Intertidal Oyster Reefs Research Articles

Spatial Dynamics of Two Host-Parasite Relationships on Intertidal Oyster Reefs

Intertidal reefs comprised of the eastern oyster (Crassostrea virginica) have long experienced habitat loss, altering habitat patch characteristics of size and distance from edge to interior, potentially influencing spatial dynamics of host-parasite relationships. Using two parasitic relationships, one between eastern oyster host and parasitic oyster pea crab (Zaops ostreum) and the other between a xanthid crab (Eurypanopeus depressus) and a parasitic rhizocephalan barnacle (Loxothylacus panopaei), we examined how host-parasite population characteristics varied on intertidal reefs by season, reef size, and distance from edge to interior. Pea crab prevalence was more related to habitat characteristics rather than host density, as pea crab prevalence was the highest on large reefs and along edges, areas of comparatively lower oyster densities. Reef size did not influence densities of parasitized or non-parasitized xanthid crabs, but densities varied from edge to interior. Non-parasitized xanthids had significantly lower densities along the reef edge compared to more interior reef locations, while parasitized xanthid crabs had no significant edge to interior pattern. Organismal size had a varied relationship based upon habitat characteristics, as pea crab carapace width (CW) varied interactively with season and reef size, whereas CW of parasitized/non-parasitized xanthid crabs varied significantly between edge and interior locations. These results demonstrated that influential habitat characteristics, such as patch size and edge versus interior, are both highly species and host-parasite specific. Therefore, continued habitat alteration and fragmentation of critical marine habitats may further impact spatial dynamics of host-parasite relationships.

A Subtropical Nudibranch, Polycera hummi (Abbott 1952), Described for the First Time from Virginia

We collected an individual Polycera hummi, a subtropical nudibranch, in association with a green macroalga Ulva sp. from an intertidal oyster reef in Burtons Bay, Wachapreague, VA. The established range of P. hummi is based solely on a handful of records from Mississippi and Florida in the Gulf of Mexico and the Carolinas in the Atlantic Ocean. This finding marks the highest latitude that this species has been found, 350 km north of its previously established range from Mississippi to Beaufort, NC. We observed the individual actively navigate the Ulva thallus which had encrusting bryozoans (unidentified genus) and arborescent bryozoans (Bugula sp.)—likely prey species. We briefly summarize the current knowledge on this rarely encountered nudibranch, provide information on the collection site, including other sea slugs often encountered in this area, note its behavior and interactions with macroalgae and bryozoans, and suggest some fruitful avenues of future work on the evolutionary ecology of rare nudibranch species like P. hummi.

A New Resilience Metric to Compare System of Systems Architecture

By combining independent systems (e.g., financial systems, power infrastructure, transportation networks), systems of systems (SoSs) can provide additional services. The ability to withstand faults, minimize service disruption, and efficiently recover (resilience) is a key performance characteristic. Current resilience metrics, however, require improvement. Each SoSs is approached with different assumptions about fault magnitude and recovery strategy. Thus, engineers currently have difficulty answering the basic question: Between alternative designs A and B, which is more resilient? SoS resilience metrics should reflect that the system interfaces are the most potent leverage point, have a standardized fault and recovery strategy, incorporate SoS dynamics, and apply to both natural and artificial systems of systems. In response, we develop the system of systems resilience metric (SoSRM). SoSRM methodology uses the definition of SoS to identify appropriate fault locations and graph theory to define fault and recovery duration. SoSRM is applied to two case studies to demonstrate application. First, an intertidal oyster reef ecosystem's system dynamics model is presented to demonstrate SoSRM methodology. Next, a military SoS demonstrates the application of SoSRM to a stochastic multi-agent system. Validation simulations show that SoSRM reflects expected fault impact and that methodological choices for fault duration do not drive SoSRM results. This article presents a new design tool capable of comparing the resilience between two SoS architectures.

