Corresponding author: Sarah J. Bourlat (
Academic editor: Urmas Kõljalg
Microscopic interstitial marine organisms, also termed ‘meiofauna’, are often defined as animals that pass a 1mm mesh but are retained on a 45 µm sieve (
In this study we used samples from muddy and sandy marine sediments to examine how results of metabarcoding based surveys of meiofaunal communities are impacted by three different meiofaunal extraction methods and three different primer pairs for COI and 18S. In order to validate the reliability of the metabarcoding approach, we compare the results obtained with traditional morphologybased taxonomic assignment for two test groups,
Samples were collected in two ecologically distinct locations along the west coast of Sweden in August 2014.
Accordingly, primers amplifiying a 313 bp fragment of the mitochondrial cytochrome oxidase 1 (COI) gene were used, as described in
For the 18S region, Illumina overhang adapter sequences were appended to the primers from Fonseca et al. (SSU_FO4SSU_R22;
Sequence overlap in the pairedend reads was calculated in Geneious
All primer sequences used are shown in Table
Most analytical steps were performed using Qiime (Quantitative Insight Into Microbial Ecology) version 1.9.1 (
The data underpinning the analysis reported in this paper are deposited at the GenBank SRA under project number PRJNA388326 (
Illumina MiSeq produced at total of 24 132 875 raw reads, of which 15 883 274 COI reads and 8 249 601 18S reads. These were quality filtered (see methods section for details) resulting in 7 954 017 COI sequences and 890 370 18S sequences. These were clustered into 2805 and 1472 representative OTUs respectively, yielding 190 metazoan OTUs for COI and 121 metazoan OTUs for 18S at 97% sequence similarity (see methods, Table
Taxonomic assignment of OTUs at a 97% similarity threshold shows community composition of the samples at the phylum level (Fig.
For the 18S dataset, 121 of 1472 OTUs (8%) were assigned to
The large numbers of unassigned OTUs reflect the incompleteness of the databases used for COI and 18S. When unassigned OTUs are disregarded, differences between the taxonomic ocverage of the markers can be observed (Fig.
Of all OTUs classified as
As well as
Taxonomic community composition at both locations surveyed is illustrated in Fig.
In Fig.
In coarse shell sand in shallow areas, such as in the Hållö island samples,
A greater number of phyla were uncovered in the Hållö Island samples than in the Gullmarn Fjord samples (Fig.
Using a sequence similarity search at 97% similarity allowed us to identify 213 COI OTUs and 243 18S OTUs to species level (Table
Five alien species were detected in in the sample, of which two are considered invasive (in bold; Table
Comparison of morphologybased assessment of
Both study sites are characterized by rich and diverse nematode fauna. The Hållö site had a total of 107 species of nematodes, belonging to 86 genera (
The final list of nematode OTUs includes 139 18S sequences. Only two 18S OTUs were positively identified using QIIME to species level using 97% similarity threshold:
When comparing the results of morphologybased assessment of nematode diversity with metabarcoding using taxonomic assignments to the phylum level in this particular study (with 80% similarity threshold; Suppl. materials
We would like to thank the Genomics Core facility platform at the Sahlgrenska Academy, University of Gothenburg. The SweBoL (Swedish Barcode of Life) network and Christer Erséus are thanked for sharing barcode databases of Swedish invertebrates. We would also like to thank Nicolas Girard for help with scripting. This work was in part supported by the project "Systematics of Swedish freeliving nematodes of the orders
Schematic workflow of bioinformatic analytical steps
Taxonomic composition overview at species level based on a 97% sequence similarity threshold. A) Percentages and counts of OTUs for the COI gene with unassigned OTUs. B) Percentages and counts of OTUs for the COI gene without unassigned OTUs. C) Percentages and counts of OTUs for the 18S gene with unassigned OTUs. D) Percentages and counts of OTUs for the 18S gene without unassigned OTUs.
Percentages of metazoan phyla uncovered in the samples using COI and 18S molecular surveys. Blue bars correspond to the cumulated frequencies of OTUs assigned to a specific phylum using the COI gene and red bars correspond to the cumulated frequencies of OTUs assigned to a specific phylum using the 18S gene. Taxonomic assignment is based on a 97% sequence similarity threshold.
Community composition per phylum in Hållö island and Gullmarn fjord samples, according to extraction method (MgCl2, H2O, Siphoning). A) For the COI gene. B) For the 18S gene. The vertical axis corresponds to percentage of OTUs. Taxonomic assignment is based on a 97% similarity threshold. The bar plots take into account number of reads for each OTU.
Alpha diversity rarefaction plots for COI and 18S datasets including unassigned OTUs. According to location for COI (A) 18S (B). Hållö Island (HI) in red, Gullmarn Fjord (GF) in blue. According to extraction method for COI (C) 18S (D). HI flotation in red, HI MgCl2 in blue, GF flotation in yellow, GF siphoning in green. According to primer pair for COI (E). CO1 Leray primer in red, COI Lobo primer in blue.
Beta diversity PCoA plots for COI and 18S datasets including unassigned OTUs. According to extraction method for COI (A) 18S (B) HI flotation in red, HI MgCl2 in blue, GF flotation in yellow and GF siphoning in green. According to primer for COI (C) COI Leray primer in red, COI Lobo primer in blue
Methodological comparison of benthic and pelagic metabarcoding studies of marine fauna published to date










