Jennifer K. Greene

A NEW IN SITU METHOD FOR MEASURING SESTON UPTAKE BY SUSPENSION-FEEDING BIVALVE MOLLUSCS

Abstract The most commonly used methods for measuring the amount of seston removed from the water column (uptake) by populations of suspension-feeding bivalve molluscs involve taking discrete water samples followed by laboratory analyses. Here we describe a new method based on in situ fluorometry that provides rapid measurement of seston removal rates. The new system is comprised of two identical units, each consisting of an in situ fluorometer, data logger and peristaltic pump with plastic tube attached to a deployment device. The deployment device allows precise placement of the fluorometer probe and intake end of the plastic tube so that in situ fluorescence (chlorophyll a) can be measured and water can be sampled for seston analyses in the laboratory from the same height. The typical setup involves placing one unit upstream and the other downstream of the study area and sampling the water at periodic intervals. Changes in seston concentration are revealed in the field by the fluorometers, and the sampled water can be analyzed in the laboratory for various seston parameters. Comparisons of the in situ data with data from laboratory analyses of pumped water samples were made for three species at four study sites: the eastern oyster (Crassostrea virginica), hard clam (Mercenaria mercenaria), and blue mussel (Mytilus edulis). Comparisons of measured upstream versus downstream seston concentrations indicated significant (t-tests, P < 0.05) differences (uptake) for six of eight trials based on in situ fluorometry, but only marginally significant (P < 0.10) differences at two of the four trials using laboratory chlorophyll a measurements. These data demonstrate that compared with sampling methods requiring laboratory analyses, the new in situ method provides much more rapid quantitative assessments and may provide more accurate estimates.

Bottom Habitat Mapping Using Towed Underwater Videography: Subtidal Oyster Reefs as an Example Application

Abstract Towed underwater video has become a widely used method for bottom habitat mapping in coastal waters, but very little has been published on this relatively new and effective approach. We use a case study on two oyster reefs to illustrate the pros and cons of towed video, visualization techniques, and future research topics. Towed video is deployed in similar fashion to single-beam sonars, yielding narrow swaths of video imagery that are recorded concurrently with global positioning system (GPS) data for georeferencing. The major advantages over acoustic (sonar) methods are that image processing and interpretation are relatively simple, and there is little or no need for subsequent ground-truthing. The system used in the present study consists of an underwater black and white camera mounted on a steel frame, differential GPS unit, and digital video camera for recording. It was assembled from off-the-shelf items, and total cost was approximately

The Effects of Sub-Regional Climate Velocity on the Distribution and Spatial Extent of Marine Species Assemblages

3500 (2006 US

Restoring Ecological Functions and Increasing Community Awareness of an Urban Tidal Pond Using Blue Mussels

). The imagery from both study reefs was of sufficient quality to allow classification of the surveyed bottom into three categories: nonreef, low-density shell, and high-density shell. Some reef characteristics such as the amount of vertical relief were easily discernable and showed substantial differences between the two reefs. Reef bottom areal coverages determined from the video imagery compared well with recent previous studies on the two reefs using other methods. Water clarity limitations represent the major obstacle to widespread use of video for routine mapping of oyster reefs. Turbidity–image quality relations remain to be quantified.

Long-term seafloor monitoring at an open ocean aquaculture site in the western Gulf of Maine, USA: development of an adaptive protocol.

Many studies illustrate variable patterns in individual species distribution shifts in response to changing temperature. However, an assemblage, a group of species that shares a common environmental niche, will likely exhibit similar responses to climate changes, and these community-level responses may have significant implications for ecosystem function. Therefore, we examine the relationship between observed shifts of species in assemblages and regional climate velocity (i.e., the rate and direction of change of temperature isotherms). The assemblages are defined in two sub-regions of the U.S. Northeast Shelf that have heterogeneous oceanography and bathymetry using four decades of bottom trawl survey data and we explore temporal changes in distribution, spatial range extent, thermal habitat area, and biomass, within assemblages. These sub-regional analyses allow the dissection of the relative roles of regional climate velocity and local physiography in shaping observed distribution shifts. We find that assemblages of species associated with shallower, warmer waters tend to shift west-southwest and to shallower waters over time, possibly towards cooler temperatures in the semi-enclosed Gulf of Maine, while species assemblages associated with relatively cooler and deeper waters shift deeper, but with little latitudinal change. Conversely, species assemblages associated with warmer and shallower water on the broad, shallow continental shelf from the Mid-Atlantic Bight to Georges Bank shift strongly northeast along latitudinal gradients with little change in depth. Shifts in depth among the southern species associated with deeper and cooler waters are more variable, although predominantly shifts are toward deeper waters. In addition, spatial expansion and contraction of species assemblages in each region corresponds to the area of suitable thermal habitat, but is inversely related to assemblage biomass. This suggests that assemblage distribution shifts in conjunction with expansion or contraction of thermal habitat acts to compress or stretch marine species assemblages, which may respectively amplify or dilute species interactions to an extent that is rarely considered. Overall, regional differences in climate change effects on the movement and extent of species assemblages hold important implications for management, mitigation, and adaptation on the U.S. Northeast Shelf.

Seston Removal by Natural and Constructed Intertidal Eastern Oyster (Crassostrea virginica) Reefs: A Comparison with Previous Laboratory Studies, and the Value of in situ Methods

Blue mussels (Mytilus edulis) were transplanted into South Mill Pond, a degraded tidal salt pond in Portsmouth NH. As part of a larger community-based project volunteers helped create three mussel reefs in each of two locations within the pond in May 2001. Restoration project methodology and success were evaluated during the summer of 2001 and again in May 2002 by 1) assessing reef population dynamics (size frequency distribution, density, and movement) and 2) comparing faunal utilization (finfish species and abundance) within the reefs to that in adjacent reference areas. Created reefs showed declines in density after the first month but then increased and showed new recruitment the following year. Reef footprints were dynamic and probably influenced by mussel density as well as local hydrology. Four finfish species were observed: Atlantic silverside (Menidia menidia), mummichog (Fundulus heteroclitus), four-spined stickleback (Apeltes quadracus), and three-spined stickleback (Gasterosteus aculeatus). The most common fish in reef and reference areas (silverside and mummichog, respectively) are highly mobile species. Reef areas had greater species diversity per sampling effort than reference areas, but no difference in overall fish abundance was found between adjacent reef and reference areas. Information collected to date indicates that mussel reefs constructed at the pond appear to be functioning as a natural system, acting to improve water quality and provide shelter for small fish and other nektonic and epibenthic invertebrates. In addition, volunteer action garnered city involvement and increased local awareness of the pond as an ecosystem rather than a sewage lagoon. Community awareness along with habitat improvements will increase the long-term prospects for rehabilitation of South Mill Pond.

Successional development of fouling communities on open ocean aquaculture fish cages in the western Gulf of Maine, USA

The seafloor at an open ocean finfish aquaculture facility in the western Gulf of Maine, USA was monitored from 1999 to 2008 by sampling sites inside a predicted impact area modeled by oceanographic conditions and fecal and food settling characteristics, and nearby reference sites. Univariate and multivariate analyses of benthic community measures from box core samples indicated minimal or no significant differences between impact and reference areas. These findings resulted in development of an adaptive monitoring protocol involving initial low-cost methods that required more intensive and costly efforts only when negative impacts were initially indicated. The continued growth of marine aquaculture is dependent on further development of farming methods that minimize negative environmental impacts, as well as effective monitoring protocols. Adaptive monitoring protocols, such as the one described herein, coupled with mathematical modeling approaches, have the potential to provide effective protection of the environment while minimize monitoring effort and costs.