Habitat Restoration from an Ecosystem Goods and Services Perspective: Application of a Spatially Explicit Individual-Based Model

Estuarine ecosystems provide many services to humans, but these ecosystems are also under pressure from human development, which has led to large investments in habitat protection and restoration. Restoration in estuaries is typically focused on emergent and submerged vegetation with the goal of achieving target areal coverage based on historic conditions. Such restoration targets assume no spatial heterogeneity in habitat value and bypass the functional target of restoring or maintaining delivery of ecosystem goods and services (EGS). We have developed a spatially explicit individual-based behavioral model intended to explore the functional role of habitat restoration on EGS delivery in an index system (Tampa Bay, FL) and for an index EGS (recreational fishing). Model scenarios are based on interaction of inter-annual differences in salinity/temperature patterns (wet, dry, average) with hindcasted “increases” in coverage and distribution of seagrass. Model predictions indicated that the effect of seagrass restoration to historic (1950s) levels on both fish and fishery production is dependent on salinity and temperature. This dependence is based on predicted fish response both to habitat changes and the effective spatial scale of different habitat components. Overall, average salinity/temperature conditions facilitated the highest positive functional response to seagrass restoration with extreme wet/dry years yielding lower or even negative functional responses, but these responses were localized and not homogenous about the estuary. The results of this study provide a methodology for using functional targets in restoration planning and highlight the importance of considering the entire habitat mosaic in valuing restored habitat from an EGS perspective.     

Differences in Relative Predation Vulnerability Between Native and Non-native Oyster Larvae and the Influence on Restoration Planning in an Estuarine Ecosystem

The costs and benefits of non-native introductions as a restoration tool should be estimated prior to any action to prevent both undesirable consequences and waste of restoration resources. The suggested introduction of non-native oyster species, Crassostrea ariakensis, into Chesapeake Bay, USA, provides a good example in which the survival of non-native oysters may differ from that of native oysters, Crassostrea virginica, during the larval stage. Experiments were conducted to compare the predation vulnerability of native and non-native oyster larvae to different predator types (visual vs. non-visual, benthic vs. pelagic). The results suggest that the non-native larvae are more vulnerable to visual and non-visual pelagic predators. Although vulnerability was similar for larvae exposed to benthic non-visual predators, the consumption of one non-native strain was higher than the consumption of native C. virginica larvae. When vulnerability data are combined with predator feeding rates, the predation mortality for non-native larvae in the wild can be much higher than for native larvae. Small changes in larval mortality rates can yield large changes in total larval delivery to the reef for settlement, so these differences among species may contribute to differences in settlement success. These results provide an example of how a comprehensive examination of the perceived benefits of non-native introductions into complex ecosystems can provide important information to inform management decisions.     

Benchmarking geoacoustic inversion methods using range-dependent field data

Over the past decade, inversion methods have been developed and applied to acoustic field data to provide information about unknown ocean-bottom environments. An effective inversion must provide both an estimate of the bottom parameters and a measure of the uncertainty of the estimated values. This paper summarizes results from the Office of Naval Research (ONR)/Space and Naval Warfare Systems Command (SPAWAR) Geoacoustic Inversion Techniques Workshop, test cases 4 and 5. The workshop was held to benchmark present-day inversion methods for estimating geoacoustic profiles in shallow water. The format of the workshop was a blind test to estimate unknown geoacoustic profiles by inversion of measured acoustic transmission loss data in octave bands and reverberation envelopes. The data sets for test cases 4 and 5 were taken at two locations in shallow water, one in the East China Sea and the other along the southwest coast of Florida. The limitations of the data and the limits to the knowledge of the sites are discussed. In both cases, impulsive sources were used in conjunction with air-deployed sonobuoys. Since the measured data was incoherent, only methods consistent with total energy matching were applicable. Comparisons between the different inversion techniques presented at the workshop are discussed. For test cases 4 and 5, a precise metric was unavailable for comparison.     

Effects of Korean littoral environment on acoustic propagation

Environmental acoustics experiments were recently conducted in shallow to intermediate water depths in the Sea of Japan, east of Korea, along the shelf and slope, covering frequencies from 25 to 800 Hz. These were operational experiments carried out in three different seasons. The primary objectives of the data reported here are: (1) to characterize the Korean coastal environment during May 1998, September 1998, and February 1999 and (2) to assess how complexities of the environment might impact acoustic propagation in May and February, as measured by its transmission loss. Propagation data were obtained from broadband explosive SUS sources and sonobuoy receivers. The tests were conducted over varying bottom depths and slopes, both approximately normal and parallel to the bathymetric contours. Two different source depths were included. Environmental and acoustic data are reviewed and discussed. While many aspects of the observed propagation remain ill understood, on the whole a consistent and useful picture has emerged of acoustic propagation in this region. Environmental impacts on propagation are associated mainly with bottom properties, somewhat less so with source depth in relationship to sound speed profiles, and almost not at all with range-dependent profiles of a water mass front     

Oyster-sea nettle interdependence and altered control within the Chesapeake Bay ecosystem

