Georgia Estuaries Research Articles

Sharks and Rays 101: A Virtual Program Connecting Families with Estuary Research

Virtual programming presents new opportunities to connect learners with aquarium ambassador animals, communicate science, and foster appreciation of coastal habitats. Educators can share additional resources, such as video footage and researcher presentations, that would otherwise be unavailable to aquarium guests viewing exhibits. Starting in the summer of 2020, the University of Georgia Marine Education Center and Aquarium (MECA) hosted new virtual public programs, including a Sharks and Rays 101 webinar. This webinar was offered twice; in summer 2020 it had 46 attendees, including 17 children and 29 adults, and in spring 2021 it had 25 attendees, including 6 children and 19 adults. The webinar used a place-based approach, introducing local elasmobranch species and shark nursery research conducted in Georgia estuaries. Estuaries are important nursery habitats for many shark species and areas where individuals recreationally fishing may interact with elasmobranchs. Activities included a virtual visit featuring a stingray and skate, participant polls, Q & A with a researcher, and interpreting maps from shark surveys. The program was evaluated with a voluntary survey and pre- and post-tests. Surveys indicated that future webinars, including those for adults, could increase engagement by incorporating videos of ambassador animals, polls, and limiting slide presentation length. An accompanying classroom activity was developed to extend learning after the webinar, utilizing a recording of the live event. This paper describes the webinar, shares the classroom activity, and suggests modifications that may be used by other educators to virtually teach about shark nurseries in estuaries.

Residence, Habitat Use, and Movement Patterns of Atlantic Tripletail in the Ossabaw Sound Estuary, Georgia

AbstractAtlantic TripletailsLobotes surinamensissupport a popular recreational fishery along the coast of Georgia; however, Atlantic Tripletail residency and movements within Georgia estuaries have not been studied. Our objective was to describe estuarine movements and residency of Atlantic Tripletails in the Ossabaw Sound Estuary, Georgia. During summer in 2010 and 2011, large juvenile and adult Atlantic Tripletails (n= 32; 42.1–71.0 cm TL) were captured with traditional angling methods and received surgically implanted ultrasonic transmitters. Tagged individuals were detected within the estuary via a stationary array of acoustic receivers that monitored the estuary continuously from June 2010 through May 2012. Manual tracking was conducted with a portable hydrophone and homing. Atlantic Tripletails were detected in the estuary during March–November at sustained water temperatures above 21°C; tagged fish were not detected by the stationary array during any other period. Movements were highly correlated with tidal stage; 100% of the tagged fish moved upstream with flood tides and returned to the sound with the ebbing tide on a daily basis. Atlantic Tripletails were observed as far upstream as river kilometer 33. Our results from acoustic telemetry provide the first information on spatial and temporal habitat use by Atlantic Tripletails within the South Atlantic Bight and suggest that these fish (1) exhibit a high degree of residency in Georgia estuaries and (2) use a large portion of the estuary during their daily movements. Although estuarine habitat use appeared to be an important component of the species’ life history, future studies of population dynamics and winter movements will be needed to obtain a better understanding of the potentially complex structure of Atlantic Tripletail stocks.Received March 18, 2013; accepted July 22, 2013

Comparison of abundance and habitat usage for common bottlenose dolphins between sites exposed to differential anthropogenic stressors within the estuaries of southern Georgia, U.S.A

AbstractThe health of common bottlenose dolphins (Tursiops truncatus) within southern Georgia estuaries is of particular concern due to high levels of anthropogenic contaminants in their tissues. Dolphins in this region have the highest polychlorinated biphenyl (PCB) concentrations recorded for any marine mammal and these concentrations correlate to distance from a Superfund point‐source in the Turtle/Brunswick River Estuary (TBRE). Currently, little is known about the population structure of dolphins in this region. This study identifies and compares baseline data on abundance, habitat use, site‐fidelity, and ranging patterns of dolphins across two adjacent field sites; Brunswick, including the TBRE, and Sapelo, including the Sapelo Island National Estuarine Research Reserve. Sapelo is relatively undeveloped and was selected for comparison to the more contaminated TBRE. Dolphin densities increased with tributary size in both sites but dolphin density and total abundance were significantly higher in Sapelo than in Brunswick. Anthropogenic stressors within the TBRE may be an important factor contributing to the differences in abundance, density, and habitat use observed in this study.

