Benthic Habitat Quality Assessment of an Oxygen Stressed

8/13/2019 Benthic Habitat Quality Assessment of an Oxygen Stressed

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arine Systems 11 ( 1991) 249-264

Cii tebnrg h iversity Kr istineberg Marine Research Station S-450 34 F iskebiickskil SwedenReceived 1February 1996; accepted 10 July 1996

ay and O~tol~ 1994 the benthic habitats in Havstensfjord (26 km), a seasonally oxygen stressed stratified fjord,were classifiedby taking sediment surface and sediment profile images (WI) at 90 stations, randomized into nine strata.Qualitative grab samples for fauna1 inspection were taken at about l/3 of the stations in both May and October to help toidentify objects in the images. The images give information on sedime nt characteristics (texture, oxic/anoxic conditions,l~~nin atiol~~ hich often can be related to functional properties of the macrofauna (bu rrows, tubes, feeding voids, reworkedsediment) or to observations on benthic epifauna. In combination, such variables mirror the quality of the benthic habitat.Analysis of sediment profile images was done with multivariate methods [Benthic Habitat Quality (BHQ) index] ar&dunivariate statistical methods to describe differences between areas and depths. Variance analysis of BHQ indices indicated asignificant interaction between area and depth. In both the northeast and northwest strata the oxygen stress had i~~duc~dhabitat degradation at depths deeper than 25 m compared to shallower northwest and northeast strata and all south depthstrata. No significant difference in mean BHQ index was found between M ay and October.application af the SPK echnique for efficient monitoring oxygen stressed marine coastal areas. 0rights reserved.Keyworrls:hypoxia; anoxia; macrofauna;&ggiuroa; burrow;bioturbation; ed ox potential; successional slope; Skager rak

1. IntroductionIn the beginning of this century, Petersen 19 15

showed that marine benthic species occurred repeat-edly in different animal associations and that organi-zation of such associations was dependant on thesedimentary habitat. It was later demonstrated thatbenthic infaunal community organization changed

* Correspondingauthor. Fax: + 46-523- 18502. E-mail: [email protected].

gradually and in predictableways along gradientsoforganic enrichment Pearson and Rosenberg, 19781,physical disturbance Rhoads and Germano, 1982)and pollution Swartz et al., 1986). As benthicmacrofauna can have life spans of several years,infaunal community structure has been one of themost frequently used tools for assessing environmen-tal quality. Detailed examination of the benthic fau-nal structurehas many advantages in habitat qualityassessment, but also some drawbacks Diaz, 1992).Such detailed analysis is labour-intensiveand costly.

0924-7963/97/$1 7.00 Copyright 8 1997 Elsevier Science B.V. All rig hts reserve d.PII SO924-7963(96)00111 -X


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tubes) and activity (e.g.~nfo~ation in the

in combination with the associated sediment, also tohabitat quality.

Lately, a variety of seplications have been demonstrated including theiruse at dumping sites (Nichols et al., 1990), environ-mental assessment of coastal cage-net aquac~lt~re(OConnor et al., 1989), sedimentological assess-ment of hydrocarbon contaminated sediments (Diazet al., 1993) monitoring of sedimentation (Rumohret al., 1992) and benthic habitat quality assessments(Grizzle and Penniman, 1991; Schaffner et al., 1992;Valente et al., 1992; Rosenberg and Diaz, 1993).This technique has some advantages compared totraditionally used methods (i.e. benthic fauna1 com-munity structure) for assessing abiotic and bioticprocesses (Rumohr and Schomann, 1992). Today,with modern computer aided image analysis, it ispossible to amplify and to speed up the interpretationof images.

This study was made in Havstensfjord (area: 26km*), which is part of a stratified estuarine fjordsystem comprising 231 km* with two connections tothe open sea (Fig. 1). The surface water temperatureis around 18C in summer and 0C in winter, and thetemperature in the bottom water below the haloclineat about 15 m is between 8C and 4C. Mean salinityin the surface water is 22 psu and in the bottomwater 32 psu. Calculated bottom water turnover timein Havstensfjord is about one year and the dailysurface water exchange is 1 to 4% (Bjiirk, 1983). In

m depth during 1992, 19 93 and 1 994 (Anon., 1992,1993 and 1994).

the northern part of a seasonal varia-

sessed by a multivariate image analysis (index ofBenthic Habitat Quality - BHQ), which is related tothe classical distribution of benthic infaunal cornmumnities in relation to organic enrichment (Rosenberg, 1978).

