Dynamics of Restored and Natural Oyster Reefs After a Hurricane

Restoration of shellfish reefs has increased exponentially over the past two decades, due in part to increased awareness of widespread oyster habitat loss. Large-scale, acute disturbances such as hurricanes have the potential to influence restoration outcomes, but because storm occurrence is unpredictable with respect to restoration timelines, the responses of restored habitats are not well understood. We quantified the ecological dynamics of a newly constructed Crassostrea virginica oyster reef and nearby reference reef in a Texas estuary immediately after Hurricane Harvey, a major category 4 storm. Biophysical structure (e.g., oyster density, shell height, sediment grain size), and community composition (abundance of reef-associated epifauna, and nearby infauna) were measured for 18 months. A sharp decrease in salinity and temporary deposition of fine sediments within the first 3 months corresponded with increases in oyster and epifaunal recruitment on the restored reef, although densities were generally below those measured on restored reefs without hurricanes. Criteria for oyster reef restoration success were met within 12–18 months post-storm. Infaunal densities decreased but returned to pre-storm densities within 2 months, but bivalves were delayed, returning to pre-storm levels after 9 months. A lack of historical baseline data on the newly restored reef limited our ability to assess the magnitude of reef recovery to pre-disturbance levels or separate the direct effects of the hurricane from the dynamics of early recruitment and growth. Results provide important information about restored and natural oyster reef dynamics after large-scale disturbance and can help inform effective management and conservation measures

Evaluating Biodegradable Alternatives to Plastic Mesh for Small-scale Oyster Reef Restoration

Polyethylene plastic mesh is commonly used for containing oyster shells in small-scale oyster reef restoration, but environmental and public health concerns have prompted investigations of biodegradable alternatives. Shallow (<0.5 m) and deep (approximately 1 m) oyster reefs (approximately 6 m2) were constructed in the Mission-Aransas Estuary, Texas, U.S.A., in March 2020 using recycled oyster shells placed into four different replicated mesh bag types: polyethylene (plastic) and three biodegradable alternatives (cellulose, cotton, and jute). Biodegradable alternatives (cellulose, cotton, and jute) all completely degraded within 2 months of deployment, leaving piles of loose shell, while polyethylene bags remained intact. Despite rapid degradation, the biodegradable/loose shell successfully recruited and developed larger oysters (mean of 46 mm) than on the polyethylene-bagged shell (mean of 40 mm) after 7 months, although at less than half the density. Associated motile fauna density in the bagged shell was 2.4 times higher than in the loose shell after 7 months at both the deep and shallow locations. Faunal community composition and diversity varied more with reef depth than by bag type. The total cost of using polyethylene bags was lower than for biodegradable alternatives (22–45% the cost of cellulose, 35–72% the cost of jute, 49–99% the cost of cotton). However, because our estimate of the environmental cost of polyethylene plastic mesh only included impacts on marine natural capital, the true cost is likely much higher. Despite higher costs, biodegradable alternatives can still be successful for use in small-scale oyster restoration events without introducing plastics into the marine environment

Water level during study and sampling periods.

<p>Mean monthly water level (NAVD 88) throughout the study duration (sampling months indicated with arrows) (A) and water level during sampling days (approximate sampling duration indicated with grey boxes) (B) in Nueces Bay, Texas.</p

Bayesian stable isotope mixing model results.

<p>Estimated proportional contribution of suspended particulate organic matter (SPOM), benthic diatoms, <i>Spartina</i> epiphytic microalgae, and <i>Spartina</i> to the diets of <i>Palaemonetes</i> spp. (A) <i>P</i>. <i>aztecus</i> (B) and <i>C</i>. <i>sapidus</i> (C) in spring and summer sampling periods in natural and restored marsh sites. Plots indicate dietary contribution estimate (<i>posterior</i> median) with 50% (hinges) and 95% (whiskers) credibility intervals.</p

<i>Spartina</i> density and biomass.

