Reef National Marine Sanctuary Research Articles

Visitors’ Environmental Concerns in Gray’s Reef National Marine Sanctuary: An Offshore Marine Protected Area

Marine sanctuaries serve as popular destinations for ecotourism, natural resource exploration, and recreation across the US. While often positive, visitation in marine and coastal areas can cause ecological threats to these ecosystems. Increased visitation in marine environments has led to the need for management due to negative ecological and social impacts. Understanding environmental values, attitudes, and perceptions is important to the success of environmental protection. Using online surveys sent via Qualtrics asking questions regarding the users’ knowledge, attitudes, and perceptions of ocean resources, goods and services, this research focused on identifying user profiles and understanding their environmental perception associated with Gray’s Reef National Marine Sanctuary, an offshore marine protected area, and surrounding coastal Georgia. The results show that across multiple types of threats or phenomena, respondents are most concerned about threats to resources related to pollution. Furthermore, they support marine protection and are willing to adjust their consumption habits, such as recycling and energy use, to ensure the sustainable use of ocean resources. The inclusion of insights achieved through research about visitor perceptions into management decision making and planning can positively contribute to the success of environmental protection.

Ocean Recreation and the Economic Contributions of Visitation in and around Gray’s Reef National Marine Sanctuary

Providing demonstrable and quantifiable evidence to substantiate the value of Marine Protected Areas like National Marine Sanctuaries is important for understanding their role in the blue economy, as well as gaining management and financial support for their protection. This study employs economic contribution analysis to estimate the economic contributions of ocean recreation spending of visitors to Gray’s Reef National Marine Sanctuary (GRNMS) and the coastal Georgia region. Employing economic contribution analysis is found to be more useful in influencing stakeholder decisions, and can therefore be a useful tool in providing inputs for management decisions related to marine protected areas. This study shows that visitors to coastal Georgia spent about USD 1.4 billion on ocean recreation activities in a single year. This translates to a total economic contribution of 18,950 jobs, USD 603 million labor income, USD 938 million value added, and USD 1.8 billion output. About USD 123 million of the total visitor spending can be attributed to GRNMS, contributing 1702 total jobs, USD 54 million in total labor income, USD 84 million in total value added, and USD 159 million in total output. This study highlights the importance of coastal Georgia and GRNMS as economic drivers of the region’s economy, supporting the need for continued management and investment in the Sanctuary and its resources.

Virtual Reality Camera Technology Facilitates Sampling of Interactions Between Reef Piscivores and Prey

AbstractPredation is an important process influencing the structure of fish communities. There are multiple approaches used to quantify predatory interactions, and all approaches are beneficial but have their limitations. For example, food habit studies only represent results of successful predation events, direct observations by divers are time limited by both depth and temperature as well as observer effects, acoustic approaches cannot directly identify species, and video has field-of-view constraints when using standard cameras. While no approach is without constraints, the recent availability of small off-the-shelf virtual reality (VR) video cameras that can be used in marine environments offers a more spatially comprehensive field-of-view for conducting studies of community composition and species interactions both on the seafloor and in the overlying water column. Here, we demonstrate an approach for collection and analysis of data from stationary VR video to quantify predator-prey interactions at subtropical reefs in Gray’s Reef National Marine Sanctuary (NW Atlantic). This approach does not substitute for other widely used census and behavioral research approaches but augments those with unique analytical products and interpretation.

Measuring and understanding receiver efficiency in your acoustic telemetry array

Methods to evaluate receiver performance within acoustic telemetry arrays are needed to quantitatively determine which receivers are the most important to maintain. A recently developed approach, the Receiver Efficiency Index (REI), expresses the proportion of transmitter activity from throughout an array that occurs at each receiver location within it. The components of this composite index equally weight the proportion of detections, individual tags, and species from the entire array that were detected at a given receiver and then adjusts for the proportion of time that each receiver was deployed. In this study, we evaluated receivers in a long-term (8+ years) telemetry array deployed in Gray’s Reef National Marine Sanctuary (GRNMS) located off the coast of Georgia (southeastern USA). Specifically, we explored the causes of fluctuations in the index over time, evaluated correlations between the REI and its component measures, and determined the sensitivity of the composite to individual components. Additionally, we examined the fish assemblages detected at each receiver over time using non-metric multidimensional scaling (nMDS) to assess how REI scores vary across fish communities. Results indicate that receiver importance varied through time. Correlations between the REI and each of its components were all positive and significant, and the REI was robust to exclusion of any one component. Sites with similar fish assemblages had very different REI values in GRNMS, but not when we reexamined the data from an array in Florida that was used to develop the REI. These findings suggest that decisions regarding which species groups (e.g. resident versus transient), time periods (e.g. seasonal versus inter-annual), or even components of the REI (e.g. duration of deployment) to include during analysis can have strong effects on the interpretation of receiver importance. We also recommend that the REI be coupled with species assemblage analyses such as nMDS to better understand how fish assemblages differ at sites with similar REI scores.