Coral reef fish gut contents  Dissection of fish gut  Roche 454 GS FLX  COI  313  UCHIME  CROP 
Moorea Biocode Database, GenBank 

Autonomous reef monitoring structures  4 fractions (Sessile, 2mm, 500μm, 106μm)  Ion Torrent  COI  313  BOLD, GenBank  

Zooplankton from 50m to the surface  200μm mesh WP2 plankton net  Roche 454 GS FLX  18S 
450  ChimeraSlayer 
UCLUST 97% 
Silva 108, GenBank 

Plankton  3 fractions (520μm, 
Pairedend Illumina Genome Analyser IIx system  18S 
USEARCH  V9_PR2, V9 rDNA, Protistan Ribosomal Reference Database  

Marine benthic meiofauna  Decanting 
Roche 454 GS FLX  18S 
364 
OCTOPUS  OCTOPUS 96%  GenBank 

Marine benthic meiofauna  Decanting 
Roche 454 GS FLX  18S 
450  AmpliconNoise  AmpliconNoise 
GenBank 

Marine benthic meiofauna  Directly from sediment, elutriated on 45μm sieve  Pairedend 100 bp reads Illumina HiSeq  18S 
87187 [ 
USEARCH 6.1. (QIIME 1.8)  UPARSE 97% 
Silva 111 

Benthic meiofauna from seagrass meadows  2mm sieve, 1mm sieve, 0.5mm sieve  Roche 454 GS FLX  COI 
450 
USEARCH 6.1 
UCLUST de novo (QIIME 1.7)  GenBank 
This study  Meiofauna from coarse shell sand and muddy benthic sediment  Siphoning 125μm, 
Pairedend Illumina MiSeq  COI 
313 
UCHIME 
CROP 
BOLD, SweBol and own databases for 
Primer sequences used in this study




mlCOIintF  5’TCGTCGGCAGCGTCAGATGTGTATAAGAGACAG 
dgHCO2198  5’GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAG 


mlCOIintF  5’TCGTCGGCAGCGTCAGATGTGTATAAGAGACAG 
LoboR1  5’GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAG 


SSU_FO4  5’TCGTCGGCAGCGTCAGATGTGTATAAGAGACAG 
SSU_R22  5’GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAG 
Number of reads per marker and per sequencing run





COI  5 859 454  5 075 735  4 948 085  15 883 274 
18S  2 803 391  3 135 331  2 310 879  8 249 601 
Total  8 662 845  8 211 066  7 258 964  24 132 875 
Number of reads remaining after each bioinformatic step






COI  15 883 274  10 412 096  8 099 507  7 976 649  7 954 017 
18S  8 249 601  2 131 102  1 071 871  1 015 874  890 370 
Total  24 132 875  12 543 198  9 171 378  8 992 523  8 844 387 
Number of OTUs and percentage per phylum for COI and 18S for the metazoan fraction. Based on a 97% similarity threshold.










