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Indian Journal of Geo Marine Sciences Vol. 47 (03), March 2018, pp. 613-622

Composition and distribution of meiobenthos in Arctic Kongsfjord (Svalbard) with reference to carbon potential of selected fauna

Krishnapriya P.P, Minu M & S. Bijoy Nandan*

Dept. of Marine Biology, Microbiology & Biochemistry, School of Marine Sciences, Cochin University of Science & Technology, Cochin 682 016, India

[ E.Mail: bijoynandan@yahoo.co.in]

Received 25 January 2017 ; revised 30 March 2017

The meiobenthic samples collected as a part of Summer Phase III group 2 – Indian Arctic Expedition 2011, forms the basis of this study. There were some vital observations regarding the sediment characteristics that, inner and outer fjords were similar in terms of granulomertic composition and also the silt dominated in the entire Kongsfjord. Total carbon (TC) and total organic carbon (TOC) were higher in the outer fjord, but the inorganic carbon (IC) was slightly lower in the inner fjord.

The meiofauna comprised of Nematoda, Foraminifera, Bivalvia, Polychaeta, Harpacticoid copepoda, Gastrotricha, and Kinoryncha. Nematodes (54%) formed the dominant phylum among the fauna followed by foraminifera (37%). Forty five nematodes belonging to nineteen families were identified, in which Anticoma eberthi (14.06 µg) contributed the highest carbon, followed by Marylynnia complexa (12.94 µg) in the Arctic Kongsfjord. Fifty six species of foraminiferans belonging to five sub orders were identified of which, Cribrostomoides jeffreysii (0.074 µg) and Globobulimina auriculata (0.071 µg) structured the maximum carbon content. Total carbon sequestered in the Kongsfjord accounted to an average of nematodes and foraminiferans respectively. The net carbon sequestrated by the nematodes and foraminiferans were higher in the outer fjord as compared to inner fjord of Kongsfjord region.

[Keywords: Kongsfjord, nematodes, foraminiferans, mineralisation, carbon sequestration.]

Introduction

Meiobenthos is a highly dynamic part of the ecosystem and their abundance and diversity exceed that of macrofauna and megafauna1. Meiobenthic communities of the arctic Kongsfjord-Spitsbergen are dominated by nematodes followed by foraminiferans.

Mineralisation and remineralisation of carbon;

sequestering and redistributing minerals and energy are the main functions of nematodes in the soil food web. Although oceans store most of the earth’s carbon, soils contain approximately 75% of the carbon pool on land – three times more than the amount stored in living plants and animals 2. Soils therefore play a major role in maintaining a balanced global carbon cycle. The primary way that carbon is stored in the soil is as soil organic

matter (SOM). SOM is a complex mixture of carbon compounds, consisting of decomposing plant and animal tissue, microbes (protozoa, nematodes, fungi, and bacteria) and humus – carbon associated with soil minerals2. Over the past 150 years, the amount of carbon in the atmosphere has increased by 30%. Most scientists believe that there is a direct relationship between increased levels of carbon dioxide in the atmosphere and rising global temperatures.

Nematodes and foraminiferans probably play a significant role in regulating the direction and magnitude of detrital carbon flow. The works done on nematode carbon sequestration is limited3,4,5,6,7&8

. Limited works are reported regarding the carbon sequestration

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potential of foraminiferans 9,10,11&12

and also no information are there on the arctic nematodes and foraminiferans on the basis of carbon.

Hence this is a pioneering study on the meiobenthic biomass and carbon potential of nematodes and foraminiferans, their contribution to SOC pool of the Kongsfjord - arctic system.

Materials and methods

The study area was Kongsfjord glacial fjord (790 N, 120 E) in Arctic (Svalbard) located north wards to Norway. Kongsfjord is a high latitude glacial fjord influenced by Atlantic and Arctic water masses. The glacial outflow of fresh melt-water containing mineral materials influences the salinity, water transparency, primary production and sedimentation rates13&14. The samples were collected from seven stations during August

Fig. 1 Map of Kongsfjord showing the study stations.

