Benthic Mapping Research Articles

Patterns of scale-dependency and the influence of map resolution on the seascape ecology of reef fish

Detection and perception of ecological relationships between biota and their surround- ing habitats is sensitive to analysis scale and resolution of habitat data. We measured strength of uni- variate linear correlations between reef fish and seascape variables at multiple spatial scales (25 to 800 m). Correlation strength was used to identify the scale that best associates fish to their surround- ing habitat. To evaluate the influence of map resolution, seascape variables were calculated based on 4 separate benthic maps produced using 2 levels of spatial and thematic resolution, respectively. Indi- vidual seascape variables explained only 25% of the variability in fish distributions. Length of reef edge was correlated with more aspects of the fish assemblage than other features. Area of seagrass and bare sand correlated with distribution of many fish, not just obligate users. No fish variables cor- related with habitat diversity. Individual fish species achieved a wider range of correlations than mobility guilds or the entire fish assemblage. Scales of peak correlation were the same for juveniles and adults in a majority of comparisons. Highly mobile species exhibited broader scales of peak cor- relation than either resident or moderately mobile fish. Use of different input maps changed percep- tion of the strength and even the scale of peak correlations for many comparisons involving hard bot- tom edge length and area of sand, whereas results were consistent regardless of map type for comparisons involving area of seagrass and habitat diversity.

Integrating Quickbird Multi-Spectral Satellite and Field Data: Mapping Bathymetry, Seagrass Cover, Seagrass Species and Change in Moreton Bay, Australia in 2004 and 2007

Shallow coastal ecosystems are the interface between the terrestrial and marine environment. The physical and biological composition and distribution of benthic habitats within these ecosystems determines their contribution to ecosystem services and biodiversity as well as their connections to neighbouring terrestrial and marine ecosystem processes. The capacity to accurately and consistently map and monitor these benthic habitats is critical to developing and implementing management applications. This paper presents a method for integrating field survey data and high spatial resolution, multi-spectral satellite image data to map bathymetry and seagrass in shallow coastal waters. Using Quickbird 2 satellite images from 2004 and 2007, acoustic field survey data were used to map bathymetry using a linear and ratio algorithm method; benthic survey field data were used to calibrate and validate classifications of seagrass percentage cover and seagrass species composition; and a change detection analysis of seagrass cover was performed. The bathymetry mapping showed that only the linear algorithm could effectively and accurately predict water depth; overall benthic map accuracies ranged from 57–95%; and the change detection produced a reliable change map and showed a net decrease in seagrass cover levels, but the majority of the study area showed no change in seagrass cover level. This study demonstrates that multiple spatial products (bathymetry, seagrass and change maps) can be produced from single satellite images and a concurrent field survey dataset. Moreover, the products were produced at higher spatial resolution and accuracy levels than previous studies in Moreton Bay. The methods are developed from previous work in the study area and are continuing to be implemented, as well as being developed to be repeatable in similar shallow coastal water environments.

Inter-nesting habitat-use patterns of loggerhead sea turtles: enhancing satellite tracking with benthic mapping

