Diversity, distribution and spatial structure of the cold-water coral fauna of the Azores (NE Atlantic)

Abstract

Cold-water corals are widely considered as important structural components of benthic habitats, potentially enhancing local abundance in a variety of fish and invertebrate species. Yet, current knowledge of the taxonomic diversity and distribution patterns of these vulnerable, slow-growing organisms is scarce and fragmented, limiting the effectiveness of spatial management and conservation measures. We have conducted an exhaustive compilation of records of alcyonaceans, antipatharians, scleractinians and stylasterids available through present day to assess the diversity, distribution and spatial structure of coral assemblages in the Azores exclusive economic zone (EEZ). The resulting database comprises 2501 entries concerning historical oceanographic expeditions and other published sources, as well as unpublished data from bottom longline by-catch. Our taxonomic inventory appears to be fairly complete for the explored habitats, accounting for 164 species (79 alcyonaceans, 58 scleractinians, 18 antipatharians and 9 stylasterids), nine of which were documented for the first time. The Azores EEZ harbours a mixed coral fauna with several zoogeographic origins, showing the closest affinity with the Lusitanian–Mediterranean region. Very few apparent endemics were found (14%), and only in part supported by consistent sampling. Coral diversity is particularly high between 300 and 900 m depths, in areas recognized as traditional fishing grounds or exploitable fish habitat within the 100-mile limit of the EEZ. The composition of coral assemblages shows significant geographical structure among longitudinal sections of the study area at comparable depths (100–1500 m). There is no evidence of a possible role of the Mid-Atlantic Ridge or latitudinal effects underlying this pattern, which suggests that it may instead reflect assemblage variability among features. Stronger changes in species composition were found along the bathymetric gradient. Notwithstanding the mix of partially overlapping steno- and eurybathic species that characterize the vertical distribution of corals, there is a distinct transition from shallow (100–600 m) to intermediate (600–1000 m) depths. The analysis presented here constitutes a valuable contribution for efficient conservation policies of coral-associated vulnerable marine ecosystems and their sustainable use as fishing areas

Census of Octocorallia (Cnidaria: Anthozoa) of the Azores (NE Atlantic) with a nomenclature update

“…Common topographic features of the Azorean deep sea are island slopes, seamounts, hydrothermal vents and abyssal plains, the latter sometimes achieving more than 3200 m depth. The topographically rich seafloor is estimated to represent 37% of the EEZ with extreme importance for the open ocean and the deep-sea habitats containing a high diversity of pelagic and benthonic animals, living or visiting the Azorean archipelago (Morato et al 2013;Braga-Henriques et al 2013, Vandeperre et al 2014. In this work, the area of study was delimited by a rectangle box between 3336´N-436´N (DM) and 3536´W-2051´W (DM) enclosing the EEZ of the Archipelago (Fig.…”

New species of Heteropathes (Anthozoa: Antipatharia) expands genus distribution to the NE Atlantic

“…Antipatharians are colonial hexacorals reported to present longevities ranging from decades to millennia (Carreiro-Silva et al 2013;Love et al 2007;Roark et al 2009), and occurring between 20 and 5440 m (Gravier 1921;Braga-Henriques et al 2013) in the Northeast Atlantic Ocean. This taxon was generally assumed to be azooxanthellate, due to a preference for low-light environments that do not allow photosynthesis, but recently, several species occurring at up to 396 m of depth were shown to associate with Symbiodinium (Bo et al 2011;Wagner et al 2011).…”

Influence of Water Masses on the Biodiversity and Biogeography of Deep-Sea Benthic Ecosystems in the North Atlantic

“…The afore mentioned turbulent ENACW-MOW boundary might allow the transport of coral larvae along the NE Atlantic margins (Somoza et al, 2014). At the Mid Atlantic Ridge, the Azores region hosts an exceptional biodiversity of CWCs (Figure 2), mostly gorgonians (75% of the octocoral species of European waters), with a greater affinity to the Lusitanian-Mediterranean biogeographic region (71% shared species) and to a lesser extent to the NW Atlantic (Braga-Henriques et al, 2013;Sampaio et al, 2019). The presence of multiple intermediate and deep water masses (NACW, subpolar origin waters, MOW, AAIW, NADW; Johnson and Stevens, 2000;Amorim et al, 2017) along the slopes of many seamounts are hypothesized to shape composition and bathymetrical distribution of coral gardens in the Azores (Braga-Henriques et al, 2013).…”

“…At the Mid Atlantic Ridge, the Azores region hosts an exceptional biodiversity of CWCs (Figure 2), mostly gorgonians (75% of the octocoral species of European waters), with a greater affinity to the Lusitanian-Mediterranean biogeographic region (71% shared species) and to a lesser extent to the NW Atlantic (Braga-Henriques et al, 2013;Sampaio et al, 2019). The presence of multiple intermediate and deep water masses (NACW, subpolar origin waters, MOW, AAIW, NADW; Johnson and Stevens, 2000;Amorim et al, 2017) along the slopes of many seamounts are hypothesized to shape composition and bathymetrical distribution of coral gardens in the Azores (Braga-Henriques et al, 2013). Braga-Henriques et al, 2013 reported maximum Antipatharian diversity at 400-500 m coinciding with the cold and less dense NACW; whilst the maximum diversity of Alcyonacea (e.g., Viminella flagellum, D. meteor, Callogorgia verticillata, and A. armata) occurs at 500-600 m coinciding with the less saline subpolarorigin waters.…”