Seascape Scale Research Articles

Depth and structure as environmental drivers of fish communities across a shallow to mesophotic gradient in the northern US Virgin Islands

The factors that drive fish communities on coral reefs are varied, complex, and often location specific. In the northern United States Virgin Islands, the large areas of mesophotic coral ecosystems across an insular shelf provide a multitude of gradients along which fish communities form. Using a stratified-random visual fish census, we collected comprehensive data on fish communities across a seascape scale. Fish density and diversity showed responses to depth and hard relief, with these factors occasionally interacting in ways that are species specific. Analysis of trophic groups showed that densities of all groups were positively associated with relief, but while herbivores and invertivores decreased with depth, planktivores and piscivores increased, and piscivores additionally showed an interaction. Some commercially important species occurred more frequently and in larger sizes on deeper reefs, suggesting that mesophotic reefs shelter more fisheries resources, although they are less commonly sampled in visual census programs. Understanding how fish communities change across the seascape informs patterns of ecosystem function, such as identifying areas of resilience and vulnerability. This dataset is a valuable contribution to more completely understanding the ecology and conservation of fishes in the western Atlantic.

Decades of eelgrass meadow dynamics across the northeast Pacific support seascape-scale conservation

Abstract Eelgrass meadows provide vital nearshore habitats and ecosystem services, but they have declined from human stressors and conservation efforts are now widespread. Dynamic ecosystems like eelgrass meadows naturally rearrange as disturbance and recruitment unfold across seascapes. However, some decisions that protect eelgrass only consider extant meadows, thus ignoring the potential for change. Here, we report decades of eelgrass dynamics observed across the northeast Pacific. Our observations support conservation expanded to the seascape scale, which includes potentially inhabitable areas along with extant meadows. We found that total seascape meadow area changed over time, and changes within seascapes were often asynchronous. Some meadows rearranged across seascapes over multiple kilometres and decades. Also, some seascapes compartmentalized meadow collapse, which enabled later recovery, or supported local recruitment that substantially increased total meadow area. These observations were consistent with hierarchical patch dynamics, which promote ecosystem persistence over larger space and time scales. Thus, to enable the dynamics that underpin eelgrass persistence, it is necessary to keep many eelgrass habitat options open across seascapes, rather than protect only extant meadows. Given that dynamic, hierarchical ecosystems are common along marine shorelines, this approach may be effective for both nearshore ecosystems in general and for eelgrass in particular.

Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

Ocean acidification threatens many marine organisms, including oysters. Seagrass habitat has been suggested as a potential refuge for oysters because it may ameliorate stressful carbonate chemistry and augment food availability. We conducted an in situ study to investigate whether eelgrass Zostera marina habitat affects the growth of juvenile Pacific oysters Crassostrea gigas and influences local carbonate chemistry or food quantity at sites where we expected contrasting conditions in two US west coast estuaries. Juvenile oysters were out-planted in typical intertidal on-bottom (just above sediment) and off-bottom (45 cm above sediment) culture positions and in adjacent eelgrass and unvegetated habitats from June to September 2019. Water quality was measured with sondes for 24 h periods each month, and discrete water samples were collected in conjuncture. Results show that eelgrass habitat did not alter average local carbonate chemistry (pH, pCO2, Ωcalcite), but consistently reduced available food (relative chlorophyll a). Eelgrass habitat had little to no effect on the shell or tissue growth of juvenile oysters but may have influenced their energy allocation; oysters displayed a 16% higher ratio of shell to tissue growth in eelgrass compared to unvegetated habitat when cultured on-bottom. At the seascape scale, average site-level pH was negatively correlated with shell to tissue growth but not with shell growth alone. Overall, these findings suggest that juvenile oysters may display a compensatory response and allocate more energy to shell than tissue growth under stressful conditions like acidic water and/or altered food supply due to reduced immersion or eelgrass presence.