Dynamics of predator-prey habitat use and behavioral interactions over diel periods at sub-tropical reefs.

The dynamics of fish communities at tropical and sub-tropical rocky reefs are influenced in many cases by predation activity and predator-prey interactions. These processes usually follow specific diel patterns in reef areas with higher rates of these interactions occurring during the crepuscular periods. However, other factors such as habitat complexity and species-specific behavior may alter these patterns, increasing variability in species interactions. A better understanding of the dynamics of these patterns and processes would allow us to manage and monitor fish communities in these productive and vulnerable areas more efficiently. We investigated behavioral changes of predators and prey fish in sub-tropical “live-bottom” (sandstone) reefs at Gray’s Reef National Marine Sanctuary (GRNMS), located 20 nautical miles off the coast of Georgia, USA, using fisheries acoustic methods in association with visual census and direct observation using SCUBA. Changes in co-location and habitat preferences of predators and prey over time throughout the diel cycle were investigated using species distribution models (MAXENT) based on habitat predictors and by means of spatial statistics. The results indicate that predator and prey distribution patterns changed considerably throughout the day. Prey and predator species exhibited complex spatial dynamics and behavior over diel periods, with prey modifying patterns of habitat use and spatial distribution, likely as a response of their interactions with predators. Crepuscular periods were confirmed to be the most active phases in terms of predator-prey interactions and consequently the most variable. The combination of tools and approaches used in this study provided valuable sources of information that support the inferences of predation risk-driven habitat selection of prey in this sub-tropical reef system.

Spatial and temporal patterns of toadfish and black drum chorusing activity in the South Atlantic Bight

Many fish species produce sounds as a part of their reproductive behavior. Using passive acoustic recording approaches, these sounds can be used to document temporal and spatial patterns of reproductive activity of fish populations. We conducted an 11-month passive acoustic survey at three different locations off the coasts of Georgia (40 km north of Grays Reef National Marine Sanctuary) and North Carolina (Onslow Bay) to understand the spawning phenology of two species of acoustically active fishes: black drum (Pogonias cromis) and toadfish (Opsanus sp.). Due to the depth of the recording locations, we could not confirm whether the toadfish calls were produced by O. tau, or another Opsanus species. Both taxa have readily identifiable, distinct sounds. Chorusing sounds from both species were detected at all three Georgia sites and at two of the three North Carolina locations; chorusing duration of both species was greater in Georgia. The onset and duration of chorusing activity for both species was correlated with water temperature. The abundance of calls of these two species from field recordings further demonstrates the value of long-term passive acoustic surveys for understanding the reproductive seasonality of acoustically active fish species.

The archeology, sedimentology and paleontology of Gray's Reef National Marine Sanctuary and nearby hard bottom reefs along the mid continental shelf of the Georgia Bight

Geoarcheological surveys undertaken over the past two decades at Gray's Reef National Marine Sanctuary, 32km offshore Georgia, and nearby JY Reef have recovered archeological and paleontological materials dating from the Late Pleistocene, primarily Marine Isotope Stage (MIS) 3, 59–24KYBP as well as the early-to-mid Holocene, 6000 BP. The paleontological materials include both invertebrate and vertebrate taxa from both the Pleistocene and Holocene while the archeological materials are Holocene age. Sediment coring has developed a more comprehensive picture of the inner-to-mid continental shelf sediment prism of the Georgia Bight. Optical petrography, scanning electron microscopy, electron dispersive spectroscopy (SEM-EDS) and wavelength dispersive X-ray diffraction (XRD) have been used to characterize Gray's Reef lithic artifacts and nearby outcrops which are both primarily Pliocene age calcareous sandstones. JY Reef is, by contrast, a coquina rich in fossil and subfossil materials but depauperate in any archeologic finds. Petrologic and geochemical data have been developed for both the outcrops and artifacts that are in good agreement with previous studies using optical petrography.