2. Materia and meIn order to assess spatial differences in Havstens-

fjord, surface and sediment profile images were col-lected at 90 stations in the spring, 18-20 May, 1994(Fig. 1). To assess temporal changes, the same sta-

Fig. 1. Map of Havstensfjordwith lo cation of stations, Areal stratificationborder ines (northwest:NW northeast:NE.South: ) anddepthstratashow the nine strata.


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tions were revisited in the autumn, N-13 October,1994. The fjord was stratified by region (northwest,northeast and south) and depth ( < 15, 15-25 and> 25 m) for a total of nine strata. In each stratum thecameras were randomly deployed ten times. Thesurface images obtained in May were of bad qualityat several stations, and as a consequence the surfaceimages from October were used to describe theepifaunal spatial distribution. The sediment profilecamera technique is described by Rhoads and Ger-mano (1982, 1986) and the equipment used in thisstudy is depicted and described in detail by Rosen-berg and Diaz (1993). At each. station one surfaceimage (area 0.06 m) was taken just before the frame

hit the sediment surface, and three sequential scdi-ment profile images with a width of 22 cm and apenetration depth between 6 and 14 cm were taken at3-second intervals after the frame was on the bottom(Fig. 3). Agfa Chrome CT 100 was used in bothcameras and all images from the sediment profilecamera were later transferred to Kodak Photo-CD.Analysis of the images was made with Adobe photo-shop 2.5 and NIH image 1.52 for Macintosh comput-ers.

The apparent depth of the Redox Potential Dis-continuity (RPD) in the images was enhanced ditally, which made it easier to accurately distinguishthe boundary layer between the upper brownish

l i irters

nameintot), Sedimentsurface S.S.) and RPD are indicated. _


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obtained index value is assigned to one of the serialstages in a successional model as given in Fig. 4.

Swedish fjord, images from that fjord gradient wereused as a reference. Analysis of spatial differences of

indices between strata was done-way ANOVA, with area and dep

as fixed factors. Analysis of poral differences inmean BHQ indices between ay and October wasdone with a balanced I-way ANOVA. Homogeneityof variance was examined using Cochrans C test(Underwood, 1981).

Qualitative macrofaunal samples of dominantspecies were taken with a modified Ponar grab (0.04m*) at 26 stations in spring and 18 in autumn with atleast 2 samples in each strata. Samples were immedi-

o the apparent redoxvalues vary between 0

A: Surface structures Faecal pellets 1Tubes 5 2 JIMI n diameter a 1or Tubes > 2 mm in diameter b 2Feeding pit or mound 21p:Subsurface structures Infauna 1

121

or Oxic void at > 5 cm depth 2C: Mean depth of Ocm 0

ii.:--i.Ocm 11.1-2.0cm ;2.1-3.5 cm 33.6-5.c cm 45 CiTi 3

(e.g. Capitella p., E& one sp., Polydora sp.).b (e.g. Meli ma sp. Terebellidae sp., Ampharetidae sp., Rhodinesp.).

ately sieved through a 1 mm sieve for taxonomicidentification.

Oxygen concentration was monitored at I

Fig. 4. The distribution o f benthic infaunal w cessinnal stages along a gradient of increased environmental disturbance from left to right(after Pearson and Rosenberg, 1978) and the associated Benthic Habitat Quality (BHQ) index (described in Table 1). The successianalstages are similar but not identical to those described by (Rho ads and Germanno, 1986).


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254 KC. Nilsson, R. Rosenberg/Journal of M ari ne Systems 11 I 997) 249-264Table 2Data from sediment profile images in nine strata in Havstensfjord [south (S), northeast (NE), northwest (NW ) * < I5 m, 15-25 m, > 25m). All data are means from M ay 1994. Number of images analysed, penetration depth (cm), sediment depth of apparent R PD icm). numberoftubes(* =few, * * = many), num ber of biogenic structures (* = l/image, * * = > l/image), number of burrow s/image, number ofoxic voids/image, Benthic Habitat Quality (BH Q) index, dominant sediment characteristics aud infaunal successional s tages. Dominantinfaunal species obtained in grab samples: (1) Amphiutcl if i l i fomis, 2) Terebel l id es st roemi, (3) Corbul a gi bbcz, 4) M uld une sarsi, (5)Nepthys sp., 6) Anobothrus gracil is, (7) Thyasira equali s, (8) Euchone papil losa, (9) Polydoru cil iat aStrata Image Penetration RPD Tubes Biogen. Burrows Voids BHQ Stage Sediment InfaunaS25mNE 25mNW 25m