2011 (Fig.1). The depth of the area ranged from 40 to 303 meters (Table 1).

Based on depth profile, the fjord stations were divided into two subsets representing the outer and inner parts of the fjord. Stations 1, 2 and 3 were considered as inner fjord whereas 4, 5, 6 and 7 as outer in the fjord.

Sediment pH was determined using Systronics analyser (No.371, [accuracy ± 0.01]). Digital Eh meter (Systronics, No.318) was used for determining oxidation reduction potential (Eh) and expressed in (mV). The moisture content of the sediment was determined by drying sediment samples at a uniform temperature of 100OC. Sediment granulometric analysis were performed with a Sympatec (KFS Magic) Serial No: 1131, 41362 laser diffraction granulometer for finding the fractions of silt, clay and sand in the sediment. Total carbon

Table 1 Details of sampling stations in Kongsfjord during summer phase 2011.

Stations Depth (m) Latitude Longitude

1 76 78◦54.299’ 12◦13.665’

2 80 78◦55.019’ 12◦04.499’

3 40 78◦57.216’ 12◦10.527’

4 303 78◦56.462’ 11◦57.295’

5 300 78◦58.530’ 11◦41.487’

6 213 79◦00.580’ 11◦36.479’

7 244 79◦00.594’ 11◦25.471’

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(TC), total organic carbon (TOC) and total inorganic carbon (TIC) concentrations were determined on dried sediment samples by thermal combustion using a TOC – analyzer (Analytik Jena multi N/C 2100s). Samples for inorganic carbon were pre-treated with HCl to remove carbonates.

The samples for the study was collected by the Principal Investigator of the programme Dr. S.

Bijoy Nandan as part of the Indian Arctic Expedition from 17 July to 6 August, 2011 at the Indian research base “Himadri Station” at Spitsbergen, Svalbard, Norway; which is a part of the International Arctic Research base, Ny- Alesund. The boat “Teisten” of Kings Bay was employed for collecting samples from the selected transects.

The samples were collected using van Veen grab (KC Denmark A/S) of 0.1 m2 area.

Sub samples for meiofauna analysis were collected using a glass corer with cross-section area of 5 cm2 that was pushed into sediment to a depth of 5 cm15. The samples were preserved in formaldehyde – seawater solution of 4%

and stained in Rose Bengal. Organisms were extracted from the sediment using decantation technique16. Meiofauna after passing through a 1mm sieve and retained on a 63 µm sieve was counted and identified to major taxa using suitable taxonomic keys1, under a stereo- microscope, Olympus - Magnus MS 24.

Identification of nematodes were done to the lowest taxonomic level possible by following the standard pictorial keys17,18,19&20

. Necessary measurements of the specimens were taken using image analyser, Dewinter Biowizard version 4.3. Mean individual nematode biomass of each sample was estimated according to Andrassy's formula3. Nematode wet weights were converted to carbon biomass by assuming that 100% wet weight corresponds to 12.4% carbon weight 5.

The sediments of >63 μm was used for the foraminiferal studies. Sediment from the upper 1 cm slice of the corer was taken for processing. Samples were soaked in 5%

hydrogen peroxide for about twelve hours and, boiled mildly before wet sieving. A representative sample of each station was taken on watch glass and oven dried overnight at 50°C and dried sand was spread on a black paper. Foraminiferans were picked and identified using an Olympus stereo zoom

binocular microscope, based on standard pictorial keys21. A semi-automated digital micro photographic approach was used to measure the biomass of foraminifera 22. Soft- body wet mass of foraminifera was converted to soft-body organic carbon equivalents (C) assuming 10 % of carbon9.

The univariate analysis (Shannon- Weaner diversity index (H’, log2)) of data was done using the PRIMER, software (Plymouth Routines in Multivariate Ecological Research, Version 6.1.6) 23.