Influence of Rising Water Temperature on the Temperate Seagrass Species Eelgrass (Zostera marina L.) in the Northeast USA

Sea surface temperature (SST) has increased worldwide since the beginning of the 20th century, a trend which is expected to continue. Changes in SST can have significant impacts on marine biota, including population-level shifts and alterations in community structure and diversity, and changes in the timing of ecosystem events. Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems, where they provide many ecosystem services. Eelgrass, Zostera marina L., is the dominant seagrass species in the Northeast United States of America (USA). Multiple factors have been cited for losses in this region, including light reduction, eutrophication, and physical disturbance. Warming has the potential to exacerbate seagrass loss. Here, we investigate regional changes in eelgrass presence and abundance in relation to local water temperature using monitoring data from eight sites in the Northeastern USA (New Hampshire to Maryland) where a consistent monitoring protocol, SeagrassNet, has been applied. We use a hurdle model consisting of a generalized additive mixed model (GAMM) with binomial and beta response distributions for modeling eelgrass presence and abundance, respectively, in relation to the local summer average water temperature. We show that summer water temperature one year prior to monitoring is a significant predictor of eelgrass presence, but not abundance, on a regional scale. Above average summer temperatures correspond to a decrease in probability of eelgrass presence (and increased probability of eelgrass absence) the following year. Cooler than average temperatures in the preceding year, down to approximately 0.5°C below the site average, are associated with the highest predicted probability of eelgrass presence. Our findings suggest vulnerability in eelgrass meadows of the Northeast USA and emphasize the value of unified approaches to seagrass monitoring, conservation and management at the seascape scale.

Where the grass is greenest in seagrass seascapes depends on life history and simple species traits of fish

Tropical seagrass meadows are critical habitats for many fish species, yet few studies have investigated the influence of multiple scale-dependent factors and marine protected areas on seagrass fish species of differing life histories. We assessed the influence of fine-scale seagrass meadow characteristics and seascape-scale variables on the abundance of fish in a seagrass-dominated seascape in the Bazaruto Archipelago, Mozambique, particularly examining patterns of nursery- vs. resident species as well as mobile- vs. sedentary species. We found that fish distribution patterns in this seagrass-dominated seascape were dependent on species’ life history characteristics; nursery taxa showed lower abundance in seagrass meadows further from adult reef habitats, while resident species within seagrass meadows occurred in higher abundances far from reefs. For taxa utilizing both mangroves and seagrass meadows as nursery habitat, proximity to mangroves was an important factor. Fish abundances were generally influenced by variables at the seascape scale (km), while sedentary species were predominantly influenced by area variables, and smaller seascapes (<500 m in radius) better explained distribution patterns. The influence of marine protected areas was taxon-specific, with the strongest effects of protection on resident species. Our results indicate that protection efforts in seagrass-dominated seascapes can have varying impacts on fish distribution, depending on the life history of the species present, and the geographical placement of the reserve within the seascape. Further, we suggest that simple species attributes can be utilised to describe generalized abundance patterns of fish in seagrass seascapes.

Influence of Seascape on Coastal Lagoon Fisheries: the Role of Habitat Mosaic in the Venice Lagoon

Fisheries are a staple human activity supported by coastal lagoons. Together with water quality and trophic status, lagoon morphology is acknowledged as one of the main ecological drivers of fishery yields; however, the role of lagoon seascape structure is still poorly understood. This paper investigates how morphological variables, habitat distribution and seascape diversity and complexity affect yields of artisanal fishery performed with fyke nets in the Venice Lagoon (northern Adriatic Sea, Italy). Two spatial scales were considered in the analysis, with water quality parameters (temperature, salinity, dissolved oxygen, turbidity, water residence times, N, P and chlorophyll-a concentrations) being measured at a fine, fyke-net scale and morphological (average bottom elevation and sediment grain size) and habitat features (habitat proportion, diversity and complexity) being measured at a broader, seascape scale. Generalised linear mixed models were employed to model 8 years of nekton and green crab catches, disentangling the role of broad-scale morphology and seascape from that of fine-scale water quality. Broad-scale variables clearly influenced fishery target species. Among them, lagoon residents were associated with specific morphological and habitat characteristics, while marine migrants showed a stronger link with overall habitat diversity and complexity. This evidence emphasises how artisanal fishery in the Venice Lagoon relies on the conservation of morphological and habitat heterogeneity. Moreover, it highlights how habitat restoration performed at the seascape level should also be taken into account, in addition to controlling hydrology and water quality, when managing fishery resources in coastal lagoons.

