The use of a volumetric method to study the abyssal macrofauna: implications for mining impact assessments

• Autor(a) principal: Leitão, Nuno Martins
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/36863
• topic: Biovolume; Biomass; Productivity gradient; Benthic macrofauna; Volumetric method; Deep-sea mining impact

Polymetallic nodule mining in the Clarion-Clipperton Fracture Zone constitutes an activity with enormous economic potential. However, it is necessary to study the impacts this activity can have on the ecosystem so their biodiversity can be protected. This study had as a main goal the use of a volumetric method to estimate biovolume, as a proxy of biomass, of benthic macrofauna collected with the use of box-cores during the SO239 and So268 expeditions. Also studied were the relation between variations in macrofaunal biovolume and the productivity gradient present in the CCZ, the adequacy of protected and reference areas selected for mining, and the impacts of deep-sea disturbance experiments on the macrofaunal communities. For this, the analysis of photographs was used to make measurements of animals, which then were used to calculate their biovolume. Statistical analysis of the data was performed, based on three parameters: abundance, biovolume and average biovolume per individual. The results obtained for the various areas were compared, so that they could make tendencies in variation of biovolumes and of the macrofaunal communities visible. It was verified that, although some tendencies could be observed, the results only partially supported a correspondence between the surface productivity gradient and a biovolume gradient. The studied protected area (APEI 3) was revealed to not be very representative as a reference for mining concessions, due to differences in community structure and significantly lower biovolume and abundance. The reference sites chosen for the BGR and GSR areas were shown to be representative in terms of biovolume and abundance; however, it was observed a variation in vertical distribution of the organisms in the sediment between the reference and the trial sites. The existence of long-term impacts from a mining experiment in the IOM area was also verified. The study of biovolume allowed the detection of variations that would not have been observed with only the study of other parameters. Likewise, the use of the volumetric method with photograph analysis allowed the attainment of results without the need for access to the rare and fragile specimens of benthic macrofauna, thus constituting an important tool for deep-sea investigation.