Characterization of benthic habitat settings in a lagoonal ecosystem using free-living nematodes as proxy

Free-living nematodes are sensitive to most of the disturbances and therefore have ability to reflect direct structural and functional changes in an ecosystem. We studied nematode assemblages of Chilika Lagoon, the largest lagoon of Asia, across spatio-temporal scales in link with environmental variables and evaluated nematode assemblages as a proxy to characterize lagoonal benthic habitat settings. Our results revealed that nematode communities showed significant variation spatially and temporally in terms of mean density (16–854/10 cm²) and mean number of species (7–74). Salinity is the key factor that controls nematode community structure across this lagoon and was strongly supported by statistical analyses. The observed nematode assemblages were further used as a proxy to assign benthic habitats of Chilika into distinct biological, topographical and hydrological settings. This study showed that nematode assemblages could be effectively used for long term ecological monitoring of dynamic sedimentary environment of lagoons globally.     

Benthic assemblages,biodiversity and invasiveness in marinas and commercial harbours: an investigation using a bioindicator group

Fouling communities on artificial marine structures are generally different from benthic communities in natural rocky habitats. However, they may also differ among different types of artificial structures. Two artificial structures in direct contact with arriving vessels were compared: floating pontoons within recreational marinas, and sea-walls within commercial harbours. Natural rocky habitats were used as a reference, and the genus Eudendrium (Cnidaria, Hydrozoa) was chosen as a bioindicator. The assemblages were different among the three types of habitat studied, with different species characterising each habitat. The probability of finding an invasive Eudendrium species was significantly higher on pontoons. Diversity was the lowest on pontoons, but it was not significantly different between sea-walls and natural rocks. In general, a barrier to the spread of exotic species exists between harbours and natural rocky habitats. Floating pontoons seem to be a less suitable habitat for native fauna and a key element in marine biological invasions.     

Aquatic biodiversity under anthropogenic stress: an insight from the Archipelago Sea (SW Finland)

The Archipelago Sea in the northern Baltic has been subjected to large-scale cultural, economic and ecological changes, especially during the last three decades. Environmental threats originate from both basin-wide sources, affecting the whole Baltic Sea, and from local sources, such as nutrient loading from nearby river outflows, intense agriculture, fish farming, ships' traffic, boating, and man's physical impacts on the landscape and seascape. Both the Åland archipelago and the Archipelago Sea have been listed as hot-spots by HELCOM, Baltic Marine Environment Protection Commission, eutrophication being the main threat to the aquatic environment. In this study we review how biological communities have reacted to an increase in man-induced multisource stresses. Changes in plankton, benthic animals, macroalgal assemblages and fish communities have been documented in most parts of the Baltic Sea since the 1970s. What remains to be understood is the importance of these structural changes for the functioning of the Archipelago Sea ecosystem under various levels of human impact.     

Mapping Habitats and Developing Baselines in Offshore Marine Reserves with Little Prior Knowledge: A Critical Evaluation of a New Approach

