..--------------

ICES C.M. 1995 ~~'l.~...... -. ·-····~Nottobe cited without prior reference to the authorOlbllothl-H CM 1995fT:3

1..', F· . ....'t~.~IHb'T!I. lI'

BIOMASS AND QUANTITATIVE INVESTIGATIONS OF THE MACROBENTHOS INTWO LOCALITIES IN THE LIMFJORD, DENMARK: SHORTTElThf EFFECTS OF

OXYGEN DEPLETION IN RELATION TO DEPTH DISTRIBUTION

by

Karen Nitschke

Danish Institute for Fisheries ResearchDK - 9850 Hirtshals

Denmark

. ABSTRACT !~

This work focuses on the possible. consequences of eutro~ation on the macrobenthosproductivity and ultimately on the suitability ofthe Lirnfjord, an enclosed fjord in northemDenmark, as feeding ground for juvenile flatfish.

Reduced oxygen concentrations in the bottom waters of the fjord is a frequently occuringevent during warm summer periods. Fish may have an opportunity to survive prolongedperiods of oxygen depletion in an area by moving inshore (altematively migrating from theeffected area) and feeding on inshore macrobenthos until conditions improve.

The effects ofoxygen depletion on macrobenthos in relation to depth distribution, especiallyinshore effect, is described for two localities: Skive Fjord, a 27 kml heavily eutroficated areawith oxygen concentrations below 2 mgll during 3-4 weeks in late summer 1994, and VenoBugt, an 86 kml less eutroficated area where oxygen concentrations below 4 mgll were onlyregistered during one week. Bottom sampIes were collected during spring and autumn from12 stations evenly distributed in three depth strata (O-2m, 2-4m, >4m depth) at both localities.Abimdance and biomass are measured and annUal production of macrobenthos are estiInated.The results indicates that the inshore areas of both Skive Fjord and Veno Bugt have thepotential for providing nursery grounds for flatfish feeding on macrobenthos.

SKIVE FJORD

VEN0 BUGT'

Figur 1: Map 01 Denmark. showing the (wo localities in the Limjjord.

..

e-

INTRODUCTION

In the Limfjord, aß enclosed fjord in the northem part of Denmark connecting the NorthSea in the west to the Kattegat in the east, the distribution and aburidance of several fishspecies have decreased since the late 1960's (Flintegärd et aI.,1982). A breeding popula­tion of flounder Platichthys flesus has disappe<ired from talge areas. The population ofplaice Pleuronectes platessa which migrates from the North Sea to especially the westernpart of the fjord as 1- and 2-year old fish has decreaSed drastically since 1967 (Fliritegardet aI., 1982)~ The reason for these changes is not clear, but may be related to eutroficationarid the subsequent reduced oxygen concentrations in the bottom waters of the fjord,which is now a frequently occuring event during warm summer i>eriods.

Recently, locaI fishery organisations have tried to enchance the decreased fishery stocksby rearing juvenile flounder and plaice for stocking. To examine the viability of thepractice of stocking iri the Limfjord, it is necessary to examine the available food forflatfish in the fjord. The official danish monitoring programme incltides sampIes ofmacrobenthos taken twice a year at 19 stations covering the whole i.imfjord (Limfjords­overVägnirigen, 1992). However, each station is placed at a water depth below 4 metersand gives little information on the inshore effects of oxygen depletion orl macrobenthos.The nursery grounds of most juvenile marine fish species are in the shaIlow; inshoreareas; arid information on the macrobenthos in the shallow regions is not available.

This work foeuses on two localities in the Limfjord. Skive Fjord, a 27 km2, heavily eutro­

ficilted area. The sediment consists mainly of silt and clay and has accumulation of H2S.Inshore, the sediment consists of sand. The organic content is 10.7-14.0% afdw and thearea is known to receive a heavy load of nutrients from freshwater run-off arid, lherefore,a great supply of organie material io the sediment from aIgaI production (Limfjords­overvägningen, upubl.). This is "aggravated by a very slow water exchange in the area.Vena Bugt is an 86 km2 less eutroficated area. The sediment in the deepest part of the bayis mainly sand and silt with an orgariiccontent of 8-12 % afdw. Along the cOaStlines thesediment is sandy, with an organie conterit of 1-3% afdw.

This study lookS ät the effects of oxygen depleuon on macrobenthos in relation to depthdistribution. Tbe results are discussed with respect to their potential for providing nurserygrouiids for flatfish feeding on macrobenthos.

METHODS

Sampling: During 1994 quaritita~ve sainples o~ macrobenthos were colleeted in May/Juneand Oetober iri Skive Fjord and Vena Bugt. At each 10CaIity 12 statioris were distributedat three depth strata (0-2 m, 2-4 in and >4 in depth)(Figur 2). At each station 10 Sampieswere taken with a HAPS corer (1/70 m2

). The Sampies were sieved through a 1 mm sieveon site arid fixed in formalin before conserved in 70 % etliariol.

Laboratory analysis: In the laboratory the macrobenthos from the sampies were sorted andcounted. The bioinass has been ineasured as ash-free dry weight by the methods outlinedby Jensen et al' (1990). Bivälvia with a totallength of more than 2,5 cm have riot beenan3.IYsed rcr weight, as they were presumed not to be consumed by flatfish, even though

Ro

L.

OR SKIVE FJORD

Figur 2: The distribution 01 the 12 stations in Vene Bugt and Sldve Fjord. Vene Bugt:Stations A, e,D and E is in the depth stratum 0-2 meter, stations H,1,O and R is placed inthe depth stratum 2-4 meter and stations J,M,P and Q is in the depth stratum >4 meter.Sldve Fjord: Stations C,E,F and G is in the depth stratum 0-2 meter, station H,J,R and Sis in the depth stratum 2-4 meter and stations L,N,O and P is in the depth stratum < 4meter. Station 8 in Vene Bugt and station 29 in Sldve Fjord is the stations Irom the officialdanish monitoring programme, and their data are included in the results olthis study.

siphons from large bivalvia is part of the diet of flatfish (De Vlas, 1979).

Data analysis: The official danish monitoring programme collects sampies of maCfQ­benthos at one station in each of the two localities in the depth stratum >4 meter; andtheir data from 1994 has been included in the data analysis of this study.

The analysis of variance was done using the GLM-procedure from the SAS-system. Thelevel of significance chosen was 5 %. The GLM-procedure type III explanation was used,where the tested hypothesis is independent of the order of the effects. As effects we havelocality, station, depth, period, and group 01 benthos anti station. The dependent variablesare density and biomass.