Results

In the summer months of August, the average sediment temperature of Kongsfjord ranged from 2.7 to 4.1OC. The mean value of pH in the inner fjord was 6.92±0.294 and that of outer fjord was 7.27±0.126. The mean value of Eh in the inner fjord was -294.33±59.28 mV and that of outer fjord was -183.75±56.68 mV.

Mean value of sediment moisture in the inner fjord was 4.99% and that of outer fjord was 6.5%. The total carbon in the inner fjord was 31.25±6.698 g/kg and that of outer fjord was 35.44±0.843g/kg. Total inorganic carbon varied from a lowest value of 13.01 g/kg in station 2 to a highest value of 27.1 g/kg in station 1. Total inorganic carbon in the inner fjord was 21.79±7.65 g/kg and that of outer fjord was 20.17 ± 2.24g/kg. Total organic carbon varied from a lowest value of 8.69 g/kg in station 1 to a highest value of 16.49 g/kg in station 7. The total organic carbon in the inner fjord was 9.47±0.967 g/kg and that of outer fjord was 15.28±1.42 g/kg (Table. 2).

Total carbon in the sediment was higher in the outer fjord, than the inner fjord but the average total inorganic carbon was slightly higher in the inner fjord, than the outer fjord. The sediment fraction consists of silt, sand and clay. The silt fraction in the Kongsfjord during the study period was 66.33

% that of inner fjord and outer fjord were 70.33% and 63.33% respectively. Average sand fraction in the entire system during the study period was 45.87 % and that of inner and outer fjords were 49.93% and 42.83 % respectively. The clay fraction in the system was 20.71 % of which, the inner and outer fjords were 21 % and 20.5 % respectively (Table 2).

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Meiofauna – Composition and abundance Seven meiofaunal groups were recorded in the summer months of Kongsfjord glacial system that was constituted of Nematoda, Foraminifera, Bivalvia, Polychaeta, Harpacticoid copepoda, Gastrotricha, and Kinoryncha. Maximum numerical abundance of the taxa was recorded in station 2 (2273 ind.

/10 cm2) station 1 (2154 ind. /10 cm2) and station 3 (1862 ind. / 10 cm2). Nematoda was the numerically dominant taxon in all the stations, constituting a minimum of 54% of total meiobenthic abundance. Percentage abundance of other subdominant taxa were, Foraminifera (37 %), Harpacticoid copepoda (0.2%), Bivalvia (3.1 %), Gastropoda (0.2 %), Polychaeta (3 %) and Kinoryncha (3%).

Nematodes formed the abundant group both in the inner and outer fjords with a percentage

abundance of 47% in the inner fjord and that of 52.7% in the outer fjord. The Shannon Wiener index (H’) varied from 1.684 in station 1 to a 1.66 in station 2 with an average of 1.61 in the inner fjord and 1.28 in the outer fjord.

Diversity of meio fauna was higher in the inner fjord. All the meiobenthic groups were present in station 1 which was located in the inner fjord and it was dominated by nematodes.

During the study period, fourty five species of nematodes representing nineteen families belonging to three orders, Chromadorida, Monhysterida and Enoplida have been taxonomically identified from the seven stations. The mean percentage abundance of the fauna in all the seven stations showed that, Dorylaimopsis sp. (39.55%) had the highest percentage of abundance followed by Terschellingia longicaudata (12.53%).

Table 2 Sediment characteristics of sampling stations in Kongsfjorden system during summer phase 2011

Stations

TC (g/kg)

TIC (g/kg)

TOC (g/kg)

Moisture

(%) pH

Eh (mV)

Clay (%)

Sand (%)

Silt (%)

1 35.79 27.1 8.69 4.56 6.66 -325 22.5 3 73.31

2 23.56 13.01 10.55 3.38 7.24 -226 20 18.58 60.79

3 34.41 25.25 9.16 7.02 6.86 -332 21.4 3.21 74.9

4 36.52 23.25 13.27 5.13 7.39 -262 19 9.6 69.87

5 35.35 19.29 16.06 5.29 7.1 -141 19.4 12 67.1

6 35.44 20.16 15.28 4.86 7.26 -189 23.1 11.65 64

7 34.46 17.97 16.49 10.72 7.34 -143 20 19.7 59

Fig. 2 Carbon content of nematodes from Arctic Kongsfjord, during summer phase 2011