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 11:77-90 (2010) - DOI: https://doi.org/10.3354/ab00296 Inter-nesting habitat-use patterns of loggerhead sea turtles: enhancing satellite tracking with benthic mapping Kristen M. Hart1,*, David G. Zawada2, Ikuko Fujisaki3, Barbara H. Lidz2 1US Geological Survey, Southeast Ecological Science Center, Davie, Florida 33314, USA 2US Geological Survey, St. Petersburg Coastal and Marine Science Center, St. Petersburg, Florida 33701, USA 3University of Florida, Ft. Lauderdale Research and Education Center, Davie, Florida 33314, USA *Email: kristen_hart@usgs.gov ABSTRACT: The loggerhead sea turtle Caretta caretta faces declining nest numbers and bycatches from commercial longline fishing in the southeastern USA. Understanding spatial and temporal habitat-use patterns of these turtles, especially reproductive females in the neritic zone, is critical for guiding management decisions. To assess marine turtle habitat use within the Dry Tortugas National Park (DRTO), we used satellite telemetry to identify core-use areas for 7 loggerhead females inter-nesting and tracked in 2008 and 2009. This effort represents the first tracking of DRTO loggerheads, a distinct subpopulation that is 1 of 7 recently proposed for upgrading from threatened to endangered under the US Endangered Species Act. We also used a rapid, high-resolution, digital imaging system to map benthic habitats in turtle core-use areas (i.e. 50% kernel density zones). Loggerhead females were seasonal residents of DRTO for 19 to 51 d, and individual inter-nesting habitats were located within 1.9 km (2008) and 2.3 km (2009) of the nesting beach and tagging site. The core area common to all tagged turtles was 4.2 km2 in size and spanned a depth range of 7.6 to 11.5 m. Mapping results revealed the diversity and distributions of benthic cover available in the core-use area, as well as a heavily used corridor to/from the nesting beach. This combined tagging-mapping approach shows potential for planning and improving the effectiveness of marine protected areas and for developing spatially explicit conservation plans. KEY WORDS: Dry Tortugas · Caretta caretta · Marine protected area · MPA · Marine spatial planning · Satellite telemetry · Benthic cover · Habitat mapping · Fixed-kernel density estimator Full text in pdf format PreviousNextCite this article as: Hart KM, Zawada DG, Fujisaki I, Lidz BH (2010) Inter-nesting habitat-use patterns of loggerhead sea turtles: enhancing satellite tracking with benthic mapping. Aquat Biol 11:77-90. https://doi.org/10.3354/ab00296Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 11, No. 1. Online publication date: November 16, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Remote sensing with SPOT-4 for mapping kelp forests in turbid waters on the south European Atlantic shelf

Remote sensing has become an increasingly used technique for the thematic mapping of large marine areas. In recent years, many researchers have successfully applied these techniques in different places for benthic mapping in clear waters; however, areas with turbid waters present important limitations that are gradually being solved by recent technological advances. In this context, the main objective of the present study is to develop and validate a methodology for mapping intertidal and subtidal kelp forests in the Galician coast (NW Spain), based on images from SPOT-4 (Satellite Pour l’Observation de la Terre). Three analysis methods have been applied: visual analysis and interpretation, unsupervised classification (cluster) and supervised classification (angular classification and maximum likelihood classification). Classification percentages higher than 70% in all substrates were obtained both using visual analysis and interpretation and maximum likelihood classification.

Why Afro-Siberian Red KnotsCalidris Canutus Canutushave Stopped Staging in the Western Dutch Wadden Sea During Southward Migration

Afro-Siberian Red Knots Calidris canutus canutus use the western Dutch Wadden Sea as a refuelling area during southward migration from Taimyr to West Africa. Here we document the decline of their food stocks in this area, based on a yearly large-scale benthic mapping effort, from 1996 to 2005. For each benthic sampling position, intake rate (mg/s, ash-free dry mass) was predicted by an optimal diet model based on digestive rate maximization. Over the ten years, when accounting for a threshold value to meet energetic fuelling demands, subspecies canutus lost 86% of its suitable foraging area. Over this period, the proportion of probable canutus in mist-net catches in July—August declined relative to overwintering islandica Knots. This suggests that canutus dropped even more in numbers than islandica, for which we showed earlier a food-explained decline in numbers. We discuss the possible causality between a decline in the quality of intertidal mudflats in the Dutch Wadden Sea and population declines of Knots in the West-African wintering quarters.

Comparison of methods for integrating biological and physical data for marine habitat mapping and classification

