Temporal distribution of intertidal macrozoobenthic assemblages in a Nanozostera noltii-dominated area (Lagoon of Venice)

Variability of soft-bottom macrobenthic invertebrates at different spatial scales: Comparisons between habitats and seasons

Studies focusing on patterns of spatial variation in marine soft-bottom assemblages suggest that variability is mainly concentrated at small spatial scale (from tens of centimeters to few meters), but there is still a lack of knowledge about the consistency of this spatial pattern across habitats and seasons. To address this issue, we quantified the variability in the structure of macrozoobenthic assemblages and in the abundance of dominant macroinvertebrate species in the Mellah Lagoon (Algeria) at three spatial scales, i.e., Plot (meters apart), Station (10's m apart) and Site (kms apart) scale, in Ruppia maritima (Ruppia) beds and unvegetated sediments (Unvegetated), and in two dates in winter and two dates in summer 2016. Spatial variability of the most dominant bivalve Mytilaster marioni varied significantly between habitats, but consistent across the two seasons, with a more heterogeneous distribution in Ruppia than in Unvegetated at the Station scale. Furthermore, a second-order interaction among the hierarchical nature of spatial variability, season and habitat emerged for the assemblage structure. Spatial variability between habitats varied significantly in winter, with the largest variation at the Plot scale in Unvegetated and more heterogenous assemblages at the Plot and Site scales than at the Station scale in Ruppia, but did not vary in summer when most of the variance was at the Site scale. We demonstrate that the scales of influence of the processes operating in the Mellah Lagoon are contingent on the specific habitat and/or period of the year at which the study was conducted, highlighting the importance of examining all these sources of variation simultaneously to increase the accuracy of explanatory models derived from the observed patterns in sedimentary environments.

Seagrass macrobenthic biodiversity does not vary in conformity with a leaky-lagoonal confinement gradient

Coastal lagoon ecology often changes on progression from the open, well-flushed mouth region to the depositional zone furthest from the open sea. This is generally considered consequent on increasing 'confinement' and associated features, rather than on the often co-occurringly decreasing salinity. The 12 km Rainbow Channel connecting part of Moreton Bay, a microtidal leaky lagoon, to the adjacent Pacific provides a gradient of increasing confinement without any significant salinity change, i.e. a tenfold increase in water residence time for a salinity decrease of <1. Macrobenthic faunal assemblages characterising intertidal Zostera seagrass at strategic points along its length were compared to test whether their nature changed in conformity with confinement models. Results suggest that it does not; faunal abundance, species richness, evenness and composition remaining effectively unchanged along the gradient. Seagrass systems may constitute a special case because they decouple renewal times of the overlying water and local organic enrichment/decomposition; as may leaky lagoons because of their high tidal velocities.

Changes in Macrozoobenthos Community after Aquatic Plant Restoration in the Northern Venice Lagoon (IT)

Responses of the macrozoobenthic community to an ecological restoration activity in the northern Venice lagoon were studied, within the scope of the project LIFE SEagrass RESTOration aimed at recreating aquatic phanerogam meadows largely reduced in recent decades. Transplants were successful in almost all project areas. Macrozoobenthos was sampled in eight stations before (2014) and after (2015, 2016, 2017) transplanting activities. An increase in abundance and fluctuations in richness and univariate ecological indices (Shannon’s, Margalef’s, Pielou’s indices) resulted during the years. Comparing non-vegetated and vegetated samples in 2017, every index except Pielou’s increased in the latter. Multivariate analysis (hierarchical cluster analysis, MDS, PERMDISP, SIMPER) grouped samples by localization rather than years, with differences between stations due to the abundance of common species. In 2017, results were also grouped by the presence or absence of aquatic plants, with differences in the abundance of grazer and filter-feeding species. Results of ecological index M-AMBI depicted conditions from moderate to good ecological status (sensu Dir.2000/60/EC) with similar fluctuations, as presented by univariate indices from 2014 to 2017. Responses of the macrozoobenthic community were more evident when comparing vegetated and non-vegetated samples, with the vegetated areas sustaining communities with greater abundance and diversity than non-vegetated samples, thus demonstrating the supporting function of aquatic plants to benthic communities.