Niche structure of marine sponges from temperate hard-bottom habitats within Gray's Reef National Marine Sanctuary

Many species of marine sponges on tropical reefs host abundant and diverse symbiont communities capable of varied metabolic pathways. While such communities may confer a nutritional benefit to some hosts (termed High Microbial Abundance (HMA) sponges), other sympatric species host only sparse symbiont communities (termed Low Microbial Abundance (LMA) sponges) and obtain a majority of their C and N from local sources. Sponge communities are widespread across large latitudinal gradients, however, and recent evidence suggests that these symbioses may also extend beyond the tropics. We investigated the role that symbionts play in the ecology of sponges from the temperate, hard-bottom reefs of Gray's Reef National Marine Sanctuary by calculating the niche size (as standard ellipse area (SEAc)) and assessing the relative placement of five HMA and four LMA sponge species within bivariate (δ13C and δ15N) isotopic space. Although photosymbiont abundance was low across most of these species, sponges were widespread across isotopic niche space, implying that microbial metabolism confers an ecological benefit to temperate sponges by expanding host metabolic capability. To examine how these associations vary across a latitudinal gradient, we also compared the relative placement of temperate and tropical conspecifics within isotopic space. Surprisingly, shifts in sponge δ13C and δ15N values between these regions suggest a reduced reliance on symbiont-derived nutrients in temperate sponges compared with their tropical conspecifics. Despite this, symbiotic sponges in temperate systems likely have a competitive advantage, allowing them to grow and compete for space within these habitats.

Temporal and vertical distributions of bacterioplankton at the Gray's Reef National Marine Sanctuary.

Large spatial scales and long-term shifts of bacterial community composition (BCC) in the open ocean can often be reliably predicted based on the dynamics of physical-chemical variables. The power of abiotic factors in shaping BCC on shorter time scales in shallow estuarine mixing zones is less clear. We examined the diurnal variation in BCC at different water depths in the spring and fall of 2011 at a station in the Gray's Reef National Marine Sanctuary (GRNMS). This site is located in the transition zone between the estuarine plume and continental shelf waters of the South Atlantic Bight. A total of 234,516 pyrotag sequences of bacterial 16S rRNA genes were recovered; they were taxonomically affiliated with >200 families of 23 bacterial phyla. Nonmetric multidimensional scaling analysis revealed significant differences in BCC between spring and fall samples, likely due to seasonality in the concentrations of dissolved organic carbon and nitrate plus nitrite. Within each diurnal sampling, BCC differed significantly by depth only in the spring and differed significantly between day and night only in the fall. The former variation largely tracked changes in light availability, while the latter was most correlated with concentrations of polyamines and chlorophyll a. Our results suggest that at the GRNMS, a coastal mixing zone, diurnal variation in BCC is attributable to the mixing of local and imported bacterioplankton rather than to bacterial growth in response to environmental changes. Our results also indicate that, like members of the Roseobacter clade, SAR11 bacteria may play an important role in processing dissolved organic material in coastal oceans.

Temporal dynamics and depth variations of dissolved free amino acids and polyamines in coastal seawater determined by high-performance liquid chromatography

Short-chained aliphatic polyamines (PAs) are a class of labile dissolved organic nitrogen (DON) that has biogeochemical similarities to dissolved free amino acids (DFAAs). Here we investigated the relative contributions of DFAAs and PAs to the total DON pool and their diurnal dynamics at different depths at the Gray's Reef National Marine Sanctuary (GRNMS) in the spring and fall of 2011. A high-performance liquid chromatography (HPLC) method that uses pre-column fluorometric derivatization with o-phthaldialdehyde, ethanethiol, and 9-fluorenylmethyl chloroformate was optimized to measure 20 DFAAs and 5 PAs in seawater simultaneously. The concentrations of DFAAs and PAs varied over 5-fold during individual diurnal cycles and between seasons; and concentrations of the former (tens to hundreds nM) were typically at least one order of magnitude higher than the latter (a few nM). An exception was noted in fall surface water samples when the total PAs reached 159nM and the ratio of PAs to DFAAs was about 2:3. Compositions of individual DFAAs and PAs also exhibited temporal dynamics, with glycine and spermidine consistently the most abundant compound in each pool, respectively. DFAA concentrations appeared to track chlorophyll a, whereas, total PA concentrations were strongly correlated with bacterial cell abundance. Our results indicate that, at least occasionally, PAs may serve as an important DON pool at the GRNMS. This view is in accordance with recent molecular data but contrasts to measurements made in some other marine environments.