An important first step in marine spatial planning and ecosystem-based management efforts is the creation of benthic habitat maps that allow scientists and managers to understand the distribution of living and non-living resources on the seafloor. However, the location of boundaries between and composition of habitats is highly dependent on the approach taken to integrate abiotic and biotic information. The purpose of this study was to test “top-down” and “bottom-up” approaches for integrating physical and biological data derived from commonly used sub-tidal benthic mapping tools to create a habitat map compatible with the US Coastal and Marine Ecological Classification Standard (CMECS). We found that a top-down framework, where we tested for differences in macrofauna assemblages among side scan sonar facies, defined two broad-scale and general habitats. Using the bottom-up approach, where patterns in abiotic and biotic variables were examined with multivariate statistics (BEST, LINKTREE, ANOSIM, SIMPER), we generated seven biotopes based on the macrofauna abundance, percent sand, water depth, and backscatter standard deviation that corresponded well to, but provided more fine-scale detail than the top-down habitats. We were able to use the statistical relationship between abiotic variables and macrofauna assemblages in the LINKTREE to predict the spatial distribution of assemblages over ∼50% of the study area. We created a local catalogue of biotopes specific to our study area that contributes to the CMECS library. In addition, we were able to fully map CMECS Geoform, Surface Geology, and Biotic Cover Components. This mapping effort represented real progress toward reconciling the “data density mismatch” between physical and biological mapping methods, and it provided further evidence that using a bottom-up methodology preserves species–environment relationships.

Objective stratification and sampling-effort allocation of ground-truthing in benthic-mapping surveys

Abstract Clements, A. J., Strong, J. A., Flanagan, C., and Service, M. 2010. Objective stratification and sampling-effort allocation of ground-truthing in benthic-mapping surveys. – ICES Journal of Marine Science, 67: 628–637. The application of statistical procedures for objective stratification of sampling effort during map ground-truthing is presented. Marine benthic mapping is usually undertaken in two stages: a remotely sensed acoustic survey followed by ground-truthing to confirm ground-type and habitat classification. The objective of this study was to assess the application of optimum allocation analysis (OAA) through the use of remotely sensed data to direct expensive ground-truthing sampling effort. At an offshore site in the Irish Sea, classification of remotely sensed data, namely bathymetry and slope angle, generated six predicted ground-types. Calculated data variances within each ground-type were assumed to be a predictor of substratum heterogeneity, and these were used in an OAA to apportion ground-truthing effort objectively within each ground-type in order to achieve a set level of sampling precision. The sampling effort recommended by the OAA was realistic and practical with regard to video footage, but the collection of grabs was limited by resource constraints. The coefficient of variation (CV) of the video ground-truthing data matched that estimated by OAA, but the inability to collect all the recommended grabs resulted in CVs greater than expected for sediment grain-size parameters. The efficient identification of substratum classes using OAA represents a first stage whereby this method could direct ground-truthing that could ultimately be used for habitat mapping.

Relationships among map resolution, fish assemblages, and habitat variables in a coral reef ecosystem

Benthic maps are broad-scale characterizations that lack the detailed environmental attributes which have been the focus of most prior empirical studies linking reef fish and habitat. We used multivariate analyses to quantify correlations among fish assemblages, local habitat variables, and reef types depicted in benthic maps. Benthic maps of a study system in the U.S. Virgin Islands with high (100 m2 minimum mapping unit) and low (4,048 m2 minimum mapping unit) spatial resolution, respectively, were evaluated. Benthic maps depicted six reef types and two shelf positions (lagoon vs. shelf). Fish assemblages and local environmental variables were quantified at random sites throughout the landscape by diver surveys. Multivariate ordination based on either fish assemblages or environmental data did not result in well-separated groups of sites. Mapped reef types were not associated with distinct values of either local environmental variables or fish assemblages. Reef types exhibited substantial overlap in ordination plots based on benthic characteristics with groupings based on fish assemblages showing even greater overlap. Ordination patterns involving reef type were largely the same for both low- and high-resolution maps. In contrast, sites showed clear groups for lagoon and shelf in ordinations based on both environmental variables and fish assemblage composition, respectively. These results suggest that knowledge of the overall fish assemblage or fine-scale environmental characteristics could not be used to predict reef type depicted in benthic maps or vice versa. In contrast, reef zone could be used to predict fish assemblage or fine-scale environmental variables and vice versa.