Natural Intertidal Oyster Reef Growth Across Two Landscape Settings and Tidal Ranges

Intertidal oyster reefs are typically restored to offset the loss of reef-associated ecosystem services (e.g., improved water quality, shoreline stabilization, and fish habitat), but the scale of enhanced services is predicated on the health and growth of the restored reef. Previous work on young (<15 years) restored reefs showed the highest growth rates along the sides of reefs where they are aerially exposed 20–40% of the time, but much is still unknown about how those positions in the tidal frame change with landscape setting, tidal range, and reef maturity. This study compared the area of maximum growth among 12 natural intertidal reefs in coastal North Carolina that range between 1395 and 62 years old. The reefs include fringing and patch landscape settings in each of two estuaries with tidal ranges of 0.94 m and 1.51 m. Peak growth rates were similar among landscape and tidal settings and were faster than the rate of sea-level rise (SLR) indicating intertidal reef resilience to accelerating SLR. Flow baffling associated with fringing reefs and higher summer air temperatures in the southern estuary likely contributed to a lower position of the optimal growth zone, where growth rates are highest, in the tidal frame. Intertidal reef growth manifests differently across the range of aerial exposures at varying stages of maturity. Once reefs reached ~50 years old, the elevation of the reef crests equilibrated to ~60–70% aerial exposure and peak growth rates stabilized between 2 and 4 cm year−1 at ~50% aerial exposure. These results are a useful guide for identifying areas and cultch configurations that optimize reef growth rates, enhancing the probability for self-sustaining restored reefs.

Estuarine fishes associated with intertidal oyster reefs characterized using environmental DNA and baited remote underwater video

AbstractIt has been widely shown that oyster reefs enhance local biodiversity and fisheries production. To determine the importance of intertidal remnant estuarine oyster reefs compared to unstructured sandy habitats over small spatial scales (&lt;1 km) to fishes, assemblages were sampled with two nondestructive methods: baited underwater remote videos (BRUVs) and environmental DNA (eDNA) metabarcoding. Fish diversity from eDNA was characterized using three metabarcoding assays, and the assemblages differed with each, as well as to that detected by BRUVs. Overall, 112 fish genera were identified, with 78 more genera detected using eDNA metabarcoding than those observed with BRUVs. Both eDNA and BRUVs resolved a higher number of fish genera associated with oyster reefs than with sand sites, and a different fish composition between habitats was also resolved using each method. Furthermore, eDNA was shown to be useful toward characterizing the gamma diversity of the estuary, due to the intertidal nature and hydrodynamics of the system, as well as the alpha diversity associated with oyster reefs and sand sites. This study reinforces the importance of using multiple metabarcoding assays along‐side BRUVs for sampling assemblages of fishes and demonstrates the utility of using both methods in studies of biodiversity and future management of intertidal estuarine systems.

Replacement of oyster reefs by mangroves: Unexpected climate-driven ecosystem shifts.

Increases in minimum air temperatures have facilitated transitions of salt marshes to mangroves along coastlines in the southeastern United States. Numerous studies have documented mangrove expansion into salt marshes; however, a present-day conversion of oyster reefs to mangrove islands has not been documented. Using aerial photographs and high-resolution satellite imagery, we determined percent cover and number of mangrove patches on oyster reefs in Mosquito Lagoon, FL, USA over 74years (1943-2017) by digitizing oyster reef and "mangrove on oyster reef" areas. Live oyster reefs present in 1943 were tracked through time and the mangrove area on every reef calculated for seven time periods. There was a 103% increase in mangrove cover on live oyster reefs from 1943 (6.6%) to 2017 (13.4%). Between 1943 and 1984, the cover remained consistent (~7%), while between 1984 and 2017, mangrove cover increased rapidly with a 6% year-1 increase in mangrove area on oyster reefs (198% increase). In 1943, 8.7% of individual reefs had at least one mangrove patch on them; by 2017, 21.8% of reefs did. Site visits found at least one mature Avicennia germinans on each tracked mangrove reef, with large numbers of smaller Rhizophora mangle, suggesting the post-1984 mangrove increases were the result of increased R. mangle recruitment and survival. Escalation in the coverage and number of mangrove stands on oyster reefs coincided with a period that lacked extreme freeze events. The time since a temperature of ≤-6.6°C (A. germinans mortality threshold) and ≤-4°C (R. mangle mortality threshold) were significantly correlated with the increased ratio of mangrove area:oyster area, total mangrove area, and number of mangrove patches, with greater variation explained by time since ≤ -4°C. The lack of freezes could lead globally to an ecosystem shift of intertidal oyster reefs to mangrove islands near poleward mangrove range limits.