3D Photogrammetry Modeling Highlights Efficient Reserve Effect Apparition After 5 Years and Stillness After 40 for Red Coral (Corallium rubrum) Conservation in French MPAs

Imaging the marine environment is more and more useful to understand relationships between species, as well as natural processes. Developing photogrammetry allowed the use of 3D measuring to study populations dynamics of sessile organisms at various scales: from colony to population. This study focuses on red coral (Corallium rubrum), as known as precious coral. Metrics measured at a colony scale (e.g., maximum height, diameter and number of branches) allowed population understanding and a comparison between an old (Cerbère-Banyuls reserve) vs. a new (Calanques National Park) MPA. Our results suggested a 5-year time step allows the appearance of a significant difference between populations inside vs. outside the Calanques National Park no-take zones. Red coral colonies were taller and had more branches inside no-take zones. A significant difference was still observable for the populations inside the Cerbère-Banyuls reserve after 40 years of protection, reflecting the sustainability and effectiveness of precautionary measures set by the reserve. The impacts at the local level (mechanical destruction) and those presumed to occur via global change (climatic variations) underline the need to develop strategies both to follow the evolutions of red coral populations but also to understand their resilience. Photogrammetry induced modeling is a time and cost effective as well as non-invasive method which could be used to understand population dynamics at a seascape scale on coralligenous reefs.

Mangrove-mudflat connectivity shapes benthic communities in a tropical intertidal system

Understanding the connectivity among seascape habitats is an important emerging topic in marine ecology and coastal management. Mangroves are known to provide many ecosystem services such as coastal protection and carbon cycling, but their functional relationships with adjacent benthic intertidal communities are less clear. We examined how spatial adjacency to mangroves affects macrobenthic communities of intertidal mudflats in a tropical estuarine ecosystem. In the Bijagós Archipelago, Guinea-Bissau, benthic macrofauna assemblages were compared among sampling locations with different connectivities between intertidal mudflats and mangrove stands. We explored how a single mangrove connectivity index (MCI), combining mangrove tidal basin size and the distance to the mangrove edge, affected macrobenthic composition, and compared this effect to sediment properties. In addition, we used structural equation modelling (SEM) and ordination to determine how different environmental predictors directly and indirectly affected macrobenthic communities. MCI strongly affected macrobenthic composition and species abundance, and SEM revealed that this effect contained both a direct component and an indirect component through mudflat NDVI (normalized difference vegetation index, an indicator for microphytobenthos). Sediment properties (grain size, organic matter) affected macrobenthos independently from MCI, nevertheless sediment properties were also affected by MCI. We show the importance of accounting for the seascape structure of tidal basins when investigating the connectivity between mangroves and macrobenthic communities of intertidal mudflats. As benthic macrofauna is a key food source for endangered fish and waders in these systems, our findings provide strong arguments for the integrative conservation of intertidal mudflats and mangroves at the seascape scale.