Landscape‐scale experiment demonstrates that Wadden Sea intertidal flats are used to capacity by molluscivore migrant shorebirds

1. Whether intertidal areas are used to capacity by shorebirds can best be answered by large-scale manipulation of foraging areas. The recent overexploitation of benthic resources in the western Dutch Wadden Sea offers such an 'experimental' setting. 2. We review the effects of declining food abundances on red knot Calidris canutus islandica numbers, based on a yearly large-scale benthic mapping effort, long-term colour-ringing and regular bird-counts from 1996 to 2005. We focus on the three-way relationships between suitable foraging area, the spatial predictability of food and red knot survival. 3. For each benthic sampling position, red knot intake rate (mg AFDM s(-1)) was predicted by a multiple prey species functional response model, based on digestive rate maximization (this model explained diet and intake rate in earlier studies on red knots). This enabled us to derive the spatial distribution of the suitable foraging area, which in each of the 10 years was analysed with a measure of autocorrelation, i.e. Moran's I. 4. Over the 10 years, when accounting for a threshold value to meet energetic demands, red knots lost 55% of their suitable foraging area. This ran parallel to a decrease in red knot numbers by 42%. Although there was also a decrease in patchiness (i.e. less information about the location of the suitable feeding sites), this did not yet lead to additional loss of birds. 5. To cope with these landscape-scale declines in food stocks, an increase in the capacity for instantaneous food processing would be required. Although we show that red knots indeed enlarged their muscular gizzards, the increase in gizzard size was not enough to compensate for the decreased feeding area. 6. Survival of islandica knots in the western Dutch Wadden Sea, based on colour-ring resightings, declined from 89% in the first half of our study period to 82% in the second half of our study period and could account for almost half of the decline in red knot numbers; the rest must have moved elsewhere in winter. 7. Densities of red knots per unit suitable foraging area remained constant at 10 knots ha(-1) between 1996 and 2005, which suggests that red knots have been using the Dutch Wadden Sea to full capacity.

Mapping of coral reefs using hyperspectral CASI data; a case study: Fordata, Tanimbar, Indonesia

Airborne remote sensing with a CASI‐550 sensor has been used to map the benthic coverage and the bottom topography of the Pulau Nukaha coral reef located in the Tanimbar Archipelago (Southeast Moluccas, Eastern Indonesia). The image classification method adopted was performed in three steps. Firstly, five geomorphological reef components were identified using a supervised spectral angle mapping algorithm in combination with data collected during the field survey, i.e. benthic cover type, percentage cover and depth. Secondly, benthic cover mapping was performed for each of the five geomorphological components separately using an unsupervised hierarchical clustering algorithm followed by class aggregation using both spectral and spatial information. Finally, 16 benthic cover classes could be labelled using the benthic cover data collected during the field survey. The overall classification accuracy, calculated on the biological diverse fore reef, was 73% with a kappa coefficient of 0.63. A reliable bathymetric model (up to a depth of 15 m) of the Pulau Nukaha reef was also obtained using a semi‐analytical radiative transfer model. When compared with independent in‐situ depth measurements, the result proved relatively accurate (mean residual error: −0.9 m) and was consistent with the seabed topography (Pearson correlation coefficient: 86%).

Improving Coral Reef Habitat Mapping of the Puerto Rico Insular Shelf Using Side Scan Sonar

Use of high resolution (0.1m) side-scan sonar for generating detailed benthic maps (4 m2 mapping unit) in coral reef environments was investigated by collecting imagery over 60 km2 of the Puerto Rico insular shelf, from shoreline to shelfedge. Visual interpretation of acoustic imagery resulted in 21 different habitat types classified within broad categories of unconsolidated sediment (7), consolidated bottom (6), and vegetated areas (8). Detailed maps showed the amount, size, and spatial distribution of habitats across the shelf. Qualitative and quantitative benthic characterizations showed habitats to be biologically distinct and ecologically relevant at multiple scales. Image collection was cost effective and amenable to small-boat use.

The effects of minimum map unit in coral reefs maps generated from high resolution side scan sonar mosaics

Changes in coral habitats from benthic maps at two minimum mapping units (4 and 400 m2) were examined across 600 ha at the Puerto Rico insular shelf. The maps were produced by visually interpreting high resolution side scan sonar seafloor mosaics. Comparisons were performed by using published spatial indices based on patch size and abundance. At the fine scale, small coral patches were dominant and had more complex shapes, while coarse scale maps lost information on small or rare habitats, but included new mixed habitat categories that helped conserve estimates of total habitat area. Variations in spatial indices occurred across spatial scales, but trends were not necessarily predictable. For instance, habitat diversity increased at the coarse scale maps, but habitat richness remained unchanged. Differences were related as much to the peculiarities of the abundance, shape and arrangement of habitats at the two sites as to changes in grain size.