Utility of mesohabitat features for determining habitat associations of subadult sharks in Georgia’s estuaries

We examined the affects of selected water quality variables on the presence of subadult sharks in six of nine Georgia estuaries. During 231 longline sets, we captured 415 individuals representing nine species. Atlantic sharpnose shark (Rhizoprionodon terranovae), bonnethead (Sphyrna tiburo), blacktip shark (Carcharhinus limbatus) and sandbar shark (C. plumbeus) comprised 96.1% of the catch. Canonical correlation analysis (CCA) was used to assess environmental influences on the assemblage of the four common species. Results of the CCA indicated Bonnethead Shark and Sandbar Shark were correlated with each other and with a subset of environmental variables. When the species occurred singly, depth was the defining environmental variable; whereas, when the two co-occurred, dissolved oxygen and salinity were the defining variables. Discriminant analyses (DA) were used to assess environmental influences on individual species. Results of the discriminant analyses supported the general CCA findings that the presence of bonnethead and sandbar shark were the only two species that correlated with environmental variables. In addition to depth and dissolved oxygen, turbidity influenced the presence of sandbar shark. The presence of bonnethead shark was influenced primarily by salinity and turbidity. Significant relationships existed for both the CCA and DA analyses; however, environmental variables accounted for <16% of the total variation in each. Compared to the environmental variables we measured, macrohabitat features (e.g., substrate type), prey availability, and susceptibility to predation may have stronger influences on the presence and distribution of subadult shark species among sites.

Potential Sources of Survey Bias Associated with Hand‐Retrieved Longline Catches of Subadult Sharks in Georgia Estuaries

AbstractLunar phase, tide stage, and bait type were examined as potential sources of survey bias affecting catch rates of subadult sharks on hand‐retrieved longlines in Georgia estuaries. Sampling occurred during April–September from 2001 to 2003 in eight of Georgia's nine estuaries; this sampling period coincides with the pupping seasons for a variety of shark species. The effects of lunar phase and tide stage on catch rates of sharks were evaluated during 2001 and 2002. The effect of bait type (i.e., squid Loligo spp. or spot Leiostomus xanthurus) on shark catch rates was evaluated during 2003. During 2001 and 2002, 420 subadult sharks representing two families (Carcharhinidae and Sphyrnidae) and nine species were caught during 212 longline sets. Catch rates were evaluated for the four most commonly occurring shark species: the Atlantic sharpnose shark Rhizoprionodon terraenovae, bonnethead Sphyrna tiburo, blacktip shark Carcharhinus limbatus, and sandbar shark C. plumbeus. Neither lunar phase nor tide stage affected catch rates of any species other than blacktip sharks. In 2003, longline sets (n = 80) resulted in the capture of 177 subadult sharks from seven species. Overall catch rates were higher with squid bait than with spot, and bait type also affected shark species catch composition. Mean sizes of Atlantic sharpnose sharks were significantly different between the two bait types, indicating a possible ontogenetic shift in bait preference. For example, catch of neonate Atlantic sharpnose sharks was higher on hooks baited with squid than on hooks baited with spot, whereas catch of juveniles was higher on hooks baited with spot. Although timing of sampling events did not influence catch rates of subadult sharks, bait choice could bias estimates of abundance for certain life stages and affect the probability of detecting some species.

