8. Active submarine volcanoes and hydrothermal vents
Map ID Number: 8
Location: Known features are north of North Island’s Bay of Plenty, located in the Kermadec Ridge/Havre Trough area. Shallow-water hydrothermal venting also occurs on the Bay of Plenty continental shelf. Vent organisms have been collected from shelf depths, with offshore biological sampling concentrated between 200-2,500m on the Kermadec Ridge/Havre Trough.
Approximate area: 105,584km2
Description of area:
Hydrothermal vents are zones of fluid expulsion from the sea floor, normally associated with sea floor spreading or tectonic plate subduction. Minerals contained within the expelled fluids are utilised as an energy source for vent bacteria. These specialised microbes form the basis of a unique class of ecosystem operating independently from the photosynthetically driven system that dominates the rest of the biosphere. In the New Zealand region, undersea volcanism and hydrothermal venting are associated with extensive back-arc basinal volcanism in the Kermadec subduction zone.
Biological attributes:
New Zealand hydrothermal vent ecosystems are in their early phase of investigation, but preliminary results indicate that their faunas are diverse and disparate (i.e. little overlap with the inhabitants of adjacent non-vent habitats). Endemism at New Zealand vents appears to be high, with recently published records of (apparently) regionally endemic vent polychaetes (Branchipolynoes); molluscs (the mussel species Bathymodiolus tangaroa and Gigantidus gladius, the latter a new genus); barnacles (Neolepas osheai); several new shrimp species (including Alvinocaris niwa), and a large and as-yet undescribed asteroid. The aforementioned taxa are mainly large, conspicuous organisms, and overseas experience suggests that a wealth of smaller, more cryptic, vent organisms are likely to be discovered at New Zealand hydrothermal vents. At a fine scale, New Zealand vents have yet to be properly categorised. It is likely, however, that a range of vent environmental conditions will be found (e.g. variation in temperature and chemical composition of fluids), and that this habitat complexity will give rise to a small-scale variability in vent communities. Vent organisms display unique and highly specialised physiological adaptations to a physical and chemical environment that would be lethal to most other forms of life. Due to the highly productive nature of vent ecosystems, local biomass of vent primary producers and consumers is usually elevated, sometimes to a level several orders of magnitude greater than the surrounding environment. Special phylogenetic groupings in vent ecosystems include particular polychaete, crustacean, and molluscan taxa. Biogeographically, New Zealand’s hydrothermal vents are significant, as demonstrated by several past and forthcoming international research expeditions intended to document the vents’ geology and fauna. Subduction-related venting has been less studied than spreadingaxis venting, and the comparison of regional faunas with global patterns of distribution is of great interest. Given the unique nature of their chemotrophic ecosystem, vent faunas represent a significant addition to New Zealand’s marine trophic and functional diversity. In terms of conservation status, vent habitats merit priority because of their uniqueness, restricted range and vulnerability (e.g. the potential commercial significance of the mineral deposits associated with venting sites). Hydrothermal vents possess a cultural appeal that transcends their inaccessibility. Despite their limited distribution, vent ecosystems figure highly in the popular conception of the deep-sea environment, perhaps because of their inherent strangeness and aesthetic appeal.
Criteria applied:
Species diversity; species richness; endemism; trophic/functional diversity; conservation status/ threat classification both nationally and globally; cultural values; extremities of range and adaptation to environment; special conditions and specialised organisms; unusual degree/proportion of biomass; special phylogenetic grouping; habitat complexity/diversity; links to global patterns.
Status and management:
Two areas of active hydrothermal venting were closed to commercial trawling in 2001: the Rumble 3 and Brothers Seamounts. These closures were framed in terms of seamount closures under the auspices of the 1996 Fisheries Act (as two of 19 seamounts closed). In this sense there is still no specific management of hydrothermal vent ecosystems. However, benthic fisheries are severely constrained in some parts of this area by nominal catch
State of information:
Research is in its early stages. Offshore sampling of New Zealand hydrothermal vents has only been undertaken seriously in the last 15 years. At least seven active venting localities are known from Kermadec Ridge seamounts, in addition to the Brothers and Rumble sites. Upcoming submersible-based investigations will dramatically increase knowledge of the distribution, biodiversity and ecology of New Zealand vents.
References
Buckeridge (2000), Clark and O’Shea (2001a, 2001b), de Ronde et al. (2001), Kamenev et al. (1993), Rowden et al. (2003), von Cosel and Marshall (2003), Webber (2004), Wright (1994).