Production models: The annual macrobenthos production was estimated in two ways.Method 1 converts the biomass data from the spring sampies into annual production byapplying variable mean production to biomass (p:B) ratios to species or major taxon. TheP:B ratios are from Robertson's (1979) review on studies of production in marinemacrobenthos. In our study the P:B ratios from offshore surveys have been left out. The

P:B ratios used are as folIows: Ampharete acutifrons 5.02, Arenicola marina 0.95,Clzaetozone setosa 1.28, Neanthes virens 1.60, Nephtys hombergii 1.86, Terebellides sp.2.31, other polychatae 2.1, Hydrobia sp. 1.46, Littorina littorea 0.53, other gastropoda2.2, Cerastodenna edule 1.62, Macoma balthica 1.33, Mya arenaria 2.54, Mytilus edulis1.02, Venernpis pullastra 0.15, other bivalvia 1.95, crustacea 3.36, Asrerias sp. 2.64,Ophiura sp. 0.4, echinodennata 1.52, others 2.23 (Robertson, 1979)(Jensen et al., 1994).

Method 2 considers the [ate of the biomass that has been produced from spring to autumn,e.g. the period of the survey. The organic matter that is produced will either remain asliving matter, will have died or will have been eaten. If Bo were the standing crop biomassin spring and BI the standing crop biomass in autumn then

Pl994 = (BI - Bo) * 7/5 + M (modified after Holme & McIntyre, 1984)

where M is the mortality due to all causes, and the factor 7/5 is to compensate for thelonger growth season for macrobenthos (7 months) in relation to the survey period (5months). In our study we do not have a measure of M, so the term

will not be the annual production, but will be the remaining amount of living matter afterthe macrobenthos's growth season at the study site in 1994.

Diversity-index: Species diversity was calculated for each depth stratum [rom the Shannon­Wiener equation:

sH' = ~ Pi log2 Pi

i=1

where Pi = n/N, ni being the number of individuals of the i'th species and N the totalnumber of individuals. s = total number of species.Evenness was estimated as:

. J = H'/H'max

H'max = log2s, (Gray, 1981)

The diversity-index was calculated from the spring sampies.

Consumption-model: A model of consumption for 0~4 year old plaice was created. Data ontotallength and wetweight of juvenile plaice at their settling to the dermersal stage wasobtained from the Danish Institute for Fisheries Research (unpublished data for plaicereared for stocking around the lth of July). The equation used to estimate AFDW as

18007

~

r J • 1'1c

11000

10000

9000

8000

7000

:§ 6000

] 5000

4000

3000

2000

1000

oE F G H J R

--0"-.....2-- 2-4 mm station

s L N 0 P 29

>4m

Figur 4: The variation of total number of individuals ofmacrobenthos perm2 in Skive Fjord. No autumn sampIes from station P.

5550

45

40

35

~ 30

~ 25Cl2Q

15105o~-+.....-+,---+.......,-+,---+.....,-+,-.-.,~"-t-'-""""r--+-"""'-+-=--+---t

C E F G

0-2 mH J R S

2-4 mstation

L N 0>4m

P 29

Figur 5: The variation of total biomass per m2 of macrobenthos in SkiveFjord. No autumn sampies (rom station 0 and P.

percentage of wetweight of fish from their wetweight condition index (K = lOOW*L"3) forplaice are:

% AFD\V = 33,1 - 15,51K (Costopoulos & Fonds, 1989)(cited in Fonds et al., 1992).

Values for daily food consumption (C, mg AFDW) are obtained from Fonds et al. (1992)using Cmax in relation to temperature and using a weight exponent of 0.78 (Fonds et al.,1992). Data on the instantaneous total mortality coefficient were ealculated from Beverton& lIes' s (1992) life table for O-group plaice in the North Sea, from the equation:

Nt = No * e-Zt (Eliassen, i982)

where Z is the instantaneous total mortality coefficient, N is the population size and t isthe time'period involved. After the first year the instantaneous mortality coefficient usedin the model is the theoretical value of 0.2.

RESULTS

Oxygen depietion is a frequently occuring event in loeal areas of the Limfjord. In Iatesummer 1994 the depletion of oxygen had the largest extend since 1988. App. 30% of thefjord was depieted of oxygen. Figur 3 shows the distribution of the oxygen depletion. InSkive Fjord oxygen concentrations were beiow 2 mg/l during 3-4 weeks, and in VemJBugt beiow 2 mg/l during onIy one week.

~.J

IQ lIdIiq< 2l1li Otpr.lill:r

2.3~<2miOtpr.1ilIOr

4- ~<2I111Otprill:r

3 mu.: ual ' t c:uX:-SC' lIlIlII <2...Ot pr.liocr.

Figur 3: The distribution 0/the oxygen-depletion in the Limjjord in lale summer 1994: Thenumbers indicate the duration 0/ time in weeks 0/ anoxia (Limjjordsovervägningen, 1995).

Skive Fjord: Total number of individuals and total biomass of macrobenthos per rn2 at al1the stations in Skive Fjord from spring and autumn is shown in figure 4 and 5. The

1100010000900080007000

~ 6000"0 5000.5

4000

300020001000

0A C 0 F H 0 R J M P a 8

Q-2m 2-4 m >4mstation

Figur 6: The variation of total number of individua/s of macrobenthos perm2 in Venl2l Bugt. No autumn samp/es (rom station P and Q.

55504540

E 35} 30

~ 25CIl2Q

15105O~R+~+'-~~'-t-L~~4L-'''''''4'-''''''f.J::II'"--P...L-t.LL--t-I~

A C 0 F H 0 R

0-2 m 2-4 mstation

J M P a 8

>4m

Figur 7: The variation of total biomass of macrobenthos per m 2 in Ven"Bugt. No autumn sampIes (rom station P and Q.

density was found between 637-6461 ind/m2 in spririg and 140-9681 ind/mi, with oneexception, station J with 18.007 irid/m2

, in autumn. All the stations in the depth stratum> 4 meter shows a drastical decrease in the abundance of macrobenthos from spririg toauturim. The total biomass varies between 0.08-22,35 g Clfdw/m2 in spring and between0.06-38.87 g afdw/m2 in autumn. Most stations have an increasing biorriass from spring toautumn, except the stations in the depth stratum >4 meter, where the biomass is very lowboth in spring and autumn:

Veno Bugt: Total riumber and total biomass per m2 at all the stations in Ven~ Bugt fromspring and autumn is displayed in figure 6 and 7. The density was found between 1029­6468 ind/m2 in spring and between 378-6230 ind/m2 in autumn. The density at one stationin the depth stratum 0-2 meter, at one station in the depth stratum 2-4 meter and at all thestations in the depth stratum >4 meter decreases from spring to autumn. The totalbiomass vanes between 1.47-15.51 g afdw per m2 in spring and between 2.02-21.64 gafdw per m2 (except at station Q (52.9 g afdw pr. m2

) in spring arid station R (78.4 g

•.- afdw pr. m~ in autunm, which have high biomasses, because of large abundances of

Cerastoderma edule).

