Spatial and temporal dynamics of Antarctic shallow soft-bottom benthic communities: ecological drivers under climate change

Abstract

Background Marine soft sediments are some of the most widespread habitats in the ocean, playing a vital role in global carbon cycling, but are amongst the least studied with regard to species composition and ecosystem functioning. This is particularly true of the Polar Regions, which are currently undergoing rapid climate change, the impacts of which are poorly understood. Compared to other latitudes, Polar sediment habitats also experience additional environmental drivers of strong seasonality and intense disturbance from iceberg scouring, which are major structural forces for hard substratum communities. This study compared sediment assemblages from two coves, near Rothera Point, Antarctic Peninsula, 67°S in order to understand the principal drivers of community structure, for the first time, evaluating composition across all size classes from mega- to micro-fauna. Results Morpho-taxonomy identified 77 macrofaunal species with densities of 464–16,084 individuals m −2 . eDNA metabarcoding of microfauna, in summer only, identified a higher diversity, 189 metazoan amplicon sequence variants (ASVs) using the 18S ribosomal RNA and 249 metazoan ASVs using the mitochondrial COI gene. Both techniques recorded a greater taxonomic diversity in South Cove than Hangar Cove, with differences in communities between the coves, although the main taxonomic drivers varied between techniques. Morphotaxonomy identified the main differences between coves as the mollusc, Altenaeum charcoti , the cnidarian Edwardsia sp. and the polychaetes from the family cirratulidae. Metabarcoding identified greater numbers of species of nematodes, crustaceans and Platyhelminthes in South Cove, but more bivalve species in Hangar Cove. There were no detectable differences in community composition, measured through morphotaxonomy, between seasons, years or due to iceberg disturbance. Conclusions This study found that unlike hard substratum communities the diversity of Antarctic soft sediment communities is correlated with the same factors as other latitudes. Diversity was significantly correlated with grain size and organic content, not iceberg scour. The increase in glacial sediment input as glaciers melt, may therefore be more important than increased iceberg disturbance. Electronic supplementary material The online version of this article (10.1186/s12898-019-0244-x) contains supplementary material, which is available to authorized users.

Biases in bulk: DNA metabarcoding of marine communities and the methodology involved

“…A notable result is that metabarcoding in the majority of cases outperformed morphotaxonomy concerning the number of taxa retrieved (see e.g. Cowart et al 2015;Lobo et al 2017;Vause et al 2019). DNA metabarcoding in seagrass sediment samples for example yielded hundreds to thousands of MOTUs (molecular operational taxonomic units) compared to only 323 species morphologically identified (Cowart et al, 2015).…”

“…DNA metabarcoding in seagrass sediment samples for example yielded hundreds to thousands of MOTUs (molecular operational taxonomic units) compared to only 323 species morphologically identified (Cowart et al, 2015). Likewise, Vause et al (2019) found 62 orders in sediment samples from Antarctica with metabarcoding compared to 37 orders based on morphology. Similar results were found for plankton communities (Abad et al, 2016;Deagle et al, 2018) and hard substrate samples (Pearman et al, 2016).…”

Global gradients in intertidal species richness and functional groups

“…However, the geographic, functional, and taxonomic generality of latitudinal diversity gradients remain lively debated as unimodal, bimodal, and inverse gradients emerge across clades, habitats, and latitudes ( Rivadeneira et al, 2002 ; Waller, 2008 ; Chaudhary et al, 2016 ; Kinlock et al, 2018 ). In the marine realm, latitudinal gradients in some groups have been shown to be closely related to oceanographic covariates, such as water temperature ( Roy et al, 2000 ), yet mammal richness peaks at high latitudes ( Grady et al, 2019 ), and more species have been reported from polar soft-sediment habitats than at many lower latitudes ( Vause et al, 2019 ).…”

“…In the marine realm, latitudinal gradients in some groups have been shown to be closely related to oceanographic covariates, such as water temperature (Roy et al, 2000), yet mammal richness peaks at high latitudes (Grady et al, 2019), and more species have been reported from polar soft-sediment habitats than at many lower latitudes (Vause et al, 2019).…”

Global gradients in intertidal species richness and functional groups

“…However, the geographic, functional and taxonomic generality of latitudinal diversity gradients remain lively debated as unimodal, bimodal and inverse gradients emerge across clades, habitats and latitudes [6][7][8][9]. In the marine realm, latitudinal gradients in some groups have been shown to be closely related to oceanographic covariates, such as water temperature [10], yet mammal richness peaks at high latitudes [11], and more species are found in polar soft-sediment habitats than at many lower latitudes [12].…”