Dynamics of a subtropical seagrass landscape: links between disturbance and mobile seed banks

Disturbance is a well known modifier of landscapes. In marine systems hurricanes may not only remove or bury subtidal seagrasses but they may also impact the seed banks of these taxa. We ask whether seagrass landscape pattern and seed dispersal are influenced by physical disturbance in a subtropical deep water setting. We examined the spatial dynamics of an offshore landscape composed of the seagrass, Halophila decipiens in summer 1999 and again in 2000 after the passage of a hurricane. A towed video camera was used to collect data within a 1 km2 area and construct benthic maps of seagrass, macroalgae, hard bottom outcrops, and sediments from over 20,000 video frames. The appearance of sand and seagrass at a portion of the site in summer 2000 that was previously hard substrate verified sediment and seed movement. Although seeds released by this seagrass are deposited into sediments near parent plants, movement en masse of the seagrass seed reservoir appears to be an important component of dispersal. The generation of new landscape patches when disturbance is large and intense suggests that large-scale disturbance, resulting in the local redistribution of sediment and the seed bank, appears to mold the spatial signature of the resulting seagrass landscape in a MidShelf area. This impact of physical disturbance differs from that previously reported for factors influencing spatial arrangements of seagrass in shallow waters but has some features similar to those of large infrequent disturbances studied in terrestrial settings.

Evaluation of spatial correlation between nutrient exchange rates and benthic biota in a reef-flat ecosystem by GIS-assisted flow-tracking

A Geographic Information System (GIS)-aided flow-tracking technique was adopted to investigate nutrient exchange rates between specific benthic communities and overlying seawater in a fringing reef of Ishigaki Island, subtropical Northwestern Pacific. Net exchange rates of NO3−, NO2−, NH4+, PO43−, Total-N and Total-P were estimated from concentration changes along the drogue trajectories, each of which was tracked by the Global Positioning System and plotted on a benthic map to determine the types of benthic habitat over which the drogue had passed. The observed nutrient exchange rates were compared between 5 typical benthic zones (branched-coral (B) and Heliopora communities (H), seaweed-reefrock zone (W), bare sand area (S), and seagrass meadow (G)). The dependence of nutrient exchange rates on nutrient concentrations, physical conditions and benthic characteristics was analyzed by multiple regression analysis with the aid of GIS. The spatial correlation between nutrient exchange rates and benthic characteristics was confirmed, especially for NO3− and PO43−, which were usually absorbed in hydrographically upstream zones B and W and regenerated in downstream zones H and G. NO3− uptake in zones B and W was concentration-dependent, and the uptake rate coefficient was estimated to be 0.58 and 0.67 m h−1, respectively. Both nutrient uptake in zone W and regeneration in zone H were enhanced in summer. The net regeneration ratio of NO3−/PO43− in zone H in summer ranged 5.2 to 34 (mean, 17.4), which was somewhat higher than previously measured NO3−/PO43− for sediment pore waters around this zone (1.1–8.5). Nutrient exchanges in zone S were relatively small, indicating semi-closed nutrient cycling at the sediment-water interface of this zone. NH4+ efflux from sediments was suggested in zone G. The data suggest that the spatial pattern of nutrient dynamics over the reef flat community was constrained by zonation of benthic biota, and that abiotic factors such as nutrient concentrations and flow rates, influenced nutrient exchange rates only in absorption-dominated communities such as zones B and W.