Intertidal mussel reefs change the composition and size distribution of diatoms in the biofilm

Migrating diatoms are microscopic ecosystem engineering organisms that have functional consequences on the seascape scale by significantly contributing to the microphytobenthos biofilm. The microphytobenthos biofilm is a thin photosynthesising layer that covers the sediment on intertidal flats. It fuels the food web, increases sediment stability, and enhances the deposition of particles, providing ecosystem services to coastal communities. Here we tested the effect of another ecosystem engineering habitat, intertidal blue mussel reefs, on the composition and properties of migrating diatom communities. Small-scale reefs constructed in the intertidal mimicked and reinforced the natural pattern in diatom community composition and function that we documented in the field. The field experiment adding small reefs to the intertidal ran from 30 April to 10 June 2015 and the field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489°, E 6.230°). Both the constructed small-scale reefs and the natural reef changed the community composition of diatoms in the biofilm by promoting higher numbers of smaller-sized cells and species. Small diatoms have higher growth and gross photosynthesis rates, indicating that this explains the higher production and chlorophyll-a concentration of the biofilm measured on natural intertidal shellfish reefs. Our results showed that shellfish reefs have a large impact on biofilm functioning. However, biofilms are also fuel for the shellfish, indicating that the two very different ecosystem engineers may facilitate coexistence on tidal flats through a positive feedback loop.

Evidence of illegal catch in the benthic artisanal fisheries of central Chile: patterns across species and management regimes

Non-compliance with fishing regulations is a widespread phenomenon in fisheries worldwide, jeopardizing the recovery of stocks and ecosystem services. There is an urgent need to fill the gaps in our understanding of the scale and nature of illegal fishing in artisanal fisheries, balancing the advances made in industrial fisheries. We explored patterns of fisher compliance with the existing minimum legal size (MLS) regulation in the small-scale benthic fisheries of central Chile. We focus on two of the most conspicuous species (loco Concholepas concholepas and keyhole limpets Fissurella spp.) and comparing two management regimes: management areas (MAs; local name for territorial use rights for fisheries) and open access areas (OAAs; no spatial entry restrictions). We also evaluated the effect of the spatial distribution of MAs, which determines the availability of OAAs on compliance. For both species, we measured the size of individuals in the catch in two consecutive years. We developed an index that accounts for the availability of open access areas per fisher. We found that a) the number of undersized individuals in the catch in OAAs is enormous, b) management regime influences both the median size and fraction of the undersized catch, and c) as the availability of OAAs per fisher decreases, illegal fishing increases, demonstrating the need to manage the levels of effort displacement in designing area-based instruments for management and conservation. Our findings also highlight the need to a) analyze the benefits of area-based instruments at the seascape scale, and b) develop and adapt instruments to prevent illegal fishing.

Quantifying Coral Reef Composition of Recreational Diving Sites: A Structure from Motion Approach at Seascape Scale

Recreational diving is known to have both direct and indirect impacts on coral habitats. Direct impacts include increasing sedimentation, breaks and diseases that lead to a decrease in the richness and abundances of hard corals. Indirect impacts include urban development, land management and sewage disposal. The ecological effects of scuba diving on the spatial composition metrics of reef benthic communities are less well studied, and they have not been investigated at seascape scale. In this study, we combine orthomosaics derived from Structure from Motion (SfM) photogrammetry and data-mining techniques to study the spatial composition of reef benthic communities of recreational diving sites at seascape scale (&gt;25 m 2 ). The study focuses on the case study area of Ponta do Ouro Partial Marine Reserve (Mozambique). Results showed that scuba-diving resistant taxa (i.e., sponges and algae) were abundant at small (&gt;850 m 2 ) and highly dived sites (&gt;3000 dives yr − 1 ), characterized by low diversity and density, and big organisms with complex shapes. Fragile taxa (i.e., Acropora spp.) were abundant at low (365 dives yr − 1 ) and moderately dived sites (1000–3000 dives yr − 1 ) where the greater depth and wider coral reef surfaces attenuate the abrasive effect of waves and re-suspended sediments. Highest taxa diversity and density, and lowest abundance of resistant taxa were recorded at large (&gt;2000 m 2 ) and rarely dived sites. This study highlights the potential applications for a photogrammetric approach to support monitoring programs at Ponta do Ouro Partial Marine Reserve (Mozambique), and provides some insight to understand the influence of scuba diving on benthic communities.