886

108

108

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3.9 * **3.6 * **2.3 * none1.9 ** **0.6 * * *1.4 ** *1.2 ** *0.2 + * *

8.08.57.37.81.15.34.30.2

1.4 9.5 II Silt-clay 1.2,3,4, 81.7 8.8 II Silt-clay I, 3.681.6 7.2 II Silt-clay 2, 3.51.0 6.8 II Silt-clay 3,4,7* 8.90 2.5 I Black mud 1,3,6,80.6 6.0 II Silt-clay 30.4 5.5 II Clay 7, 8.90.1 1.2 I Black mud 7

tions in spring and 8 stations in autumn with a by the high penetration depth and smelled of hydro-Winkler-calibrated YSI oxygen-meter about 20-30 gen sulphide (Table 2). Methane bubbles were notcm above the bottom (model 58 and SOB). observed in any images.

3. Remlltssampling in the south strata, oxygen con-

s in the bottom water were > 7.5 mg 0,I- I in both May and October 1994. In the northerntwo strata, bottom en concentrations declinedsharply at depths de han 30 m to 2.9-2.5 mg 6,and to 13O-Q.& g 8, I * I in Oc

Lt at stations above the haloclinen the two northern strata and at all depthsin the south strata was characterized as silt-claysediment at many stations, but also traces of sandwere found occasionally. In the northwest deep stra-tum the bottom sediment was very soft, as indicated

Analysis of sediment profile images and fauna1samples are summarized for each stratum in Table 2.A total number of 78 sediment profile images fromMay and 28 from October were sufficiently clear tobe used in a detailed analysis. Sediment profileimages described below originate from the May sur-vey.

pits or impoundswere observed at 35% ofthe stations ire the south area (Fig. 5a). 4% in thenortheast area, and 7% in the northwest area. Faecalpellets were present in most images except at sta-tions refered to as successional stage Q (see below).Polychaete tubes at the sediment surface were pre-sent in 46% of all the images with a maximum of 35tubes in one image at station 81. Characteristic tubesprotruding several centimetres above sediment sur-

Fig, 5. Sedimentprofile images (computer enhanced) from six stations with an oxidized top sediment and a black sulphidic layer below.Vertical scale is in centimeters. T he white above the sediment wate r interface is an artifact (flash reflection), (a) Station 17 at 1 6.5 m depthin May 1994. Mean apparent RPD is 3.9 cm; thicker in the mound to the left and thinner to the right. 3 tubes, 2 oxic voids and 3 burrowsare seen. (b) Station 43 at 18.5 m depth in May 1994. Mean apparent RPD is 2.5 cm. The tubes protruding several centimeters into the waterbelong to the polychaete E;irckonepapiflosa 2 oxic voids and about 10 burrows vertical ight brown stripes) arc noted. (c) Station 34 at 12m dep th in May 1994. Obvious is the horizontal layer of about 5 oxic voids. Mean apparent RP D is 2.3 cm. (d) Station 13 at 23 m depth in

Mean apparent RPD is 4.0 cm. Two oxic voids are seen in the center and one red worm to the left at 3 to 4 cm depth in thesediment. ndicationof about IO vertical burrows in the sediment and some polychaete tubes are seen at the surface. (e) Station 55 at 3 0 m

Mean apparent RPD is at 0.8 cm with no biogenic structures below this, which is indicative of an oxygen-stressed benthichabitat, Small polychaete tubes are seen at the sediment surfaceand oneanoxic void in the sediment. (f) The same station as in Fig. 5e butin Octob er 1 994. Mean ap parent R PD is 0.7 cm. Som e larger polych aete tubes are at the sediment surface, but still no obvious activitybelow the RPD.


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Fig 6 (a) Distribution of mean depths of apparent Redox Potential Discontinuity (R PD) in Havstensfjord in May 19 94. (b) Distribution ofbenkc infaunal successional stages, which are based on the Benthic Habitat Quality (BHQ ) index (Fig. 41, in Havstensfjord in May 19 94.


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258 ?f.C. Nilsson, R. Rosenberg/Journal of Murine Systems 11 f1997) 249-264face of the sabellid polychaete Euchone papihaidentified from grab samples) were observed at 8stations between 13 and 20 m depth (Fig. 5t.G. Sev-eral burrows an= identified from the vertical bands ofoxic sediment that surround the burrow wall in thisimage.