The recently declared Australian Commonwealth Marine Reserve (CMR) Network covers a total of 3.1 million km² of continental shelf, slope, and abyssal habitat. Managing and conserving the biodiversity values within this network requires knowledge of the physical and biological assets that lie within its boundaries. Unfortunately very little is known about the habitats and biological assemblages of the continental shelf within the network, where diversity is richest and anthropogenic pressures are greatest. Effective management of the CMR estate into the future requires this knowledge gap to be filled efficiently and quantitatively. The challenge is particularly great for the shelf as multibeam echosounder (MBES) mapping, a key tool for identifying and quantifying habitat distribution, is time consuming in shallow depths, so full coverage mapping of the CMR shelf assets is unrealistic in the medium-term. Here we report on the results of a study undertaken in the Flinders Commonwealth Marine Reserve (southeast Australia) designed to test the benefits of two approaches to characterising shelf habitats: (i) MBES mapping of a continuous (~30 km²) area selected on the basis of its potential to include a range of seabed habitats that are potentially representative of the wider area, versus; (ii) a novel approach that uses targeted mapping of a greater number of smaller, but spatially balanced, locations using a Generalized Random Tessellation Stratified sample design. We present the first quantitative estimates of habitat type and sessile biological communities on the shelf of the Flinders reserve, the former based on three MBES analysis techniques. We contrast the quality of information that both survey approaches offer in combination with the three MBES analysis methods. The GRTS approach enables design based estimates of habitat types and sessile communities and also identifies potential biodiversity hotspots in the northwest corner of the reserve’s IUCN zone IV, and in locations close to shelf incising canyon heads. Design based estimates of habitats, however, vary substantially depending on the MBES analysis technique, highlighting the challenging nature of the reserve’s low profile reefs, and improvements that are needed when acquiring MBES data for small GRTS locations. We conclude that the two survey approaches are complementary and both have their place in a successful and flexible monitoring strategy; the emphasis on one method over the other should be considered on a case by case basis, taking into account the survey objectives and limitations imposed by the type of vessel, time available, size and location of the region where knowledge is required.     

Algal Assemblages in Multiple Habitats of Restored and Extant Wetlands

The functional and structural attributes of algal assemblages were studied in 25 restored and 20 extant depressional wetlands in southern central Michigan. Environmental conditions and algal assemblages were compared between restored and extant wetlands and among habitats within wetlands. Restored marshes generally had lower shading by macrophytes, nutrient concentrations, and sediment organic matter. Relative biovolume of non-diatom algae was significantly different among plankton, macrophyte and sediment habitats in restored wetlands, but did not differ between macrophytes and sediments in extant wetlands. Species composition of diatom assemblages was not significantly different between plants and sediments in both restored and extant wetlands. The observed differences in non-diatom algae could not be attributed to any measured environmental variable; however, diatom assemblage differences between habitats increased with light irradiance. Differences in sediment diatom assemblages were observed between restored and extant wetlands and were related to differences in nutrients, pH, and canopy cover. Differences were also observed between epiphytic diatom assemblages in restored and extant wetlands and they were related to light and dissolved oxygen. In summary, differences in light and nutrient availability were the main environmental factors differentiating algal communities in wetlands.     

A benthic perspective in assessing the ecological status of estuaries: The case of the Mondego estuary (Portugal)

In transitional waters the process of defining reference conditions (in the scope of the WFD) must account for the natural great variability of such environments. Therefore, stretches reflecting different physical–chemical and biological conditions throughout the system should be defined in order to correctly establish benthic specific reference conditions. Both salinity and sediment structure are major factors controlling physical–chemical conditions and therefore organisms’ distribution within an estuary. These environmental variables (salinity, sediment grain size composition and organic matter content) patterns were studied in the Mondego estuary and some clear gradients emerged. Also, ecological indices (AMBI, Margalef and Shannon-Wiener) were applied to subtidal benthic communities of the Mondego estuary and, generally, there was not only evidence of a decrease in diversity in the estuary from the downstream section towards its inner parts, but also differences were found between areas of distinct sediment composition. After comparing environmental patterns with biodiversity trends, the information was used to define homogeneous sectors along a temperate estuary in Portugal. In the Mondego estuary six zones, covering the main physical gradients affecting benthic communities, were defined: four in the northern arm and two in southern arm. Zones established will allow future determination of benthic reference conditions adjusted for each of the sectors, according to their characteristics, and consequently the conditions they provide for benthic assemblages settlement.     

