Benthic Megafauna Biodiversity Associated to Vulnerable Marine Ecosystems in Norwegian waters

Abstract

The biodiversity of benthos is influenced by habitat forming taxa defining Vulnerable Marine Ecosystems (VME). Such indicator taxa are used to identify and designate VME areas, but their numerical relation to benthic biodiversity is not known. In this thesis I address the relationship between abundance of VME indicator-taxa and megabenthos biodiversity in Norwegian waters. The main objectives were to i. compare benthic biodiversity patterns across different VMEs, ii. assess the effect of abundance of VMEs indicator species on taxonomic richness, and iii. investigate the relationship between VMEs indicator species abundance and occurrence of commercial fish species. The approach is based on field survey data collected via video recordings on 5276 transects by the MAREANO project, part of the Institute of Marine Research (IMR). The study area includes the Norwegian Sea, Western Barents Sea, and Svalbard. There were 45 VME indicator-taxa among the 488 megabenthos taxa identified and included in the MAREANO database which included 4340 transects occupied by VME taxa. The VME indicator-taxa were grouped into 10 distinct VME types used for data analysis. Taxonomic richness was computed based on 443 taxa of megabenthos (excluding the VME indicator taxa). Commercial fish species selected for analysis of habitat suitability as a function of VME indicator-taxa abundance were Molva molva, Sebastes sp., Brosme brosme, Pollachius virens, Gadus morhua, Reinhardtius hippoglossoides, Melanogrammus aeglefinus. The effects on the taxonomic richness of megabenthos of environmental factors latitude, water temperature, depth and sediment type, as well as the effects of VME indicator-taxa abundance, were estimated via Generalized Linear Models (GLM). The effects of VME indicator-taxa abundance on occurrence were estimated via GLMs assuming a binomial error distribution. The megabenthos biodiversity varied substantially across transects, ranging between 3 and 48 taxa, and decreased steadily below depths of ca 500 m, but increased at lower temperatures. Overall, the environmental factors accounted for 7.7% of the variation in taxonomic richness. The taxonomic richness of megabenthos showed a strong positive relationship to total abundance of VME indicator-taxa, which accounted for 21% of the variation in taxonomic richness. Taxonomic richness was positively associated with the abundance of five VME indicator taxa. The occurrence of fish also showed a significant association with abundance of VME indicator taxa, with four species showing a positive relationship, and Gadus morhua and Reinhardtius hippoglossoides displaying a negative relationship. By elucidating the relationships between VMEs, biodiversity and commercially important species, the study highlights the importance of conserving these ecosystems for both ecological integrity and socioeconomic sustainability.