Abstract
Discovery and understanding of fragile deep-sea habitats like sponge aggregations, are being outpaced by anthropogenic resource exploitation. Sustainable ocean development in the Faroe-Shetland Channel Nature Conservation Marine Protected Area (FSC NCMPA; northeast Atlantic), which harbours sponge aggregations, now requires adaptive management in the face of encroachment of multisectorial activities in this area (e.g. fishing, oil and gas, shipping) and climate change. We examined sponge morphotype composition, richness, diversity, density and body-size distribution inside and outside the FSC NCMPA, and the role of environmental variability and human impact in these sponge aggregations. Analyses were based on the examination of 465 high resolution images from 13 towed-camera transects. A catalogue for regional sponge morphotypes was also developed and applied for these analyses. Analysis revealed that morphotype composition did not differ between inside and outside the FSC NCMPA but richness, diversity and densities of massive/spherical/papillate and flabellate/caliculate sponges were higher inside than outside the boundary. The sponge aggregations occurred within a narrow zone between 450 and 530 m depth, within relatively warm and saline water masses. Furthermore, multiple size cohorts of sponges were recorded inside the FSC NCMPA, in contrast to the single cohort outside. Distance-based linear modelling showed that demersal fisheries, substratum, salinity and temperature explained a statistically-significant amount of variation (48%, p<0.001) of sponge density across the study area. Findings on density and size cohorts suggest that the FSC NCMPA boundary currently encloses the most vulnerable area, which also demonstrates normal ecosystem functions (e.g. recruitment). However, sponges were constrained to a narrow environmental niche shaped by fisheries and interactions of FSC NCMPA water masses with the slope that in turn likely determine, food supply to the sponge aggregations. Our study illustrated the vulnerability of the FSC NCMPA sponge aggregations to fisheries and changes to water mass properties over time. The morphotype catalogue and suite of indicators (i.e. density and body-size distribution) allow for baseline and future assessments of anthropogenic and climate change impacts on sponge aggregations’ environmental status in the FSC NCMPA, thus guiding management as sectoral encroachment continues in this area.
Highlights
Sponges (Phylum Porifera) are widespread benthic organisms being found from the intertidal zone down to the abyss (Maldonado et al, 2017)
The Faroe-Shetland Channel (FSC) is characterized by complex hydrography as five water masses flow through it: North Atlantic Water (NAW), Modified North Atlantic Water (MNAW), Modified East Icelandic Water (MEIW), Norwegian Sea Arctic Intermediate Water (NSAIW), and Norwegian Sea Deep Water (NSDW) (Hansen and Østerhus, 2000)
The present study provided evidence that the FSC NCMPA boundary currently encloses the most vulnerable area encompassing sponge communities with high richness, diversity, density and several size classes
Summary
Sponges (Phylum Porifera) are widespread benthic organisms being found from the intertidal zone down to the abyss (Maldonado et al, 2017). Method standardization (e.g., units used in reporting faunal density) will enable the comparability of findings among studies and will enable the identification of gaps, challenges, strengths, and opportunities for the exploration of sponge grounds and deep-sea ecosystems, in overall. Another important step for advancing our understanding on deep-sea sponge grounds is to unravel the environmental parameters that shape their distribution, which in turn will facilitate the development of efficient conservation strategies (Howell et al, 2016; Johnson et al, 2018). Existing studies (both modeling and observations) about the role of water mass properties on the environmental parameters shaping the distribution of deep-sea sponge grounds suggest important roles of hydrography and temperature (Rice et al, 1990; Bett, 2001; Murillo et al, 2012), ocean chemistry (e.g., salinity and silicate) (Beazley et al, 2015; Howell et al, 2016), and biological parameters such as the concentration of particulate organic carbon (Barthel et al, 1996; Howell et al, 2016)
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