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Among the nineteen families Comesomatidae was dominant followed by Sphaerolaimidae, Linhomoeidae and Oncholaimidae. The mean biomass of nematodes in the Kongsfjord during August 2011 was 0.88 mg/10 cm2. In the outer fjord the average biomass was 0.12 mg/ 10 cm2 while that of the inner fjord had 0.14 mg/ 10 cm2. Biomass of nematodes was higher in station 2 (0.16 mg/ 10 cm2) followed by stations 1 and 3. The taxonomic identification of faunal assemblage

of Foraminifera in the Kongsfjord consists of fifty six species representing thirty six genera, twenty one sub families, twenty three families, nineteen super families and five sub orders.

The faunal assemblages of the outer fjord stations showed an overall dominance of Nonionellina labradorica (18.30%) and Cassidulina teretis (8.85%) while inner fjord have a predominance of Hyalinonetrion sp.

(7.89%), Quinqueloculina arctica (7.01%) and Cribrostomides jeffreyssi (6.14%). Among the suborders higher percentage abundance was recorded in the suborders Rotaliina (59.22%) followed by Textulariina (15.74%) and Lagenina (14.89%). Total biomass of foraminiferans in the inner fjord was 0.212 mg/10 cm2 and that of the outer fjord was 0.972 mg/10cm2 with mean value of 0.592 mg/10 cm2 in the Kongsfjord.

Carbon potential of nematodes and foraminiferans

The carbon content in the individual nematodes, foraminiferans and the total carbon sequestered by them was calculated in the study. It was found that, among the twenty nematode species, Anticoma eberthi has the highest carbon content in their body (14.06 µg), followed by Marylynnia complexa (12.94 µg). The lowest value was recorded in Halalaimus longicaudatus (0.122µg) (Fig. 2).

Among the twenty five nematode genus, Polygastrophora sp. (4.0238 µg) had the highest carbon content followed by Sabatieria sp. (2.145374 µg) and Comesoma sp. (1.943365µg) (Fig. 3).

When these nematodes die and decay, the carbon in their body will be sequestered into the sediment and it will form part of the carbon pool in the arctic system. This carbon will subsequently become a part of the carbon cycle. The total carbon sequestered by the nematodes in each station was calculated.

The total carbon sequestered by the nematodes in the sediment of station 6 (281.93 µg/10 cm2) was higher among all the stations followed by station 1 (209.3 µg/10 cm2) and 7 (199.87µg/10 cm2) (Fig.5).

The mean value of carbon sequestered by nematodes in the Kongsfjord during the study period was 160.34 ± 76.99 µg/10 cm2. The mean value in the inner fjord was 137.25±62.53 µg/10 cm2 and that of outer fjord was 177.66±91.19 µg/10 cm2. From the results it is clear that the net carbon sequestrated by the nematodes was higher in the outer fjord and much lower in inner fjord.

The carbon content of the foraminiferans Cribrostomoides jeffreysii and Globobulimina auriculata were also found to be more when compared to other species.

Cribrostomoides jeffreysii have an average of 0.74 µg carbon and Globobulimina auriculata, have 0.71 µg of carbon in their body (Fig.4).

Fig. 3 Carbon content of nematodes from Arctic Kongsfjord, during summer phase 2011

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Carbon sequestered by foraminifera was higher in station 4 (29.9 µg) followed by station 7 (25.0 µg) (Fig.6). Total carbon sequestered by foraminiferans in the sediment of Kongsfjord was 118.0 µg /10 cm2. The mean amount of carbon sequestered in the inner and outer fjord stations were 7.0 µg /10 cm2 and 24.32 µg /10cm2 respectively. From the results it is clear that the net carbon sequestrated by the foraminifera was higher in the outer fjord and much lower in the inner fjord. Similar results were also observed24.