57  30.00  29  23.97 

52  27.37  14  11.57 

5  2.63  3  2.48 

0  0.00  1  0.83 

1  0.53  0  0.00 

12  6.32  7  5.79 

8  4.21  4  3.31 

13  6.84  5  4.13 

1  0.53  9  7.44 

1  0.53  0  0.00 

26  13.68  6  4.96 

0  0.00  10  8.26 

3  1.58  6  4.96 

0  0.00  13  10.74 

1  0.53  0  0.00 

2  1.05  3  2.48 

1  0.53  0  0.00 

2  1.05  0  0.00 

1  0.53  1  0.83 

0  0.00  1  0.83 

4  2.11  9  7.44 
Total OTUs 
190  100  121  100 
Nonparametric ttest results with 999 MonteCarlo permutations for both datasets with and without unassigned OTUs (97% taxonomic assignment)



Excluding unassigned OTUs  Including Unassigned OTUs  Excluding unassigned OTUs  Including Unassigned OTUs  
Test value  Pvalue  Test value  Pvalue  Test value  Pvalue  Test value  Pvalue  
Location  
HI vs. GF  14.453  0.001  21.455  0.001  6.929  0.001  7.170  0.001 
Method  
HI H2O vs. HI MgCl2  0.437  1.0  0.691  1.0  0.906  1.0  0.174  1.0 
GF flotation vs. GF siphoning  1.567  0.792  1.546  0.99  1.427  1.0  0.744  1.0 
Primer  
COI Leray vs. COI Lobo  0.508  0.596  1.614  0.111         
ANOSIM test results (999 permutations) for both COI and 18S datasets with and without unassigned OTUs (97% taxonomic assignment)



Ho: Sample composition differs according to  Excluding unassigned OTUs  Including unassigned OTUs  Excluding unassigned OTUs  Including unassigned OTUs  
Rvalue  Pvalue  Rvalue  Pvalue  Rvalue  Pvalue  Rvalue  Pvalue  
Location  0.976  0.001  1.0  0.001  0.935  0.001  0.929  0.001 
Method  0.660  0.001  0.738  0.001  0.889  0.001  0.895  0.001 
Primer  0.200  0.003  0.218  0.001         