Regional patterns and local variations of sediment distribution in the Hudson River Estuary

The Hudson River Benthic Mapping Project, funded by the New York State Department of Environmental Conservation, resulted in a comprehensive data set consisting of high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom data, as well as over 400 sediment cores and 600 grab samples. This detailed data set made it possible to study the regional pattern and the local variations of the sediment distribution in the Hudson River Estuary. Based on these data we describe the distribution of sediment texture and process-related sedimentary environments for the whole 240-km long estuary together with along-river variations of depth, cross-sectional area, and grain size distribution. We compare these parameters with changes in surrounding geology and tributary input and, as a result, divide the Hudson River Estuary in eight sections with distinct combinations of channel morphology, bedrock type, sediment texture, and sediment dynamics. The regional sediment distribution consists of marine sand-dominated sediments near the ocean end of the estuary, a large, mud-dominated central section, and fluvial sand-dominated sediments in the freshwater section of the Hudson River Estuary. This regional trend is highly modified by small-scale variations in the sediment distribution. These local variations are controlled by changes in morphology, bedrock, and tributary input, as well as by anthropogenic modifications of the estuary. In some areas these local variations are larger than the overall trend in sediment distribution and control the actual sediment type, as well as the condition of erosion and deposition in the estuary.

Benthic mapping using local aerial photo interpretation and resident taxa inventories for designing marine protected areas

Given the frequent socioeconomic, political and concomitant ecological failures of science-driven marine protected area (MPA) programmes, it is now important to design MPAs by integrating natural and social science research more comprehensively. This study shows how indigenous peoples assisted in the design of MPAs by identifying marine substrates and related resident taxa on aerial photos, information which was then incorporated into a geographical information system (GIS) database, along with dive survey data. Two questions were asked: (1) Is indigenous ecological knowledge accurate enough for mapping the benthos and associated taxa? (2) Is such an approach an appropriate way for assisting in the biological and social design of MPAs in Oceania? Conventional quadrat field dive surveys were used to measure the accuracy of substrate identification by local informants and a visual survey was used to test hypotheses formulated from local knowledge regarding the spatial distribution and relative abundance of non-cryptic species within certain benthic habitats. Equivalence rates between indigenous aerial photo interpretations of dominant benthic substrates and in situ dive surveys were 75–85% for a moderately detailed classification scheme of the benthos, which included nine locally-defined abiotic and biotic benthic classes for the MPA seabed. Similarly, the taxa inventory showed a strong correspondence between the qualitative predictions of local fisherfolk and the quantitative analysis of non-cryptic species distribution, including their relative abundance and geophysical locations. Indigenous people's predictions about the presence or absence of fish in different benthic habitats corresponded 77% and 92% of the time (depending on scoring schema) with in situ visual measurements. These results demonstrate how incorporating local knowledge of benthic heterogeneity, existing biological communities, and particular spatio-temporal events of biological significance into a GIS database can corroborate the production of scientifically reliable base resource maps for designing MPAs in an environmentally and culturally sound fashion. This participatory approach was used to design and then establish MPAs in the Roviana and Vonavona region of the Western Solomon Islands. Under appropriate conditions, interdisciplinary work can complement the design of scientific fishery management and biodiversity conservation prescriptions for coastal Oceania.

An alternative approach for managing scuba diving in small marine protected areas

1. As the interest of divers in exploring marine protected areas grows, so does their impact on sensitive marine organisms and communities. This situation has led managers to adopt a variety of measures to manage scuba diving in marine reserves. However, if marine areas need to be managed and protected from the adverse effects of human activities, then the characterization of marine habitats and the communities they contain, along with the potential effects of scuba diving, will need to be evaluated on scientific lines. 2. To this end, the use of benthic mapping, together with an evaluation of community vulnerability, constitutes a complementary tool for managing scuba diving, as is demonstrated in the present study. 3. The identification and evaluation of the different communities observed in Cabo de Palos-Islas Hormigas Marine Reserve enables managers to propose different measures for controlling potential diver impact and also for evaluating the effects of these measures, thus reducing the degradation of the benthic organisms and communities, benefiting the local tourism industry and allowing a more sustainable use of the marine reserve resources. Copyright © 2006 John Wiley & Sons, Ltd.