Spatial and temporal effects of management on the reef seascape of a marine protected area in the Mexican Caribbean

Ecological degradation on Marine Protected Areas (MPAs) still occur as a result of anthropogenic pressure and environmental variation. Considering that protected areas can be restrictive to human activities, it is essential to assess their effectiveness. In this study, we evaluated the spatial and temporal effects of management on the seascape of the Cozumel Reefs National Park (CRNP) in the Mexican Caribbean. Quantitative estimates of the percentage of coverage of benthic substrates, and the location of coral reefs, were used to construct benthic habitat maps based on the supervised classifications of high resolution satellite images. Using spatially explicit analyses, the variation of seascape metrics for the period 2004–2015, was compared between two adjacent areas (inside and outside the protected area). Habitat β-diversity and connectivity between the Marine Protected Area (MPA) and the adjacent uncontrolled area, suggest that the CRNP is having an effect over time on the coral reef seascape (p < 0.05). These metrics decreased over time, but change was reduced inside the protected area. The shape complexity of patches and benthic habitat coverage also changed over time, but with no relation to the MPA. In general, with the exception of the habitats dominated by sand over rock, sandy beds with minimum or no vegetation, and dominated by macroalgae, patches became less compact. Management in the CRNP limits the physical damage to benthic habitats and the protected area has characteristics that have been recognised as important on effective MPAs. However, our results indicate that the ability of this MPA to counteract change at a seascape scale is limited. Furthermore, funding on MPAs in the country has been consistently reduced over the last decade. Considering the importance of sufficient funding on effectiveness and the necessity to maintain ecological services provided by coral reef systems in the region, this needs to be re-considered.

Gigapixel big data movies provide cost-effective seascape scale direct measurements of open-access coastal human use such as recreational fisheries.

Collecting data on unlicensed open‐access coastal activities, such as some types of recreational fishing, has often relied on telephone interviews selected from landline directories. However, this approach is becoming obsolete due to changes in communication technology such as a switch to unlisted mobile phones. Other methods, such as boat ramp interviews, are often impractical due to high labor cost. We trialed an autonomous, ultra‐high‐resolution photosampling method as a cost effect solution for direct measurements of a recreational fishery. Our sequential photosampling was batched processed using a novel software application to produce “big data” time series movies from a spatial subset of the fishery, and we validated this with a regional bus‐route survey and interviews with participants at access points. We also compared labor costs between these two methods. Most trailer boat users were recreational fishers targeting tuna spp. Our camera system closely matched trends in temporal variation from the larger scale regional survey, but as the camera data were at much higher frequency, we could additionally describe strong, daily variability in effort. Peaks were normally associated with weekends, but consecutive weekend tuna fishing competitions led to an anomaly of high effort across the normal weekday lulls. By reducing field time and batch processing imagery, Monthly labor costs for the camera sampling were a quarter of the bus‐route survey; and individual camera samples cost 2.5% of bus route samples to obtain. Gigapixel panoramic camera observations of fishing were representative of the temporal variability of regional fishing effort and could be used to develop a cost‐efficient index. High‐frequency sampling had the added benefit of being more likely to detect abnormal patterns of use. Combinations of remote sensing and on‐site interviews may provide a solution to describing highly variable effort in recreational fisheries while also validating activity and catch.

