Polar Biol (2004) 27: 447–457 DOI 10.1007/s00300-004-0618-0
O R I GI N A L P A P E R
Barbara Urban-Malinga Æ Lech Kotwicki Tom L. A. Gheskiere Æ Katarzyna Jankowska Krzysztof Opalin˜ski Æ Michałł Malinga
Composition and distribution of meiofauna, including nematode genera, in two contrasting Arctic beaches Received: 10 February 2003 / Revised: 18 March 2004 / Accepted: 22 March 2004 / Published online: 30 April 2004 Springer-Verlag 2004
Abstract The meiofauna of two tidal beaches, one exposed and one more sheltered, on Bjornoya (Bear Island) was investigated in summer 2000. Both meiofaunal densities and composition seem to be controlled by physical properties of the sediment, which in turn are controlled by exposure. The moderately and poorly sorted sediments in the sheltered beach were more abundant in terms of meiofaunal densities than the well sorted sediments in the exposed beach (254–481 individuals in 10 cm2 vs 7–269 individuals in 10 cm2, respectively). In total, seven higher meiofaunal taxa were found. Turbellaria were the numerically dominant taxon in the exposed beach. In the sheltered beach, Turbellaria also dominated, followed by Nematoda and Harpacticoida. The vertical distribution of the meiofauna was in accordance with what has been reported from other intertidal beaches. Nematoda were studied in detail and their densities ranged over 0.7–7.7 individuals in 10 cm2 in the exposed beach and 2.7–186.0 individuals in 10 cm2 in the sheltered beach. Nematodes were identified to genus level and a total of eight nematode
B. Urban-Malinga Æ L. Kotwicki Æ K. Opalin˜ski Centre for Ecological Research PAS, Dziekano´w Les´ ny, ul. Konopnickiej 1, 05-092 Łomianki, Poland T. L. A. Gheskiere Marine Biology Section, University of Gent, Krijgslaan, 281-S8, 9000 Gent, Belgium K. Jankowska Gdan´sk University of Technology, ul Narutowicza 11/12, 80-952 Gdan´sk, Poland M. Malinga Department of Vertebrate Zoology and Ecology, University of Gdan´sk, Legiono´w 9, 80-341 Gdan´sk, Poland B. Urban-Malinga (&) Institute of Oceanology PAS, Powstan´co´w Warszawy 55, 81-712 Sopot, Poland E-mail:
[email protected] Tel.: +48-58-5517283 Fax: +48-58-5512130
genera were found. Sediment community respiration, measured as oxygen consumption, ranged between 2.3 cm3 O2 m)2 h)1 in the exposed beach and 7.3 cm3 O2 m)2 h)1 in the sheltered beach (respectively, the equivalent of 24 mg and 75 mg of organic carbon metabolised per day). Values from the sheltered site are within the range of results registered in much warmer localities.
Introduction Although gravel and sandy beaches are a common coastal type on Svalbard (We˛sławski et al. 1993), the biotic communities they support and their function are poorly known. In view of the relatively low biomass and density of macrobenthos in the Arctic intertidal (We˛sławski et al. 1993, 1997), it has been suggested that the meiobenthos may have a comparatively more important ecological role. Published estimates of Arctic intertidal meiobenthic densities cover a wide range, from zero individuals (ind.) to more than 10,000 ind. in 10 cm2 (Szymelfenig et al. 1995). Although extremely low densities have been reported, mean densities and taxon diversities are within the range observed in boreal beaches and may approach the upper part of that range (Szymelfenig et al. 1995). The presence of fast ice, pack ice and specific sea currents (Szymelfenig et al. 1995), together with beach exposure (Radziejewska and Stan´kowska-Radziun 1979; We˛sławski et al. 1997), are considered the principal factors responsible for the high variability in density, biomass and diversity of the littoral meiobenthos in Svalbard. However, except for the study by Radziejewska and Stan´kowska–Radziun (1979), there is a general paucity of information on the abiotic characteristics of the beaches (sediment texture, organic matter content) in relation to the distribution and community structure of the meiobenthos. Data on the vertical distribution of Arctic beach meiofauna are also lacking.