Benthic Mapping Using Sonar, Video Transects, and an Innovative Approach to Accuracy Assessment: A Characterization of Bottom Features in the Georgia Bight

Benthic maps provide the spatial framework for many science and management activities in coastal areas such as identification and protection of fish distributions and associated habitat as well as for monitoring changes in benthos and fish communities. To meet this need at Gray's Reef National Marine Sanctuary off the Georgia, U.S.A., coast, we created fine-scale benthic maps by visual interpretation of sonar imagery within a geographic information system. The major bottom types in the sanctuary—flat sand, rippled sand, hard bottom that is sparsely colonized with sessile invertebrates, and densely colonized hard bottom—were delineated through combined analysis of backscatter from side-scan sonar, bathymetry from multibeam sonar, scuba surveys, and video transects. Maps showed that unconsolidated sediments cover 75% of the bottom of this region; 8% occurs as flat sand plains with obvious burrowing and reworking of surface material by mobile benthic invertebrates, whereas 67% occurs as rippled sand without such fauna. The rest of the sanctuary consists of limestone bottom in two types of formations; either flat, sparsely colonized regions (25% of the sanctuary's total area) or as vertical ledges that are densely colonized with a diverse fauna of sessile invertebrates (<1%). Despite their limited area, these 0.5–2-m-tall ledge features harbor the majority of the sanctuary's biodiversity and biomass of both sessile invertebrates as well as ichthyofauna. A modified accuracy assessment procedure was used to account for spatial autocorrelation in the validation data and to separate thematic from positional accuracy. Overall thematic accuracy of maps is 95% for those areas of the map in which thematic accuracy and positional accuracy could be separated (87% of the mapped area). This fine-scale characterization provides a benthic inventory for a marine sanctuary and novel methods for mapping using sonar and accuracy assessment using transects.

A new synthetic index and a protocol for monitoring the status ofPosidonia oceanica meadows: a case study at Sanremo (Ligurian Sea, NW Mediterranean)

1. The status of a Posidonia oceanica meadow in front of the town of Sanremo, Italy, was studied through a combined use of benthic mapping and synthetic indices. 2. Mapping was accomplished by integrating side scan sonar imagery and data collected by scuba diving along transects placed perpendicularly to the coastline. A thematic map (scale 1:5000) was produced. Extent of the meadow, occurrence of dead matte areas, and morphology of the lower limit (with new definition) are all described. 3. Two synthetic environmental indices were applied to transect data in order to quantify the status of the meadow: the Conservation Index and the Substitution Index. The former is related to the proportion of dead matte; the latter is a novel index measuring the amount of replacement of the ‘constructional’ seagrass P. oceanica by the ‘non-constructional’ seagrass Cymodocea nodosa. The potential of a ‘phase shift’ in Ligurian Sea seagrass meadows is discussed. 4. The approach here proposed, based on detailed mapping plus synthetic indices, may provide immediate information to evaluate the state of Mediterranean Posidonia oceanica for monitoring and management. Copyright © 2006 John Wiley & Sons, Ltd.

Process-related classification of acoustic data from the Hudson River Estuary

Acoustic surveying provides valuable information on the distribution of sedimentary environments in subaqueous settings. Frequently, differences in acoustic backscatter strength are used to distinguish sedimentary environments on the basis of their grain size composition. Here, we are presenting acoustic backscatter data from the Haverstraw Bay section of the Hudson River Estuary that has been mapped using sidescan, sub-bottom profiling, and multibeam bathymetry as part of the Benthic Mapping Project of the Hudson River Estuary Program, funded by New York State. In addition, hundreds of gravity cores, and grab samples provide ground truth for a classification of the river bottom into discrete substrate types. Analyses of sedimentary environments reveal patterns in backscatter strength beyond those that can be related to the sediment grain size distribution alone. An integrated interpretation of sidescan, sub-bottom profiling, and high-resolution bathymetry data indicates that the backscatter pattern can be attributed to spatial variations in the modern depositional environments which cause differences in bottom roughness and sediment compaction. Based on an integrated interpretation of the acoustic and sample data sets, we distinguished eight different sedimentary classes. Many of the classes can be linked to dynamic processes including contemporary deposition, erosion, and sediment migration in sand waves. The results provide a better understanding of the dynamic processes of the Hudson River Estuary and improve the interpretation of the acoustic backscatter data from fine grained sedimentary environments.