OTU ID  Nb of reads  Phylum  Class  Order  Species  HI  GF 
HE6.Lobo_7972794  3 




+   
HE1.Lobo_933012  14954 




+  + 
HF8.Lobo_5239705  241 




+  + 
HF4.Lobo_97092  29391 




+  + 
HF5.Lobo_3297996  1 




+   
TS1.Leray_545620  7370 




  + 
HF1.Lobo_4996219  4596 




+  + 
TF6.Lobo_5247622  9030 



  +  
TS1.Lobo_4669404  5 



  +  
TF5.Lobo_6394093  2 



  +  
TS3.Leray_6813257  1852 



  +  
HF5.Leray_4035802  1 




+   
TS2.Leray_4445240  8815 




+  + 
TF3.Leray_6645504  5196 



+  +  
TS5.Lobo_6031643  5089 



+  +  
HF9.Lobo_7587930  1 



+    
HE8.Leray_7284535  2 



+    
TS5.Leray_1557252  88 



  +  
TS3.Leray_6744085  1 



  +  
TS3.Leray_6805306  2 




  + 
TS3.Lobo_1308935  4213 




+  + 
HE6.Leray_2958692  69642 




+  + 
HF7.Leray_1672792  69 




+  + 
TF5.Leray_2872180  7754 




  + 
HF1.Lobo_5059232  13 




+   
HF9.Lobo_7695035  1 




+   
HE6.Lobo_7972042  2 




+   
HF9.Lobo_7688887  3 




+   
HF2.Lobo_2136301  178929 




+  + 
HE3.Leray_364663  59407 




+  + 
TS4.Leray_7471107  1 




  + 
HE5.Lobo_493462  571790 


+  +  
TS2.Lobo_6962270  4595 




+  + 
TS2.Leray_4491798  316559 



+  +  
TS4.Lobo_1502925  195999 



+  +  
HF9.Lobo_7588557  891 



+    
TS6.Leray_5665274  936 



  +  
TF1.Lobo_2668551  874 



  +  
HE4.Leray_3067470  3 




+   
HF1.Lobo_4965916  1 




+   
HF9.Leray_4404528  1 




+   
HF5.Lobo_3178682  2894 




+  + 
TF1.Leray_2314881  29235 



+  +  
TF1.Lobo_2832834  9348 



+  +  
TS1.Leray_614419  788 



+  +  
HE8.Lobo_858951  1 



+    
TS2.Lobo_6889557  184 



  +  
TS6.Lobo_255019  3 



  +  
TS2.Lobo_6860909  1 



  +  
TS5.Leray_1638640  1 



  +  
TF1.Lobo_2848745  1305 




+  + 
TS3.Leray_6729893  1 




  + 
HF4.Lobo_96799  102 




+   
HF2.Lobo_2052205  285 




+   
TS5.Leray_1638834  102 




+  + 
HE9.Lobo_2191024  8 




+  + 
TF1.Leray_2475372  6353 




+  + 
HE1.Lobo_982378  38 




+   
TF5.Lobo_6391642  10097 




+  + 
HF9.Lobo_7623741  1 




+   
TS4.Leray_7402581  10 



+  +  
TS3.Lobo_1162454  2 




+  + 
HF4.Lobo_5006  1 




+   
TF5.Leray_2910679  6 



+  +  
HF9.Lobo_7599310  3 




+  + 
HE5.Lobo_479906  152 




+  + 
HE2.Lobo_2023271  21589 



+  +  
HF1.Leray_2493444  3911 



+    
HE8.Lobo_860608  1 



+    
HE3.Lobo_4900763  1 




+   
HF4.Leray_6193380  66039 




+  + 
HE8.Leray_7216397  1 




+   
HE6.Lobo_7849183  1 




+   
HE1.Lobo_914374  14588 




+  + 
TF1.Leray_2445583  56 




  + 
TF6.Leray_5321299  11588 



+  +  
HF9.Leray_4291607  1372 




+   
HF8.Leray_5586003  2864 




+  + 
HF8.Leray_5612792  37 




+   
HE1.Lobo_952576  3739 




+   
TF5.Lobo_6459477  1279 




+  + 
HE4.Lobo_4138563  42 




+  + 
HE8.Leray_7306131  2 




+   
TS3.Lobo_1213146  17 




+  + 
TF5.Leray_2897128  3 




  + 
HF3.Leray_7129076  22 




+  + 
TF6.Leray_5332240  7399 




+  + 
HF7.Leray_1683272  927 




+  + 
HE2.Lobo_2010882  1 




+   
TS2.Leray_4478240  2 




  + 
HF7.Lobo_5810493  41 




+  + 
HF8.Lobo_5106754  82 




+  + 
HE8.Leray_7251655  1 




+   
HE7.Leray_3803390  5325 




+  + 
HF9.Leray_4411242  1 




+   
TS4.Leray_7515925  2 




  + 
TS3.Lobo_1208165  1 




  + 
TF5.Lobo_6373065  809 




+  + 
TF1.Leray_2453024  1 




  + 
HF4.Leray_6242499  45 



+    
HF4.Leray_6206299  2 



+    
HE8.Lobo_823478  108 



+    
TS3.Lobo_1208905  116 




+  + 
HE1.Lobo_995710  1 




+   
HF4.Leray_6092514  1 



+    
HF9.Leray_4391714  11307 




+  + 
HF4.Leray_6295260  1079 




+  + 
HF7.Leray_1785147  2 




+   
HE1.Leray_1117391  1 




+   
HE9.Lobo_2173983  63 




+   
HF7.Leray_1838377  98 




+   
HE3.Lobo_4881810  541 




+   
HF6.Lobo_2617384  2 




+   
HF5.Lobo_3158598  5 




+   
HE6.Leray_2983148  31 



+    
TS1.Leray_646185  73 




+  + 
HF4.Lobo_208606  1 




+   
HF1.Leray_2487062  288 




+   
HF3.Lobo_3538759  472 




+   
TF1.Lobo_2807051  486 




+  + 
HF9.Lobo_7596943  8 




+   
HF5.Lobo_3273051  43 




+   
HE2.Lobo_1914646  81 




+   
HE8.Lobo_879846  265 




+   
HE8.Lobo_756051  34 




+   
HF3.Lobo_3595218  14 




+   
HE8.Lobo_873511  131011 


 

