PHYSICAL–BIOLOGICAL COUPLING ON OYSTER REEFS: HOW HABITAT STRUCTURE INFLUENCES INDIVIDUAL PERFORMANCE

A large-scale field experiment was conducted to test whether the physical structure of biogenic reef habitat controls physical conditions (hydrodynamics and hydrographics) with subsequent influence on the performance (recruitment, growth, and survival) of a benthic suspension feeder. The experimental system consisted of restored subtidal oyster reefs inhabited by the eastern oyster Crassostrea virginica. To determine whether the size of reefs influences the flow environment and oyster performance, reefs of four heights-tall (2 m), short (1 m), dredged (0.6 m), and low (0.1 m)-were constructed at 3-m water depth in the Neuse River estuary, North Carolina, USA. To test whether oyster performance varies with water depth and hydrographic conditions, tall and short reefs were also constructed at 6-m water depth. Flow speed, sedimentation, temperature, salinity, dissolved oxygen, and the performance of oysters were measured as a function of reef height, position on reef, and water depth over a 10-mo period. Flow speed was found to increase on reefs with reef height and elevation on reefs. Rates of sediment deposition were seasonally highest where flow speed was lowest, at the bases of reefs, and seasonally decreased with increasing water depth. More than 90% of the surface area of low reefs was buried after only 16 mo of exposure in the estuary, indicating that reef height controls habitat quality (and quantity) indirectly through its effect on flow. Short reefs and the bases of tall reefs at 6-m depth were exposed to a total of 26 d of hypoxia/anoxia. No other reef treatment was exposed to >5 d of hypoxia. Physical conditions on experimental reefs had a profound influence on the performance of oysters as the flow environment alone explained 81% of variability in oyster growth and mortality. Recruitment of oysters over a 2-mo period was slightly higher on the front bases than the crests of reefs, but did not vary with reef height or water depth. After 10 mo, the shell growth and condition index of genetically similar, hatchery-raised oysters were greatest on the crests of tall and short reefs, where flow speed and quality of suspended food material were highest, and sediment deposition was lowest. Growth was greatest overall at the crests of tall reefs located at 6-m water depth where flow speed was high, and the numbers of days exposed to hypoxia/anoxia and variation in salinity were lowest. Total percentage mortality of oysters after 10 mo was greater on low reefs located at 3-m depth than on all other reef types and was greater on the bases than crests of tall, short, and dredged reefs. Predation by crabs and fishes accounted for 4-20% of total oyster mortality and showed no pattern across reef treatments. Results of this experiment indicate (1) that the physical structure and location of biogenic habitat controls local physical variables and (2) that, in turn, physical variables, especially flow speed, have a profound influence on the performance of a resident species. Realization that an ecological function of habitat is to indirectly control local population production through physical-biological coupling should improve our ability to conserve, restore, and manage habitat and associated species diversity. Better ecological engineering of restored oyster reef habitat is likely to improve fishery production and help maintain estuarine biodiversity

Conserving oyster reef habitat by switching from dredging and tonging to diver-harvesting

A major cause of the steep declines of American oyster (Crassostrea virginica) fisheries is the loss of oyster habitat through the use of dredges that have mined the reef substrata during a century of intense harvest. Experiments comparing the efficiency and habitat impacts of three alternative gears for harvesting oysters revealed differences among gear types that might be used to help improve the sustainability of commercial oyster fisheries. Hand harvesting by divers produced 25−32% more oysters per unit of time of fishing than traditional dredging and tonging, although the dive operation required two fishermen, rather than one. Per capita returns for dive operations may nonetheless be competitive with returns for other gears even in the short term if one person culling on deck can serve two or three divers. Dredging reduced the height of reef habitat by 34%, significantly more than the 23% reduction caused by tonging, both of which were greater than the 6% reduction induced by diver hand-harvesting. Thus, conservation of the essential habitat and sustainability of the subtidal oyster fishery can be enhanced by switching to diver hand-harvesting. Management schemes must intervene to drive the change in harvest methods because fishermen will face relatively high costs in making the switch and will not necessarily realize the long-term ecological benefits