At all stations in south Havstensfjord at least onesubsurface structure (burrow, void or infauna) waspresent in each image, and in 78% of the images twoor more different structures were present. In theSouth strata a higher number of burrows was recordeddeeper than 15 m compared to above 15 m, whichw&s lk contrast to a higher number in shallow watersin the two northern strata. In the northeast depthstrata, high densities of oxic voids were detected inthe shallow stratum at stations 32-37, as illustratedfor station 34 (Fig. SC). Aerobic voids indicate sub-surface irrigation and probably feeding activity.For the 15-25 m south stratum a representativeimage (Fig. 5d) sho ws an upper reworked sedimentsurface area of 3-4 cm coinciding with the apparentRPD depth, two oxic feeding voids, one red worm(at 3 -4 cm), indication of about ten vertical burro ws,polychaete tubes at the surface, and black reducedsediment at the bottom, At many stations in thedeepe st stratum in the two northern strata it seem sthat fresh material has sedimen ted an top of an

r (Fig S e), Six layers can be identified in; (1) an upper brown layer with fmxalan oxid yellow sediment layer, (3) athin black hypoxic r, (4) a white band of possi-bly Beggiutoa spp., (5) a mixture of oxic and hy-poxic sedimen t and (6) below a sulphidic blackanoxic sediment, These thin up per two layers ap-pears reworked with an apparent RPD depth of 0.8cm. Som e small polychaete tubes (S 2 mm in diame-ter) are seen at the surface. An image from the samestation in O ctober show s approximately he same topsediment activity and RPD, but also five largerpolychaete tubes (> 2 mm in diameter) and somesmall ones (Fig. 5f). No oxic voids were observed at$tations below 25 m depth in any of the two northernstrata. Laminatedstructureswere seen as vague hori-zontal structures at some stations from the verysoft-bottoms (Stations 82, 85 and 89) in the deepnorthw est stratum.At station 78 two sha low laminaeand five deep er laminae were found.The spatial distribution of the m ean of apparent

RPD depth in Havstensfjord was predominantly be-tween 1.1 and 3.5 cm (Fig. 6a). Depths of theapparent RPD varied, however, between 0.0 ancm. A mean maximum of 3.9 cm was recordedsouth stratum at 15-25 m depth, and a mean mini-mum of 0.2 cm in the northwest stratum at > 25 mdepth (Table 2). Thin RPDs were recorded at mostdeep (> 25 m) stations in the two north&n strata,and also at some medium deep (15-25 m) stations inthe northeast and northwest Havstensfjord. At station17 a highly convoluted apparent RPD was found(mean 4.0, min. 1.1, max. 9.0 cm; Fi

The BHQ index in Havstensfjordand 12 with a mean of 7.0 in May and 6.1 inOctober. Mean BHQ indices for all depth intervals inthe south strata and at < 15 m depth in the north-west were > 7.0, whereas it was < 7,0 in otherareas, Infaunal successional stage (Fig. 4) in Maywas mostly stage 2 (Fig. 6b). All stations in the threesouth depth strata were classified as successionalstage 2, except station 15 and 29 which were classi-fied as stage 3. In the northeast and northwest strata,16 and 36 stations were assigned to successionalstage 1 and 2, and 8 stations were assigned to stage0. Successional stage 0, with no fauna in the images,was restricted to depths > 25 m.

Mean BHQ May for the nine strata showa significant ( p < 0.001, degree of free-dom (df) = 4 ,451 interiction between area and depth(Fig. 7). N o significant (SN M , p > 0.05) differencesin mean BH Q indices was obs&v ed between eithersouth, northeast or northw est strata at depths < 15m. Mean BHQ indices were significantly (SNK,p < 0.05) higher in the south strata com pared o bo th

12

0South Northeast Northwest

AREAL STRATAFig. 7. Means of the Benthic Habitat Quality (BHQ) index* SD(n = 6) in the nme strata in Havstensfjord in May 1994.


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Fig. 8. Distributionof epibenthic organismsas observed in the surfacecamera mages (0.06 m*) in Havstensfjord n October 1994.