Sensitivity of Heterogeneous Marine Benthic Habitats to Subtle Stressors

It is important to understand the consequences of low level disturbances on the functioning of ecological communities because of the pervasiveness and frequency of this type of environmental change. In this study we investigated the response of a heterogeneous, subtidal, soft-sediment habitat to small experimental additions of organic matter and calcium carbonate to examine the sensitivity of benthic ecosystem functioning to changes in sediment characteristics that relate to the environmental threats of coastal eutrophication and ocean acidification. Our results documented significant changes between key biogeochemical and sedimentary variables such as gross primary production, ammonium uptake and dissolved reactive phosphorus flux following treatment additions. Moreover, the application of treatments affected relationships between macrofauna communities, sediment characteristics (e.g., chlorophyll a content) and biogeochemical processes (oxygen and nutrient fluxes). In this experiment organic matter and calcium carbonate showed persistent opposing effects on sedimentary processes, and we demonstrated that highly heterogeneous sediment habitats can be surprisingly sensitive to subtle perturbations. Our results have important biological implications in a world with relentless anthropogenic inputs of atmospheric CO₂ and nutrients in coastal waters.     

Quantifying Fish Assemblages in Large,Offshore Marine Protected Areas: An Australian Case Study

As the number of marine protected areas (MPAs) increases globally, so does the need to assess if MPAs are meeting their management goals. Integral to this assessment is usually a long-term biological monitoring program, which can be difficult to develop for large and remote areas that have little available fine-scale habitat and biological data. This is the situation for many MPAs within the newly declared Australian Commonwealth Marine Reserve (CMR) network which covers approximately 3.1 million km² of continental shelf, slope, and abyssal habitat, much of which is remote and difficult to access. A detailed inventory of the species, types of assemblages present and their spatial distribution within individual MPAs is required prior to developing monitoring programs to measure the impact of management strategies. Here we use a spatially-balanced survey design and non-extractive baited video observations to quantitatively document the fish assemblages within the continental shelf area (a multiple use zone, IUCN VI) of the Flinders Marine Reserve, within the Southeast marine region. We identified distinct demersal fish assemblages, quantified assemblage relationships with environmental gradients (primarily depth and habitat type), and described their spatial distribution across a variety of reef and sediment habitats. Baited videos recorded a range of species from multiple trophic levels, including species of commercial and recreational interest. The majority of species, whilst found commonly along the southern or south-eastern coasts of Australia, are endemic to Australia, highlighting the global significance of this region. Species richness was greater on habitats containing some reef and declined with increasing depth. The trophic breath of species in assemblages was also greater in shallow waters. We discuss the utility of our approach for establishing inventories when little prior knowledge is available and how such an approach may inform future monitoring efforts within the CMR network.     

Seasonal patterns of sediment loading and benthic invertebrate community dynamics in Lake Tanganyika, Africa

1. This study investigated the spatiotemporal dynamics of benthic invertebrate communities located close to the mouths of the Kalambo and Lunzua Rivers, at the southern end of Lake Tanganyika, and subject to varying degrees of sediment load. 2. Metrics of exposure to riverine sediments were associated inversely with abundance and diversity of benthic organisms at sampling locations adjacent to both river mouths, indicating a major effect of riverine sediments on the structure of near‐shore benthic communities. 3. A lower abundance of benthos was found at the mouth of the Lunzua River, which exports significantly higher sediment loads than the Kalambo. 4. Seasonal cycles of abundance and diversity in the benthos varied with distance from river mouths. This has important implications for monitoring programmes investigating benthic communities close to the mouths of rivers. 5. Our findings suggest that recent increases in the sediment loading of Lake Tanganyika, owing to anthropogenic catchment disturbance, impact significantly on biological diversity throughout the lake littoral, which provides habitat for the majority of species in the lake.     

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.     