Assessing Withering Syndrome Resistance in California Black Abalone: Implications for Conservation and Restoration

Our overall research objectives were to (1) assess population trends along San Nicolas Island and in Monterey County; (2) optimize black abalone spawning methods; (3) develop and validate a real-time PCR assay for quantification of RLP loads (infection intensity); and (4) examine if progeny of surviving black abalone along the California islands are more resistant to WS than are animals without this disease pressure. At UCSB we were focused primarily on objective (2). We tested the following hypotheses to fulfill our objectives.Hypothesis 1: Black abalone spawning requires environmental conditions similar to their intertidal and shallow subtidal habitat, and not standard methods that were developed for subtidal species. Hypothesis 2: Quantitative real-time PCR can be used to quantify loads of the WS rickettsial bacterium (infection intensity) in abalone. Hypothesis 3: Juvenile black abalone recruiting along the California Channel Islands are more resistant to WS than are black abalone in northern Central California that have not experienced high disease (WS) selection pressure

HOW HABITAT DEGRADATION THROUGH FISHERY DISTURBANCE ENHANCES IMPACTS OF HYPOXIA ON OYSTER REEFS

Oysters are ecosystem engineers that create biogenic reef habitat important to estuarine biodiversity, benthic-pelagic coupling, and fishery production. Prevailing explanations for the dramatic decline of eastern oysters (Crassostrea virginica) during the last century overlook ecosystem complexity by ignoring interactions among multiple environmental disturbances. To explain oyster loss, we tested whether (1) mortality of oysters on natural oyster reefs varies with water depth (3 m vs. 6 m), (2) harvesting by oyster dredges reduces the height of oyster reefs, and (3) bottom-water hypoxia/anoxia and reduction in reef height through fishery disturbance interact to enhance mortality of oysters in the Neuse River estuary, North Carolina, USA. The percentage of oysters found dead (mean ± 1 SD) during a survey of natural reefs in May 1993 was significantly greater at 6-m (92 ± 10%) than at 3-m (28 ± 9%) water depth. Less than one scason's worth of oyster dredging reduced the height of restored oyster reefs by ∼30%. During stratification of the water column in summer, oxygen depletion near the seafloor at 6 m caused mass mortality of oysters, other invertebrates, and fishes on short, deep experimental reefs, while oysters and other reef associates elevated into the surface layer by sufficient reef height or by location in shallow water survived. Highly mobile blue crabs (Callinectes sapidus) abandoned burrows located in hypoxic/anoxic bottom waters but remained alive in shallow water. Our results indicate that interaction of reef habitat degradation (height reduction) through fishery disturbance and extended bottom-water hypoxia/anoxia caused the pattern of oyster mortality observed on natural reefs and influences the abundance and distribution of fish and invertebrate species that utilize this temperate reef habitat. Interactions among environmental disturbances imply a need for the integrative approaches of ecosystem management to restore and sustain estuarine habitat

Fish and Invertebrate Use of Restored vs. Natural Oyster Reefs in a Shallow Temperate Latitude Estuary