Environmental interference factors affecting detection range in acoustic telemetry studies using fixed receiver arrays

Historically, acoustic telemetry studies tracking movement of aquatic organisms have lacked rigorous, long-term evaluations of detection range. The purpose of the present study was to identify potential sources of variability in long-term acoustic telemetry data, focusing specifically on environmental variability. The study was conducted for 15 mo in Gray's Reef National Marine Sanctuary, Georgia, USA, using 2 submersible Vemco VR2W hydrophone receivers and 2 stationary range test transmitters (controls). Tag detections (±1 SE) decreased from 54.2 ± 2.5 to 11.4 ± 0.5 detections d �1 as transmission distance increased from 100 to 300 m. Detections varied seasonally (likely due to stratification), with the direction of flood and ebb tidal currents (12.4 h cycle), and with tidal current speed (6.2 h cycle). Tides explained up to 92% of the short-term variability in hourly detection data. Detections also increased or decreased during episodic weather events depending on the season and type of event. These results suggest that stationary control tags are useful for characterizing variability in sound transmission in open water marine acoustic telemetry studies.

Macroalgae at Gray's Reef National Marine Sanctuary, Georgia

Macroalgal assemblages were described from Gray's Reef National Marine Sanctuary (GRNMS), GA and compared to records from 25 years ago. For quantitative comparisons in species richness and biomass, divers collected algae from Searle's four northern sites and another four southern sites (n = six 400-cm2 quadrats per site). To compare species richness among sites, algae were also collected across limestone reefs at each site, and any new species were added to those recorded from the quadrat samples. Of the 55 species identified, 8 were new GRNMS records, 4 were new records to Georgia, and 36 had been recorded previously. Nine species were present at all of the 8 sites. Although species richness per site was significantly greater in southern GRNMS, biomass and species richness per 400 cm2 were similar between northern and southern sites. Sediment movement likely contributed to variability in species composition across the reefs.

Benthic Features as a Determinant for Fish Biomass in Gray's Reef National Marine Sanctuary

A recent focus of the National Oceanic and Atmospheric Administration (NOAA) National Marine Sanctuaries Program is the characterization and assessment of marine resources associated with coral reef and live bottom habitats in protected areas. Detailed bottom maps have been produced making it possible to quantify bottom features within Gray's Reef National Marine Sanctuary, Georgia, USA. Hydroacoustic fisheries surveys were used to estimate fish biomass in the context of underlying features and bottom types by applying spatial techniques and regression analysis. Variables relating bottom features to estimated fish biomass differed based upon depth in the water column. Distance to rock ledges was the best predictor of fish biomass in the bottom 2 m of the water column, whereas the area of two bottom habitat types combined was a reliable predictor of estimated fish biomass in the mid water column.

Influence of Benthic Features and Fishing Pressure on Size and Distribution of Three Exploited Reef Fishes from the Southeastern United States

AbstractDistribution, habitat preference, and size structure were examined for three commonly targeted bottom fishes (black sea bass Centropristis striata, gag Mycteroperca microlepis, and scamp M. phenax) in the southeastern United States. Fish communities and bottom characteristics of limestone ledges within Gray's Reef National Marine Sanctuary (located centrally along the southeastern continental shelf) were surveyed. Black sea bass occurred at 98% of the ledges and were evenly distributed throughout the sanctuary in much‐higher numbers than either gags or scamps, which were concentrated at only 11% of the ledges. Gag or scamp presence was most strongly related to height of ledge undercut, whereas abundance of black sea bass was best explained by percent cover of sessile biota. In addition, lower abundance of black sea bass occurred in the presence of either gags or scamps, which are generally larger than black sea bass. In all three species, an abrupt decline in abundance was observed for size‐classes above the size limit of the fishery. Also, modal size of gags or scamps was smaller and the percentage of fish exceeding the fishery size limit was lower in heavily fished areas than in less intensively fished areas.

Incidence of marine debris and its relationships with benthic features in Gray’s Reef National Marine Sanctuary, Southeast USA

Gray’s Reef National Marine Sanctuary (GRNMS) is an increasingly popular site for recreational fishing and diving in the South Atlantic Bight (SAB). As a result, there has been heightened concern about potential accumulation of marine debris and its consequent effects on sanctuary resources. Field surveys were conducted at GRNMS in 2004 and 2005 to provide a spatially comprehensive characterization of benthic communities and to quantify the distribution and abundance of marine debris in relation to bottom features. The spatial distribution of debris was concentrated in the center of the sanctuary and was most frequently associated with ledges rather than other bottom types. On ledges, the presence and abundance of debris was significantly related to observed boating activity and physiographic features including ledge height, ledge area, and percent cover of benthic organisms. The results from this study will aid managers in optimizing cleanup efforts and long-term monitoring of debris accumulation patterns at GRNMS and other hard bottom areas in the SAB.