A comparative study of carbon dioxide degassing in river‐ and marine‐dominated estuaries

The partial pressure of carbon dioxide (pCO2), concentration of total dissolved inorganic carbon, and total alkalinity were measured at both high tide and low tide in the surface water of three Georgia estuaries from September 2002 to May 2004. Of the three estuaries, Sapelo and Doboy Sounds are marine‐dominated estuaries, while Altamaha Sound is a river‐dominated estuary. During all sampling months, the three estuaries were supersaturated in CO2 with respect to the atmosphere (39.5–342.5 Pa, or 390–3380 [atm) because of CO2 inputs from within the estuarine zone (mainly intertidal marshes) and the river. Overall, pCO2 in the river‐dominated estuary is much higher than that in the marine‐dominated estuaries. The calculated annual air‐water CO2 flux in Altamaha Sound (69.3 mmol m−2 d−1) is 2.4 times those of Sapelo and Doboy Sounds (28.7–29.4 mmol m−2 d−1). The higher CO2 degassing in the river‐dominated estuary is fueled largely by CO2 loading from the river. Because of the substantial differences between river‐ and marine‐dominated estuaries, current estimates of air‐water CO2 fluxes in global estuaries (which are based almost entirely on river‐dominated estuaries) could be overestimated.

Concentrations and patterns of perfluoroalkyl acids in Georgia, USA surface waters near and distant to a major use source

Perfluoroalkyl acids (PFAAs) are widespread contaminants emanating from, among other sources, the production/degradation of fluorinated chemicals used in surface repellant applications, such as carpet manufacturing. The goal of the present study was to assess the concentrations of PFAAs, including perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUA), and perfluorooctane sulfonamide (PFOSA), in surface waters both near a wastewater land application system (LAS) in Dalton (GA, USA), home to North America's largest carpet manufacturing site, and distant to this location (Altamaha River, GA, USA) to understand the fate of PFAAs in freshwater. Levels of PFAAs were high in the Conasauga River (GA, USA) downstream of the LAS (PFOA, 253-1,150 ng/L; PFOS, 192-318 ng/L; PFNA, 202-369 ng/L; PFDA, 30.1-113 ng/L; PFUA, 58.0-99.2 ng/L; PFOSA, 162-283 ng/L) and in streams and ponds in Dalton (PFOA, 49.9-299 ng/L; PFOS, 15.8-120 ng/L), and were among the highest measured at a nonspill or direct-release location. Perfluoroalkyl acids in the Altamaha River were much lower (PFOA, 3.0-3.1 ng/L; PFOS, 2.6-2.7 ng/L), but were a source of PFAAs to Georgia's estuaries. A preliminary hazard assessment indicated that concentrations of PFOS at two sites in the Conasauga River exceeded the threshold effect predicted for birds consuming aquatic organisms that are exposed continuously to the PFOS levels at these sites. Assuming that toxicity for all PFAAs quantified is equal to that of PFOS, the sum total PFAAs at two sites within the Conasauga River exceeded PFOS thresholds for aquatic and avian species, warranting additional research.

Quantification of enterococci and bifidobacteria in Georgia estuaries using conventional and molecular methods

Fecal pollution is a serious threat to the estuarine environment along the Georgia coast. Culture-dependant and molecular methodologies were utilized to compare and evaluate the abundance of fecal indicator bacteria in four Georgia estuaries (Darien River, Frederica River, Gulley Hole Creek, and St. Marys River). The functionality of enterococci and bifidobacteria as indicator organisms in marine environments was assessed, as well as Bifidobacterium adolescentis densities. At each study site, enterococci were enumerated as colony forming units (CFU) on mEI agar. For quantitative polymerase chain reaction (qPCR), genus- and species-specific primer sets were used to quantify bifidobacteria and B. adolescentis as 16S rRNA gene copies and enterococci as tuf gene copies. A high correlation ( r = 0.925) was observed between CFU and qPCR enumeration of enterococci. Enterococci densities in the estuarine rivers ranged from 3–449 CFU/100 ml on mEI plates and 4.58–5.39 Log 10 gene copies/100 ml by qPCR. Bifidobacteria densities ranged from 3.62–4.14 Log 10 gene copies/100 ml and suggested the Frederica River as least affected by fecal bacteria and the Darien River as most affected by fecal pollution. A correlation of 0.46 was observed among qPCR densities of enterococci and bifidobacteria at all sample sites. Quantitative polymerase chain reaction detection of B. adolescentis was a rapid (i.e., less than 2 h) indicator of presumptive human fecal pollution and suggested that Gulley Hole Creek, the Darien River, and the St. Marys River were affected by fecal bacteria derived from a human source. Gulley Hole Creek and the Darien River had the highest levels of fecal pollution detected in the studied estuaries. Molecular quantification of bifidobacteria may be a more accurate method of determining immediate health risks associated with fecal pollution in estuarine water than traditional and contemporary assessments of enterococci.