Long-term data reveal greater intertidal oyster biomass in predicted suitable habitat

Habitat suitability models have been used for decades to develop spatially explicit predictions of landscape capacity to support populations of target species. As high-resolution remote sensing data are increasingly included in habitat suitability models that inform spatial conservation and restoration decisions, it is essential to validate model predictions with independent, quantitative data collected over sustained time frames. Here, we used data collected from 12 reefs over a 14 yr sampling period to validate a recently developed physical habitat suitability model for intertidal oyster reefs in coastal Virginia, USA. The model used intertidal elevation, water residence time, and fetch to predict the likelihood of suitable conditions for eastern oysters Crassostrea virginica across a coastal landscape, and remotely sensed elevation was the most restrictive parameter in the model. Model validation revealed that adult oyster biomass was on average 1.5 times greater on oyster reefs located in predicted ‘suitable’ habitat relative to reefs located in predicted ‘less suitable’ habitat over the 14 yr sampling period. By validating this model with long-term population data, we highlight the importance of elevation as a driver of sustained intertidal oyster success. These findings extend the validation of habitat suitability models by quantitatively supporting the inclusion of remotely sensed data in habitat suitability models for intertidal species. Our results suggest that future oyster restoration and aquaculture projects could enhance oyster biomass by using habitat suitability models to select optimal site locations.

Associations Between Winter Temperatures and the Timing and Duration of Annual Larval Recruitment of a Non-native Anomuran Crab

The green porcelain crab, Petrolisthes armatus, a subtropical/tropical species, was first recorded on intertidal oyster reefs in South Carolina in 1995. Since then, its range has expanded north in a series of surges and setbacks that appear to be associated with particularly cold winters that may cause mortality. Petrolisthes armatus reproduces year-round in its native range whereas its reproductive season in the non-native range is limited to warmer months. Variation in the timing and duration of larval recruitment is not known for the non-native range and these factors may affect further range expansion. To determine whether P. armatus larval recruitment is related to temperature variation, in particular, the severity of winter temperatures, archival biweekly (every 2 weeks) larval samples collected 1994–2018 near its northern range limit in the North Inlet Winyah Bay National Estuarine Research Reserve (NERR) were examined. The goal was to determine whether the timing and duration of larval ingress varied over time and was related to temperature variation. Petrolisthes armatus larvae were first observed in samples collected in 1995. There was considerable interannual variability in the timing of the start of recruitment (coefficient of variation 29%), which ranged from the last week of March at the earliest to the last week of July at the latest, for all years but one. Earlier annual recruitment was positively correlated with a longer recruitment duration. The timing of first larval recruitment was also related to the severity of the preceding winter, with later larval recruitment occurring in years with several consecutive days of cold temperatures. Cold winter temperatures appear to affect overwintering populations and their ability to reproduce in the early spring. A decreasing frequency of severe winters along the coastal South Atlantic Bight may promote further poleward range expansion of P. armatus.

Introduced marine ecosystem engineer indirectly affects parasitism in native mussel hosts

