Figure 1.
Cold seep sites on the Hikurangi Margin of New Zealand.
Labelled circles indicate regions referred to in the text, crosses show individual seep sites at which live chemoautotrophic communities have been sampled (see Table 1 and Greinert et al. [12] for site details).
Table 1.
Cold seep sites on the Hikurangi Margin sampled by towed camera transects.
Figure 2.
Hikurangi Margin cold seep habitats and fauna (1).
(A) bacterial mats on soft sediments at North Tower; (B) sulphide-rich sediment patch with high density ampharetid polychaete population and (inset) characteristic ‘raindrop’ patterning at North Tower; (C) extensive Calyptogena sp. shell valves surrounding a population of live clams (yellow outline) with live and dead Bathymodiolus sp. mussels at Tui; (D) high density Lamellibrachia sp. tubeworm population at Southwest Moa showing tubes emerging from upper surface of carbonate concretions; (E) high densities of Stelletta n. sp. sponges and Bathymodiolus sp. mussels (along ledge at top) at Southwest Moa, and (F) scleractinian and gorgonian corals on weathered carbonates at Moa. Scale bars show 0.2 m.
Figure 3.
Hikurangi Margin cold seep habitats and fauna (2).
(A) ‘Chemoherm’ habitat at Southwest Moa showing Lamellibrachia sp. tubeworms in association with authigenic carbonates, live Calyptogena sp. clams (yellow outline) and disarticulated shell valves, two spherical Stelletta n. sp. sponges, grey bacterial mats on carbonates (at upper left), and sulphidic sediments; (B) Underside of a carbonate block recovered by grab from chemoherm at North Tower, showing Lamellibrachia sp. tubes rooted in soft, grey, sulphide-rich, anoxic material at the base of the block; (C) Gracilechinus multidentatus sea urchins with Calyptogena sp. shell debris on soft sediments at the periphery of Tui seep; (D) Lithodes aotearoa crabs amongst Calyptogena sp. shell debris at Tui seep. Scale bars show 0.2 m.
Figure 4.
North Tower seep, Opouawe Bank.
Observations from towed video camera transects showing distributions of: authigenic carbonate rocks (red, “chemoherm”; orange, “large blocks (>20 cm)”; yellow, “small blocks (<20 cm)”); Lamellibrachia sp. siboglinid tubeworms; disarticulated shell valves of Calyptogena sp. vesicomyid clams; live Calyptogena sp. clams; bacterial mats, and dark, sulphide-rich sediment patches colonised by ampharetid polychaetes. Transects are plotted against a side-scan sonar image of the seabed generated during SO191-2 (darker pixels indicate stronger acoustic backscatter). Labels in the top left panel show voyage and deployment number for each transect: TAN0616, RV Tangaroa 2006; SO191, RV Sonne 2007; SO214, RV Sonne 2011.
Figure 5.
Representative profiles across selected seep sites at Opouawe Bank.
Site name abbreviations: NTR, North Tower; PIW, Piwakawaka; TUI, Tui; TAK, Takahe (numbers on North Tower profiles show station numbers; see Figure 4. Station numbers for other sites: PIW, SO214-070; TUI, SO191-129; TAK, SO214-065). Data are from analyses of still images taken during towed camera transects across each site. Point markers show population densities of seep-associated fauna (individuals m−2, log scale, left y-axis), area fills show substratum type as proportion of the full image area (% of image area, right y-axis). Profiles are scaled to horizontal distance travelled (x axis).
Figure 6.
Representative profiles across selected seep sites at Uruti Ridge, Omakere Ridge, Rock Garden, and Ritchie Ridge.
Site name abbreviations: HIH, Hihi; SWM, Southwest Moa; BPW, Bear's Paw; LM3, LM-3; BPL, Builder's Pencil (figures on Builder's Pencil profiles show station numbers. Station numbers for other sites: HIH, TAN0616-066; SO214-094; BPW, SO191-52-3; LM3, SO191-042). Data, symbols, and scale as for Figure 5.
Figure 7.
Non-metric multivariate scaling (NMDS) ordination of Hellinger distances between seep communities observed in video transects.
Underlying data are log-transformed occurrence records of chemoautotrophic megafauna (Lamellibrachia sp. tubeworms, Calyptogena sp. clams, Bathymodiolus sp. mussels, Stelletta n. sp. sponges), seep-associated substrata (bacterial mats, ampharetid patches and Calyptogena sp. clam shells), and intact scleractinian coral matrix. A – Transects distinguished by region (symbols; see Figure 1 for context) and seep site (labels; see Table 1 for full names). B – Contributions (Pearson correlations) of faunal variables to between-sample distances. C – Relationships (Pearson correlations) between three environmental variables and the distribution of transects in the ordination: depth (−0.57); % carbonate rock substratum (0.52), and number of trawls per site from 1998 to 2005 (0.41).
Figure 8.
Trawl intensity at seep sites by region.
Selected seep sites are identified by name (see Table 1 for full names). Trawl data are cumulative totals for the period 1989–90 to 2004–5 [24] calculated as the number of trawl tracks intersecting a 250 m radius circle around seep site positions given in Greinert et al. [12].
Figure 9.
Cold seep communities and gas hydrates.
Distribution of cold seep faunal communities (black crosses, regions as in Figure 1) on the Hikurangi Margin in relation to occurrence of bottom simulating reflectors (BSR) in seismic survey data and sites of potential interest for gas hydrate exploration (white stars): A, channel system north of Uruti Ridge; B, Pegasus Basin; C, Tuaheni Basin; D, Opouawe Bank; E, Porangahau Ridge.
Figure 10.
Hypothetical succession sequence at Hikurangi Margin cold seep sites.
Labels ‘S1’, ‘S2’, etc., indicate Successional Stages as described in the discussion text.
Figure 11.
Interaction between seep site age and disturbance from trawling.
NMDS ordination of seep site communities (see Figure 7) showing conceptual illustration of the relative influences of seep site age and trawling on observed seep characteristics.