Estuaries and Coasts最新文献

The Gulf toadfish (Opsanus beta) is a soniferous and abundant species native to Gulf of Mexico estuarine environments—now considered a likely invasive species in coastal Brazil. Males produce distinctive boatwhistle calls during their reproduction behaviors, offering an acoustic cue for ecological functions such as mate selection, prey detection, and predator avoidance. Their calls can also be readily detected with passive acoustics to monitor Gulf toadfish distributions and serve as acoustic indicators for their preferred nesting habitats. In this study, we describe the spatial, annual, seasonal, monthly, daily, daytime, and diel variation of Gulf toadfish call occurrence in Cedar Key, Florida (USA), with multiple sampling efforts at seagrass and dock sampling locations in the years 2019–2022. From April through June during our dock sampling, calls were detected across almost all our sampled dates and often every hour of the day, with daily and diel fluctuations in call occurrence. In our seagrass meadow sampling, call occurrence showed some positive correlation with manatee grass (Syringodium filiforme) and salinity. Moreover, snapshot recordings as short as 5 min were sufficient to detect calls in 37 of our 45 sampling events compared to only five where trawls captured Gulf toadfish. Our findings demonstrate the efficacy of listening to Gulf toadfish calls for monitoring applications and can support future efforts seeking to understand the availability of a prevalent acoustic cue in estuarine soundscapes.

We compared elevation trajectories from 14 rod surface elevation table (RSET) stations and 60 real-time kinematic (RTK) global positioning system (GPS) transects within the Blackwater National Wildlife Refuge (BNWR) from 2010–2013. The results were similar, 7.3 ± 0.9 (mean ± standard error; RSET) versus 6.2 ± 0.6 mm year⁻¹ (RTK) (P = 0.216), and were greater than relative sea level rise (RSLR) computed at the nearest long-term tide station (3.9 ± 0.29 mm year⁻¹). Despite having shown elevation gain, these wetlands continue to drown and convert to open water. Episodic, multi-day GPS measurements on geodetic control marks at BNWR between 2005 and 2023 revealed a substantial vertical land motion (VLM) signal. From 2005 to 2015, three reference marks used to control the 2010–2013 RTK study lost on average 6.0 ± 0.7 mm year⁻¹, corresponding to 80% and 94% of the elevation gain measured by the RSET and RTK techniques, respectively. The longer 18-year subsidence trend measured on one of these marks was lower, 3.9 ± 0.7 mm year⁻¹, highlighting important interannual variability. Wetland elevation change measurements need to account for VLM occurring below the reference marks used to measure elevation change. Estimates from the nearest long-term tide station may not be applicable to the wetland if the tide station is in a different geological setting. At BNWR, VLM was higher than the VLM at the Cambridge tide station, which helps explain why wetlands at BNWR are not keeping pace with RSLR despite the measured high rates of elevation gain.

Coastal risk assessment requires accurate coastal bathymetry, which is largely lacking in many regions of the world’s coastal oceans. This is particularly true in Guinea-Bissau, where the tidal range is the highest of any country in West Africa, affecting several socio-economic sectors such as agriculture and urban development. Here, we present a selection of coastal bathymetry datasets available for generally poorly sampled coastal regions. These include the General Bathymetric Chart of the Oceans (GEBCO), digital nautical charts (CMAP), and depth retrieval from satellite wave detection (S2Shores). While GEBCO provides the right regional envelope of bathymetry, the coastal zone is plagued with random bumpiness at scales below 10 km (“orange peel” texture). S2Shores can be used to correct these errors and instead reveal the presence of small-scale channels, reminiscent of very high-resolution satellite color images. These structures are also confirmed by nautical charts, which show the channels to be well correlated but deeper than that indicated by the satellite retrieval (with a 40% higher variance, and 40 m instead of 20 m for Orango, the main and deepest channel). Simulations with a coastal ocean hydro-sedimentary model (CROCO) further show that submerged rivers can help drive a smooth flow of tidal energy into the main estuary of Guinea-Bissau. Tidal energy flux is better channeled in the CMAP and S2shores cases, while GEBCO produces an order of magnitude greater form drag, resulting in a stronger response from the sediment bed. Tides therefore have the effect of smoothing bathymetry along fine-scale channels, minimizing friction on the way to equilibrium. This result highlights the potential of combining different approaches to estimate updated coastal bathymetry and its effect on coastal dynamics in the most challenging areas.