Discussion

Kongsfjord is frozen during winter but open and influenced by the warmer and more saline Atlantic waters during summer. Mean value of sediment moisture in the outer fjord was higher when compared to inner fjord.

Moisture content indicates the water holding capacity of sediment. Station seven had higher water holding capacity but the rest of the stations depicted a uniform nature. Fine sediment with higher water content was probably a more difficult barrier to the upward burrowing activity of fauna than coarse

sediment25. Fig. 4 Carbon content of some major foraminiferans from Arctic Kongsfjord during summer phase 2011

0 50 100 150 200 250 300

St. 1 St. 2 St. 3 St. 4 St. 5 St. 6 St. 7

Carbon content g/10cm²)

Stations

Fig. 5 Station wise variation in total carbon sequestered by nematodes in the Arctic Kongsfjord during summer phase 2011

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The amount of water in the sediment is an important factor determining the distribution of organisms. Among the two forms of carbon (organic and inorganic) present in the soil, total organic carbon is the major form of carbon which is available to the food web which gets transferred from one trophic level to another. The decreasing concentration of organic matter in the sediment could be the result of glacial mixing14. Proportion of silt, sand and clay in the sediment in all the seven stations were almost similar, hence the inner and outer fjords also were similar in terms of granulometric composition. Similar results were also observed in several studies26&27. In the present study, it was also observed that, silt dominated in sediment fractions in Kongsfjord.

Granulometric characteristics, quantity of organic carbon and the stability of sediments all reflect the glacial sedimentation gradients in the Arctic glacial fjord. Sedimentation rates of suspended particulate matter were reported to be highest in the glacier’s proximal inner basin28. Salinity and temperature gradients are produced by the inflow of fresh and cold glacial melt waters, in the Kongsfjord, which is controlled by the glacial activity. During the summer months, the high influx of terrigenous materials transported by the glacial inputs produces high particle flux which affected both the benthic food availability and substrate condition while the lack of sediment stability and permanent mineral sedimentation processes appear to be much more important in influencing the meiofaunal distribution and macro faunal densities in Kongsfjord26&27. But

it is also important that the high levels of mineral sedimentation and sediment deposition have shown to be an acute disturbance agent causing a dramatic decrease in benthic densities and diversity.

The number of meiobenthic taxa recorded as well as their average abundance was relatively lower in the outer basin but higher abundance and diversity towards the inner fjord. The persistence in stability of meiofaunal abundance in the inner fjord of Kongsfjord revealed that the meiofauna can be less sensitive than macro fauna28&29 to sediment disturbance caused by decreased sediment re-suspension due to glacial activity.

Glacial inputs and the inflow of Atlantic water masses also contributed to the distribution of meiofauna13,14&30

. In the present study Nematoda was the numerically dominant taxon throughout the fjord and the finding corroborates well with other studies 26&31. Likewise, fjords other than Kongsfjord were also dominated by meiobenthic nematodes32. Because of these specific features meiofauna could be used in marine monitoring programmes and the nematode community structure could be used to assess changes in soil quality since these organisms respond rapidly to new resources33&34.

Macro fauna generally increase the rates of detritus degradation35,36&37

. Conversely, direct macrofaunal respiration of detrital carbon is probably a minor component of total carbon flow in benthic systems. Some macrofauna physically shred large fragments of detritus thereby decreasing particle size and increasing rates of decomposition and bringing

Fig. 6 Station wise variation in total carbon sequestered by foraminiferans in the Arctic Kongsfjord during summer phase 2011

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up nutrients from deeper sediment layers38. While several macrofaunal species are known to affect rates of decomposition, there are very few similar studies with meiofauna. Meiofauna probably are an important component of benthic energy flow because of their high abundance and metabolic rates39. Thus meiofauna in general, and particularly nematodes and foraminiferans the dominant taxons, affect detrital decomposition and carbon transformation. The observed increase in carbon mineralization due to the presence of nematodes and foraminiferans will decrease the standing stock of detrital carbon available to other detritivores. Both affect microbial abundance and/or activity will play a major role in benthic carbon flow than would be expected on the basis of nematode biomass or production6.

