Changes in benthic community structure and sediment characteristics after natural recolonisation of the seagrass Zostera muelleri

Abstract

Macrofauna are important contributors to estuarine ecosystem services within and outside of seagrass beds. Here we documented the natural recolonisation of a temperate seagrass (Zostera muelleri) community over 15 years in an urban estuary (Waitemata Harbour, North Island, New Zealand). We also investigated the change in macrofaunal communities in relation to seagrass cover over time, from transition from bare sandflat to seagrass. Colonisation by seagrass was associated with an increase in macrofaunal species diversity (from an average of 32 species per core in 2001 to 46 species per core in 2015) and abundance (from 482 to 2273 individuals per core), as well as an increase in sediment mud (from 4.09% to 12.37%) and organic matter content (from 0.90% to 1.41%). The most abundant species within both seagrass and adjacent unvegetated sandflat were similar, the polychaetes Heteromastus filiformis, Aricidea sp., and Prionospio aucklandica, and the amphipod Paracalliope novizealandiae. The difference in macrofaunal community structure between seagrass and unvegetated sandflat was primarily associated with higher abundance of P. novizealandiae and lower abundance of Pseudopolydora sp. in seagrass. A successional effect was observed in macrofaunal communities over the 15 years following seagrass expansion, primarily associated with an increase in the abundance of Aricidea sp., H. filiformis, and P. novizealandiae, and a reduction in the abundance of the bivalve Linucula hartvigiana. This study is the first to document long-term changes in seagrass and their associated communities during a natural recolonisation event, providing insight into timeframes required both for the regrowth of a seagrass meadow from initial colonisation of individual patches, as well as the trajectories and timeframes of change from a sandflat to a seagrass-associated macrofaunal community. This research enhances our understanding of how changes in seagrass distributions due to seagrass loss or restoration may affect macrofaunal community composition and ultimately ecosystem function.

Multiple stressors and disturbance effects on eelgrass and epifaunal macroinvertebrate assemblage structure

“…Eelgrass complexity influences the associated communities. Typically, the presence of seagrassat low or high densities -will increase the associated community stability, species richness and total abundance, influence assemblage composition, and increase the habitat carrying capacity (Edgar & Robertson 1992, Calizza et al 2017, Lundquist et al 2018). On the other hand, a reduction in seagrass density would probably decrease seagrass self-shading in a similar way to self-thinning with increased depth owing to acclimation to low light (Krause-Jensen et al 2000).…”

Nitrogen enrichment increases greenhouse gas emissions from emerged intertidal sandflats

“…Approximately 28% of the harbour flushes each tide, and about half (54 km 2 ) of the harbour area is intertidal 20,21 . Approximately two thirds of the intertidal area is composed of unvegetated, intertidal flats, with the remainder being mangrove forest and seagrass meadows, both of which have expanded in recent decades 22,23 . Land use in the catchment varies, with high proportions of pastoral agriculture and plantation forestry alongside urban areas and areas of native vegetation 20 .…”

Climate change mitigation by coral reefs and seagrass beds at risk: How global change compromises coastal ecosystem services

“…Furthermore, an unstable sediment surface is likely to be uninhabitable for many currently existing benthic species within natural tropical bays, such as calcifying algae, urchins and juvenile lobster (Lozano-Álvarez et al, 2009). The benthic community has been shown to be tightly linked to the presence or absence of seagrass (Lundquist et al, 2018;Seitz and Ewers Lewis, 2018;Cadier and Frouws, 2019;Githaiga et al, 2019). Once seagrass is lost, the community assemblage often shifts toward bioturbating organisms that can further hinder seagrass reestablishment (Cadier and Frouws, 2019).…”