Biodiversity of Spongosorites coralliophaga (Stephens, 1915) on coral rubble at two contrasting cold-water coral reef settings

The authors would like to thank Bill Richardson (Master), the crew of the RRS James Cook, Will Handley and the Holland-I ROV team. We also thank all the specialists in taxonomy that provided important help with identification of species: Professor Paul Tyler (ophiuroids), Dr. Tammy Horton (amphipods), Dr. Graham Oliver (bivalves), Dr. Rob van Soest (sponges), Susan Chambers, Peter Garwood, Sue Hamilton, Raimundo Blanco Pérez (polychaetes). Also we would like to thank Val Johnston (University of Aberdeen) for her contribution to cruise preparations and John Polanski (University of Aberdeen) for his help onboard the RRS James Cook. Special thanks to Dr. Alexios P. Lolas (University of Thessaly, Greece) for all the artwork. Funding for the JC073 cruise was provided by the Natural Environment Research Council (NERC) UK Ocean Acidification (UKOA) research programme’s Benthic Consortium project (NE/H017305/1 to JMR). JMR acknowledges support from Heriot-Watt University’s Environment and Climate Change theme. GK was funded by a Marine Alliance for Science and Technology for Scotland (MASTS) Ph.D. scholarship.Peer reviewedPublisher PD

Hidden structural heterogeneity enhances marine hotspots’ biodiversity

Studies in terrestrial and shallow-water ecosystems have unravelled the key role of interspecific interactions in enhancing biodiversity, but important knowledge gaps persist for the deep sea. Cold-water coral reefs are hotspots of biodiversity, but the role of interspecific interactions and “habitat cascades” (i.e. positive effects on focal organisms mediated by biogenic habitat formation) in shaping their biodiversity is unknown. Associations between macrofaunal hosts and epifauna were examined in 47 stations at the Mingulay Reef Complex (northeast Atlantic). In total, 101 (group level) and 340 (species level) unique types of facultative associations formed by 43 hosts and 39 epifaunal species were found. Molluscs and empty polychaete tubes had higher values for the type and number of host-epifaunal associations, the Shannon–Wiener (H) and Margalef (d) indices of the epifauna than the rest of the taxonomic groups (p < 0.05). Hosts’ body size, orientation, surface smoothness, and growth form explained a significant amount of variability (32.96%) in epifauna community composition. Epifaunal species richness (S), H and d were 27.4 (± 2.2%), 56.2 (± 2.8%) and 39.9 (± 2.3%) of the respective values for the total sessile communities living on coral framework. This is intriguing as coral framework is orders of magnitude larger than the size of macrofaunal hosts. It is suggested that bivalves, tunicates and empty polychaete tubes increase habitat heterogeneity and enhance biodiversity through “habitat cascades”, in a similar way that epiphytes do in tropical rainforests. Most macrofaunal habitat suppliers in the studied cold-water coral reef are calcified species and likely susceptible to ocean acidification. This indicates that the impacts of climate change on the total biodiversity, structure and health of cold-water coral reefs may potentially be more severe than previously thought

Seasonal and diel patterns in singing activity of humpback whales migrating through Bermuda

Humpback whales (Megaptera novaeangliae) produce song and non-song vocalisations, which allows their presence to be detected through passive acoustic monitoring. To determine the seasonal and diel acoustic presence and acoustic behaviour of humpback whales at the migratory stopover site off Bermuda, three hydrophones were deployed between March 2018 and April 2019 on Challenger Bank and the Bermuda platform. Song was the predominant vocalisation type encountered, with 65% of song recordings containing whale chorus and a clear seasonal trend of humpback whale occurrence in the spring and winter months from late December to mid-May. A strong diel pattern in singing activity was detected. Singing activity significantly increased at night relative to the daytime (p<0.01), whilst twilight periods were characterised by intermediate levels of singing. The song structure encountered in spring 2018 consisted of 18 units, 6 themes and 5 transitional phrases. The high occurrence of whale chorus and the strong seasonal and diel patterns of male humpback whale singing activity highlights the importance of Bermuda not just on their northward migration during spring, as described historically, but also on their southward migration during winter. Bermuda therefore constitutes a two-way migratory stopover site for humpback whales. The present study also provides Bermuda’s planning authorities with better constraints on the duration and intensity of anthropogenic activities in these waters

A decade of humpback whale abundance estimates at Bermuda, an oceanic migratory stopover site