Rapid detection of human fecal contamination in estuarine environments by PCR targeting of Bifidobacterium adolescentis

Detection of Bifidobacterium adolescentis was used as an effective genetic marker of human fecal contamination in Georgia estuaries. Enterococci enumerations on mEI media indicated that a tributary to the Little Satilla River with 516 CFU/100 ml was the most polluted of all the rivers tested. Extracted DNA from eight river water samples was subjected to a two-step nested PCR protocol using genus and species specific primers for Bifidobacterium spp. and B. adolescentis. B. adolescentis was detected from extracted DNA in Dunbar River, Black Bank Creek, and in a Little Satilla River tributary which demonstrates the presence of human fecal contamination in these three rivers. In the five other estuaries tested including West Point–Federica River and the Altamaha River, which both had less than 16 CFU/100 ml of enterococci, B. adolescentis was not detected.

Analysis of tidal marsh vegetation patterns in two Georgia estuaries using aerial photography and GIS

Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients of the estuaries of the Altamaha and Satilla Rivers in coastal Georgia. Vegetation maps were constructed from 1993 U.S. Geological Survey Digital Orthophoto Quarter Quads, 1∶77,000-scale color infrared photographs taken in 1974 and 1∶24,000-scale black and white photographs taken in 1953, Changes between years were identified using a GIS overlay analysis. Four vegetation classifications were identified and groundtruthed with field surveys: salt marsh (areas containing primarilySpartina alterniflora), brackish marsh (Spartina cynosuroides andS. alterniflora), Juncus (Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). There was no evidence for an upstream shift in marsh vegetation along the longitudinal axis of either estuary over the time frame of this analysis, which implies there has not been a long-term increase in salinity. Although the inland extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded to similar average high tide salinities in each estuary: areas classified as salt marsh occurred from the mouth up to where average high tide salinity in the water was approximately 15 psu;Juncus ranged from 21 to 1 psu; brackish marsh ranged from 15 to 1 psu; and fresh marsh was upstream of 1 psu. Approximately 63% of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 75% of the 10,220 ha mapped in the Satilla remained the same in all 3 yr.Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between areas classified asJuncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger number of factors affecting the frequently changing borders of vegetation patches.

Use of a Date-specific Method to Examine Variability in the Flushing Times of Georgia Estuaries

The fraction of freshwater method (Dyer, 1973) was used to examine the general characteristics of flushing time in five riverine estuaries in Georgia, U.S.A. Median flushing times over a 30-year period (1968–1997) were as follows: Savannah (5·6 days), Ogeechee (20·7 days), Altamaha (5·8 days), Satilla (66·8 days), and St. Marys (71·6 days), although there was considerable inter- and intra-annual variability in these estimates. For estimation of intra-annual flushing times, a date-specific method is used in which it is assumed that the appropriate time period over which to average discharge is equivalent to the flushing time. Although still technically a steady-state calculation, this approach improves flushing time estimates. When applied to a 9-year data set for four of these estuaries (all but the Savannah), the date-specific method yielded different flushing times than those calculated using a fixed discharge period, especially during periods of low or abruptly changing discharge. Flushing time is the freshwater volume divided by discharge; therefore, the relationship between flushing time and discharge is a power function: at fast discharge rates flushing time is relatively stable, but as discharge slows flushing time increases quickly. As a consequence of this relationship, (1) decreases in discharge have proportionately more impact on flushing times than do increases, and (2) flushing times in estuaries with slower discharge are more sensitive to changes in river flow.