SAS analysis: In testing of the total biomass of macrobenthos per station as the dependentvariable, data from station Q in spring and from station R in autumn from Ven" Bugthave been excluded, sirice large abundances of Cerasioderma edule resultect in givingthese stations comparatively higher biomass (figur 7).

•

The biomass was' significantly different between the three depth-strata (p=0.0002), whilethere were no significant difference between the total biomass of macrobenthos per stationbetWeen Skive Fjord and Ven" Bugt or between spring and autumn sampies.

Since the density was extremely high (due to a ver.; high aburidance of Chaetozone setosa,Polydora sp., Afya arenaria and Venerupis pullastra) data from station J from the autumnsampies from Skive Fjord have been left out in. testing of the density,of macroberithos asthe dependent variable of various effects (loca1ity, station, depth, period, group ofbenthos). The tests did not give an indication of which effect could explain the variationof the density among the stations.

Testing the total density of macrobenthos per station on the data material from 0-4 metersdepth only, showecl a significant difference (p=0.0492) between Skive Fjord (0-2 and 2-4meter) arid Ven" Bugt (0-2 and 2-4 meter), but no difference between the two depth strataor between spring and autumn sampies.

Since the total biomass of macrobenthos per station was significantly different among thethree depth strata, the results are presented accordirig to each depth strata.

Sldve Fjord. spring: Table 1 shows the mean abundance and mean biomass per depthstratum in spring 1994 in Skive Fjord.The depth strata 0-2 m and 2-4 mare very muchalike, with an abundance of 3000-4000 ind/m2 arid a biomass of 10-12 g afdw/m2•

According to the bioma.ss I find the same dominance e.g. Neanrhes/Nereidae,Heteromastus filiformis, Littorina littorea and Scolo]Jlos anniger. According to nuinbersthe dominating species at 0-2 meter is: HeteromaStus filifonnis, Neanthes spp., Hydrobiasp., Chaetozone setosa, Corophium spp. and Capitella capitata, while oligochaeta,

Table 1: The composition of the infauna per depth stratum in Skive Fjord, spring 1994. A =abundance (ind1m'), B =biomass (g afdw/m'). Data do not include bivafves>25cm

OEPTH STRATA 0-2 meter 2-4 meter >4 meter

A S.E. 8 S.E. A S.E. B S.E. A S.E. B S.E.

INFAUNA 3043, 274.3 12.2558 3.7291 4037 402.1 10.6916 2.7315 3244 1310 1.2982 0.469

ANNELIOA (LEOORME) 2357 179.3 10.9134 3.6279 3803 394.3 6.2027 2.2661 459 135.0 0.2926 0.10332Polychaeta (Havbl!lrsteorme) 1636 110.4 10.8220 3.6294 2637 267.5 6.0928 2.2388 392 133.6 0.2813 0.10150Oligochaeta (Saddelbl!lrsteorme) 721 160.5 0.0914 0.0423 1166 199.1 0.1099 0.0432 67 17.0 0.0113 0.00418

MOLLUSCA (BL0OOYR) 516 99.7 1.1645 0.5448 205 25.9 4.0460 1.3009 69 39.5 0.3392 0.302Bivalvja (Muslinger) 196 77.5 0.3040 0.1277 128 23.9 0.5625 0.1853 63 39.4 0.0459 0.0250Gastropoda (Snegle) 320 46.8 0.8605 0.5303 77 15.4 3.4836 1.1920 6 3.4 0.2933 0.2930

ARTHROPOOA(LEOOYR) 165 127.8 0.0413 0.0312 26 8.2 0.0086 0.0050 8 4.7 0.0091 0.00809Crustacea (Krebsdyr) 165 127.8 0.0413 0.0312 26 8.2 0.0086 0.0050 8 4.7 0.0091 0.00809

NEMATOOA (RUNOORME) 4 2.4 0.0007 0.0007 4 2.4 0.0009 0.0009 2706 1191.6 0.3447 0.13972

ECHINOOERMATA (PIGHUOE) 2 1.8 0.0746 0.0746 2 1.8 1 1.4 0.2954 0.2954Asteroidae (Sl!lstjerner) 2 1.8 1 1.4 0.2954 0.2954Holothuroidea (Sl!lpl!llser) 2 1.8 0.0746 0.0746

UNIOENTIFIEO FRAGMENTS 0.0609 0.0565 0.4335 0.3900 0.0172 0.0172

Table 2: The 10 most dominating invertebrates in the depth stratum 0-2 meter in Skive Fjord,spring 1994.

Numbers

Heteromastus filiformis .Neanthes spp.Hydrobia sp.Chaetozone setosaCorophium sp.Capitella capitataMytJ1us edulisPhyllodoce maculatalmucosaPolydora ligniEteone longa

ind/mz

768410303156150100

70635126

Biomass

Neanthes spp.Heteromastus filiformisUttorina littoreaSco/oplos armigerMacoma balthicaOligochaetaHo/othuroidea sp.Hydrobia sp.Phyllodoce maculatalmucosaChaetozone setosa

9 afdw/mZ

8.20642.16840.78610.25110.17920.09140.07460.07440.06210.0445

Table 3: The 10 most dominating invertebrates in the depth stratum 2-4 meter in Skive Fjord,spring 1994.

Numbers

OligochaetaChaetozone setosaHeteromastus f./Mediomastus f.Nere/äaePolydora c/7iataSco/oplos armigerPygospio elegansMysella bidentataHydrobia sp.Phyflodoce maculatalmucosa

ind/mz

116681061751632616658474232

Biomass

NereidaeUttorina littoreaSco/oplos armigerHeteromastus f./Mediomastus f.Macoma balthicaNephtys hombergliHinia reticulataChaetozone setosaOligochaetaSpionidae

9 afdw/mZ

3.71473.21491.18410.54650.36230.29280.24240.17360.10990.0823

Table 4: The 10 most dominating invertebrates in the depth stratum >4 meter i Skive Fjord,sprinQ 1994..

