Linking regional variation of epibiotic bacterial diversity and trophic ecology in a new species of Kiwaidae (Decapoda, Anomura) from East Scotia Ridge (Antarctica) hydrothermal vents

Abstract

We analyzed the diversity of bacterial epibionts and trophic ecology of a new species of Kiwa yeti crab discovered at two hydrothermal vent fields (E2 and E9) on the East Scotia Ridge (ESR) in the Southern Ocean using a combination of 454 pyrosequencing, Sanger sequencing, and stable isotope analysis. The Kiwa epibiont communities were dominated by Epsilon- and Gammaproteobacteria. About 454 sequencing of the epibionts on 15 individual Kiwa specimen revealed large regional differences between the two hydrothermal vent fields: at E2, the bacterial community on the Kiwa ventral setae was dominated (up to 75%) by Gammaproteobacteria, whereas at E9 Epsilonproteobacteria dominated (up to 98%). Carbon stable isotope analysis of both Kiwa and the bacterial epibionts also showed distinct differences between E2 and E9 in mean and variability. Both stable isotope and sequence data suggest a dominance of different carbon fixation pathways of the epibiont communities at the two vent fields. At E2, epibionts were putatively fixing carbon via the Calvin-Benson-Bassham and reverse tricarboxylic acid cycle, while at E9 the reverse tricarboxylic acid cycle dominated. Co-varying epibiont diversity and isotope values at E2 and E9 also present further support for the hypothesis that epibionts serve as a food source for Kiwa.

Keywords: East Scotia Ridge; Kiwa sp.; epibionts; hydrothermal vent; microbial diversity; stable isotopes.

Figure 1

(A) Kiwa sp. nov. East Scotia Ridge (ESR), (B) ventral view, showing the setae covering the ventral side. (C) individual setae covered with epibiotic bacteria, (D and E) SYBR green staining of epibiotic bacteria. Scale bars: (A, B) – 5 cm, (C, D) – 100 μm, (E) – 50 μm.

Figure 2

Neighbor joining tree of 16S rRNA sequences of Kiwa sp. nov. ESR (blue), Kiwa hirsuta (green), Kiwa puravida (yellow), Shinkaia crosnieri (red), Rimicaris exoculata (black), and Vulcanolepas sp. (pink). (A) Epsilonproteobacteria, (B) Gammaproteobacteria and Bacteroidetes. The tree was calculated within arb using neighbor joining with the Felsenstein correction using only sequences >1300 nt. Shorter sequences were then added by parsimony within arb. The length of each sequence is shown in the tree, followed by the Genbank accession number. Bootstrap values were calculated with the arb parsimony interactive tool. Only bootstrap values >50% are shown.

Figure 3

Phylogenetic analysis of 454 sequencing data of epibionts from 15 Kiwa sp. nov. ESR individuals. OTUs are defined at a cutoff of 0.03. ESR, East Scotia Ridge; OTUs, operational taxonomic units.

Figure 4

PCoA of Kiwa sp. nov. East Scotia Ridge (ESR) epibionts of 15 specimen at four E2 and E9 sampling sites based on 454 data.

Figure 5

Isotopic niche of Kiwa sp. nov. East Scotia Ridge (ESR) δ¹³C and δ¹⁵N values for female (squares) and male (circles) Kiwa sp. nov. ESR from E2 and male (triangle) Kiwa sp. nov. ESR from E9 with their respective standard ellipse area (solid line) with a boundary plotted (dotted line) around the extreme points to aid visualization. The dashed and solid vertical lines represent the range of δ¹³C values for different carbon fixation pathways: <−20‰ for the Calvin-Benson-Bassham (CBB) cycle, >−16‰ for the reductive tricarboxylic acid (rTCA) cycle and −20‰ to −16‰ for mixing of the two carbon sources.

Figure 6

Plots of δ¹³C against carapace length (mm) for Kiwa sp. nov. East Scotia Ridge (ESR) for samples collected from E2 female (squares and solid line), E2 male (circles and long dash line), and E9 male (triangles and short dash line) Kiwa. In male Kiwa sp. nov. ESR there was an increase in δ¹³C with carapace length (mm) (CL) in E2 (δ¹³C = −25.78 + 0.118 CL; F_1,16 = 12.93, r²_adj = 0.41, P < 0.01) and E9 (δ¹³C = −13.06 + 0.059 CL; F_1,50 = 67.81, r²_adj = 0.58, P < 0.001). However, female Kiwa sp. nov. ESR did not increase in δ¹³C with CL (δ¹³C = −21.52 + 0.118 CL; F_1,17 = 0.2428, r²_adj = −0.04, P = 0.69).