Biodiversity between sand grains: Meiofauna composition across southern and western Sweden assessed by metabarcoding

Abstract

The meiofauna is an important part of the marine ecosystem, but its composition and distribution patterns are relatively unexplored. Here we assessed the biodiversity and community structure of meiofauna from five locations on the Swedish western and southern coasts using a high-throughput DNA sequencing (metabarcoding) approach. The mitochondrial cytochrome oxidase 1 (COI) mini-barcode and nuclear 18S small ribosomal subunit (18S) V1-V2 region were amplified and sequenced using Illumina MiSeq technology. Our analyses revealed a higher number of species than previously found in other areas: thirteen samples comprising 6.5 dm³ sediment revealed 708 COI and 1,639 18S metazoan OTUs. Across all sites, the majority of the metazoan biodiversity was assigned to Arthropoda, Nematoda and Platyhelminthes. Alpha and beta diversity measurements showed that community composition differed significantly amongst sites. OTUs initially assigned to Acoela, Gastrotricha and the two Platyhelminthes sub-groups Macrostomorpha and Rhabdocoela were further investigated and assigned to species using a phylogeny-based taxonomy approach. Our results demonstrate that there is great potential for discovery of new meiofauna species even in some of the most extensively studied locations.

Keywords: Acoela; Gastrotricha; Macrostomorpha; Platyhelminthes; Rhabdocoela; High Throughput Sequencing; Illumina Mi-Seq; Species Identification.

Figure 1.

Location of each of the sampling sites along the Swedish western and southern coasts. (1) Tjärnö near the Tjärnö Marine Laboratory (formerly Sven Lovén Centre for Marine Sciences Tjärnö), 58°52’41.0 N, 11°06’56.0 E; (2) Fiskebäckskil near the Sven Lovén Centre for Marine Sciences Kristineberg, 58°14’52.1 N, 11°27’05.8 E; (3) Halmstad at Påarp Beach, 56°36’10.0 N, 12°54’48.3 E; (4) Kåseberga, just east of Ales stenar, 55°23’00.6 N, 14°03’46.5 E; (5) Landön western side, 55°58’20.6 N, 14°24’29.6 E.

Figure 2.

A graphical summary of the higher level composition for all samples combined by (A) the percent of OTUs as determined by 18S sequences; (B) the percent of sequence reads as determined by 18S sequences; (C) the percent of OTUs as determined by COI sequences; (D) the percent of sequence reads as determined by COI sequences.

Figure 3.

A graphical summary of the Metazoa OTUs identified to phylum level for each sample, as well as all samples combined, as shown by (A) the percent of OTUs based on 18S sequences; (B) the percent of sequence reads based on 18S sequences; (C) the percent of OTUs based on COI sequences; (D) the percent of sequence reads based on COI sequences. 1: Tjärnö, 2: Fiskebäckskil, 3: Halmstad, 4: Kåseberga, 5: Landön. Total: all samples combined.

Figure 4.

Diversity measurements, based on 18S gene sequences, including (A) rarefaction curves; (B) Chao1 diversity box plots; (C) principal coordinate analysis (PCoA) emperor plots for each sample site.

Figure 5.

Diversity measurements based on 18S gene sequences, including (A) rarefaction curves; (B) Chao1 diversity box plots; (C) principal coordinate analysis (PCoA) emperor plots for each sample site.