The alteration of habitat structure by introduced ecosystem engineers imposes direct impacts on native biota but can also exert trait-mediated indirect effects. In this study, we show that the habitat structure provided by invasive Pacific oysters (Crassostrea gigas) can also indirectly affect parasitism in native blue mussels (Mytilus edulis). We conducted a 3-month field experiment, in which uninfected mussels were positioned at the bottom and top of two intertidal oyster reefs in the Wadden Sea. On one reef, we detected a significantly higher prevalence of parasitic copepods (Mytilicola spp.) in mussels positioned on top of oysters than in mussels at the bottom, but no difference in infection intensity. For trematodes (Renicola roscovita), a different pattern was observed, with higher prevalence (one reef) and significantly higher infection intensities (both reefs) in mussels positioned at the bottom of the oyster reef. We suggest that the contrasting pattern results from differences in parasite life cycles. Mytilicola spp. larvae spend 2–3 weeks in the water column before infecting their hosts and, therefore, mussels positioned at the top are exposed to higher numbers of planktonic larvae than mussels at the bottom. In contrast, infective trematode larvae spend less than 12 h in the water column and primarily infect mussels during low tide, which may explain higher prevalence and intensity of R. roscovita in mussels near the bottom of the oyster reef. Our results demonstrate that indirect effects leading to alterations of parasite-host interactions may be a more common but hitherto rarely considered impact of biological invasions.

Seasonal and Temporal Changes in the Kumamoto Oyster Crassostrea sikamea Population and Associated Benthic Macrofaunal Communities at an Intertidal Oyster Reef in China

Oyster reefs (OR) once dominated coastal estuaries but are now one of the most severely impacted marine habitats on Earth. There is little information available regarding the status of natural OR in China. This study examined the seasonal and temporal changes in the Kumamoto oyster Crassostrea sikamea population and associated benthic macrofaunal communities at the largest intertidal OR (Liyashan) of the China Sea in four field surveys (spring and fall in 2013 and 2018). The oyster densities exhibited no evident seasonal variations in either 2013 or 2018 but showed significant temporal changes and declined by 89.66% in spring and 96.27% in fall between 2013 and 2018. The total densities of benthic macrofaunal communities at the reef area of the OR were significantly higher than those at the degraded oyster habitat (DOH) and dramatically decreased by 80.73% in spring and 64.87% in fall between 2013 and 2018. Nonmetric multidimensional scaling ordination indicated the benthic macrofaunal communities differed significantly between the OR and DOH or among the four sampling periods. Analysis of similarity indicated that the benthic communities at the OR had greater seasonal and temporal changes than did those at the DOH, and that temporal changes in benthic communities were greater than seasonal changes at each habitat. The study concluded that the OR had decreased habitat values as the oyster populations and the benthic macrofaunal communities dramatically declined from 2013 to 2018.

Biodiversity on intertidal oyster reefs in the Hab River mouth: 35 new records from Pakistan

The present study investigated the biodiversity of sessile and motile organisms using intertidal reef habitats constructed by giant oysters Magallana cuttackensis (Newton & Smith, 1912) and backwater oysters Magallana bilineata (Röding, 1798) at the Hab River Delta in Pakistan. A one year (February 2017 to January 2018) field survey was carried out to investigate the species diversity and abundance on the reefs and surrounding area. Monthly samples were taken and the abundance of macro-organisms was observed. Oysters were brought to the laboratory for a detailed examination of shells for the presence of other species. Specimens of 122 species were collected, including 35 new records for Pakistan. The most abundant phylum was Mollusca, represented by 55 species. Overall biodiversity was highest in the pre-monsoon season, declining in monsoon and post-monsoon periods. April was the month with the highest number of species observed. This study constitutes a baseline and an important step to gain a better understanding of oyster reefs and their ecological value as habitat for other species.

Trends in Oyster Populations in the Northeastern Gulf of Mexico: An Assessment of River Discharge and Fishing Effects over Time and Space

AbstractWithin the Big Bend region of the northeastern Gulf of Mexico, one of the least developed coastlines in the continental USA, intertidal and subtidal populations of eastern oyster Crassostrea virginica (hereafter referred to as “oyster”) are a critical ecosystem and important economic constituent. We assessed trends in intertidal oyster populations, river discharge, and commercial fishing activity in the Suwannee River estuary within the Big Bend region using fisheries‐independent data from irregular monitoring efforts and publicly available environmental data. We used generalized linear models to evaluate counts of oysters from line‐transect surveys over time and space. We assessed model performance using simulation to understand potential bias and then evaluated whether these counts were related to freshwater inputs from the Suwannee River and commercial oyster fishing effort and landings at different time lags. We found that intertidal oyster counts have declined over time and that most of these declines are found in inshore intertidal oyster bars, which are becoming degraded. We also found a significant relationship between oyster counts and a 1‐year lag on mean daily Suwannee River discharge, but including commercial fishery trips or landings did not improve model fit. It is unclear whether declines in intertidal oyster bars are offset by formation of new oyster reefs elsewhere. These results quantify rapid declines in intertidal oyster reefs in a region of coastline with high conservation value that can be used to inform ongoing and proposed restoration projects in the region.