Salt marshes exist at the terrestrial-marine interface, providing important ecosystem services such as nutrient cycling and carbon sequestration. Tidal inputs play a dominant role in salt marsh porewater mixing, and terrestrially derived freshwater inputs are increasingly recognized as important sources of water and solutes to intertidal wetlands. However, there remains a critical gap in understanding the role of freshwater inputs on salt marsh hydrology, and how this may impact marsh subsurface salinity and plant productivity. Here, we address this knowledge gap by examining the hydrologic behavior, porewater salinity, and pickleweed (Sarcocornia pacifica also known as Salicornia pacifica) plant productivity along a salt marsh transect in an estuary along the central coast of California. Through the installation of a suite of hydrometric sensors and routine porewater sampling and vegetation surveys, we sought to understand how seasonal changes in terrestrial freshwater inputs impact salt marsh ecohydrologic processes. We found that salt marsh porewater salinity, shallow subsurface saturation, and pickleweed productivity are closely coupled with elevated upland water level during the winter and spring, and more influenced by tidal inputs during the summer and fall. This seasonal response indicates a switch in salt marsh hydrologic connectivity with the terrestrial upland that impacts ecosystem functioning. Through elucidating the interannual impacts of drought on salt marsh hydrology, we found that the severity of drought and historical precipitation can impact contemporary hydrologic behavior and the duration and timing of the upland-marsh hydrologic connectivity. This implies that the sensitivity of salt marshes to climate change involves a complex interaction between sea level rise and freshwater inputs that vary at seasonal to interannual timescales.

This field study examined how sediment macroinfauna change patterns of sediment oxygen demand (SOD) throughout a diel oxygen cycle. Sediments with a greater faunal presence would be expected to have greater overall SOD, and at night may alter their behavior and influence SOD depending on their response to low-oxygen stress. Dynamic faunal bioturbation or bioirrigation behavior would also result in corresponding variation in SOD values on short time scales. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. Sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. Where more macroinfauna were present, they drove greater SOD during nightly low oxygen, presumably by enhancing their burrowing and irrigation activities. SOD was also more variable on a sub-diel timescale in sediments with more macroinfauna. Sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna, and their interaction produces heretofore unaccounted complexity in patterns of SOD particularly in shallow coastal systems. Extrapolations of temporally and spatially limited SOD measurements to a system-wide scale that do not account for the short-term and spatially variable effects of fauna may produce imprecise and misleading estimates of this critical ecosystem function.

Conservation efforts have raised awareness about the impact of small-scale fisheries on the distribution of seagrass plants. The patterns of recovery of the seagrass Zostera noltei and of the commercial bivalves Cerastoderma edule, Ruditapes decussatus and Ruditapes philippinarum after shellfish harvesting were studied in a field experiment in a shellfish bed in NW Spain. Sample plots were subjected to a single disturbance in two types of shellfish harvesting treatments in three zones characterized by different harvesting frequency and seagrass density. The photosynthetic efficiency (F_v/F_m), shoot density, leaf length and carbohydrate content of Z. noltei were monitored every three months during one year, and the C and N content of leaves and biomass of plants were measured one year after the disturbance. The abundance of adults, juveniles and recruits and the condition index of adult bivalves were quantified after the experimental harvesting. Shoot density and biomass of Z. noltei remained low during the ten months after the disturbance but recovered to control values after one year. Carbohydrate contents of apical rhizomes were lower in disturbed (treated) plots, whereas no effect was observed on F_v/F_m. Denser and more complex seagrass patches recovered faster. The abundance of adult bivalves below commercial size was lower in the disturbed plots, while the abundance of adults of commercial size, juveniles and recruits did not vary, indicating that abundance and condition were not hampered by harvesting pressure. The findings also suggest that Z. noltei meadows can recover within one year of the impact of shellfish harvesting if the havesting areas are rotated and dense patches are preserved.

As a consequence of anthropogenic activities and climate change, accelerated terrestrial sediment runoff is causing the gradual mudification of soft sediment estuarine habitats worldwide. Increased sediment mud content (< 63 µm) has been recognised to alter seagrass morphology and cause declines in primary production in unvegetated habitats. However, the effect of increased mud content on primary production in seagrass meadows remains largely unknown. To address this, primary production in intertidal seagrass meadows (Zostera muelleri) and adjacent unvegetated habitats was measured in situ using benthic incubation chambers across an existing sedimentary gradient (nine sites spanning 5–33% mud content). An additional two unvegetated mudflat sites (39–49% mud content) were also sampled to expand the gradient. Seagrass net (NPP) and gross primary production (GPP) was greater than in the adjacent unvegetated habitat and did not vary with mud content, even after standardising GPP by photosynthesising biomass (i.e. photosynthetic efficiency). In contrast, in the adjacent unvegetated habitat, photosynthetic efficiency declined with increasing mud content. Inclusion of the additional mudflat sites negatively impacted NPP, GPP, and photosynthetic efficiency in the unvegetated habitat. Thus, while primary production in seagrass meadows may have some resilience to future increases in mud content (up to ~33%), further degradation and loss of seagrass habitats could result in the expansion of unvegetated habitats and ultimately lead to production losses, likely to be most acute in areas with high mud content (≥ 39%).