Observations on Extant Populations of the Softshell Clam, Mya arenaria Linné, 1758 (Bivalvia: Myidae), from Georgia (USA) Estuarine Habitats

The softshell clam, Mya arenaria Linné, 1758, is reported from Georgia (USA) estuarine habitats based on studies conducted between 1969 and 1972. Observations on Georgia estuarine habitats where extant populations of softshell clams occurred are described. On several occasions, fresh shells with periostracum and tissue remnants were found in a brackish drainage system on Sapelo Island. These shells represent the first southern records of extant populations of softshell clams from such a specialized habitat type. Living specimens of M. arenaria from the benthos and specimens in the stomach contents of stingrays (Dasyatis sabina) were collected at four stations during 1969 in the North and South Newport Rivers. mesohaline tidal systems forming part of the southern and northern headwaters of St. Catherines and Sapelo Sounds.The stomach of a stingray collected near the mouth of Little Ogeeche River during another study also contained specimens of M. arenaria. Ephemeral, intertidal, winter populations of juvenile softshell clams are reported from exposed Pleistocene beach faces along tidal rivers in Chatham, Georgia. The associated fauna collected with softshell clams and occurrence of other cold temperate and boreal species from Georgia estuaries are discussed. The distribution of M. arenaria appears to be mainly limited by a critical maximum temperature of 28º. The relatively cooler summer temperatures observed at the Sapelo Island tidal ditch site may enable the species to survive in this restricted habitat. Data from the present study indicate that during winter and spring, softshell clams appear to be bionomically important components of the benthos and the diet of stingrays in some Georgia estuarine habitats. Whether or not reproducing populations of M. arenaria occur year-round in Georgia estuaries still remains an open question.

Boat Disturbance of Ciconiiformes in Georgia Estuaries

Boat Disturbance of Ciconiiformes in Georgia Estuaries

Mesotidal Estuarine Sequences: A Perspective From The Georgia Bight

ABSTRACT Although much has been written about estuaries and estuarine sediments, very few facies models have been proposed to date and considerable ambiguity remains in coastal classification schemes. Current stratigraphic concepts fail to elucidate not only the differences between certain deltaic, estuarine, and lagoon-fill sequences, but also the pronounced similarities between many riverine and salt-marsh estuarine sequences. These distinctive latero-vertical successions, recent and ancient, warrant increased scrutiny and conceptual refinement. Preliminary stratigraphic models and definitions presented here--based largely upon modern Georgia estuaries--should provide a broad framework for further evaluation and clarification of the above facies relationships. From that standpoint, an estuarine sequence consists of complex, intertidal to subtidal, mostly channel-form facies dominated to some extent by tidal effects, typically displaying abrupt variations in sediment texture and composition, and in physical and biogenic sedimentary structures. Subtle to pronounced salinity gradients may be discernible; nevertheless, the features most diagnostic of the overall sequence are 1) tidally influenced channel-form deposits, and 2) characteristic bioturbate textures and trace fossils.

Implications of clay-provenance studies in two Georgia estuaries; discussion and reply

Implications of clay-provenance studies in two Georgia estuaries; discussion and reply

Implication of Clay-Provenance Studies in two Georgia Estuaries: REPLY

Implication of Clay-Provenance Studies in two Georgia Estuaries: REPLY

Role of Bioerosion in Mass-Wasting of Pleistocene Outcrops on Georgia Coast: ABSTRACT