Residency and reproductive patterns of the green porcelain crab, Petrolisthes armatus, on an intertidal oyster reef in its non-native range

The green porcelain crab Petrolisthes armatus is an abundant invader on intertidal oyster reefs along the southeastern coast of the United States. Its range expansion appears to be thermally limited and is predicted to shift poleward as water temperatures rise. Little is known about how P. armatus' seasonal residency patterns affect its reproductive potential near its northern range limit. To study these factors, P. armatus was collected every two weeks over a 20-month period (April 2017 to November 2018) on an intertidal oyster reef within its non-native range in Charleston, SC. Crab abundance, size, sex, and ovigery status were recorded. In addition, a laboratory experiment was conducted to determine the time elapsed between broods for large vs. small adult females. Petrolisthes armatus abundances varied seasonally and were highest in the summers of both years. Adults were collected in April after a mild winter (2017), indicating overwintering occurred, but after a harsh winter (2018), no crabs were collected on the reef the following spring, with adults first collected in July. Peak ovigery rates reached 95% of adult female crabs in some summer months. Juvenile recruits matured and contributed to the reproductive population 6–8 weeks after first being collected in the intertidal oyster habitat. In the laboratory experiment, the median time between broods was 6 days (range 2–22 days). Females were observed with new broods immediately post-molt and also several days following their molt, suggesting mating occurs for females in intermolt and post-molt states. Study results indicate that overwintering success affects the timing of the start of the reproductive season, its duration, and total annual brood production. The laboratory observations suggest rapid sequential brood production occurs for this species in the non-native range. Brood production rates and evidence that females mate in intermolt and post-molt states are new information for this species and are consistent with previous observations of high reproductive output in the non-native range. Further poleward range expansion seems likely, in part due to high reproductive output and rapid recovery following harsh winters.

Deep learning for coastal resource conservation: automating detection of shellfish reefs

AbstractIt is increasingly important to understand the extent and health of coastal natural resources in the face of anthropogenic and climate‐driven changes. Coastal ecosystems are difficult to efficiently monitor due to the inability of existing remotely sensed data to capture complex spatial habitat patterns. To help managers and researchers avoid inefficient traditional mapping efforts, we developed a deep learning tool (OysterNet) that uses unoccupied aircraft systems (UAS) imagery to automatically detect and delineate oyster reefs, an ecosystem that has proven problematic to monitor remotely. OysterNet is a convolutional neural network (CNN) that assesses intertidal oyster reef extent, yielding a difference in total area between manual and automated delineations of just 8%, attributable in part to OysterNet's ability to detect oysters overlooked during manual demarcation. Further training of OysterNet could enable assessments of oyster reef heights and densities, and incorporation of more coastal habitat types. Future iterations will be applied to high‐resolution satellite data for effective management at larger scales.

Remote sensing of live and dead intertidal oyster reefs using aerial photo interpretation in Northeast Florida

The eastern oyster, Crassostrea virginica, has been classified as a keystone species as well as an ecosystem engineer because of the significant benefits that oysters and oyster reefs provide. Oyster reefs are being recognized as valuable for shoreline protection within coastal areas. The severe loss of oyster reef coverage has encouraged different types of conservation, mapping, monitoring and restoration efforts throughout its native range. Intertidal oyster reefs are an important habitat as well as an important industry in Florida, which makes accurate habitat monitoring a key element of resource management for this species. This project focused on creating a continuous intertidal oyster reef habitat map in northeast Florida. Existing aerial photography was used to identify oyster reef signatures, and map the distribution of intertidal oyster reefs throughout the study region using ArcGIS software. When accuracy assessment was completed, we found the number of observed agreements was 97% of the total observations. This mapping effort represents the first successful attempt at fine-scale oyster reef mapping across the entire northeast Florida region and resulted in a total of 17,953 individual reefs being mapped, with a total reef coverage of 651.86 ha. By using existing aerial photography, this methodology represents a low-cost method for reef mapping, compared to other methods such as drone imagery or field-based mapping. This baseline map of current oyster distribution will serve many functions for management this particular ecosystem. Future changes to reef distribution can be mapped and used to identify potential negative or positive impacts to the habitat.