Numbers

NematodaPolydora spp.Chaetozone setosaOligochaeta .Heteromastus f./Mediomastus f.Mytilus edulisHarmothoe sp.Caulleriella sp.Malacoceros sp.Nereidae

ind/mz

27061576967535035201511

Biomass

NematodaAsterias rubensHinia reticulataHarmothoe sp.Nephtys hombergiiMytilus edulis .Sco/oplos armigerChaetozone setosaMalacoceros sp.Oligochaeta

g afdw/mz

0.34470.29540.29150.10700.07040.04350.03390.01620.01610.0113

Table 5: The composition of the infauna per depth stratum in Skive Fjord, autumn 1994. A =abundans (ind1m'), B =biomssse (g afdw/m'). Data do not incfude bivafves>2.5cm.

DEPTH STRATA 0-2 meter 2-4 meter >4 meter

A S.E. B S.E. A S.E. B S.E. A S.E. B S.E.

INFAUNA 5934 642.2 19.2337 5.2658 9236 1350.8 22.2423 8.0167 219 56.0 0.0858 0.0366

ANNELIDA (LEDORME) 4750 522.3 13.9081 4.6549 4954 771.1 2.5232 0.8226 161 47.8 0.0352 0.0296Polychaeta (Havb",rsteorme) 3323 530.6 13.6554 4.4854 4121 675.1 2.4338 0.7818 159 47.8 0.0352 0.0296Oligochaeta (Saddelb",rsteorme) 1426 270.5 0.2527 0.1710 833 253.3 0.0894 0.0491 2 1.8

MOLLUSCA (BL0DDYR) 1099 296.4 5.2686 3.221 4114 684.8 18.9807 7.0506 40 9.3 0.0492 0.0183Bivalvia (Muslinger) 485 128.9 4.5334 3.1952 3313 697.6 17.4114 6.9525 25 6.9 0.0422 0.0182Gastropoda (Sne9Ie) 614 190.6 0.7352 0.2196 799 154 1.5693 0.6503 16 6.4 0.007 0.0053

ARTHROPODA (LEDDYR) 74 39.7 0.0201 0.0174 163 64.9 0.7377 0.5430 12 4.9 0.0007 0.0007Crustacea (Krebsdyr) 74 39.7 0.0201 0.0174 163 64.9 0.7377 0.5430 12 4.9 0.0007 0.0007

NEMATODA (RUNOORME) 12 6.6 0.0004 0.0004 5 3.1 0.0007 0.0007 5 3.0

ECHINODERMATA (PIGHUDE)Asteroidae (S",stjerner)

UNIDENTIFIED FRAGMENTS 0.0366 0.0321

Table 8: The 10 most dominating invertebrates in the depth stratum 0-2 meterin 5kive Fjord, autumn 1994.

Numbers indlnr Biomass 9 afdw/nr

Chaetozone setosa 1950 Hediste diversicolor 6.5105O/igochaeta 1426 Heteromastus fi/iformi 3.4704Hydrobia sp. 607 Neanthes sp. 3.1500Heteromastus filiformis 557 Mya arenaria 3.2069Hediste diversicolor 334 Cerasroderma edule 0.5761Spionidae 239 Mytilus edulis 0.4918Mya arenaria 173 Uttorina littorea 0.4750Neanthes sp. 149 Macoma ba/thica 0.3983Mytilus edulis 119 Chaetozone setosa 0.3852Corophium sp. 56 Hydrobia sp. 0.2602

Table 7: The 10 most dominating invertebrates in the depth stratum 2-4 meterin 5kive Fjord, autumn 1994.

Numbers indlmz Biomass 9 afdw/mz

Chaetozone setosa 2793 Mytilus edulis 14.6670Myti/us edulis 1551 Mya arenaria 1.2154Oligochaeta 833 Capite/lidae 1.0549Hydrobia sp. 788 Hydrobia sp. 0.7978Mya arenaria 745 Macoma balthica 0.7593Capite/lidae 575 Csrcinus maenas 0.7173Polydors sp. 481 Nereidae 0.6180Venerupis pu/lastra 343 Chaetozone setosa 0.4742Csrdium nodosum 271 Hinis reticulats 0.4340Petricola pholadiformis 205 Venerupis pu/lastra 0.2620

Table 8: The 9 most dominating invertebrates in the depth stratum >4 meter in5kive Fjord, autumn 1994.

Numbers

Polydora sp.Cspitells capitataNereidaeRissos sp.Corophium insidiosumCerastoderma edu/eMytilus edulisChaetozone setosaNematoda

9044151411

9775

Biomass

Mytilus edulisSpionidaeCspitells capitataCardium nodosumRissos sp.NereidaeCersstoderma eduleMys arenariaChsetozone setoss

9 afdw/mz

0.02990.01860.01170.00740.00670.00390.00230.00210.0011

Chaetozone setosa, Heteromastus filifonnis/MediomastlLS jragilis, Nereidae, PolydoradUata and Scoloplos anniger dominates in numbers at 2-4 meter depth stratum (table 2and 3).

Even though the abundance of 3244 ind/m2 in the depth stratum > 4 meter is like thedensities inshore, the biomass and the composition of the fauna is quite different.Nematoda is the one phyla dominating the fauna and contribute to 83 % of the density.The mean biomass for the stratum is 1.2982 g afdw/m2

, Nematoda, Asterias rubens andHinia reticulata being the dominating species (Table 4).

Skive Fjord, autumn: Table 5 shows the mean adundance and mean biomass per depthstratum in autumn 1994 in Skive Fjord. Both the mean abundance and the mean biomassper m2 have increased from spring to autumn in the depth strata 0-2 meter and 2-4 meter.In the depthstratum 0-2 meter the abundance is dominated of Chaetozone setosa,Oligochaeta, Hydrobia sp, Heteromastus filifonnis and Hediste diversicolor, whereas thebiomass is dominated of Hediste dil.'ersicolor, Heteromastus filifonnis, Neanthes spp. andMya arenaria (table 6). In the depth stratum 2-4 meter the abundance increased to 9236 •ind/m\ caused by a heavy bivalvia settlement (e.g. Mytilus edulis, Afya arenaria,Venerupis pullastra). The dominating species in numbers are Chaetozone setosa, Mytilusedulis, Oligochaeta, Hydrobia sp. and Mya arenaria. The increase in mean biomass forthe depth stratum 2-4 meter is because of the bivalvia settlement, since the biomass ofpolychaeta have decreased from spring to autumn. Afytilus edulis is dominating withrespect to biomass (table 7).

In the depth stratum >4 meter both the abundance. and the biomass are very low and havedecreased since spring. The sparse abundance of 219 ind/m2 consists of Polydora sp.,Capitella capitata, juvenile Nereidae, Rissoa sp. and Corophium insidiosum and thebiomass of 0.0858 g afdw/m2 consists mainly of Mytilus edulis, Spionidae and Capitellacapitata (table 8).