The soft-bottom macrobenthos of Gray's Reef National Marine Sanctuary and nearby shelf waters off the coast of Georgia, USA

As part of an ongoing ecological assessment of the Gray's Reef National Marine Sanctuary (GRNMS), a 58-km 2 marine protected area 32 km off the coast of Georgia, USA, surveys of benthic macroinfaunal communities, contaminant levels in sediments and biota, and general habitat conditions were conducted during 2000–2002 at 20 stations within the sanctuary and along three cross-shelf transects in nearby shelf waters. Macroinfaunal community structure and composition exhibited distinct cross-shelf patterns associated with sediment granulometry, depth and possibly other factors related to shoreline proximity (e.g., erosional effects, recruitment of estuarine species). Finer-scale spatial patterns of benthic fauna among stations within the sanctuary appear to be related to proximity to live-bottom habitat and other features of seafloor structure (e.g., rippled vs. flat sand). Population densities of dominant fauna within the sanctuary also varied considerably among years, resulting in shifts in the ranking of dominants at most stations. Chemical contaminants generally were at low background concentrations below probable bioeffect levels and thus are not a likely cause of the observed spatial patterns of benthic fauna. However, trace concentrations of pesticides, PCBs, and PAHs were detectable in sediments and biota throughout the study area, demonstrating that chemicals originating from human activities are capable of reaching the offshore sanctuary environment, possibly from atmospheric deposition or cross-shelf transport of materials outwelled through coastal sounds. Highly diverse infaunal assemblages also were observed within the sanctuary and nearby sites of similar depth, suggesting that the sanctuary is an important reservoir of marine biodiversity. Results of this study should be useful in addressing long-term science and management needs of the GRNMS and in furthering our understanding of broader ecological patterns and dynamics of the surrounding South Atlantic Bight (SAB) ecosystem.

Benthic Mapping Using Sonar, Video Transects, and an Innovative Approach to Accuracy Assessment: A Characterization of Bottom Features in the Georgia Bight

Benthic maps provide the spatial framework for many science and management activities in coastal areas such as identification and protection of fish distributions and associated habitat as well as for monitoring changes in benthos and fish communities. To meet this need at Gray's Reef National Marine Sanctuary off the Georgia, U.S.A., coast, we created fine-scale benthic maps by visual interpretation of sonar imagery within a geographic information system. The major bottom types in the sanctuary—flat sand, rippled sand, hard bottom that is sparsely colonized with sessile invertebrates, and densely colonized hard bottom—were delineated through combined analysis of backscatter from side-scan sonar, bathymetry from multibeam sonar, scuba surveys, and video transects. Maps showed that unconsolidated sediments cover 75% of the bottom of this region; 8% occurs as flat sand plains with obvious burrowing and reworking of surface material by mobile benthic invertebrates, whereas 67% occurs as rippled sand without such fauna. The rest of the sanctuary consists of limestone bottom in two types of formations; either flat, sparsely colonized regions (25% of the sanctuary's total area) or as vertical ledges that are densely colonized with a diverse fauna of sessile invertebrates (<1%). Despite their limited area, these 0.5–2-m-tall ledge features harbor the majority of the sanctuary's biodiversity and biomass of both sessile invertebrates as well as ichthyofauna. A modified accuracy assessment procedure was used to account for spatial autocorrelation in the validation data and to separate thematic from positional accuracy. Overall thematic accuracy of maps is 95% for those areas of the map in which thematic accuracy and positional accuracy could be separated (87% of the mapped area). This fine-scale characterization provides a benthic inventory for a marine sanctuary and novel methods for mapping using sonar and accuracy assessment using transects.

Phenology and Floristics of Seaweeds from the Offshore Waters of Georgia

Seaweeds were studied from rock outcrops in two areas on the Georgia continental shelf, Gray's Reef National Marine Sanctuary on the inner shelf and an area known as the "Snapper Banks" on the outer shelf. The seaweeds observed are seasonal; only a few plant persist through the winter. In this study a gradual increase in number and size of plants and number of species was observed through June; by July-early August, when all 68 species reported were present, the quantity of plants also appeared maximal. Of the 68 species, 43 are species not previously reported from Georgia; eight additional taxa are identified only to genus, but are also new to the region. Sixty-five of the species were collected at Gray's Reef and 22 at the Snapper Banks; three of the latter did not occur at Gray's Reef. In late August and September, when water temperatures were still near the seasonal high, there was a rapid decline in number of species and algal cover.