+  + 
TF3.Leray_6588680  3869 



+  +  
TF6.Lobo_5251371  1 




  + 
HE9.Lobo_2164485  2 




+   
TF6.Leray_5512978  1481 




+  + 
HF5.Lobo_3253786  232 




+  + 
HE3.Leray_361248  14 




+  + 
HE2.Leray_6553538  1 



+    
HE2.Leray_6571642  184 




+   
HE7.Leray_3802459  570 




+   
HE3.Leray_388102  85 




+   
HF4.Leray_6293728  71 




+  + 
HE8.Leray_7326980  315 




+   
HE6.Lobo_7886165  1 



+    
TF3.Leray_6591339  2079 




+  + 
HF7.Leray_1843674  94 




+   
TS5.Lobo_6025603  11 




+  + 
TS3.Leray_6733304  1027065 



+  +  
TS1.Leray_663710  3 




  + 
TF1.Lobo_2726978  298 




  + 
TF1.Leray_2426830  16603 




+  + 
TF5.Leray_2879711  1 




  + 
HF3.Leray_7012508  44 

_ 

+    
HE1.Lobo_948618  14 



+    
TS2.Leray_4506244  1 




  + 
HF3.Leray_7058438  371 




+  + 
HE1.Lobo_894587  22 




+   
TS1.Lobo_4571224  4 


Nuculida 

  + 
TS3.Leray_6727248  56213 




+  + 
HE4.Lobo_4121128  25 




+  + 
TF5.Leray_2915847  1911 




+  + 
TS6.Leray_5683559  2 




  + 
HF1.Leray_2592679  33 




+   
HE7.Leray_3779267  14392 




+  + 
HF5.Lobo_3246886  1 




+   
TS1.Lobo_4750257  2 



  +  
TS1.Lobo_4792606  2 



  +  
HF8.Lobo_5143779  2 




+   
HE3.Lobo_4838288  34 




+  + 
HF6.Lobo_2622544  37 




+   
HE2.Lobo_1993552  50 



+    
HE6.Leray_2935130  2 



+    
HF1.Leray_2520121  559 




+   
HE2.Lobo_1978270  5 




+   
HE2.Lobo_1939813  155 




+   
HE2.Lobo_1938412  10 




+   
HF5.Leray_3991765  847 




+   
HF4.Leray_6295954  2965 




+  + 
HF5.Lobo_3167773  166 




+   
HE4.Lobo_4138137  2 




+   
TS1.Lobo_4644275  2 


_  +  +  
HE4.Lobo_4203493  3 


_ 

+   
TF1.Lobo_2662495  1 


_ 

  + 
HF7.Lobo_5876008  353 

_  _ 

+   
HE8.Lobo_843910  13 




+   
HE4.Leray_3148053  1664 




+  + 
TS5.Leray_1547671  2628 




+  + 
HF5.Leray_3885266  5 




+   
HE3.Leray_357208  2 



+    
HF8.Lobo_5184437  1 




+   
TS1.Lobo_4586276  14 

_ 

  +  
TS3.Lobo_1178177  4 

_ 


  + 
HF9.Lobo_7719366  2 

_ 


+   
HF9.Lobo_7734506  1 

_ 


+   


OTU ID  Nb of reads  Phylum  Class  Order 

HI  GF 
TF5.SSU_460284  121639 

_  _  +  +  
TS3.SSU_470635  59 

_  _    +  
HF9.SSU_7624  12 



+    
TF5.SSU_453927  2687 




+  + 
HF3.SSU_985477  1090 


_  +  +  
HF6.SSU_322303  10 


_ 

+   
HF4.SSU_622170  1 


_ 

+   
HF9.SSU_25735  3753 


_ 

+   
TS3.SSU_480632  189 



  +  
HE6.SSU_371492  49226 



+  +  
HE4.SSU_913344  37252 



+  +  
HF5.SSU_997904  64 




+  + 
TS5.SSU_870099  69 




  + 
TF6.SSU_42415  2 




  + 
HE6.SSU_350003  5 



+    
HF6.SSU_324605  2 




+   
HE7.SSU_239005  67220 




+  + 
HE2.SSU_637269  49 




+   
HE8.SSU_832291  1 




+   
HE8.SSU_834197  1 




+   
HF2.SSU_202737  4 




+   