Assessing the ecological health status using macrobenthic communities of tropical coastal water

The relative contributions of natural and anthropogenic fluctuations are different in shaping habitat health status and natural benthic communities in tropical coastal water. Understanding responses of coastal benthic communities to these fluctuations are still equivocal and thus available data are inadequate. Here, multiple analytical approaches were used to address the significant risk factors and their impacts on coastal benthic habitat health through space and time. A total abundance of 1436 ± 612 individuals of 33 benthic species were counted and identified from 22 sampling stations across eight sampling periods over the two years of study. Bioassay results showed that the benthic community is moderately exposed to anthropogenic pollutants in Klang Strait coastal water. The results showed that there were no significant temporal changes of habitat health status and macrobenthic community structure; however, spatial changes were significant and synchronized with anthropogenic and natural fluctuations. This study demonstrates that Cd and Hg levels and sediment characteristics played the primary role in shaping the habitat health and macrobenthic assemblages, whereas the influence of other factors were insignificant.     

Functional diversity of marine macrobenthic communities from sublittoral soft-sediment habitats off northern Chile

Benthic communities show changes in composition and structure across different environmental characteristics and habitats. However, incorporating species biological traits into the analysis can provide a better understanding of system functioning within habitats. We compare the functional diversity of macrobenthic communities from a contrasting shallow (15 m) and deep (50 m) sublittoral soft-sediment habitats in northern Chile, using biological traits analysis. Our aim was to highlight the biological characteristics responsible for differences between habitats and the implications for ecosystem functioning. Trait analysis showed that the deep habitat was restricted in providing functionally important biogenic structure and bioturbation and supports less diverse feeding-related energy pathways. The shallow habitat is characterized by more diverse energy pathways and a higher potential for matter exchange through bioturbation. We provide support to the predictions of transfer of energy from the benthos to upper trophic levels in the shallow, which is characterized mainly by normoxia and little organic matter content in the sediment. In the deep habitat, characterized by hypoxia and more organic matter, energy appears to be transferred to microbial components. We suggest that trait analysis should be added to the traditional approaches based on species diversity, because it provides indicators of ecosystem stress.     

Fish Species and Community Distributions as Proxies for Seafloor Habitat Distributions: The Stellwagen Bank National Marine Sanctuary Example (Northwest Atlantic, Gulf Of Maine)

Defining the habitats of fishes and associated fauna on outer continental shelves is problematic given the paucity of data on the actual types and distributions of seafloor habitats. However many regions have good data on the distributions of fishes from resource surveys or catch statistics because of the economic importance of the fisheries. Fish distribution data (species or communities) have been used as a proxy for the distribution of habitats to develop precautionary conservation strategies for habitat protection (e.g., marine protected areas, fishing gear restrictions). In this study we assessed the relationships between the distributions of fish communities and species derived from trawl survey data with the spatial distribution of sediment types determined by sampling and acoustic reflectance derived from multibeam sonar surveys in Stellwagen Bank National Marine Sanctuary. Fish communities were correlated with reflectance values but all communities did not occur in unique sediment types. This suggests that use of community distributions as proxies for habitats should include the caveat that a greater number of communities within an area could indicate a greater range of habitat types. Single species distributions showed relationships between abundance and reflectance values. Trawl catches with low abundances had wide variations in reflectance values while those with high abundances had narrower ranges indicating habitat affinities. Significant non-random frequency-dependent relationships were observed for 17 of 20 species although only 12 of 20 species had significant relationships based on rank correlation. These results suggest that species distributions based on trawl survey data can be used as proxies for the distribution of seafloor habitats. Species with known habitat associations can be used to infer habitat requirements of co-occurring species and can be used to identify a range of habitat types.     

Depth and Medium-Scale Spatial Processes Influence Fish Assemblage Structure of Unconsolidated Habitats in a Subtropical Marine Park