Production: Estimates of annual production of macrobenthos in Skive Fjord is shown intable 9. PIM gives an idea of the expected annual production estimated from the biomass inthe spring sampies. Pl994 gives an estimate of the remaining amount of living matter at theend of the macrobenthos's growth season in 1994. At the depth stratum 0-2 m and 2-4meter the production of polychaeta is 15-22 g afdw/m2

• The largest production in 1994 isin the depth stratum 2-4 meter and is according to bivalvia. In the depth stratum >4meter the annual production is very low and there is no accumulation of biomass at theend of the macrobenthos's growth season.

Veno Bugt, spring: Table 10 shows the mean abundance and mean biomass per depthstrata in spring 1994 in VenO' Bugt. The depth stratum 0-2 meter has the lowest abundanceand the lowest mean biomass of the three strata. The abundance is 2096 ind/m2 dominatedby Scoloplos anniger, Nematoda and Oligochaeta (table 11). The biomass is 5.9098 gafdw/m2

, dominated by Scoloplos armiger, Macoma balthica, Afacoma balthica, Littorinalittorea and Nereidae.

The highest abundance is in the depth stratum 2-4 meter, with 3741 ind/m2• The biomassis 11.1684 g afdw/m2

• According to number the dominating species are: Abra alba,Scoloplos armiger, Mysella bidentata, Oligochaeta and Spionidae (table 12). The biomass

Table 9: Production of macrobenthos in Skive Fjord. P ann: Annual production (g afdw/m 2/year) estimated from P:Bratios. P 1994: The remaining amount of living matter after the macrobenthos's growth season in 1994.

DEPTHSTRATA 0-2 meter 2-4 meter >4 meter

Pann P1994 Pann P1994 Pann P1994

INFAUNA 22.0528 9.7691 15.2718 16.1709 2.9011 -1.6975

ANNELIDA (LEDORME) 20.6752 4.1927 11.3648 -5.1513 0.5842 -0.3604Polychaeta (Havb"rsteorme) 20.4834 3.9668 11.1340 -5.1212 0.5604 -0.3445Oligochaeta (Saddelb"rsteorme) 0.1918 0.2259 0.2308 -0.0287 0.0238 -0.0159

MOLLUSCA (BL0DDYR) 0.9882 5.7457 2.9096 20.9086 0.6994 -0.4061Bivalvia (Muslinger) 0.4630 5.9212 0.6258 23.5885 0.0491 -0.0052Gastropoda (Sne9Ie) 0.5252 -0.1754 2.2838 -2.6800 0.6504 -0.4008

ARTHROPODA(LEDDYR) 0.1388 -0.0296 0.0288 1.0208 0.0306 -0.0118Crustacea (Krebsdyr) 0.1388 -0.0296 0.0288 1.0208 0.0306 -0.0118

NEMATODA(RUNDORME) 0.0016 -0.0005 0.0020 -0.0002 0.7686 -0.4826

ECHINODERMATA (PIGHUDE) 0.1133 -0.1044 0.7799 -0.4136Asteroidae (S"stjerner) 0.7799 -0.4136Holothuroidea (S"p"lser) 0.1133 -0.1044

UNIDENTIFIED FRAGMENT 0.1358 -0.0341 0.9666 -0.6069 0.0384 -0.0241

•Table 10: The composition of the infauna per depth stratum in Ven" Bugt, spring 1994. A = abundans (ind1m 2), B = biomasse (g afdw/m 2

). Data do not include>? f) r.m

DEPTH STRATA 0-2 meter 2-4 meter >4 meter

A S.E. B S.E. A. S.E. B S.E. A S.E. B S.E.

INFAUNA 2096 400 5.9098 0.9796 3741 422.6 11.1684 2.1616 2262 214.8 14.8729 9.6280

ANNELIDA (LEDORME) 1436 159.7 2.9574 0.7266 1856 139.3 9.0861 2.4703 365 75.3 2.0748 0.8035Polychaeta (Havbl!lrsteorme) 1039 86.8 2.8947 0.759 1468 95.7 9.0264 2.4543 290 70.0 2.0657 0.804Oligochaeta (Saddelbl!lrsteorme) 397 150.8 0.0627 0.0588 388 69.6 0.0597 0.022 76 29.2 0.0091 0.0033

MOLLUSCA (BL0DDYR) 114 21.9 2.7312 1.2537 1650 306.0 1.763 0.6419 1884 196.6 12.6217 9.2513Bivalvia (Muslinger) 89 19.5 1.4355 .1.0847 1599 300.5 0.8433 0.1956 1873 197 12.1421 9.3653Gastropoda (Snegle) 25 11.3 1.2957 1.2660 50 11.2 0.9197 0.4481 11.2 3.7 0.4796 0.4153

ARTHROPODA (LEDDYR) 81 27.3 0.069 0.0457 133 62.0 0.0303 0.0242 2.8 2.8 0.0004 0.0004Crustacea (Krebsdyr) 81 27.3 0.069 0.0457 133 62.0 0.0303 0.0242 2.8 2.8 0.0004 0.0004

NEMATODA(RUNDORME) 464 273.7 0.0048 0.0041 14 6.9 0.0027 0.0015 7 5.0

ECHINODERMATA (PIGHUDE) 9 5.3 0.2293 0.2293 2.8 2.8 0.1525 0.1525Asteroidae (S"stjerne) 7 4.3 0.2293 0.2293Ophiuroidea (Slangestjerner) 2.8 2 0.1525 0.1525

NEMERTINEA (BANOORME) 2 1.9 0.1452 0.0961 81 23.8 0.0162 0.0084

UNIDENTIFIED FRAGMENT 0.1452 0.0961 0.0410 0.0356 0.0235 0.0191

Table 11: The 10 most dominating invertebrates in the depths!rafum 0=2 me!erjn Yen" Bug! sPring 1994

. Numbers

Scoloplos armigerNematodaOligochaetaSpionidaeCapiteffidaeMacoma ba/thicaNereidaeHarmothoe sp.Jassa sp.Phyl/odocidae

ind/m2

698464397

76645757323027

Biomass

Sco/oplos armigerMacoma ba/thicaUttorina littoreaNereläae sp.Hinia reticulataNephtys hombergiiPolynoidaeSpionidaeEnsis sp.Oligochaeta

9 afdw/m2

1.77931.30940.89600.66720.36300.14350.13220.09660.07210.0627

• Table 12: The10 most dominating invertebrates in the depthstratum 2-4 meter i Yen" Bugt. spring 1994.