HE2.SSU_640060  3 



+    
TS5.SSU_869292  123 



  +  
TS3.SSU_517096  1407 



  +  
HE3.SSU_123438  1952 



+  +  
TS5.SSU_882766  60 




  + 
HF2.SSU_193854  1 



+    
TF6.SSU_63146  669 



  +  
TS5.SSU_883475  4155 




  + 
TF4.SSU_139713  193 


_    +  
HE5.SSU_184679  149 


_  +    
HE8.SSU_832214  1 



+    
HF5.SSU_994971  7 




+   
TF6.SSU_56595  65992 


_  +  +  
HF9.SSU_15855  31800 


_  +  +  
HF2.SSU_208480  21241 


_  +  +  
TS2.SSU_812824  433 


_  +  +  
TF3.SSU_955499  185 


_  +  +  
TF5.SSU_470101  360 




  + 
HE1.SSU_864375  1160 




+  + 
HE7.SSU_253407  2584 




+  + 
HE5.SSU_181011  1 




+   
HE2.SSU_646490  123 



+    
HE2.SSU_638224  23 

_  _  +    
HE6.SSU_373369  2 




+   
HE1.SSU_850917  4 




+   
TF5.SSU_412099  18 




  + 
HE7.SSU_239963  45 



+  +  
HE3.SSU_123107  4 


_  +    
HF9.SSU_12142  727 



+  +  
HF4.SSU_611685  114 




+  + 
HE2.SSU_639404  209 



+    
HE9.SSU_314754  616 




+   
HE8.SSU_834024  11058 


_  +    
TF1.SSU_674740  2212 




+  + 
TS3.SSU_472524  2741 


_  +  +  
TS3.SSU_518760  7860 



+  +  
HE2.SSU_639670  1 




+   
TF4.SSU_152912  61418 

_  _  +  +  
HE5.SSU_186025  8038 

_  _  +  +  
TF4.SSU_155631  5491 

_  _  +  +  
TS5.SSU_881395  25 

_  _    +  
HE4.SSU_914821  1 



+    
HF9.SSU_2577  1006 

_ 

+  +  
HE7.SSU_244283  249 

_ 


+   
HF5.SSU_996540  161 

_ 

+    
HF5.SSU_995416  636 

_ 

+    
HF2.SSU_192734  479 

_ 

+    
HF7.SSU_385728  6934 

_ 

+  +  
HE7.SSU_242889  3013 

_ 


+   
HF1.SSU_770513  339 

_ 


+   
HF1.SSU_760431  5 

_ 

+    
TF6.SSU_44832  3816 


_  +  +  
HF2.SSU_208561  14 



+  +  
HF8.SSU_788507  1 




+   
TF3.SSU_924397  11725 



+  +  
HE9.SSU_317977  1982 




+  + 
TF4.SSU_132537  1581 




+  + 
HF1.SSU_779114  65 



+  +  
TF6.SSU_48167  2940 



+  +  
TF1.SSU_710679  639 



+  +  
HF2.SSU_192072  2 




+   
HF1.SSU_759758  4 



+    
HF9.SSU_20251  636 



+  +  
HE3.SSU_124287  13 



+    
HE3.SSU_110275  8 



+    
HE5.SSU_188855  27 



+  +  
TS6.SSU_587229  493 




+  + 
TF3.SSU_938615  642 

_  _  +  +  
TF6.SSU_49192  265 


_ 

+  + 
HE4.SSU_908113  877 


_ 

+  + 
HF9.SSU_3582  6 


_ 

+   
HE3.SSU_121696  12053 


_ 

+  + 
TF5.SSU_434928  1760 


_ 

+  + 
TS2.SSU_818002  1 



  +  
HE9.SSU_303121  1939 




+   
HF1.SSU_773830  1 




+   
HE2.SSU_650311  8 



+    
HE5.SSU_177399  4 




+   
HF9.SSU_23023  8367 




+  + 
TS2.SSU_822141  938 




  + 
TF6.SSU_52738  214 




  + 
TF5.SSU_433159  2 




  + 
HF9.SSU_24513  59 




+  + 
HF2.SSU_201740  2 




+   
TS6.SSU_592673  245 



+  +  
HF4.SSU_616041  771 



+    
HE3.SSU_117223  181 


_  +  +  
HE7.SSU_223989  12 




+   
HF9.SSU_26977  8 




+   