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northern strata at depths between 15 and 25 m. Atdepths > 25 m in both the northeast and northweststrata, mean BHQ indices w ere significantly (SNK ,d to at all other strata. No> 0.05, df = 1, 46) differ-ences were found in mean BHQ indices betweenMay and O ctober.From the surface images, presence or density ofophiuroids, polychaete tubes. the anthozoan Virgu-k-aria i mbi l i s, ulphur bacterial mats and animaltracks found irr October 1994 are depicted in Fig. 8.Epifaunal ophiuroids were observedat 59% of all thestations with a dominance of Qphiuru l bidu.Ophi-uroids and V. mi rabil is w ere concentrated to thesouth of Havstensfjord.Sulphu r bacterial mats, pre-sumably Btzggiutou pp., covered the surface sedi-ment at four areas in the northwest depth strata.Polychaete tubes w ere visible at several stations inthe two no rthern strata, Animal tracks were observedin all im ages except at stations classified as succes-sional stage 0,A qualitative inspection of the grab sam ples fromstations > 15 m deep in the south stratum showedthat Amghiura f i r i fomis and Ophiura spp. werecommon.A, ir i formiswas not recorde d in the twonorthern strata, but instead conspicuousspecies wereJXJguali,v nd Corbula i bba and

tes Euchonrrpapi l lma nd Polymens of one of the two bivalvesmacrofauna at some

4. DismsslonMarine ben thic infaunal com munities are orga-nized both structurally and functionally along gradi-ents of richent oxygen deficiency andothet di as described n the Pearson-Ro-

senberg mod el (Pearsonand R osenberg,1978xFig.4), This mod el has nxeived a wide-spread accep-tance and applies o man y coastalareas all over the(Heip, 1995b,and is used in this study as a

for benthic habitat quality assessment. Theactivity of deepersturbedend of thessional stages 0 or 1) towards theundisturbedsuccessional tage 3). Along this gradi-ent activities, u ch as reworking,rrigation, burrow -

ing and sub-surface feeding, will have an increas-ingly significant impact on the biogeochemistry ofthe sedimentary habitat. This is visually obviouc insediment profile images, which are non-destructivead the oxii: and anoxic sediments are distinguish-able at some distance from the sediment surface andalso associated with burrows, voids and tubes. Theboundary line, the RPD, has been shown to beassociated with the fauna1 distribution in the Pear-son-Rosenberg model (Pearson and Stanley, 1979).Thus, parameterization of sediment and animal fea-tures may be a useful ation to describeassess habitat quality ( and Germano, 19Modem computer programmes used in this study toenhance contrasts in the images have been of greatvalue for the interpretation, in particular of the depthof the RPD and in the identification of biogenicstructures.

In this study we have used the BH Q index, whichdiffers from the Organism-Sediment Index proposedby (Rhoad s and Germano, 1986 ) and also used byOConnor et al. ( 1989).Rhoads and German0 1986)based their index on mean depth of the apparentRP D, the pre sence of g as vo ids, and on a visualclassification of the infauna into successional stages.We have used surface and subsurface structures inmean depth of the apparent RPDQ index (Table I), which then isthe different infaunal successionalin Fig* 4, The param eters in thepresent study w ere all measured from the im ages andthe scoring could be seen as an objective assessmentof the successional stages. Deep subsurfa ce activity,such as feeding voids and many bunrows, whichoften is associated with a thick RPD , have a highscoring and contribute to a high BHQ index. Wesuggest that the scoring used in this study may bevalid for many boreal and temperate areas, as in

these areas the benthic infauna is similarly structuredand has a similar distribution and activity within thesediment (Thorson, 1957; Pearson and Rosenberg,1978; Rhoads and Germano, 1986).A benthic quality assessme nt based on numericalscoring, as used in the B HQ index , allows statisticalcomparisons between strata. Lately the statisticalpow er in environmental monitoring sampling designshas been discussed (Fairweathe r, 199 1), includingthe need for statistical hypothesis testing in such


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the main object of monitoring studies. The smallestspatial scale statistically analysed in this study wasthe stratum which was chosen as an appropriate scaleto test the hypothesis on the interaction betweendepth and area. The randomized sampling in eachstratum indicate, however, a larger variation in ben-thic habitat quality and in the depth of RPDs aroundthe halocline (15-25 m) than above ( < 15 m) andbelow the halocline (> 25 m)(Fig. 7). The possibilityto detect small-scale variations in sediment condi-tions with the SPI camera technique has also beenshown in an embayment in Ireland, where localorganic enrichment occurred in association with fishfarms and mussel culture (OConnor et al,, 1989).

