Polymetallic nodule size and distribution of filter feeders in the Clarion-Clipperton Zone, Eastern Pacific.
Supervisor: Erik Simon-Lledó (NOCS)
The availability of hard substratum is a key factor structuring seabed communities from shallow to deep ecosystems worldwide. Hard surfaces provide stable sites for anchoring and development of filter-feeding sessile species, which can be abundant or even dominate in particular deep-sea habitats. Abyssal polymetallic nodule fields, such as the Clarion-Clipperton Zone (CCZ) in the northeastern Pacific, are a mosaic habitat where the hard substratum provided by nodules combined with the background sediment increases habitat heterogeneity, promoting the development of highly diverse communities. Increases in substratum patch sizes are usually associated with increases in the diversity and size of inhabiting fauna. This study used a large image-based dataset to study common sessile megafaunal taxa, with different life-history traits, known to inhabit nodules in the eastern CCZ. I assessed, for each taxon, their size frequency distribution and whether they exhibit a preference for a particular substratum type. I evaluated if nodule size influences the number and size of dwelling individuals and if specimens express any spatial settlement preference within it. Taxa show intraspecific variations in body size across the eastern CCZ, likely owing to differences in environmental conditions. Preference for a substrate type depended on taxa’s life-history traits, although they were mostly nodule-dwellers. Even if strategies vary, all taxa elevate themselves from the seafloor to benefit from stronger water flows. Nodule length does not fully explain body size ranges of taxa. Animals are not evenly distributed across the eastern CCZ, possibly as a result of variations in POC flux. Polymetallic nodule fields appear to act as mosaic habitats. However, environmental and species-specific data are needed to understand its dynamics, which could be affected by commercial-scale deep-sea mining.