HE6.SSU_383060  3 




+   
HE6.SSU_348954  2 




+   
TF3.SSU_927927  2 

_  _    +  
HE3.SSU_116025  28 

_ 

+  +  
HF9.SSU_26335  1 

_ 

+    
TS2.SSU_815721  2 

_ 

  +  
TS2.SSU_815970  1 

_ 

  +  
HF2.SSU_190395  2386 

_ 

+    
HF1.SSU_758202  74 

_ 

+  +  
HF9.SSU_13290  5 

_ 


+   
TS6.SSU_601153  28 

_ 


  + 
Invasive species (in bold) and species on alert lists (not bold) found in the samples. X indicates where the species were found.





Hållö island  Gullmarn Fjord  Hållö island  Gullmarn Fjord  


x  x  


x  x  


x  x  x  


x  x  


x 
Taxonomic composition and relative abundance (% of the total number of specimens) of











1 

1.03  0  0  0 
2 

3.78  0  0  0 
3 

1.03  0  0  0 
4 

2.06  0  0  0 
5 

3.44  0  0  0 
6  25.09  0  0  0  
7 

43.99  0  0  0 
8 

0.34  0  0  0 
9  cf. 
4.81  0  0  0 
10  0.34  0  0  0  
11  2.06  100  88.71  0  
12 

3.09  0  
13  0.34  0  0.81  0  
14 

0  0  2.42  0 
15  0  0  0.81  0  
16 

0  0  0.81  0 
17  0  0  0.81  0  
18 

0  0  5.65  0 


19 

8.25  0  0  0 
20 

0.34  0  0  0 
Total number of





Hållo, flotation with MgCl2  7  11  8  6 
Hållö, flotation with fresh water  0  15  11  6 
Hållö, total  7  16  12  7 
Gullmarn Fjord, siphoning  15  11  9  4 
Gullmarn Fjord, flotation with fresh water  1  13  2  0 
Gullmarn Fjord, total  15  19  10  4 
Total number of nematode taxa or OTUs distinguished based on morphology (after





Hållo, flotation with MgCl2  88  71  12  11 
Hållö, flotation with fresh water  101  78  14  14 
Hållö, total  107  95  16  17 
Gullmarn Fjord, siphoning  81  47  8  4 
Gullmarn Fjord, flotation with fresh water  102  67  4  2 
Gullmarn Fjord, total  113  78  9  4 
OTUs identified to species level in the samples using 97% sequence similarity, all organism groups
Data type: Occurrence records from Metabarcoding for Hållö island and Gullmarsfjord, Sweden.
Brief description: Sequence similarity search at 97% similarity allowed us to identify some OTUs to species level. 215 COI OTUs and 243 18S OTUs were identified to species from both sites (Hållö island and Gullmarsfjord).
File: oo_137797.xlsx
OTU table for 18S
Data type: Metagenomic, OTU table
Brief description: OTU table showing all 18S OTUs, their taxonomic assignment at 80% similarity and number of reads per sample (HE: Hållö Flotation, HF: Hållö Flotation MgCl2, TS: Gullmarn Fjord Siphoning, TF: Gullmarn Fjord Flotation)
File: oo_124225.txt
OTU table for COI
Data type: Metagenomic, OTU table
Brief description: OTU table showing all COI OTUs, their taxonomic assignment at 80% similarity and number of reads per sample (HE: Hållö Flotation, HF: Hållö Flotation MgCl2, TS: Gullmarn Fjord Siphoning, TF: Gullmarn Fjord Flotation)
File: oo_124226.txt