Beschreibung: The early life-history stages of polar marine invertebrates are understudied, particularly in deep water. We present the results from a long-term (1999 – 2017) colonization experiment at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the Fram Strait (Arctic Ocean, 79⁰ N, 04⁰ E, 2500 m water depth). Recruitment panels were constructed from plastic and brick and deployed attached to a metal frame in 1999. The experiment was monitored using an ROV in 2003 and 2011 and recovered in 2017. Recruitment was very low, with only foraminiferans being visible after 4 years (2003) and one metazoan species, the hydroid Halisiphonia arctica, being visible on the panels after 12 years (2011). After 18 years underwater, panels were colonized by 13 metazoan species as well as calcareous and agglutinating foraminiferans. Recruitment was higher on brick panels than on plastic, but while some species were more common on panels at higher altitude (H. arctica and the crinoid Bathycrinus carpenterii), others were more common on panels closer to the seafloor (serpulid polychaetes, agglutinating foraminifera) or on panels in line with the predominant bottom current (small round white sponge). The most common recruiting species can be described as opportunistic and are rare or absent in older communities on natural substrata nearby. Meanwhile, large hexactinellid sponges that are common in natural communities did not recruit to our panels. These results suggest that succession in the Arctic deep sea takes decades and involves early dominance by opportunistic species, with slower-growing, structureforming species appearing later on.

Beschreibung: Epibenthic megafauna play an important role in the deep-sea environment and contribute significantly to benthic biomass, but their population dynamics are still understudied. We used a towed deep-sea camera system to assess the population densities of epibenthic megafauna in 2002, 2007, and 2012 at the shallowest station (HG I, ∼1300 m) of the deep-sea observatory HAUSGARTEN, in the eastern Fram Strait. Our results indicate that the overall density of megafauna was significantly lower in 2007 than in 2002, but was significantly higher in 2012, resulting in overall greater megafaunal density in 2012. Different species showed different patterns in population density, but the relative proportions of predator/scavengers and suspension-feeding individuals were both higher in 2012. Variations in megafaunal densities and proportions are likely due to variation in food input to the sea floor, which decreased slightly in the years preceding 2007 and was greatly elevated in the years preceding 2012. Both average evenness and diversity increased over the time period studied, which indicates that HG I may be food-limited and subject to bottom-up control. The community of HG I may be unique in its response to elevated food input, which resulted in higher evenness and diversity in 2012.

Beschreibung: During a survey of the H°akon Mosby mud volcano (HMMV), located on the Bear Island fan in the southwest Barents Sea at �1250m water depth, different habitats inside the volcano caldera and outside it were hotographed using a towed camera platform, an Ocean Floor Observation System (OFOS). Three transects were performed across the caldera and one outside, in the background area, each transect was �2 km in length. We compared the density, taxa richness and diversity of nonsymbiotrophic megafauna in areas inside the volcano caldera with different bacterial mat and pogonophoran tubeworm cover. Significant variations in megafaunal composition, density and distribution were found between considered areas. Total megafaunal density was highest in areas of dense pogonophoran populations (mean 52.9 ind.m−2) followed by areas of plain light-coloured sediment that were devoid of bacterial mats and tube worms (mean 37.7 ind.m−2). The lowest densities were recorded in areas of dense bacterial mats (mean �1.4 ind.m−2). Five taxa contributed to most of the observed variation: the ophiuroid Ophiocten gracilis, lysianassid amphipods, the pycnogonid Nymphon macronix, the caprellid Metacaprella horrida and the fish Lycodes squamiventer. In agreement with previous studies, three zones within the HMMV caldera were distinguished, based on different habitats and megafaunal composition: “bacterial mats”, “pogonophoran fields” and “plain light-coloured sediments”. The zones were arranged almost concentrically around the central part of the caldera that was devoid of visible megafauna. The total number of taxa showed little variation inside (24 spp.) and outside the caldera (26 spp.). The density, diversity and composition of megafauna varied substantially between plain lightcoloured sediment areas inside the caldera and the HMMV background. Megafaunal density was lower in the background (mean 25.3 ind.m−2) compared to areas of plain light-coloured sediments inside the caldera. So the effect of the mud-volcano environment on benthic communities is expressed in increasing of biomass, changing of taxa composition and proportions of most taxonomic groups.