Local Habitat and Seascape Structure Influence Seagrass Fish Assemblages in the Venice Lagoon: The Importance of Conservation at Multiple Spatial Scales

Seagrass meadows are a critical component of estuarine and coastal seascapes, and their structure influences fish assemblages at multiple spatial scales. The patch mosaic model, which defines the seascape as a collection of interacting habitat types, is increasingly adopted to prioritise protected areas and design ecological restoration schemes, hence helping to preserve seagrass meadows and the associated fish assemblages. Despite that, there are few studies investigating the relative contribution of environmental characteristics measured at different spatial scales in determining the distribution of seagrass fish. This study collects fish and environmental observations taken at both site and seascape scales in seagrass meadows in the Venice lagoon (Adriatic Sea, Italy). By means of generalised linear models, it aims to disentangle the relative influence of local water quality and habitat characteristics from that of habitat mosaic properties, investigating the response of whole fish assemblage descriptors, feeding guilds and dominant species. While confirming the primary importance of local habitat quality, the study highlights that also seagrass habitat structure at the seascape scale is relevant for seagrass fish assemblages, influencing total biomass, biomass of macrobenthivorous and hyperbenthivorous/piscivorous species and seagrass specialists such as syngnathids. Conservation of seagrass fish assemblages can therefore be promoted in Mediterranean coastal lagoons by preserving or restoring some features of the habitat mosaic, namely the extension of seagrass patches and their shape complexity, in addition to local water quality and seagrass cover.

Mesoscale spatiotemporal variability in a complex host-parasite system influenced by intermediate host body size.

BackgroundParasites are essential components of natural communities, but the factors that generate skewed distributions of parasite occurrences and abundances across host populations are not well understood.MethodsHere, we analyse at a seascape scale the spatiotemporal relationships of parasite exposure and host body-size with the proportion of infected hosts (i.e., prevalence) and aggregation of parasite burden across ca. 150 km of the coast and over 22 months. We predicted that the effects of parasite exposure on prevalence and aggregation are dependent on host body-sizes. We used an indirect host-parasite interaction in which migratory seagulls, sandy-shore molecrabs, and an acanthocephalan worm constitute the definitive hosts, intermediate hosts, and endoparasite, respectively. In such complex systems, increments in the abundance of definitive hosts imply increments in intermediate hosts’ exposure to the parasite’s dispersive stages.ResultsLinear mixed-effects models showed a significant, albeit highly variable, positive relationship between seagull density and prevalence. This relationship was stronger for small (cephalothorax length >15 mm) than large molecrabs (<15 mm). Independently of seagull density, large molecrabs carried significantly more parasites than small molecrabs. The analysis of the variance-to-mean ratio of per capita parasite burden showed no relationship between seagull density and mean parasite aggregation across host populations. However, the amount of unexplained variability in aggregation was strikingly higher in larger than smaller intermediate hosts. This unexplained variability was driven by a decrease in the mean-variance scaling in heavily infected large molecrabs.ConclusionsThese results show complex interdependencies between extrinsic and intrinsic population attributes on the structure of host-parasite interactions. We suggest that parasite accumulation—a characteristic of indirect host-parasite interactions—and subsequent increasing mortality rates over ontogeny underpin size-dependent host-parasite dynamics.

Sediment properties, biota, and local habitat structure explain variation in the erodibility of coastal sediments

AbstractSediment resuspension is a frequent phenomenon in coastal areas and a key driver for many ecosystem functions. Sediment resuspension is often linked to biological and anthropogenic activities, which in combination with hydrodynamic forcing initiate sediment erosion and resuspension, if the erosion threshold (τc) is exceeded. Despite its importance to ecosystem functions very few studies have provided measurements on natural assemblages for subtidal sediments. The aim of this study was to determinate key environmental variables regulating sediment resuspension potential across a sedimentary gradient in a subtidal coastal environment. In order to explore this, we sampled 16 sites encompassing a wide variety in environmental variables (e.g., grain size distribution, macrofaunal communities, vegetation) in the Gulf of Finland, Baltic Sea. A core‐based erosion device (EROMES) was used to determine sediment resuspension potential measures of erosion threshold, erosion rate (ER), and erosion constant (me). Based on abiotic and biotic properties sampled, sediments diverged into two distinct groups; cohesive (“muddy”) and noncohesive (“sandy”) sediments. Results showed that abiotic sediment properties explained 38–53% and 15–36% of the total variation in resuspension potential measures in “muddy” and “sandy” sediments, respectively. In cumulative models, biota accounted for 12–26% and 6–24% to the total variation in “muddy” and “sandy” sediments, respectively. Sediment erodibility and resuspension potential of natural sediments is highly variable from local habitats to a larger seascape scale. Our results underline the importance of biota to resuspension potential measures in spatially variable environments.