Regional environmental variation and local species interactions influence biogeographic structure on oyster reefs.

Although species interactions are often assumed to be strongest at small spatial scales, they can interact with regional environmental factors to modify food web dynamics across biogeographic scales. The eastern oyster (Crassostrea virginica) is a widespread foundational species of both ecological and economic importance. The oyster and its associated assemblage of fish and macroinvertebrates is an ideal system to investigate how regional differences in environmental variables influence trophic interactions and food web structure. We quantified multiple environmental factors, oyster reef properties, associated species, and trophic guilds on intertidal oyster reefs within 10 estuaries along 900km of the southeastern United States. Geographical gradients in fall water temperature and mean water depth likely influenced regional (i.e., thenorthern, central and southern sections of the SAB)variation in oyster reef food web structure. Variation in the biomass of mud crabs, an intermediate predator, was mostly (84.1%) explained by reefs within each site, and did not differ substantially among regions; however, regional variation in the biomass of top predators and of juvenile oysters also contributed to biogeographic variation in food web structure. In particular, region explained almost half (40.2%) of the variation in biomass of predators of blue crab, a top predator that was prevalent only in the central region where water depth was greater. Field experiments revealed that oyster mortality due to predation was greatest in the central region, suggesting spatial variation in the importance of trophic cascades. However, high oyster recruitment in the middle region probably compensates for this enhanced predation, potentially explaining why relatively less variation (17.9%) in oyster cluster biomass was explained by region. Region also explained over half of the variation in biomass of mud crab predators (55.2%), with the southern region containing almost an order of magnitude more biomass than the other two regions. In this region, higher water temperatures in the fall corresponded with higher biomass of fish that consume mud crabs and of fish that consumejuvenile and forage fish, whereas biomas oftheir prey (mud crabs and juvenile and forage fish, respectively)was generally low in the southern region. Collectively, these results show how environmental gradients interact with trophic cascades to structure food webs associated with foundation species across biogeographic regions.

Site Fidelity of Oyster Reef Blennies and Gobies in Saltmarsh Tidal Creeks

Blennies and gobies are among the most abundant fishes in western Atlantic and Gulf of Mexico estuaries. They establish nests and maintain territories in oyster reefs and around other shallow-water structures during warm months. In this study, site fidelity and movements were determined for adult striped blenny, naked goby, freckled blenny, crested blenny, and feather blenny, in descending order of abundance. Recaptures among 221 tagged fishes at nine intertidal oyster reefs in a southeastern U.S. saltmarsh estuary provided information about fidelity for individual oyster reefs and nest sites as well as the size of territories (areas used) around nest sites. An overall recapture rate of 94% for fishes on reefs where they were tagged indicated high fidelity. Total recapture rates for the four blenny species ranged from 38 to 50%, but the naked goby recapture rate was only 9%. Within a breeding season, fidelity for specific nest sites was 58% for all blennies and 17% for gobies. Movements away from nest sites were limited with 56% of all fishes re-occurring ≤ 1 m from the original tagging site. Territories of 84% of the recaptured fishes. Differences in species composition and abundance between reefs suggested species-specific preferences for habitat features. Crested blenny and freckled blenny were recaptured at nest sites with significantly more oyster cover than nest sites occupied by striped blenny. Blennies occupied nest sites for several months and across annual breeding seasons suggesting continued residency within small areas of individual oyster reefs throughout their lives. Strong fidelity for reefs and nest sites potentially makes blennies more susceptible to disturbances than gobies, but both may be vulnerable to habitat disturbance at scales < 5 m. Thus, blennies and gobies may be useful indicator species for changes within estuarine habitats and ecosystems.