Composition, uniqueness and connectivity across tropical coastal lagoon habitats in the Red Sea

Background

Tropical habitats and their associated environmental characteristics play a critical role in shaping macroinvertebrate communities. Assessing patterns of diversity over space and time and investigating the factors that control and generate those patterns is critical for conservation efforts. However, these factors are still poorly understood in sub-tropical and tropical regions. The present study applied a combination of uni- and multivariate techniques to test whether patterns of biodiversity, composition, and structure of macrobenthic assemblages change across different lagoon habitats (two mangrove sites; two seagrass meadows with varying levels of vegetation cover; and an unvegetated subtidal area) and between seasons and years.

Results

In total, 4771 invertebrates were identified belonging to 272 operational taxonomic units (OTUs). We observed that macrobenthic lagoon assemblages are diverse, heterogeneous and that the most evident biological pattern was spatial rather than temporal. To investigate whether macrofaunal patterns within the lagoon habitats (mangrove, seagrass, unvegetated area) changed through the time, we analysed each habitat separately. The results showed high seasonal and inter-annual variability in the macrofaunal patterns. However, the seagrass beds that are characterized by variable vegetation cover, through time, showed comparatively higher stability (with the lowest values of inter-annual variability and a high number of resident taxa). These results support the theory that seagrass habitat complexity promotes diversity and density of macrobenthic assemblages. Despite the structural and functional importance of seagrass beds documented in this study, the results also highlighted the small-scale heterogeneity of tropical habitats that may serve as biodiversity repositories.

Conclusions

Comprehensive approaches at the “seascape” level are required for improved ecosystem management and to maintain connectivity patterns amongst habitats. This is particularly true along the Saudi Arabian coast of the Red Sea, which is currently experiencing rapid coastal development. Also, considering the high temporal variability (seasonal and inter-annual) of tropical shallow-water habitats, monitoring and management plans must include temporal scales.

Effects of Zostera marina on the patterns of spatial distribution of sediments and macrozoobenthos in the boreal lagoon of Furen (Hokkaido, Japan)

Understanding patterns of spatial variations in benthic seagrass assemblages is a central issue in seagrass ecology. However, how patterns of spatial variations in macrozoobenthos and associated sediments differ between vegetated and unvegetated areas remain largely unexplored. In the present study, two different habitats represented by dense Zostera marina beds (Zostera) and unvegetated sediments (Bare) were compared at three locations, 100's meters apart, located at progressive distance from the Furen river in the boreal lagoon of Furen (Hokkaido, Japan). We tested the hypothesis that Z. marina influences the patterns of spatial distribution of abiotic and biotic components along an environmental (estuarine) gradient. The results showed considerable differences between Zostera and Bare, as well as between and within locations, in the distribution of both sediment variables (mud, total organic carbon [TOC] and total nitrogen, acid volatile sulfide, chlorophyll-a and pheopigments) and macrozoobenthic assemblage metrics (total number of species [S], Shannon-Weiner diversity index [H'], total abundance and abundance of dominant species). TOC content, associated to a high mud content, was highest in Bare irrespective of differences between locations (all being above a critical TOC threshold of 3.6%), while S and H' were higher in Zostera than in Bare at all locations. Significant location x habitat effects were found in the abundance of dominant species, represented mainly by mollusks and crustaceans. Furthermore, the proportions of spatial variance were greater at the scale of replicates (meters apart) than at the scale of stations (10's meters apart) for both sediment variables and the dominant species. Importantly, for the dominant species the spatial variance at the smaller scale was much higher in Zostera than in Bare, indicating that at the scale of meters Zostera beds increase the patchiness in the spatial distribution of individuals compared to bare sediments. Overall, our results demonstrate that Z. marina has a strong effect on the spatial heterogeneity in the intensity of the ecological processes influencing patterns of sediment and macrozoobenthos distribution along an environmental gradient. The present study provides a general framework to evaluate patterns of spatial distribution across various scales within several hundreds of meters in seagrass-dominated, eutrophic coastal lagoons.