The study shows that the carbon sequestering potential of nematodes was higher when compared to other meiofauna because of higher abundance and better re- mineralization efficiency 6,7&8. In the sediment the net effect of carbon sequestered includes all the organisms especially the benthic organisms. Since, nematodes have a higher biomass and density in meiobenthos, this in turn contributed to the carbon potential or pool of the trophic realm. Nematodes form one of the major groups which provide the nutrient and carbon sources to higher tropic levels40. When the bacterivorous and fungivorous nematodes graze on these microbes, they give off CO2 affecting carbon mineralization directly. Nematodes excrete a majority of assimilated carbon that they consumed from the bacteria and fungi. When they die and decay, the carbon content in their body will be sequestered into the soil and will get transferred to the next trophic level. Therefore, nematodes play an important role in soil carbon cycling41. carbon sequestered in the sediment by nematodes depends on the length width ratio in spite the number of organism3&5. The species in station 6 were relatively higher in length width ratio compared to nematodes of other stations, hence station 6 have high carbon sequestration values.

Only few reports are there regarding the carbon potential of benthic foraminifera24. The present study shows that the foraminifera (37%) form the second dominant taxa in the Kongsfjord that have contributed a significant portion of carbon to the SOC pool in the arctic

sediment. A marked difference in the carbon sequestering potential of foraminiferans in the inner and outer fjord stations were observed.

In the present study, changes in the test diameter of foraminifera were also noted between inner and outer fjords. It was found that the biomass and associated carbon amount was found to be decreasing towards the glaciated environment which may be due to smaller foraminiferal test size or absence of larger species and higher occurrence of juvenile foraminifera. The decrease in the organic flux to the bottom of the inner fjord stations may be the controlling factor for reducing the foraminiferal test size. In the outer fjord stations the test size of foraminifera was found to be more when compared to the same species found at the glaciated inner fjord.

The number and size of the foraminifera was found to be larger in the outer fjord. This higher amount might be correlated with the higher productivity in the outer fjord. The reduction in their test size and number has been reflected in the carbon sequestering potential. The decrease in the test size of foraminifera in the inner fjord may be due to its opportunistic response to environmental stress 24.

Bacteria and fungi are the primary decomposers in the soil food web. These microbes immobilize inorganic nutrients and carbon in the soil. When nematodes and foraminiferans graze on these microbes, they spin-off CO2 and will affect carbon mineralization significantly. Subsequently when these major meiofauna die and decay the carbon content in their body get sequestered into the soil and further gets transferred to the next trophic level. Therefore, nematodes and foraminiferans play an important role in soil carbon cycling. The change in the carbon content in these meiofauna will affect the amount of carbon in the Kongsfjord SOC and carbon pool of arctic system.

Conclusion

The sediment characteristics revealed that, inner and outer fjords were similar in terms of granulomertic composition and silt was the dominating component in the entire Kongsfjord. Nematodes (54%) had the highest mean percentage abundance followed by Foraminifera (37 %) of meiofaunal community. Among nematodes Anticoma eberthi has the highest carbon content in their

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body, followed by Marylynnia complexa.

Carbon content of foraminiferans, Cribrostomoides jeffreysii and Globobulimina auriculata are found to be more when compared with other species. Net carbon sequestrated by the nematodes and foraminiferans were high in the outer fjord and much lower in inner fjord. In the present study it can also be concluded that the nematodes have higher carbon sequestration potential than foraminiferans, in the Kongsfjorden system. From the literature survey it is found that no work has been done nationally or internationally to found out the carbon content in Arctic nematodes and foraminiferans.

Acknowledgements

The authors are thankful to the National Centre for Antarctic and Ocean Research (NCAOR), Govt. of India and to the Head, Dept. of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences, Cochin University of Science and Technology for providing the financial support and necessary facilities for undertaking the study.

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