Numbers ind/m2 Biomass 9 afdw/m2

Abra alba 910 Neanthes virens 2.7647Sco/oplos armiger 770 Scoloplos armiger 2.7964

. Myseffa bidentata 605 .Terebeffidae 2.3672Oligochaeta 388 Hinia reticulata 0.7028Spionidae 254 Abra alba 0.4533Phyl/odocidae 88 Nephtys hombergii . 0.3271Nemertinea 81 Macoma ba/thica 0.2504Corophium sp. 81 Asterias rubens 0.2293Macoma ba/thica 54 Spionidae 0.2054Pholoe sp. 47 Uttorina littorea 0.2007

• Table 13: The 10 most dominating invertebrates in the depthstratum >4 meter in Ven" Bugt. spring1994.

Numbers ind/m2 Biomass 9 afdw/m2

Abra alba 1600 Cerastoderma edul 10.6747Mysel/a bidentata 185 Nereidae 1.6169Nephtys hombergii 105 Abra alba 0.7481Cerastoderma edul 90 Philine aperta 0.4460Oligochaeta 76 Nephtys sp. 0.3185Spionidae 63 Ophiura sp. 0.1525Capitel/idae 28 Myseffa bidentata 0.0886Scoloplos armiger 18 Ensis sp. 0.0484Pho/oe sp. 15 Harmothoe sp. 0.0490Chaetozone setos 13 Lepidonotus squam 0.0337

Table 14: rhe composition cf in fauna per depth stratum in Ven" Bugt, autumn 1994. A = abundans (ind/m'), B =biomasse (g afdw/m'). Data do not includebivalves >2,5 cm.

DEPTH STRATA 0-2 meter 2-4 meter >4 meter

A S.E. B S.E. A S.E. B S.E. A S.E. B S.E

INFAUNA 2077 153.6 11.0660 3.3798 4022 652.1 28.4882 17.0726 727 139.8 4.6381 1.0054

ANNELIDA (LEDORME) 2019 152.2 7.0945 1.8745 2287 404.6 5.2978 1.1286 205 31.4 2.7217 0.9316Polychaeta (Havb"rsteorme) 1971 155.8 7.0913 1.8738 994 120 5.0978 1.0786 187 29.4 2.7185 0.933Oligochaeta (Saddelb"rsteorme) 49 14.1 0.0031 0.0017 1294 321.0 0.2000 0.1035 18 8.4 0.0032 0.0029

MOLLUSCA (BL0DDYR) 51 12.3 2.1868 1.3956 1111 248.3 19.7005 17.3427 513 117.5 1.8088 0.9306Bivalvia (Muslinger) 25 6.7 0.7772 0.3765 1052 251.3 19.2671 17.4609 512 117.7 1.7993 0.9350Gastropoda (Snegle) 25 11.3 1.4096 1.4088 56 14.3 0.4317 0.2301 2 1.8 0.0095 0.0095Polyplacophora (Chiton) 2 2.3 0.0018 0.0018

ARTHROPODA (LEDDYR) 4 3.0 1.7568 1.7568 562 254.8 2.0659 2.0557Crustacea (Krebsdyr) 4 3.0 1.7568 1.7568 562 254.8 2.0659 2.0557

ECHINODERMATA (PIGHUDER) 20 10.4 1.1843 1.1843 2 1.8 0.0916 0.0916Asteroidea (S"stjerne) 20 10.4 1.1843 1.1843 2 1.8 0.0916 0.0916

NEMATODA (RUNDORME) 2 2.1 7 5 0.0008 0.0008 7 4.3

NEMERTINEA (BANDORME) 34 14.5 0.0045 0.0045

UBESTEMTFRAGMENT 0.0280 0.0177 0.2065 0.1339 0.0161 0.0161

Table 15: The 10 most dominating invertebrates in the depth stratum 0-2meter in Venl1l Buat. autumn 1994.

Numbers ind/m2 Biomass 9 afdw/m2

Spionidae 689 Arenicola marina 3.7695Scoloplos armiger 581 Carcinus maenas 1.7568Heteromastus filiformis 250 Uttorina littorea 1.4090Nereidae 138 Nereidae 1.3099Chaetozone setosa 74 Cap/1ellidae 0.9347Oligochaeta 49 Scoloplos armiger 0.8012Capitella capitata 45 Macoma balthica 0.3452Eteone longa 38 Ensis sp. '0.2283Uttorina littorea 21 Spionidae 0.1995Arenicola marina 17 Cerastoderma edule 0.1465

•Table 16: The 10 most dominating invertebrates in the depth strata 2-4meterin Venl1l Bugt, autumn 1994.

Numbers ind/m2 Biomass 9 afdw/m2

Oligochaeta 1294 Cerastoderma edule 13.9443Cerastoderma edula 483 Mytilus edulis 3.2230Sco/oplos armiger 465 Terebellidae 2.8296Aoridae sp. 411 Carcinus maenas 2.0100Mysella bidentata 312 Ensis sp. 1.2753Mytilus edulis 111 Scoloplos armiger 1.1905Nereidae sp. 93 Asterias rubens 1.1843Corophium sp. 90 Nereidae 0.5012Ensis sp. 77 Te/lina tenuis 0.2198Platynereis dumerillli 52 Venus striatula 0.1980

• Table 17: The10 most dominating invertebrates in the depth strata >4meter in Venl1l Bugt, autumn 1994.

Numbers ind/m2 Biomass 9 afdw/m2

Mysella bidentata 257 Myt/7us edulis 1.2204Abra alba 176 Nereidae 0.9596Nephtys homberg/i 111 Terebellidae 0.8794Mytilus edulis 47 Nephtys hombergii 0.7811Capitel/idae 27 Abra alba 0.2952Nereidae 22 Cultellus pellucidus 0.1204Oligochaeta 18 Ophiura sp. 0.0916Corbula gibba 16 Ensis sp. 0.0721Cultellus pellucidus 13 Polynoidae 0.0921Polydora sp. 9 Mysella bidentata 0.0475

is dominated of Neanthes virens, Scoloplos anniger and Terebellidae.

The highest biomass for Ven" Bugt is in the depth stratum >4 meter. The mean biomassis 14.8729 g afdw/m2 and the mean abundance 2262 ind/m2

• Abra alba is the dominatingspecies with respect to number, wheras Cerasrodenna edule contributes to most of thebiomass (table 13).

