Microphytobenthos of Arctic Kongsfjorden (Svalbard, Norway): biomass and potential primary production along the shore line

Abstract

During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline of Kongsfjorden (Svalbard, Norway) at B5 m water depth and at two stations at five different water depths (5, 10, 15, 20, 30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment cores under controlled light (ca. 100 lmol photons m -2 s -1 ) and temperature (2-4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down to 30 m showed high biomass of up to 317 mg chl a m -2 . In spite of increasing water depth, no significant trend in ''photoautotrophic active biomass'' (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from B5 to 30 m water depth exhibited variable rates of net production from -19 to ?40 mg O 2 m -2 h -1 (-168 to ?360 mg C m -2 day -1 ) and gross production of about 2-62 mg O 2 m -2 h -1 (17-554 mg C m -2 day -1

Benthic primary production and mineralization in a High Arctic fjord: in situ assessments by aquatic eddy covariance

“…Despite year-round cold bottom water temperatures, the benthic ecosystems are able to mediate high rates of ecosystem carbon cycling that are comparable in magnitude to many shallowwater benthic habitats at lower latitude such as those in sub-Arctic and temperate settings (Glud et al 2010, Attard et al 2014. This observation is in line with studies performed in other permanently cold settings, indicating that the overall community level efficiency of mineralization and benthic primary production does not depend strongly on ambient water temperature (Kostka et al 1999, Hancke & Glud 2004, Woelfel et al 2010. Benthic GPP and CR showed comparable daily rates (2.7 and 3.1 t C d −1…”

“…Indeed, seafloor primary production is frequently the dominant source of organic carbon in Arctic waters ≤40 m depth (Krause-Jensen et al 2007, Glud et al 2009, Woelfel et al 2010. Because benthic primary production is measured at small scales relative to the vastness of shelf areas, scaling up the effects of local processes to larger extents is required in order to get a broadscale perspective (Gattuso et al 2006, Glud et al 2009).…”

Macroalgal detritus and food-web subsidies along an Arctic fjord depth-gradient

“…It is, however, questionable as to whether microphytobenthos could be relevant at the deep stations in Isfjorden. Estimates of production in shallow waters in Arctic systems are comparable to pelagic productivity (Woelfel et al, 2010), but both pelagic and macroalgal productivity will exceed these values in deeper waters. A final possibility is that isotopic enrichment of pelagic POM during sinking may have a similar signal to that of brown macroalgae.…”

“…Minimal sea-ice has been observed in Isfjorden for well over 5 years, and there is little terrestrial vegetation around the fjord, suggesting these two sources may contribute very little to food webs here. Microphytobenthos, however, may exhibit photosynthetic rates equaling or exceeding that of phytoplankton in shallow water (<30 m) Arctic systems (Glud et al, 2002(Glud et al, , 2009Woelfel et al, 2010). This source would likely provide a heavy δ 13 C signal analogous to that from brown macroalgae (Nadon and Himmelman, 2006), but this source was not sampled in this study.…”

“…Microphytobenthos is common on both soft sediments and rocky bottoms in euphotic areas of the Arctic. In these shallow (>30 m) waters, it has primary production rates comparable to that of pelagic phytoplankton (Glud et al, 2009;Woelfel et al, 2010;McTigue et al, 2015), but its role in benthic food-webs has not been investigated.Surprisingly little attention has been given to the role of macroalgae in coastal food webs of the Arctic, especially considering their importance in sub-Arctic food-webs (e.g., Fredriksen, 2003), and the role organic detritus may play in promoting stability in benthic communities (Moore et al, 2004;McMeans et al, 2013). Where it has been investigated, however, kelp detritus has been shown to contribute significantly to shallow-water benthic food-webs in the Arctic (Dunton and Schell, 1987;McMeans et al, 2013) and Antarctic (Dunton, 2001;Norkko et al, 2007), and it is presumed to comprise a significant component of sedimentary organic matter found in some systems (Sokołowski et al, 2012).…”