Near-bottom zooplankton aggregations in Kongsfjorden with link to images from the optical zooplankton sensor MOKI

• Main Authors: Hirche, Hans-Jürgen, Laudien, Jürgen, Buchholz, Friedrich
• Format: Dataset
• Language: English
• Published: PANGAEA 2015
• Subjects: AWI_BPP; Bentho-Pelagic Processes @ AWI; DATE/TIME; DEPTH; water; File name; File size; Kongsfjorden; Spitsbergen; Arctic; Latitude of event; Longitude of event; M1; M1_NearBlomstrand; M2; M2_NearKongsbreen; M3; M3_Kongsfjordneset; M4; M4_CrossNyAlesund; M5; M5_Juttaholmen; M6; M6_Midtholmen; MOKI; Moored onsight keyspecies investigation; Moored onsight keyspecies investigation (MOKI); Optional event label; Uniform resource locator/link to image; Svalbard; Calanus hyperboreus; Kongsfjord*; Polar Biology; Zooplankton; Copepods; Thysanoessa inermis
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.840353; https://doi.org/10.1594/PANGAEA.840353

Near-bottom zooplankton communities have rarely been studied despite numerous reports of high zooplankton concentrations, probably due to methodological constraints. In Kongsfjorden, Svalbard, the near-bottom layer was studied for the first time by combining daytime deployments of a remotely operated vehicle (ROV), the optical zooplankton sensor moored on-sight key species investigation (MOKI), and Tucker trawl sampling. ROV data from the fjord entrance and the inner fjord showed high near-bottom abundances of euphausiids with a mean concentration of 17.3 ± 3.5 n/100 m**3. With the MOKI system, we observed varying numbers of euphausiids, amphipods, chaetognaths, and copepods on the seafloor at six stations. Light-induced zooplankton swarms reached densities in the order of 90,000 (euphausiids), 120,000 (amphipods), and 470,000 ind/m**3 (chaetognaths), whereas older copepodids of Calanus hyperboreus and C. glacialis did not respond to light. They were abundant at the seafloor and 5 m above and showed maximum abundance of 65,000 ind/m**3. Tucker trawl data provided an overview of the seasonal vertical distribution of euphausiids. The most abundant species Thysanoessa inermis reached near-bottom concentrations of 270 ind/m**3. Regional distribution was neither related to depth nor to location in the fjord. The taxa observed were all part of the pelagic community. Our observations suggest the presence of near-bottom macrozooplankton also in other regions and challenge the current view of bentho-pelagic coupling. Neglecting this community may cause severe underestimates of the stock of elagic zooplankton, especially predatory species, which link secondary production with higher trophic levels.