Abstract
Among the complex ecosystems and habitats that form the deep sea, submarine canyons and open slope systems are regarded as potential hotspots of biodiversity. We assessed the spatial and temporal patterns of biodiversity in sediment communities of a NW Mediterranean Canyon and its adjacent open slope (Blanes Canyon) with DNA metabarcoding. We sampled three layers of sediment and four different depths (900–1750 m) at two seasons, and used a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI) as a metabarcoding marker. The final dataset contained a total of 15,318 molecular operational taxonomic units (MOTUs). Metazoa, Stramenopiles and Archaeplastida were the dominant taxa and, within metazoans, Arthropoda, Nematoda and Cnidaria were the most diverse. There was a trend towards decreasing MOTU richness and diversity in the first few cm (1 to 5) of the sediment, with only 26.3% of the MOTUs shared across sediment layers. Our results show the presence of heterogeneous communities in the studied area, which was significantly different between zones, depths and seasons. We compared our results with the ones presented in a previous study, obtained using the v7 region of the 18S rRNA gene in the same samples. There were remarkable differences in the total number of MOTUs and in the most diverse taxa. COI recovered a higher number of MOTUs, but more remained unassigned taxonomically. However, the broad spatio-temporal patterns elucidated from both datasets coincided, with both markers retrieving the same ecological information. Our results showed that COI can be used to accurately characterize the studied communities and constitute a high-resolution method to detect ecological shifts. We also highlight that COI reference databases for deep-sea organisms have important gaps, and their completeness is essential in order to successfully apply metabarcoding techniques.
Highlights
The world’s oceans cover ca. 71% of Earth’s surface, and the average depth of the global ocean is 3688 m [1]
This study focuses on the Blanes Canyon, one of the main canyons in the NW Mediterranean [15,40], and the adjacent open slope; both habitats are considered potential biodiversity hotspots [7]
Most reads were lost during paired-end alignment, demultiplexing and quality filtering
Summary
The world’s oceans cover ca. 71% of Earth’s surface, and the average depth of the global ocean is 3688 m [1]. 71% of Earth’s surface, and the average depth of the global ocean is 3688 m [1]. The deep sea is defined as any environment (including the water column and the seabed) beyond continental shelf depths, that is, below 200 m depth, and it forms the largest biome on Earth, representing more than 60% of the Earth’s surface [2,3,4,5]. The Mediterranean Sea is a suitable model to investigate deep-sea biodiversity patterns because of its palaeoecological history and topographic characteristics [6]. Harris and Whiteway [8] produced a global inventory of 5849 separate large submarine canyons, where 8.86% of them (that is, 518) are located in the Mediterranean Sea (which only represents 0.8% of the world’s oceans [1]). Deep-sea Mediterranean communities are neglected compared to their shallow-water counterparts in terms of conservation and management efforts [5]
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