Enhalus acoroides (L.f.) Royle is a large and important foundation seagrass species in the tropical Indo-Pacific. The northern marginal populations in China have been declining over the last decades. The reproductive phenology and fruit set of this dioecious seagrass were investigated from June 2017 to February 2018 in two areas in Li’an lagoon, Hainan Island, China. We found that E. acoroides flowered year-round. However, the flowering intensity varied among seasons and was highest in the summer and lowest in the winter. The shoot sex ratio was male-biased, and the pollen-ovule ratio was approximately 10⁴: 1, based on the sex ratio and the number of male florets per inflorescence. Female and male plants flowered at the same time in this population. Despite the high reproductive investment in terms of flower formation observed throughout the year, the abundance of the mature fruits was low, possibly due to physical disturbance and cover by epiphyte and algae. This study provides insight into the reproductive ecology of E. acoroides, which will be useful for the future conservation of this threatened seagrass.

Impermeable infrastructure such as traffic causeways can reduce the natural hydrodynamic flushing of an estuary, resulting in reduced water quality and increased incidence of harmful algal blooms (HABs). A series of cuts through the three causeways spanning Old Tampa Bay, FL, (OTB) are being considered to help restore the natural circulation of the region, but the number of possible location combinations is computationally challenging to fully assess. A prototype genetic algorithm (GA) was developed to identify the optimal configuration of these cuts through one of the bridge sections that maximizes flushing as represented in a numerical ocean circulation model of OTB. Flushing was measured by integrating the trajectories of over 21,000 passive Lagrangian “particles” using the model velocity fields. The rate of loss of particles initialized near Feather Sound (a region subject to frequent HABs) was used to quantify the “fitness” over which the configurations were optimized. The highest-scoring solution produced a 42% increase in net flushing compared to a no-change baseline. Six independently initialized applications of the GA were conducted. All converged to the same solution within no more than 7 generations. The small population size of the prototype allowed testing of the complete solution space, and verification the found solution was optimal. Elitism (preservation of the highest-ranking solution) was required for convergence. The GA also identified configurations that had similar, but slightly slower, flushing rates. These results will help area managers prioritize or rank combinations of causeway modifications to improve overall water quality conditions in Tampa Bay.

Marsh lateral expansion and retreat are often attributed to sediment availability, but a causal link is difficult to establish. To shed light on this problem, we analyzed changes in salt marsh area along the ~ 200-km-long Georgia coast (USA) from the 1850s to 2010s in relation to total suspended sediment (TSS) and to proxies for river sediment input and local sediment resuspension. Marsh area is characterized by large gains and losses (up to 200 m²/m/yr), but relatively small net change (-50 to 50 m²/m/yr or -0.1 to 0.1%/yr). This has resulted in a general loss of marsh area, except close to the mouths of major rivers, where there is net gain. Net expansion rates decreased in the Savannah Estuary but increased in the Altamaha Estuary from the 1850s–1930s period to the 1930s–2010s period, which are consistent with observed decreases and likely increases in sediment discharge in the two estuaries, respectively. To explain the spatial patterns in the 1930s–2010s marsh area change, we estimated TSS from satellite measurements (2003 to 2020). Along the northern part of the Georgia coast, net marsh gain is positively correlated to the average TSS within the estuarine region. However, this correlation breaks down in more southern areas (Cumberland Sound). Coast-wide, there is a better correlation between TSS associated with new input from the rivers, estimated as the TSS difference between high-discharge (Jan–Mar) and low-discharge (Sept–Nov) months. To identify the effect of wave resuspension in the nearshore, we consider the TSS difference between high-wave, low-discharge (Sept–Nov) and low-wave, low-discharge periods (Jun–Aug). Wave resuspension is relatively uniform along the coast and does not explain spatial patterns of marsh area change. Sediment input from the nearshore is likely contributing to the estuarine sediment budget in Georgia, but it is not sufficient to prevent marsh lateral retreat. To identify the role of tidal resuspension and advection, we consider differences in TSS between low and high tide. This differential is relatively constant along most of the coast, but it is much lower in the southern part of the coast, suggesting a lower tidal action in this region. Sediment resuspended by tides is likely originating from internal recycling (i.e., erosion) within the estuary, and thus does not contribute to marsh lateral expansion. The proposed approach to partition TSS is a general demonstration and could be applied to other coastal regions.