Where biological datasets are spatially limited, abiotic surrogates have been advocated to inform objective planning for Marine Protected Areas. However, this approach assumes close correlation between abiotic and biotic patterns. The Solitary Islands Marine Park, northern NSW, Australia, currently uses a habitat classification system (HCS) to assist with planning, but this is based only on data for reefs. We used Baited Remote Underwater Videos (BRUVs) to survey fish assemblages of unconsolidated substrata at different depths, distances from shore, and across an along-shore spatial scale of 10 s of km (2 transects) to examine how well the HCS works for this dominant habitat. We used multivariate regression modelling to examine the importance of these, and other environmental factors (backscatter intensity, fine-scale bathymetric variation and rugosity), in structuring fish assemblages. There were significant differences in fish assemblages across depths, distance from shore, and over the medium spatial scale of the study: together, these factors generated the optimum model in multivariate regression. However, marginal tests suggested that backscatter intensity, which itself is a surrogate for sediment type and hardness, might also influence fish assemblages and needs further investigation. Species richness was significantly different across all factors: however, total MaxN only differed significantly between locations. This study demonstrates that the pre-existing abiotic HCS only partially represents the range of fish assemblages of unconsolidated habitats in the region.     

Contrasting community assembly processes structure lotic bacteria metacommunities along the river continuum

The heterogeneous nature of lotic habitats plays an important role in the complex ecological and evolutionary processes that structure the microbial communities within them. Due to such complexity, our understanding of lotic microbial ecology still lacks conceptual frameworks for the ecological processes that shape these communities. We explored how bacterial community composition and underlying ecological assembly processes differ between lotic habitats by examining community composition and inferring community assembly processes across four major habitat types (free-living, particle-associated, biofilm on benthic stones and rocks, and sediment). This was conducted at 12 river sites from headwater streams to the main river in the River Thames, UK. Our results indicate that there are distinct differences in the bacterial communities between four major habitat types, with contrasting ecological processes shaping their community assembly processes. While the mobile free-living and particle-associated communities were consistently less diverse than the fixed sediment and biofilm communities, the latter two communities displayed higher homogeneity across the sampling sites. This indicates that the relative influence of deterministic environmental filtering is elevated in sediment and biofilm communities compared with free-living and particle-associated communities, where stochastic processes play a larger role.     

Subtle population structure and male-biased dispersal in two <Emphasis Type="Italic">Copadichromis</Emphasis> species (Teleostei,Cichlidae) from Lake Malawi,East Africa

Marine protected areas are generally designed and managed on the basis of the presence and extent of specific habitat types or the habitats of important species. However, it has become clear that in addition to including these ‘structural’ elements of marine systems, management strategies should incorporate a consideration of the functional aspects of the ecosystems. Biological traits analysis (BTA) has been successfully used to describe ecological functioning in marine benthic systems. BTA uses a number of biological characteristics expressed by the taxa present as indicators of key ecosystem functions. Two expert workshops were used to examine the potential for the application of BTA in the designation and management of MPAs. They concluded that BTA represented the best tool currently available for quantifying ecological functioning and agreed on 10-key ecological functions delivered by marine benthic communities. Twenty-four biological traits were also identified by the workshops as indices of these ten functions. In order to demonstrate the practical utility of the approach, BTA using these traits, was applied to a dataset covering benthos from within and around the proposed Eddystone Special Area of Conservation (SW England). The case study demonstrated that with the type of data normally available from conservation assessment type surveys, and a knowledge of the relevant biological traits, it is possible to use a consideration of ecological functioning to set boundaries for the MPA and to inform the site management objectives. The use of structure and function information to inform the designation process and subsequent management of marine protected areas is discussed. Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan Challenges to Marine Ecosystems     

Integrating Multibeam Backscatter Angular Response,Mosaic and Bathymetry Data for Benthic Habitat Mapping