Veno Bugt, autumn: Table 14 shows the mean abundance and mean biomass per depthstrata in autumn 1994 in Ven" Bugt. The abundance in the depth stratum 0-2 meter and 2­4 meter is almost the same as in the spring sampies, while there is an increase in thebiomass of both strata (table 10 and 14). The dominating species according to number atdepth stratum 0-2 meter is mostly polychaeta: Spionidae, Scoloplos anniger, Heteromastusfilifonnis and Nereidae (table 15). The dominating species according to biomass isArenicola marina, Carcinus maenas, Littorina littorea and Nereidae. In the depth stratum2-4 meter the dominating species are Oligochaeta, Cerastodenna edule, Scoloplosanniger, Aoridae sp., Mysel/a bidentata and Mytilus edulis (table 16), and for biomass thedominating species are Cerasrodenna edule, Mytilus edulis, Terebellidae, Carcinus •maenas, Ensis sp, Scoloplos anniger and Asterias rubens.

Both the abundance and the biomass of macrobenthos have decreased in Ven" Bugt in thedepth stratum >4 meter from spring to autumn. The mean abundance for the stratum is727 ind/m2, dominated by Mysel/a bidentata, Abra alba and Nephrys hombergii. The meanbiomass is 4.6381 g afdw/m2 dominated by Myti/us edulis, Nereidae, Terebellidae andNephrys hombergii (table 14 and 17).

1000

100000 N

C 800

- 80000lJ)...QJ

'3.c 600E ~::J.s CIS

60000 C)QJ ~ •u -ro 400

cCi 0- ä0 Ec 40000 ::J0 lJ)

~ c"3 200 8Co0Co 20000QJ=:

0

0

-6 0 6 12 °18 24 30 36 42 48 54 60

age of fish (months)

Figur 8: A model ofconswnption for an 0-4 year old population ofplaice. 11le initial 0­group counts ]00 ()()() individuals with a mean length 0/4.5 cm and a mean weigth 0/0.3443 g afdw.

Table 18: Production of macrobenlhos in Ven" Bugt. P ann: Annual production (g afdw/m1/year) eslimated from P:Bralios. P 1994: The remaining amount of living matter after the macrobenthos's growth season in 1994.

DEPTH STRATA 0-2 meter 2-4 meter >4 meter

Pann P1994 Pann P1994 Pann P1994

INFAUNA 9.8429 7.2188 21.9027 24.2477 25.0845 -14.3287

ANNELIDA (LEDORME) 5.9589 5.7919 17.8740 -5.3036 3.7506 0.9057Polychaeta (Havb0rsteorme) 5.8272 5.8753 17.7486 -5.5000 3.7315 0.9139Oligochaeta (Saddelb0rsteorme) 0.1317 -0.0835 0.1254 0.1964 0.0191 -0.0083

MOLLUSCA (BLl2lDDYR) 3.3127 -0.7621 3.1883 25.1125 21.2191 -15.1381Bivalvia (Muslinger) 1.9506 -0.9216 1.4879 25.7933 20.1544 -14.4799Gastropoda (Snegle) 1.3621 0.1595 1.7005 -0.6806 1.0647 -0.6582

ARTHROPODA (LEDDYR) 0.2319 2.3629 0.1017 2.8499 0.0014 -0.0006Crustacea (Krebsdyr) 0.2319 2.3629 0.1017 2.8499 0.0014 -0.0006

NEMATODA (RUNOORME) 0.0106 -0.0067 0.0060 -0.0026

NEMERTINEA (BANOORME) 0.0050 -0.0032 0.0361 -0.0164

ECHINODERMATA (PIGHUDE) 0.6052 1.3371 0.0610 -0.0852Asteroidae (S0stjerne) 0.6052 1.3371Ophiuroidea (Slangestjerner) 0.0610 -0.0852

UNIDENTIFIED FRAGMENTS 0.3637 -0.164 0.0913 0.2318 0.05245 -0.0104

Producrion: Estimates of annual production of infauna in Vena Bugt is shown in table 18.The remaining amount of biomass of polychaeta in the depth stratum 0-2 m is like theannual production estimate, while there is no bivalvia biomass. The annual production inthe depth strata 2-4 meter and > 4 meter is high. In stratum 2-4 meter the biomass ofbivalvia is high, while there is no accumulation of polychaeta biomass. In the depthstrata> 4 meter there is no accumulation of organie material in 1994, even though the annualproduction estimate is high.

Consumption model: Figur 8 shows the population decline and the theoretica1 consumptionfor a population of plaice (Pleuronectes platessa). The initial O-group counts 100.000individuals at the start of their demersal stage, since this is a probable stocking size. Thenatural mortality excerted on the population results in a population of 4000 4-year oldfish. This population consumes approx. 800 kg. afdw in their lifetime from 0-4 year oldfish.

DISCUSSION

Since there are no statistical difference in the biomass of macrobenthos between springand autumn sampIes 1994, either the oxygen-depletion in Skive Fjord did not have aneffect on macrobenthos, or the area in spring were still effected from earlier oxygendepletions. The last thing is the most probable, since the biomass and species richness waslow in spring also in the depth stratum >4 meter.

Skive Fjord and Vena Bugt is not two very distinct areas, despite their differences in timeof exposure to oxygen-depletion. Both areas have a low diversity of species and anincreasing dominance of individual species in the depth stratum > 4 meter compared to theinshore areas (table 19). The diversity-index and species evenness is calculated from thespring sampIes. Usually there are very large seasonal fluctuations in the number of speciesand species density of macrobenthos, and early spring is the time of the year, where thespecies to find, is species which have a relatively permanent population at the site (Jensenet al.,1990).

Table 19: The Shannon-Wiener diversity·index (H)and evenness (J) for the three deplh·strata in SkiveFjord and Ven" Bugt.

•

SKIVE FJORD VEN0 BUGT

H' J' H' J'

0-2 meter 3.4759 0.6576 3.1114 0.5770

2 - 4 meter 3.3534 0.6301 3.6350 0.6014

>4 meter 1.4766 0.3009 1.9184 0.3605

The species composition in the two areas > 4 meter suggest Skive Fjord to be moreeffected by eutroficatiori, with the dominatirig sPecies typical of areas with largedisturbänces e.g. Polydora sp., .Oligochaeia, Heteromastus filiformis (Limfjordskomiteen,1989), while the species found in Yenri Bugt is partly representative of an Abra alba­community (Abra alba, Nephtys hombergil), partly representative of a Macoma- .community (Cerastoderma edule, Scoloplos armiger). Capitella sp. and Polydora ligni aresmall spedes, they spawn several times a year, they have a short lifecycle, and are seimeof ihe first species to recolonize an area which have suffered from oxygen depletion(Arniz & Rumohr, 1986). In Skive Fjord >4 meter these are the dominating species inthe aurumn sampies together with other small p'olychates, and confir!TIs the area asseriously effected. The small polychaetes are described by Arntz & Rumohr (1986) asirruptive species, iaking over when other species decline, but breaking down very rapidlywhen normal conditions reestablis. Even though the biomass and density of species wasreduced in Yen" Bugt > 4 meter from spring to autumn, the fauna is dominated by theSame species as were represented in the spring sampies.

