Taxonomic and Functional Patterns of Benthic Communities in Southern Temperate Tidal Flats

Coastal ecosystems are vulnerable to anthropogenic disturbances which can cause loss of benthic macrofauna and their ecosystem functioning. Despite the importance of functional assessments for conservation and management, knowledge gaps persist on the generality of how the diversity and functional traits of benthic communities influence ecosystem functioning. We investigated eight sites in three different habitats across ~1,260 km of coastline, to evaluate patterns between taxonomic and functional diversity of benthic macrofauna, and the relationship between benthic macrofauna, functional traits and environmental conditions. A total of 74 benthic macrofauna taxa were identified. Significant differences across sites and season were found for metrics based on taxonomic and functional traits. Multivariate analysis revealed spatial-temporal differences, which were more evident based on taxa than functional traits. Functional diversity also showed spatial and temporal differences and was positively correlated with the number of taxa. The dominant functional traits modalities were deposit feeders, with large (>20 mm) body size, burrowers, bioirrigators, deeper than 3 cm in sediments, and irregular morphology. Novel Generalized Linear Latent Variable Models (GLLVM) uncovered several site-dependent relationships between taxa, traits and environmental conditions. Functional redundancy was lowest in a highly modified lagoon, and highest in a more pristine embayment. The outcomes from this study showed site-dependent patterns of benthic communities based on either taxonomic or functional metrics, highlighting that both perspectives are complementary to obtain a holistic understanding of the functioning in marine sediments under environmental change.

Intraspecific Abundance–Occupancy–Patchiness Relations in the Intertidal Benthic Macrofauna of a Cool-Temperate North Sea Mudflat

The macroecological variable of patchiness (Lloyd’s Ip index of patchiness, P) has recently been shown to be related inter- and intraspecifically to those of abundance (numbers m−2, A), and occupancy (% occurrence in samples, O) in lower latitude seagrass macrofaunas. For the first time in higher latitudes, intraspecific relationships between three spatial variables were investigated in the intertidal mudflat macrobenthos of the Scolt Head barrier island, southern North Sea (53° N, 01° E). Sampling was conducted between early July and late September 2009–2013 using 710-µm mesh for sample processing. Strong positive interspecific A-O and negative interspecific P-O and P-A relationships were present. Two of the most numerous and widespread assemblage components, however, occurred with effectively constant occupancy (Peringia ulvae, 100%, and Tubificoides benedii, 93%) across the whole 20-ha locality and therefore could not show intraspecific relationships of occupancy with other macroecological metrics. These two apart, only one other dominant species failed to show a significant positive intraspecific A-O relationship; no species showed significant P-A relations of any form; and only two showed the negative P-O ones that have been described elsewhere. The intraspecific A-O patterns appear to contrast with those of an earlier study at another North Sea locality (the Dutch Wadden Sea), although differences are more apparent than real, but the Scolt Head fauna showed fewer intraspecific P-O and P-A relations than those characterising similar circumstances in the two lower-latitude localities previously investigated. Neither developmental mode nor variation in local abundance appears to influence these patterns. A-O-P relations therefore seem widespread but may be subject to latitudinal modification.

Sediment Bulk Density Effects on Benthic Macrofauna Burrowing and Bioturbation Behavior

Benthic macrofauna are a key component of intertidal ecosystems. Their mobility and behavior determine processes like nutrient cycling and the biogeomorphic development of intertidal flats. Many physical drivers of benthic macrofauna behavior, such as sediment grain size, have been well-studied. However, little is known about how sediment bulk density (a measure of sediment compaction and water content) affects this behavior. We investigated the effect of bulk density on the burrowing rate, burrowing depth, bioturbation activity, and oxygen consumption of bivalves (Limecola balthica, Scrobicularia plana, and Cerastoderma edule) and polychaetes (Hediste diversicolor and Arenicola marina) during a 29-day mesocosm experiment. We compared four sediment treatments consisting of two sediments of differing grain size classes (sandy and muddy) with two bulk densities (compact and soft). Overall, bulk density had a strong effect on benthic macrofauna behavior. Benthic macrofauna burrowed faster and bioturbation more intensely in soft sediments with low bulk density, regardless of grain size. In addition, L. balthica burrowed deeper in low bulk density sediment. Finally, we found that larger bivalves (both C. edule and S. plana) burrowed slower in compact sediment than smaller ones. This study shows that benthic macrofauna change their behavior in subtle but important ways under different sediment bulk densities which could affect animal-sediment interactions and tidal flat biogeomorphology. We conclude that lower bulk density conditions lead to more active macrofaunal movement and sediment reworking.

Changes of community structure and functional feeding groups of benthic macrofauna after mangrove afforestation in a subtropical intertidal zone, China

Afforestation is a primary response to the loss and degradation of mangroves worldwide. The successful restoration of mangrove ecosystems is in part indicated by the rebuilding of macrobenthic community. However, the community dynamic of benthic macrofauna after mangrove afforestation was poorly known. Here, three quarterly surveys (2006–2007, 2014–2015, 2019–2020) of the benthic macrofauna and sediment grain size were conducted in a mix-planted mangrove stand (Kandelia obovata + Sonneratia apetala) in Xiamen Tong'an Bay, China. Our results showed that the community structure of benthic macrofauna differed significantly after mangrove afforestation. These differences were accompanied by the declines in the species number, abundance, biomass, and diversity (H'), as well as the fining of sediments. We also found that the epifauna and infauna exhibited different adaptabilities to mangrove vegetation. Additionally, shifts in the composition of the functional feeding groups were observed, indicating the modification of trophic structure after mangrove afforestation. We recommend that future mangrove afforestation programs call for a guide to coordinate habitats for different taxa.