exploration at multiple spatial scales. Abundance time series modeling for multiple species in the Southeast U.S. LME reveals that fishing and trophodynamics may be relatively more influential drivers than climate variability in this sub-tropical system