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Although nematodes are often the dominant meiobenthic taxon in Arctic intertidal beaches (Gerlach 1965; Radziejewska and Stan´kowska-Radziun 1979; Szymelfenig et al. 1995), detailed information on nematode community structure is limited to the sole report given by Gerlach (1965). The present study reports density and community composition of the meiobenthos, with special emphasis on the free-living marine nematodes, of two intertidal beaches on Bjornoya, an oceanic island of the Svalbard archipelago. The two beaches are characterized by contrasting hydrodynamics and, as a result, different sediment types, one beach being sheltered, the other exposed. Data on the density and meiofaunal community composition were studied in relation to environmental factors, especially sediment type. Sediment oxygen consumption as a measure of community respiration was determined. There is again a general paucity of data on the metabolic activity of intertidal environments, most efforts in the Arctic so far having been concentrated on deeper sediments (Pfannkuche and Thiel 1987; Piepenburg et al. 1995; Arnosti et al. 1998; Kostka et al. 1999; Glud et al. 1998; Rysgaard et al. 1998, 2000). The aim of this work was to include intertidal beaches in the discussion about the relative importance of temperature and organic matter as determinants of benthic community activity in the Arctic. Fig. 1 Map of the investigation area
Materials and methods Meiobenthic sampling and treatment Study sites and beach characteristics Bjornoya (74N, 17E), the southernmost island of the Svalbard archipelago (Fig. 1), is a rocky island about 20 km long on a large, shallow extension of the Barents Sea shelf (Bjornoyabanken). It is situated in the frontal zone of two major water masses: the warm West Spitsbergen Current, with a summer surface water temperature of 4–8C, and the cold Barents Current, with a summer surface water temperature of 0–1C. High rocky cliffs bordered with sandy-gravel beaches predominate along the coast, but various types of small ‘‘pocket’’ sandy and gravel beaches are also quite common. Salinity is 34 and tides are semidiurnal, with an amplitude of up to 1 m (We˛sławski et al. 1997). Two beaches that differ substantially in exposure and sediment texture were selected. The first, Kobbebukta (KB), is a very exposed beach several kilometers long on the north coast of the island, with a wide surf zone and a continuous and strong wave action. The second beach, Kvalrossbukta (KV), is a pocket beach, well sheltered by cliffs, with a quite narrow surf zone and much calmer wave conditions. The sediment in both beaches consists of quartz sand and seashell detritus. At both beaches, a transect was sampled from the high to low tide marks, with sampling stations at the high (HW), medium (MW) and low water (LW) levels.
Triplicate samples for meiobenthic community structure were taken (using perspex cores with a surface area of 10 cm2) along the transect line parallel to the waterline (the distance between replicates being approximately 70 cm). The sediment was sectioned into four depth layers: 0–1, 1–2, 2–5 and 5–10 cm. These samples were fixed with a neutral 4% formaldehyde solution. The meiofauna was extracted from the sediment by decantation ten times over a 47-lm mesh sieve. The fraction retained on this sieve was stained with Rose Bengal and identified to a suitable taxon level under a stereomicroscope. All nematodes were sorted by hand and mounted on permanent glycerine slides, following the procedure described by Vincx (1996), and were identified to genus level. Bacteria Bacterial density and biomass were determined on triplicate cores with a surface area of 3.14 cm2 taken to a depth of 10 cm in the vicinity of the meio-cores. Samples were stored frozen until analysis. After quick thawing, the samples were treated with sonication, following the method described by Epstein and Rossel (1995). Bacteria were stained with acridine orange, counted and measured.
12.4 14.4 0.6 0.5 0.0 0.1 37.7 14.3 11.3 32.5 2.1 7.3 47.0 53.4 29.9 31.6 3.5 8.0 12.8 5.6 17.0 19.6 7.2 7.0 38.2 30.2 68.2 66.5 94.1 90.2 0.7 0.7 26.9 16.5 48.4 22.3 1.8 0.9 1.3 1.4 2.4 1.6 0.3 0.4 17.3 9.5 35.2 19.6 0 0 0 0 0 0 0 0 0 0 0 0
Coarse sand (%) Medium sand (%) Fine sand (%) Very fine sand (%)
3.69 4.32 2.74 2.54 16.94 10.59 2.06 6.19 1.69 2.16 6.48 1.30 HW
MW
LW 9.5 12 Sheltered (KV)
HW
MW
95
2
LW
0–5 5–10 0–5 5–10 0–5 5–10 0–5 5–10 0–5 5–10 0–5 5–10
0.69 0.56 1.11 1.10 1.40 1.35 )1.27 )1.87 0.18 )0.14 1.41 )0.22
0.74 0.74 0.50 0.50 0.24 0.31 1.09 0.93 1.76 1.49 1.22 1.99
)0.47 )0.56 )0.63 )0.56 )0.56 )1.65 0.40 1.95 )0.32 0.03 )1.83 0.09
Silt (%) Ku Sk So Mean diameter(phi) Sediment depth (cm) Water mark Beach slope ()
Exposed (KB)
The meiofaunal density and sediment metabolism of the two beaches were compared using the non-parametric Mann–Whitney U-test. Correlations among the meiofauna and sediment variables were assessed with Spearman rank tests.
