Megabenthic ecology of abyssal polymetallic nodule fields

Abstract

Abyssal polymetallic nodule fields constitute an unusual deep-sea habitat. The mix of soft sediment and the hard substratum provided by nodules increases the complexity of these environments, and is thought to promote the occurrence of some of the most biologically diverse seafloor assemblages in the abyss. This unusual and diverse habitat is potentially subject to imminent large-scale human impacts in the form of seafloor mining. Mining disturbances are likely to extend over extremely large seafloor areas and have a clear potential to drive major changes in the resident fauna. Predicting the nature of such changes remains difficult; the ecology of this remote and vast habitat is poorly understood. The large seafloor areal coverage that can be investigated using photographic surveys presents an opportunity to numerically quantify variation in megafaunal communities inhabiting these abyssal plain environments. In this thesis, the fundamental drivers of megabenthic community variations in abyssal polymetallic nodule fields are explored based on extensive acoustic and imagery data collected using autonomous underwater vehicles. First, baseline ecological patterns of megafaunal distribution are investigated at different factor-operating scales, i.e. different environmental factors, in the proposed conservation zone ‘Area of Particular Environmental Interest 6’ of the Clarion Clipperton Zone (NE Pacific; water depth: 3950-4250 m). Broad-scale (tens of kilometres) variations in seafloor geomorphology appear to control megabenthic standing stock, while fine-scale (tens of meters) variations in nodule occurrence appear more important in the regulation of diversity and community composition. Both of these factors seem to play a key role in the functional structuring of megafauna assemblages across a nodule field. Second, long term effects of disturbance on megafaunal distribution patterns are investigated in the Peru Basin (E Pacific; 3800-4300 m water depth), 26 years after simulated mining impacts were induced during the “DISturbance and reCOLonization” experiment. Distinct ecological patterns are found across different seafloor disturbance levels; i.e. suspension feeder standing stock remains strongly reduced in directly disturbed seafloor areas, suggesting that the megabenthos of the DISCOL area has not yet recovered from simulated mining impacts. The findings of this thesis provide evidence of the habitat heterogeneity of polymetallic nodule field ecosystems, which appears promoted by both geomorphological and nodule occurrence variations across space. The nodule field is likely better considered as a mosaic habitat where nodules act as keystone structures, modulating a continuous community variation across a gradient of this resource. Consequently, successful conservation actions will likely require the preservation of areas comprising the full range of nodule cover and not just the low cover areas that are least attractive to mining.

More information

Identifiers

Catalogue record

Export record