We constructed annual abundance of a migratory baleen whale at an oceanic stopover site to elucidate temporal changes in Bermuda, an area with increasing anthropogenic activity. The annual abundance of North Atlantic humpback whales visiting Bermuda between 2011 and 2020 was estimated using photo-identification capture-recapture data for 1,204 whales, collected between December 2009 and May 2020. Owing to a sparse data set, we combined a Cormack-Jolly-Seber (CJS) model, fit through maximum likelihood estimation, with a Horvitz-Thompson estimator to calculate abundance and used stratified bootstrap resampling to derive 95% confidence intervals (CI). We accounted for temporal heterogeneity in detection and sighting rates via a catch-effort model and, guided by goodness-of-fit testing, considered models that accounted for transience. A model incorporating modified sighting effort and time-varying transience was selected using (corrected) Akaike’s Information Criterion (AICc). The survival probability of non-transient animals was 0.97 (95% CI 0.91-0.98), which is comparable with other studies. The rate of transience increased gradually from 2011 to 2018, before a large drop in 2019. Abundance varied from 786 individuals (95% CI 593-964) in 2016 to 1,434 (95% CI 924-1,908) in 2020, with a non-significant linear increase across the period and interannual fluctuations. These abundance estimates confirm the importance of Bermuda for migrating North Atlantic humpback whales and should encourage a review of cetacean conservation measures in Bermudian waters, including area-based management tools. Moreover, in line with the time series presented here, regional abundance estimates should be updated across the North Atlantic to facilitate population monitoring over the entire migratory range

A road map for defining Good Environmental Status in the deep-sea

The development of tools to assess the Good Environmental Status (GES) in the Deep Sea (DS) is one of the aspects that ATLAS WP3 is addressing. GES assessment in the DS is challenging due to 1) the lack of baseline data, 2) the remoteness of the DS ecosystems, and 3) the limitations of the sampling methods currently available. Throughout the duration of the project, ATLAS will develop a suitable approach to address GES in the DS. During the 2nd General Assembly, we will present a draft for a “road map” to address GES in the DS as well some of the aspects discussed during the 2017 ICES WG on Deep Sea Ecosystems. The temporal and spatial scale at which GES should be assessed in the deep-sea is an important aspect to be considered. Due to the data limited situation and challenges posed to monitoring, it may well be the case that GES will have to be assessed at large spatial and temporal scales when comparing the shallower waters of the European Seas. For similar reasons, the type of indicators to be used may have to be simplified and likely be based on high-level analyses related to traits, pressures/risks, and habitat /ecosystem resilience. Ultimately, the results of the combined analyses of GES descriptors might bring to a potential refining or redefinition of the GES concept for the deep-sea

Ecohydrodynamics of Cold-Water Coral Reefs:A Case Study of the Mingulay Reef Complex (Western Scotland)

Ecohydrodynamics investigates the hydrodynamic constraints on ecosystems across different temporal and spatial scales. Ecohydrodynamics play a pivotal role in the structure and functioning of marine ecosystems, however the lack of integrated complex flow models for deep-water ecosystems beyond the coastal zone prevents further synthesis in these settings. We present a hydrodynamic model for one of Earth's most biologically diverse deep-water ecosystems, cold-water coral reefs. The Mingulay Reef Complex (western Scotland) is an inshore seascape of cold-water coral reefs formed by the scleractinian coral Lophelia pertusa. We applied single-image edge detection and composite front maps using satellite remote sensing, to detect oceanographic fronts and peaks of chlorophyll a values that likely affect food supply to corals and other suspension-feeding fauna. We also present a high resolution 3D ocean model to incorporate salient aspects of the regional and local oceanography. Model validation using in situ current speed, direction and sea elevation data confirmed the model's realistic representation of spatial and temporal aspects of circulation at the reef complex including a tidally driven current regime, eddies, and downwelling phenomena. This novel combination of 3D hydrodynamic modelling and remote sensing in deep-water ecosystems improves our understanding of the temporal and spatial scales of ecological processes occurring in marine systems. The modelled information has been integrated into a 3D GIS, providing a user interface for visualization and interrogation of results that allows wider ecological application of the model and that can provide valuable input for marine biodiversity and conservation applications

Environmental Variability and Biodiversity of Megabenthos on the Hebrides Terrace Seamount (Northeast Atlantic)

We present the first remotely operated vehicle investigation of megabenthic communities (1004–1695 m water depth) on the Hebrides Terrace Seamount (Northeast Atlantic). Conductivity-temperature-depth casts showed rapid light attenuation below the summit and an oceanographic regime on the flanks consistent with an internal tide, and high short-term variability in water temperature, salinity, light attenuation, aragonite and oxygen down to 1500 m deep. Minor changes in species composition (3–14%) were explained by changes in depth, substratum and oceanographic stability, whereas environmental variability explained substantially more variation in species richness (40–56%). Two peaks in species richness occurred, the first at 1300–1400 m where cooler Wyville Thomson Overflow Water (WTOW) mixes with subtropical gyre waters and the second at 1500–1600 m where WTOW mixes with subpolar mode waters. Our results suggest that internal tides, substrate heterogeneity and oceanographic interfaces may enhance biological diversity on this and adjacent seamounts in the Rockall Trough