The temporal variability of the macrofauna at the deep-sea observatory HAUSGARTEN (Fram Strait, Arctic Ocean)

Regular biological observations of the deep sea bottom fauna are very important for understanding the role benthic biota plays in ocean ecosystems. Temporal variability in macrobenthos structure is usually studied in terms of general community characteristics including density, biomass and diversity. In this investigation, we also focused on the species composition and their individual characteristics in terms of temporal dynamics. The deep-sea macrofauna was studied based on the material collected in the Eastern Fram Strait during two expeditions in July–August 2003 and July 2012. Stations were taken at depths of about 2500 m at the deep-sea observatory using the USNEL box corer (0.25 m 2 ). Three stations at varying distances were sampled in 2003 (three cores per station). In 2012, the same stations were resampled with an additional station taken close to the central HAUSGARTEN permanent sampling site (one core per station). No significant changes in the total density and biomass were found between the two sampling events. However, the density of several common species has changed significantly (e.g. densities of Mendicula ockelmanni and Chaetozone cf. jubata have increased). Four species out of total 64 were unique for the 2003 samples, while six species out of 52 were unique for 2012 samples. The absence of several particular species in the samples from the different years is estimated to be not random: the number of samples required to find these species was less than the number of samples collected. The differences in time between the very same stations exceeded the inner spatial heterogeneity of each of the three stations. However, the spatial heterogeneity within the scale of 20–25 km exceeded the temporal differences.