Impact of habitat structure on fish populations in kelp forests at a seascape scale

Impact of habitat structure on fish populations in kelp forests at a seascape scale

Discontinuities concentrate mobile predators: quantifying organism–environment interactions at a seascape scale

AbstractUnderstanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop‐off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land‐ or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass (Morone saxatilis) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four‐monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop‐off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop‐offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co‐occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high‐quality telemetry andGISdata accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation.

Acoustic discrimination of relatively homogeneous fine sediments using Bayesian classification on MBES data

Modern seafloor mapping is based on high resolution MBES systems that provide detailed bathymetric and acoustic intensity (backscatter) information. We examine and validate the performance of two unsupervised MBES classification techniques for discriminating acoustic classes of sedimentary units with small grain size variability. The first technique, based on a principal components analysis (PCA), is commonly used in literature and has been applied for comparison with the more recent approach of Bayesian statistics. By applying these techniques to a MBES dataset from an estuarine area in The Netherlands, we tested their ability to discriminate fine grained sediments (at least 70% silt) holding small percentages of coarser material such as sand, shell hash or shells. We focus on the Bayesian technique as it outputs acoustically significant classes related to backscatter values. This technique utilizes backscatter values averaged over scatter pixels (projected pulse lengths) inside the footprint of each beam. The originality of our application lies in the fact that, the optimal number of classes is derived by utilizing a number of beams simultaneously. It is assumed that the backscatter values per beam vary relatively to the varying seafloor types. By treating the beams separately, across track variation in the seafloor type can also be accounted for. Thereby the classification is guided by outer, more discriminative beams. Additionally we control the optimal number of classes by employing the quantitative criterion of goodness of fit (χ2). The Bayesian acoustic classes show correlation with grain size parameters such as coarse fraction (>500μm) percentage and mean of the grain size (<500μm) when analyzed with multiple linear regression. In order to examine the relative scale of the acoustic classification results we compare the Bayesian acoustic classes with underwater video interpretation. Our results reveal that the Bayesian approach enhances the sedimentological interpretation of MBES high resolution data, by providing classification on seascape scale (here meters to tens of meters). Hence we suggest that backscatter processing techniques are more commonly applied to produce classes that discriminate sediments with low grain size contrast. To describe this ability we introduce the term geoacoustic resolution. We want to encourage the use of the Bayesian technique also in deep sea applications, based on AUV data, where sediments express low variability but sampling would be time consuming and costly. The advantages of this method would favor mapping of macro-habitats which appear at meter-scale and require datasets of sufficient resolution in order to be quantitatively described.

DEVELOPMENT IN EASTERN INDONESIA: ARE THERE ALTERNATIVE APPROACHES?

Development in Wallacea, and eastern Indonesia generally, is gaining momentum. Here we query the applicability of what has become the standard or western Indonesia, model of development, for that part of Indonesia east of Wallace’s line. The numerous small islands with their finer grain of biological and cultural diversity suggest that alternative models focused locally with strong local community engagement might promote a different kind of economic development that maintains the natural resource base, including biodiversity, while providing opportunities for profitable enterprises to flourish. We describe some current examples that might be applicable more widely. The main problem with wider implementation is scaling up. Multiple conflicting goals have to be accommodated and because these are often not compatible with one another, the problem can only be solved at the landscape or seascape scale. We describe some modern methods for data management and computational analyses that can be used as decision support tools to help achieve this.