Since there were no accumulation of bioIriass in Yeno Bugt at the depth >4 meterimmediately after the macrobenthos's growthseason, either a heavy mortality has occuredor the production was not as high aS. expected. The moriaIity can be due to eitherpredation or environrriental effects. With no biomass accumulated it does. not seempossible to reach a biamass of 14 g/m2 the following spring.

Amomeritary picture of the bottom fauna have the value to show the magnitude andcomPosition of the fauna, which is part of an essential food supply for fish. In a11 theinshore areas the food supply is variable and covers the speclfe of food for flatfish. Thereis ci great variety in the food preference for plaice and flounder. Polychaetes arid molluscsare the most important phyla (Braber & Groot, 1973)(De Vlas, 1979). An accumulätion ofbiomass has occured in the inshore areas. It is important to have an accumulatlon ofbiomass after the macroberithos's growth season to make sure there is a food stipply forfish untill the growth of benthos starts in the following spring.

AccoreÜng to the consumptlon model a population of 100 000 plaice consumes app. 800kg afdw in their lifetime from 0-4 year old fish (Figur 8).

D6es their food requirements apply to the prey preiductions? The results of the estimatedanriual production suggests the macroberithos's capacity to be food for predatory fish.

The annua! production of macrobenthos for the inshore areas in Skive Fjord waS estiIriatedto 147 634 kg afdw for the wholearea of 0-2 meter, depth and 133 384 kg afdw for thewhole area of 2-4 meters depth. The annual production of macrobenthos for the inshoreareas in Yeno Bugt was estimated to 120 477 kg afdw for the 0-2 meters depth area arid251 333 kg afdw for the 2-4 meters depth area.

This means that the population of plaice only consumes app. 0,3 % of the production ofmacrobenthos in Skive Fjord and app. 0,2 % of the production in Yen" Bugt, even thoughthere is no production in the depth stratum >4 meter. Even though we da not have cimeasure of the predation pressure from fish and crustaceans livirig in the two aIeaS, it

. seems possible that the inshore areas in Skive Fjord and Ven" Bugt have the capacity toprovide feod for the modelIed population of plaice. New questions anses though: How bigapropOrtion of the benthos production is actuaIly available for the fish fauna? How big is

the existing fish fauna and how much do they consume? Is there a certain time of theyear, where the fishfauna is foodlimited? Are other factors regulating the number of fish,which can live in the area? Pihl (1989) found demersal fish to migrate inshore whenstressed from oxygen depletion( <3 mgl"l). The success of this migration depends on thespecies tolerance for high temperatures and fluctuations in dissolved oxygen.

•

REFERENCES:

Arntz, \V.E. & H. Rumohr (1986). Fluctuations of benthic macrofauna during successionand in an established community. Meeres/orschung, 31: 97-114.

Beverton, R.I.H. & T.C. Iles (1992). MoIta1ity rates of O-group plaice (pleuronectesplatessa L.), Dab (Limanda limanda L~) and torbot (Scophthalmus maximus L.) ineuropean waters. Netherlamis Journal 0/Sea Research, 29 (1-3): 49-59. .

Braber, L. & I. De Groot (1973). The food of five flatfish species (pleuronectiformes) inthe southern nortli sea~ Netherlamis Journal 0/Sea Research, 6 (1-2): 163:172.

Costopoulos, C.G. & M. Fonds (1989). Proximate body composition and energy contentof plaic~ (pleuronectes platessa) in relation to the condition factor. Netherlamis Journal 0/Sea Research, 24: 45-55.

De Vlas, I. (1979). Annual food intake by plaice and flounder in a tidal flat area in thedutch wadden sea, with special reference to consumption of regenerating parts ofmacrobenthic prey. Netherlamis Journal 0/Sea Research, 13 (1): 117-153.

Eliassen, I~E. (1982). Forelesningskompendium i fiskeribiologi Deli: Innledning,bestandens parametre. Institutt for Fiskerifag, Universitetet i Tromsa. Serie B:Ressursbiologi 3.

Flintegärd, H.,. 1.0. Frier & E. Hoffmann (1982). Fiskeribiologiske undersagelser iLimfjorden 1980-81. Danmarks Fiskeri- og Havundersagelser, intern rapport nr. 169.

Fonds, M, R. Cronie, A.D. Vethaak & P. Van Der Puyl (1992). Metabolism, foodconsumption and growth of plaice (pleuronectes platessa) and flounder (platichthys flesus)in relation to fish size and temperature. Netherlamis Journal 0/Sea Research, 29 (1-3):127-143.

Gray, I.S. (1981). The Ecology of Marine Sediments. Cambridge University Press,Cambridge. 185 pp.

. Holme, N.A. & A.D.McIntyre (1984). Methods for the Study of Marine Benthos.Blackwell Scientific Publications, IBP Hand Book 16.

Iensen, K., I.N.Iensen & L.Moseholm (1990). Retningslinier for bundfauna.Miljastyrelsens Havforureningslaboratorium.

Ienseri, I.N., A.B.Iosefson & G. Dinesen (1994). Effekter af springlagsopblomstring päberithos. Havforskning fra MiIjastyrelsen, 34. 30 pp.

Limfjordskomiteeri (1989). Bearbejdning af bundfaunadata 1983-87. LFK-rapport nr. 40.

Limfjordsovervägningen (1993). Samlerapport 1992, Linifjorden - Vandmilj0 1992.Rapport nr. 3.

LimfjordsoverVägningen (1995). Vandmilja i Limfjorden 1994. Vandmilja Overvägning.

Limfjordsovervägningen (upubl.) SedimentundersfJgelser i Limfjorden 1988-199l.Udarbejdet af BioConsult for Limfjordeovervägningen. Ikke publiceret notet.

Pihl, L. (1989). Effects of oxygen depletion on demersal fish in coastal areas of the south­east Kattegat. Fra: Ryland, I.S. & P.A. Tyler: Reproduction, Genetics and Distributionsof Marine Organisms. 23rd European Marine Biology Symposium, University of Wales,Swansea.

Robertson, A.I. (1979). The relationship Between Annual Production: Biomass Ratios andLifespan for Marine Macrobenthos. Oecologia (Berl.), 38: 193-202.

•