Outcrops of semiconsolidated Pleistocene sands, exposed by meandering tidal rivers and creeks in the Georgia estuaries, are undergoing rapid disaggregation by a variety of plants and animals. Bioeroders include large and small mammals, wasps, crabs, isopods, and pelecypods. In this area, bioerosion is responsible for retreat of bluffs as high as 15 m and contributes significantly to mass-wasting and subsequent erosion by currents and waves. Blocks initially break away from the bluffs along fractures created by plant roots. As the blocks move downslope they serve as substrates for numerous supralittoral, littoral, and sublittoral invertebrate organisms which burrow, bore, and scrape the blocks as well as the bluff itself. Different organisms are restricted to distinct vertical zones and the degree of bioerosion increases to a maximum at the low-water line where boulders are riddled with borings, mainly by the isopod Sphaeroma destructor. Multiple isopod borings are in turn further eroded to form large burrows and galleries occupied by crabs. Rates of excavation and colonization of exposed surfaces are rapid, and obvious changes occur in periods of less than 2 weeks. End_of_Article - Last_Page 424------------

Implications of Clay-Provenance Studies in Two Georgia Estuaries

ABSTRACT The amount of kaolinite and illite in bottom muds of Altamaha River and Sound, a partially-mixed estuary, does not vary appreciably downstream, indicating that the bulk of the clays is river-supplied. In contrast, much of the bottom mud of Sapelo Sound, a tidal-water body with minor freshwater discharge, seems to be derived from erosion of coastal outcrops. Our results suggest that the clay flux from ocean sources is minimal in either case, and tends to have been overestimated by previous workers. On the other hand, the clay flux from shore erosion tends to have been underestimated in sediment-budget studies of Georgia estuaries.

The Origins of Detritus in Georgia Salt Marsh Estuaries

The current view that estuarine food chains are in large part supported by influx of plant detritus from bordering tidal wetlands may not be correct for all cases. In Georgia estuarine ecosystems, salt marshes dominated by the cordgrass, Spartina altaerniflora Loisel., are thought to be the major source of particulate detritus in the estuarine waters. However, I present three lines of evidence which suggest that Spartina detritus may not form a significant fraction of the organic seston in Georgia estuaries: 1) For Spartina salt marshes, attempts to document the net loss of plant material to the estuary have yielded contradictory results. 2) The stable carbon isotopic composition of organic seston in Georgia coastal waters does not match the isotopic composition of Spartina carbon; however, the seston 1'C/12C ratios are compatible with phytoplankton or terrestrial detritus sources. 3) Estimates of potential input of organic materials to Georgia estuaries of 770 g m-2 yr-1 by phytoplankton and 600 g m-2 yr-1 by terrestrial plant matter are of the same magnitude as the hypothetical detritus input of 780 to 1660 g m-2 yr-1 from the Spartina salt marshes. A revision of the concepts about the role of salt marshes in estuarine production may be in order.

Stable carbon isotope ratios in the biota, soils and tidal water of a Georgia salt marsh

The stable carbon isotope composition of the biota, soils and tidal water particulate material was surveyed in a salt marsh near Sapelo Island, Georgia. Samples were taken in six intertidal zones: bare creekbank, Spartina alterniflora low marsh, S. alterniflora high marsh, Salicornia virginica high marsh, sand flat and high marsh mixed vegetation stands. The marsh plants analyzed segregated into three groups with respect to their 13C 12C ratios. The grasses, including S. alterniflora, had δ 13C values of −12.3 to −13.6‰; the other vascular plants had values between −22.8 and −26.0‰; and benthic diatoms had intermediate values of −16.2 to −17.9‰. Marsh soils and to some extent the invertebrate fauna reflected the carbon isotope composition of the major primary producer species in the various zones. Five samples of the particulate organic carbon (POC) in marsh tidal water showed δ 13C values of −19.8 to − 22.8‰. These values fell within the range of δ 13C found for offshore POC, most of which is presumed to originate from phytoplankton photosynthesis. This result requires a re-examination of the assumption that the bulk of detrital carbon in Georgia estuaries is derived from S. alterniflora production.