As little as we know: current understanding and future outlook of benthic tanaid diversity and distribution in the Clarion–Clipperton Zone (CCZ)

Abstract In the present Paper, we provide an overview of the diversity and distribution of benthic tanaid crustaceans, a dominant macrofaunal taxon, found in 4000 to 6000 m water depth in the Clarion–Clipperton Zone (CCZ) (north-eastern Pacific). There is increasing recognition that the CCZ is a potentially promising area for minerals supply through polymetallic nodules, with abundance estimates in the magnitude of billions of tons, representing significant economic potential involving metals such as nickel, cobalt, manganese, and copper. In the CCZ, Tanaidacea (called tanaids) are represented by 33 formally described species. With the current sampling effort, many of the taxa found in the CCZ are represented by one or two individuals (58%), With up to 70% found in one surveyed contract area. Their spatial distribution and abundances are influenced by a combination of environmental factors, including water depth, sediment type, and food availability. Our study, including datasets from various sources, highlights several challenges, including scarce and uneven sampling efforts, the use of non-standardised sampling protocols, and limited collaboration between scientists, contractors, and other stakeholders. Additionally, a significant number of species that are new to science further complicate biodiversity assessment. To improve our understanding of the diversity of tanaids in the CCZ, we suggest increasing sampling efforts in a standardised manner, increasing taxonomic studies, as well as facilitating the exchange of samples and data among scientists and contractors. This increased knowledge can contribute to appropriate environmental management measures to conserve deep-sea biodiversity of the CCZ.