Research on the effects of declining abundances of the Eastern oyster (Crassostrea virginica) in Chesapeake Bay and other estuaries has primarily focused on the role of oysters in filtration and nutrient dynamics, and as habitat for fish or fish prey. Oysters also play a key role in providing substrate for the overwintering polyp stage of the scyphomedusa sea nettle,Chrysaora quinquecirrha, which is an important consumer of zooplankton, ctenophores, and icthyoplankton. Temporal trends in sea nettle abundances in visual counts from the dock at Chesapeake Biological Laboratory, trawls conducted in the mesohaline portion of the Patuxent River, and published data from the mainstem Chesapeake Bay indicate that sea nettles declined in the mid 1980s when overfishing and increased disease mortality led to sharp decreases in oyster landings and abundance. Climate trends, previously associated with interannual variation in sea nettle abundances, do not explain the sharp decline. A potentially important consequence of declining sea nettle abundances may be an increase in their ctenophore prey (Mnemiopsis leidyi), and a resultant increase in predation on icthyoplankton and oyster larvae. Increased predation on oyster larvae by ctenophores may inhibit recovery of oyster populations and reinforce the current low abundance of oysters in Chesapeake Bay.     

Effects of East China Sea shallow-water environment on acoustic propagation

Operational environmental acoustics experiments were conducted over the frequency range of 25 to 800 Hz in September 1997 in the East China Sea, where the water depth was about 100 m. Objectives of the data analysis reported here are to characterize this environment and to assess its complexities as they may impact acoustic propagation as measured by its transmission loss (TL). Conductivity-temperature-depths and expendable bathy-thermographs sampled the ocean, such that its spatial and temporal variability could be approximately separated. The sound-speed profiles are downward refracting, involve two water masses associated with the Kuroshio Current and Taiwan Warm Current, and have thermocline variations caused by internal tides. The bottom geoacoustic characteristics, presumed to be approximately horizontally isotropic, were based on data atlases and were estimated from the measured TL, for some interpretations. The TL data were obtained in octave bands from explosive signal underwater sound sources and sonobuoy receivers, both deployed at a depth of about 18 m. Tests were conducted in directions approximately normal and parallel to the bathymetric contours and the measured TL was, to zero order, independent of the direction of propagation. To higher order, directional differences in the TL were observed and ascribed to anisotropies in bottom properties. A state-of-the-art TL model was adopted, based on environmental idealizations typical of operational forecasting and compared with the measured TL. The comparison yields a probability density function that quantifies the uncertainty of such a TL model, caused by the stochastic variability of the environment, typically unknown a priori. For the model used, the pdf has a standard deviation of about 2 dB from 50 to 800 Hz and larger below 50 Hz.     

Subbottom profile of ARSRP sediment pond as determined from vertical towed array data

 The Acoustic Reverberation Special Research Program (ARSRP) acquired a unique set of towed vertical array data across a sediment pond adjacent to the mid-Atlantic ridge. Processing of the deep-towed vertical array data to map the subbottom structure within the sediment pond provided the basis for a geological interpretation of the pelagic sediments contained within the pond. The layering in this pond is parallel and subparallel in nature with very gentle dips increasing with depths of the sediment. The gentle dips and the faults within the sediment layers are the result of differential compaction and slumping of the sediments. Received: 20 February 1997 / Revision received: 1 October 1997     

Subbottom profile of ARSRP sediment pond as determined from vertical towed array data

The Acoustic Reverberation Special Research Program (ARSRP) acquired a unique set of towed vertical array data across a sediment pond adjacent to the mid-Atlantic ridge. Processing of the deep-towed vertical array data to map the subbottom structure within the sediment pond provided the basis for a geological interpretation of the pelagic sediments contained within the pond. The layering in this pond is parallel and subparallel in nature with very gentle dips increasing with depths of the sediment. The gentle dips and the faults within the sediment layers are the result of differential compaction and slumping of the sediments.     

Late Cretaceous basement foundering of the Rosario embayment, Peninsular Ranges forearc basin: backstripping of the El Gallo Formation, Baja California Norte, Mexico

Excellent exposure, well-controlled palaeobathymetry, and tightly-spaced, high-precision radiometric age control in the El Gallo Fm. permit rigorous quantitative analysis. Backstripping of these proximal nonmarine, forearc basin deposits reveals that, during the Late Cretaceous, the Rosario embayment of the Peninsular Ranges forearc was undergoing an episode of rapid tectonic subsidence. This subsidence had several marked effects on the sedimentology of the Rosario embayment: formation of a broad alluvial plain consisting of coarse-grained clastics; rapid (∼ 600 m Myr^-1) aggradation of sediments; and a retrogradational succession of facies, capped by a marine transgression, as deposition failed to keep pace with eustatic rise and subsidence.
Long-term sedimentation is driven by some combination of two allocyclic mechanisms: tectonic subsidence and eustatic sea-level rise. In order to evaluate which force predominated during deposition of the El Gallo Fm., the processes of sedimentation, compaction, and isostasy are evaluated through the interval in question. A sensitivity analysis is performed, in which the maximum tectonic and maximum eustatic contributions are estimated, along with the best-fit model. These results are qualitatively the same: tectonic subsidence was the major driving force of sedimentation in the Rosario embayment in late Campanian time. Regional sedimentological similarities suggest that this tectonic subsidence may have characterized the Peninsular Ranges forearc margin at this time, reflecting an episode of active down-faulting during the Late Cretaceous.