Distribution of Deep-Sea Sponge Aggregations in an Area of Multisectoral Activities and Changing Oceanic Conditions

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 harbors 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 catalog 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 modeling 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 catalog and suite of indicators (i.e., density and body-size Frontiers in Marine Science | www.frontiersin.org 1 April 2019 | Volume 6 | Article 163 Kazanidis et al. Monitoring Deep-Sea Sponge Aggregations 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.

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

“…Murillo et al, 2018 further noted that the structureforming Geodia species were found in areas with high primary production and fast currents that would provide the high food supply needed to reach their large biomasses. The importance of current regime and interactions between water masses has also been shown for the Faroe-Shetland Channel deep-sea sponge aggregations (Kazanidis et al, 2019), the Arctic sponge ground on the Schultz Seamount (Arctic Mid-Ocean Ridge; Roberts et al, 2018) and deep-sea aggregations of hexactinellids in the NE Atlantic (Rice et al, 1990;Barthel et al, 1996).…”

“…One of the first reports of these habitats was by Rice et al (1990), who observed dense aggregations (density values ∼1.5 ind•m −2 ) of the hexactinellid Pheronema carpenteri (Figure 2) in the Porcupine Seabight (NE Atlantic). Subsequently, records of sponge grounds came both from the eastern (e.g., Klitgaard and Tendal, 2004;Howell et al, 2016;Roberts et al, 2018;Kazanidis et al, 2019) and western deep North Atlantic (e.g., Murillo et al, 2012Murillo et al, , 2016aMurillo et al, , 2018Knudby et al, 2013;Kenchington et al, 2014;Beazley et al, 2018). These included records not only of hexactinellids, but also of demosponges and especially those from the family Geodidae (Order Astrophorida, commonly known as ostur; Figure 2).…”

“…Hydrography plays an important role in shaping the distribution of these dense sponge grounds, and several authors have noted the association of sponges with particular water masses due to their temperature and salinity characteristics or the hydrodynamic conditions, such as tides and internal waves, which enhance the food supply (Bett, 2001;Klitgaard and Tendal, 2004;Murillo et al, 2012;Beazley et al, 2015Beazley et al, , 2018Roberts et al, 2018;Davison et al, 2019;Kazanidis et al, 2019). For example, in the continental margin offshore of Newfoundland (eastern Canada), there is evidence for a relationship between dense sponge aggregations with a warm (∼3.0-3.5 o C), and salty (∼34.85-34.90), water mass that occurs between ∼1300 and 1723 m depth and is thought to be a remnant of the Irminger Current (Beazley et al, 2015).…”

ROV’s Video Recordings as a Tool to Estimate Variation in Megabenthic Epifauna Diversity and Community Composition in the Guaymas Basin

“…The underlying substratum and habitat-forming organisms provide a significant proportion of three-dimensional habitat in marine communities (Ferrari et al, 2016). Numerous studies have documented that structure-forming organisms such as sponges and CWC s play a key structural and functional role in the marine benthos, because they can modified physical properties of the sea floor and influence composition, abundance and distribution of epibenthic megafauna (Schlacher et al, 2007;Beazley et al, 2013;Howell et al, 2016;Huvenne et al, 2016;van den Beld et al, 2017;Kazanidis et al, 2019). Taxa identified in the NW limit of Guaymas basin and Sonoran Margin span several trophic levels including filter and suspension feeders, deposit feeders and carnivorous benthophages (Sokolova, 2000).…”

“…To aid the identification we supplemented these sources with a previous study that identified specimens of taxa collected during dive D347 (Villalobos Vazquez de la Parra, 2014). Additionally, to maximizes the comparability of our results with other studies, we grouped specimens and coverage data of sponges recorded in each benthic images into one of the following morphotypes categories based on the criteria proposed by Boury-Esnault and Rützler (1997) and Kazanidis et al (2019): amorphous, tubular and clavate ("club-shaped") (see the sponge morphotype examples provide as Supplementary Material). Taxonomic richness described the total number of morphospecies per image.…”