<p>Mean ± standard error of <i>Spartina</i> shoot density (A), above ground (AG) biomass (B) and below ground (BG, 0–20 cm) biomass (dry weight) (C) of <i>Spartina</i> per 35.4 cm² core in restored and natural marsh sites in each sampling period in Nueces Bay, Texas. Significant differences between restored and natural marshes within seasons indicated by *, and within marsh seasonal contrast groupings indicated under x-axis (ANOVA contrasts <i>P</i> < 0.05).</p

Ecological structure and function in a restored versus natural salt marsh

<div><p>Habitat reconstruction is commonly employed to restore degraded estuarine habitats and lost ecological functions. In this study, we use a combination of stable isotope analyses and macrofauna community analysis to compare the ecological structure and function between a recently constructed <i>Spartina alterniflora</i> salt marsh and a natural reference habitat over a 2-year period. The restored marsh was successful in providing habitat for economically and ecologically important macrofauna taxa; supporting similar or greater density, biomass, and species richness to the natural reference during all but one sampling period. Stable isotope analyses revealed that communities from the natural and the restored marshes relied on a similar diversity of food resources and that decapods had similar trophic levels. However, some generalist consumers (<i>Palaemonetes</i> spp. and <i>Penaeus aztecus</i>) were more ¹³C-enriched in the natural marsh, indicating a greater use of macrophyte derived organic matter relative to restored marsh counterparts. This difference was attributed to the higher quantities of macrophyte detritus and organic carbon in natural marsh sediments. Reduced marsh flooding frequency was associated with a reduction in macrofaunal biomass and decapod trophic levels. The restored marsh edge occurred at lower elevations than natural marsh edge, apparently due to reduced fetch and wind-wave exposure provided by the protective berm structures. The lower elevation of the restored marsh edge mitigated negative impacts in sampling periods with low tidal elevations that affected the natural marsh. The results of this study highlight the importance of considering sediment characteristics and elevation in salt marsh constructions.</p></div

Developing a bioassessment framework to inform tidal stream management along a hydrologically variable coast

Tidal streams are spatiotemporally varying areas that encompass tidally influenced limnetic and oligohaline zones within estuaries. These areas are important for many biogeochemical processes and for the life cycles of many fishery species. However, tidal streams are also susceptible to impairment from coastal development and watershed-derived runoff, which potentially affects faunal assemblages within the ecosystem. This study developed indices of biotic integrity (IBIs) for nekton and benthic macroinfauna in tidal streams along the southern Texas coast. Fifteen tidal stream sites with mean salinities ranging from 0.4 to 11.9 were classified as degraded if their surrounding land use was > 20 % urban or agricultural, watershed population density was > 50 km−2, and nutrient and chlorophyll concentrations exceeded specific screening limits. Otherwise, sites were classified as reference. Nekton and benthic macroinfauna communities were then sampled at these fifteen stream sites in 2020 and 2021. Historical metrics and metrics derived from multivariate analyses were considered for inclusion in the IBIs, and were assessed for collinearity, redundancy, suitability for score assignment, and agreement with historical literature. Nine univariate nektonic metrics (including total abundance, number of invertebrate taxa, and the percent abundance of five species, one family, and one functional group) and six benthic macroinfauna metrics (including Shannon’s diversity, total abundance and biomass, and the percent abundance of two taxa and one functional group) were incorporated into separate nektonic and benthic IBIs. Mean IBI scores of reference sites were greater than degraded sites by 42 % for nekton and 30 % for benthic macroinfauna. Seven out of eight reference sites had greater mean nekton IBI scores than the mean scores of all seven degraded sites, while four of eight reference sites had greater benthic IBI scores than all degraded sites. However, overlap in the ranges of scores calculated for degraded and reference sites occurred, which is likely caused by spatiotemporal variability, including stream size variation and the changing climatic and biogeographical gradient along the southern Texas coast. The IBIs developed in this study represent an important preliminary step in bioassessment development for Texas tidal streams, and will help to provide a useful tool for coastal environmental management

Restored and natural reference marsh sites.

<p>Map of study region (A) and study site with labeled restored and natural salt marsh sampling sites (B) in Nueces Bay, Texas. TCOON: Texas coastal ocean observation network.</p

Water level during study and sampling periods.

<p>Mean monthly water level (NAVD 88) throughout the study duration (sampling months indicated with arrows) (A) and water level during sampling days (approximate sampling duration indicated with grey boxes) (B) in Nueces Bay, Texas.</p

Macrofauna density, biomass, and richness.

<p>Mean ± standard error of macrofauna density (A), macrofauna biomass (dry weight) (B) and macrofauna species richness (C) in restored and natural marsh habitats during each sampling period in Nueces Bay, Texas. Significant differences between restored and natural marshes within seasons indicated by *, and within marsh seasonal contrast groupings indicated under x-axis (ANOVA contrasts <i>P</i> < 0.05).</p