Coastal marine habitats continue to be degraded, thereby compelling largescale restoration in many parts of the world. Whether restored habitats function similarly to natural habitats and fully recover lost ecosystem services is unclear. In estuaries, oyster reefs have been degraded by multiple anthropogenic activities including destructive fishing practices and reduced water quality, motivating restoration to maintain oyster fisheries and other ecosystem services, often at relatively high cost. We compared fish and invertebrate communities on recently restored (0–1 year post-restoration), older restored (3–4 years post-restoration), and natural oyster reefs to determine if and when restored reefs support functionally similar faunal communities. To test the influence of landscape setting on the faunal communities, the restored and natural reefs, as well as a control without reef present, were distributed among three landscapes (on the edge of salt marsh away from seagrass [salt marsh landscape], on mudflats [mudflat landscape], and near to seagrass and salt marsh [seagrass landscape]). Oyster density and biomass were greatest on restored reef habitat, as were those of non-oyster bivalve species. Total abundance of invertebrates was much greater on oyster reefs than in control plots, regardless of reef or landscape type, yet were frequently highest on older restored reefs. Meanwhile, juvenile fish densities were greatest on natural reefs, at intermediate densities on older restored reefs, and least abundant on controls. When comparing the effects of reef age and landscape setting, juvenile fish densities were greatest on younger reefs within the mudflat landscape. Collectively, these results indicate that oyster reefs harbor higher densities of resident invertebrate prey, which may explain why reef habitat is also important for juvenile fish. Laboratory and field experiments supported the notion that gag grouper (a predatory demersal fish) forage more effectively on oyster reefs than on unstructured mud bottom, whereas our experiments suggest that flounders that utilize oyster reefs likely forage on adjacent mud bottom. Because landscape setting influenced fish and invertebrate communities on restored reefs, the ecological consequences of landscape setting should be incorporated into restoration decision making and site selection to enhance the recovery of ecosystem goods and services

Oyster Reefs at Risk and Recommendations for Conservation, Restoration, and Management

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and ecoregions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the world\u27s remaining wild capture of native oysters (\u3e 75%) comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services

TiO2 Nanoparticles Are Phototoxic to Marine Phytoplankton

Nanoparticulate titanium dioxide (TiO2) is highly photoactive, and its function as a photocatalyst drives much of the application demand for TiO2. Because TiO2 generates reactive oxygen species (ROS) when exposed to ultraviolet radiation (UVR), nanoparticulate TiO2 has been used in antibacterial coatings and wastewater disinfection, and has been investigated as an anti-cancer agent. Oxidative stress mediated by photoactive TiO2 is the likely mechanism of its toxicity, and experiments demonstrating cytotoxicity of TiO2 have used exposure to strong artificial sources of ultraviolet radiation (UVR). In vivo tests of TiO2 toxicity with aquatic organisms have typically shown low toxicity, and results across studies have been variable. No work has demonstrated that photoactivity causes environmental toxicity of TiO2 under natural levels of UVR. Here we show that relatively low levels of ultraviolet light, consistent with those found in nature, can induce toxicity of TiO2 nanoparticles to marine phytoplankton, the most important primary producers on Earth. No effect of TiO2 on phytoplankton was found in treatments where UV light was blocked. Under low intensity UVR, ROS in seawater increased with increasing nano-TiO2 concentration. These increases may lead to increased overall oxidative stress in seawater contaminated by TiO2, and cause decreased resiliency of marine ecosystems. Phototoxicity must be considered when evaluating environmental impacts of nanomaterials, many of which are photoactive

Managing Bay and Estuarine Ecosystems for Multiple Services

Abstract Managers are moving from a model of managing individual sectors, human activities, or ecosystem services to an ecosystem-based management (EBM) approach which attempts to balance the range of services provided by ecosystems. Applying EBM is often difficult due to inherent tradeoffs in managing for different services. This challenge particularly holds for estuarine systems, which have been heavily altered in most regions and are often subject to intense management interventions. Estuarine managers can often choose among a range of management tactics to enhance a particular service; although some management actions will result in strong tradeoffs, others may enhance multiple services simultaneously. Management of estuarine ecosystems could be improved by distinguishing between optimal management actions for enhancing multiple services and those that have severe tradeoffs. This requires a framework that evaluates tradeoff scenarios and identifies management actions likely to benefit multiple services. We created a management action-services matrix as a first step towards assessing tradeoffs and providing managers with a DOI 10.1007/s12237-013-9602-7 decision support tool. We found that management actions that restored or enhanced natural vegetation (e.g., salt marsh and mangroves) and some shellfish (particularly oysters and oyster reef habitat) benefited multiple services. In contrast, management actions such as desalination, salt pond creation, sand mining, and large container shipping had large net negative effects on several of the other services considered in the matrix. Our framework provides resource managers a simple way to inform EBM decisions and can also be used as a first step in more sophisticated approaches that model service delivery