Beach width (m)
Data analysis
Beach type
Sediment granulometry was determined for each of three replicate samples (taken with the same type of core as for meiofauna) and sectioned into two depth layers: 0– 5 cm and 5–10 cm. Analysis was done by standard sieving. The sediment fractions were defined according to the Wentworth scale. Additional parameters like medium grain size, sorting coefficient, skewness and kurtosis were calculated according to Boggs (1987). The slope of the beach was measured using a level. Three sediment cores 3.14 cm2 in area were taken at each site in the vicinity of the meio-cores to a depth of 10 cm for carbon and nitrogen analyses. Then the samples were frozen until analysed. Total carbon (Ctot), organic carbon (Corg) and organic nitrogen (Norg) were determined on dried samples by thermal combustion, using a CHN analyser (Perkin Elmer 2400 series). Samples for Corg were pretreated with HCl fumes to remove carbonates. Inorganic carbon (Cinorg) was determined as Ctot–Corg.
Table 1 Physical characteristics of the beaches. So Sorting index, Sk skewness, Ku kurtosis
Sediment characteristics
Very coarse sand (%)
Sediment community metabolism was measured in terms of sediment oxygen consumption. Six undisturbed sediment cores were taken intact (using perspex cores, 16 cm inner diam.) between the MW and LW marks during the low tide. After a 24-h stabilization period, the overlying water was taken off by a syringe and then ambient sea water was added to the surface of each core. Cores were tightly closed with perspex lids (air bubbles were removed) and incubated in the dark (wrapped in aluminum foil) for 6 h. A mechanical stirrer was pushed through the lid into the overlying water, which was stirred occasionally (every 1 h for 15 min) without resuspending the surface sediment. An oxygen electrode measured the oxygen concentration in the overlying water. The decrease in oxygen content (the difference between the initial and final oxygen concentrations) was related to the total sediment oxygen consumption. Parallel measurement of oxygen consumption in sea water in the absence of sediment was performed as a control, in order to estimate the corrected sediment oxygen consumption (background respiration). Carbon requirements were estimated using a respiratory quotient (RQ) of 0.85 (Patching and Raine 1983). On this basis, 1 cm3 of O2 respired translates into 0.43 mg of utilized organic carbon.
0 0 0 0 0 0 0 0 0 0 0 0
Gravel (%)
Community metabolism
0.6 1.1 0.0 0.0 0.0 0.0 48.4 78.9 27.2 21.8 6.7 43.4
449
450 Table 2 Environmental characteristics at the study sites Beach
Water mark
Ctot (%)
Corg (%)
Norg (%)
Cinorg(%)
C/N ratio
Total bacterial number (· 107 · g)1dw)
Bacterial biomass (lg C dm-3)
Exposed (KB)
LW MW HW LW MW HW
8.899 9.038 8.797 6.735 8.036 7.425
0.101 0.159 0.082 0.232 0.123 0.102
0.021 0.027 0.014 0.034 0.016 0.017
8.798 8.879 8.715 6.503 7.934 7.302
5.6 6.8 6.8 8.0 9.2 7.0
0.81 1.79 1.07 1.18 0.96 1.07
0.36 0.55 0.20 0.29 0.24 0.24
Sheltered (KV)
Results The water and air temperature at the time of this study ranged over 4–7C and 5–14C, respectively. The sediment temperature was 4–6C, consistently decreasing with depth (on average 0.1–0.2C cm)1). Sediment characteristics Table 1 lists the main sediment characteristics of both beaches. The exposed beach (KB), was characterized by well sorted sediments dominated by two fractions: medium sand (up to 94% at HW) and coarse sand (up to 53.4% at LW). Other fractions comprised