Multibeam echosounders (MBES) are increasingly becoming the tool of choice for marine habitat mapping applications. In turn, the rapid expansion of habitat mapping studies has resulted in a need for automated classification techniques to efficiently map benthic habitats, assess confidence in model outputs, and evaluate the importance of variables driving the patterns observed. The benthic habitat characterisation process often involves the analysis of MBES bathymetry, backscatter mosaic or angular response with observation data providing ground truth. However, studies that make use of the full range of MBES outputs within a single classification process are limited. We present an approach that integrates backscatter angular response with MBES bathymetry, backscatter mosaic and their derivatives in a classification process using a Random Forests (RF) machine-learning algorithm to predict the distribution of benthic biological habitats. This approach includes a method of deriving statistical features from backscatter angular response curves created from MBES data collated within homogeneous regions of a backscatter mosaic. Using the RF algorithm we assess the relative importance of each variable in order to optimise the classification process and simplify models applied. The results showed that the inclusion of the angular response features in the classification process improved the accuracy of the final habitat maps from 88.5% to 93.6%. The RF algorithm identified bathymetry and the angular response mean as the two most important predictors. However, the highest classification rates were only obtained after incorporating additional features derived from bathymetry and the backscatter mosaic. The angular response features were found to be more important to the classification process compared to the backscatter mosaic features. This analysis indicates that integrating angular response information with bathymetry and the backscatter mosaic, along with their derivatives, constitutes an important improvement for studying the distribution of benthic habitats, which is necessary for effective marine spatial planning and resource management.     

The role of waves in the colonisation of terrestrial sediments deposited in the marine environment

Elevated rates of sediment run-off, as a result of changes in land-use and climate, are a significant threat to marine coastal communities, with a potential to cause broad-scale, long-term alteration of habitats. Individual sedimentation events can smother estuarine flats with terrigenous sediments, creating a significant disturbance to local benthic communities. Variations in the degree to which a habitat is altered, the rate at which mixing occurs, and species-specific dispersal and responses to the altered habitat, suggest that colonisation of terrestrial sediment depositions will vary with location, both between and within estuaries. This study was designed to explore the effect that variations in wave-induced hydrodynamics would have on long-term colonisation of terrestrial sediment depositions on intertidal flats. Sites for the experimental deposition of terrestrial sediment were located along a gradient in wave exposure, with only limited variation in immersion times (30 min) and ambient sediment particle sizes (predominantly fine sand). Over 20 months, periodic measurements were made of factors predicted to affect colonisation: the sediment characteristics of the deposited sediment; local-scale wave climate; bioturbation of the deposited sediment; and local populations of benthic invertebrates. Neither opportunistic use of the new resource, progressive recovery or facilitation by colonising macrofauna was observed. Little vertical mixing of the deposited and existing sediment by either waves or bioturbators occurred; instead bedload transport was the dominant process. Local differences in hydrodynamic conditions and macrobenthic communities resulted in site-specific colonisation of the experimental plots. The strength and duration of the macrofaunal response to deposited sediment observed in this study suggest that chronic small-scale (m's) patchy deposition of terrestrial sediment in the intertidal marine environment has a strong potential to alter both habitats and communities.     

Coral and fish distribution patterns in Mafia Island Marine Park, Tanzania: fish–habitat interactions

We examined coral reef communities at 11 sites within Mafia Island Marine Park using a point count method for substrate and visually censused belt transects for fish populations. Multivariate ordinations showed that the benthic habitat differed among reefs. The patterns were mainly attributed to variations in depth, hydrodynamics and benthic composition. In total, the substratum was dominated by dead coral (49%) and algae (25%), with a live coral cover of only 14%. Three hundred and ninety-four fish species belonging to 56 families were recorded. According to MDS-ordinations and RELATE procedures, fish assemblage composition varied among sites in concordance with the habitats provided. Sites with highest proportion of dead coral exhibited highest degree of dispersion in the multivariate ordinations of fish assemblages. Stepwise multiple regression was used to determine the proportion of variance among sites which could be explained by depth, exposure, rugosity, substrate diversity, branching substrate, live coral cover, dead coral cover and different types of algae. The results showed that habitat variables explained up to 92% of the variation in species numbers and in total, and taxon-specific, abundance. Live coral cover was the foremost predictor of both numerical and species abundance, as well as of corallivores, invertivores, planktivores and of the families Pomacentridae, Chaetodontidae and Pomacanthidae. Our results suggest that habitat characteristics play a dominant role in determining fish assemblage composition on coral reefs.