In-situ measurements of turbulent flow over intertidal natural and degraded oyster reefs in an estuarine lagoon

Oysters are ecosystem engineers that form reefs with rough surfaces. The complex surface of a reference-condition reef contains clusters of live oysters that protrude into and interact with flows. A degraded oyster reef contains fewer live oyster clusters and subsequently has different bed roughness. Such morphological differences may translate to varied hydrodynamic function, with influence to local and larger-scale flow fields and sediment transport, as well as larval recruitment and long-term reef sustainability. The objective of this study is to compare a degraded and a reference-condition intertidal oyster reef, and assess how differences in structure (reef morphology and roughness) influence near-bed hydrodynamic function within the roughness sublayer defined by oysters. Sediment entrainment and bed deformation were observed only on the reference oyster reef, despite that mean velocities were lower than those at the degraded reef. This was attributed to slightly finer bed material and higher turbulent kinetic energy, k, at the reference reef (k = 29.2 ± 4.5 cm2/s2 with mean velocity 11.5 ± 0.6 cm/s at 1 cm above the bed) compared to the degraded reef (k = 22.6 ± 4.2 cm2/s2 with mean velocity 16.1 ± 1.7 cm/s at 1 cm above the bed). At 1 cm above the bed, shear turbulence production at the degraded reef was significantly larger than turbulence dissipation rate, while at the reference reef this pattern was observed only for time periods with low turbulent kinetic energy. For measurements 5 cm above the bed at the reference reef, shear turbulence production and turbulence dissipation rates exhibited a relatively balanced pattern, with dissipation exceeding shear production for the time period with elevated turbulence. Four bed shear stress calculation methodologies converged over the degraded oyster reef but deviated considerably at the reference oyster reef. The drag coefficient associated with bed shear stress at the reference reef was almost two times greater than that at the degraded reef and almost an order of magnitude greater than those observed at sand and mud beds.

A preliminary study on spatial assessment using conservation metrics for intertidal oyster reefs at the Hab River mouth in Pakistan

The oyster reefs in Pakistan are on the verge of extinction as a consequence of environmental and anthropogenic factors. A qualitative survey of oyster reef habitat was conducted from March-2017 to February-2018 in the Hab River Delta along the Balochistan coast (Arabian Sea), Pakistan. A combination of field survey and Geographical Information System (GIS) based approach (reef categorization, universal metrics and habitat suitability analysis), universal environmental variables, restoration goal-based metrics, sounding, condition indices, grain size composition and oyster spat-fall were determined for planning future oyster reef restoration efforts. The reefs were categorized into three main groups as dispersed, patch and continuous on the basis of fragmented spatial geometry. Dispersed reefs were more numerous than continuous and patch categories. The differences between morphometric measurements and density of oysters amongst reefs types were statistically insignificant. Habitat suitability analysis was done by ‘Benthic Terrain Modeler’ using ArcGIS software. The moderate, positive values of Bathymetric Position Index (BPI) of the oyster reef indicate an area of high or open slope with sea bottom (-2 to 6). The area of reef location shows high to moderate values of rugosity (0.7 to 0.9), indicates good to intermediate conditions; whereas, the aspect analysis showed slope orientation in the Northeast direction but mostly flat area. The environmental and restoration goal-based metrics were favorable for oyster growth and survival. The dispersed reefs showed lowest bathymetry points compared to patch and continuous reefs. The values of condition indices reveal not significant difference among reef types (continuous, dispersed and patch). Fine sand has the highest percentage (71%) followed by silt/clay fraction (18%). The higher density and spat size were recorded in monsoon (June to September) season. The current study suggests that the present reefs are viable and have potential for successful restoration and may be converted into a sizeable ecologic sanctuary.

Quantifying and mapping intertidal oyster reefs utilizing LiDAR-based remote sensing

Quantifying and mapping intertidal oyster reefs utilizing LiDAR-based remote sensing