All areas in Havstensfjord down to 15 m depthwere classified as successional stage 2, except station70 which was classified as stage I. The uniformity ofthis benthic habitat is probably due to the continuouswater renewal above the halocline [EjGrk, 1083).Also in the depth interval 15-25 m, most ofHavstensfjord was classified as successional stage 2,with exceptions in the northwest and northeast wherestage 1 was found, These areas may be affected byhypoxia, as minimum oxygen saturations down to12% recently (1987- 1991) have been reported fromnorthern Havstensfjord at these depths @berg, 1992).

Below 25 m depth in the two northern strata, 80%of the images were classified as successional stages1 or 0. This is most likely related to the seasonallyoccurring hypoxic conditions at these depths (Axels-son and Rydberg, 1993).

s of such effeabundance and mass of benthic

infauna between 1976 and 1986 in five fjordic areasnea Rosenberg, 1988), includinthe ullmarsfjorden in the winter1979/80 (Josefson and Widbom, 1988). The reduc-tion in benthic fauna is suggested by these authors tobe an effect of increased periods of hypoxia.

The SPI camera technique has been used to evalu-ate eutrophication-induced hypoxic effects on sedi-ment-fauna1 relationships in and in twNorth American estuaries, Ch ay and IonIsland Sound. In these areas fauna1 activity ansediment properties (e.g. lamination) were coincidentwith gradients in oxygen stress (Schaffn~r et al.,1992; Ru~~~hr, 1993). Thus, this techniquea rapid assessment of hypoxia related chdifferent marine environments,

The statistical comparison between BHQ indicesin May and October showed no differences. Thedeeper bottoms were rather well oxygenated (> 2.5mg 0, 1-r) from May, with a peak in June (7.8 mgO2 l- and high through the summer, with a declinein the autumn to a minimum in October (0.8 mg O21-r ; Fig. 2). The summer period may not have beenlong enough for the benthic fauna to develop theirvertical activity and deepen the RPD. Also the sedi-ment structure may have been too loose and thesediment sulphidic content too high to allow cola-nization of subsurface active organisms in a shorttime (Rosenberg, 1972). Declining oxygen concen-trations may later have reduced the fauna.

Deeper bottom areas of Havstensfjord seem to bepermanently and severely damaged by seasonal hy-


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poxia. The presence of lamina in the images indi-c a t e s that some of the deep bottoms in the northwere, at least periodically, not inhabited by an activesubsurface infauna. In October Beggi at oa spp. werefound on the surface sediment at 4 stations in thenorthwest stratum, which shows a degradation ofthese habitats since in May.

The temporal effects on the benthic fauna inHavstensfjord cannot be assessed in detail. However,severe disturbances were reported already in 1971 at32-40 m depth, when a poor fauna associated withhypoxic conditions was found in the vicinity ofstations 54 and 56, with 24 ind. rn- at 32 m depthand no macrofauna at 40 m depth (Rosenberg, 1977).A ow biomass ( < 20 g wet wt m-) was alsoreported in the area of stations 47 and 57 at the sametime. Thus, the benthic macrofauna in the deeperpart of Havstensfjord was most likely affected byhypoxia also in 1971.

Fauna1 reworking activity in May in large areas ofnorthern Havstensfjord was restricted to approxi-mately the top centimetre of the sediment. This willprobably reduce the nitrification and denitrificationrates and also the pool of iron and manganese in thesediment (Santschi et al,, 1990). Later in the autumn,sulphur bacteria Be g g i a t m spp.) will spread at thesediment surface as oxygen concentrations decline,which also w ill affect the hiogeochemical cycles(Rhoads and Oermano, 1986; Rosenberg and Diaz,

63n oncentration (Ro-gest that larger areas of bottomhabitat degradation today than

es ago. As a consequence, the transfer ofenergy through macrobenthic fauna and to dem ersalfish is likely to be reduced and the diet to bethan in areas affected by seasonal hypoxia (Pear-son Rosenberg,1992; Pihl et al,, 1992, Pihl,199~0, Hypoxiaand associated negative effects onbenthic macrofauna are spreading rapidly in manystratified and enclosed coastal areas over the w o r l d ,and in man y cases this seems to be coupled w i t hi tr c t ~ ~ d cu?:ophication Diaz and Rosenberg, 1995).Mapping f Havstensfjord bases (t picture imilar o thatofthe sout several areas havecm. These comparatively deep apparent RPDs

es&ted to water depths > 15 m, with one

exception, and dre indicative of deeper infaunal ac-tivity in the tc*p sediments at depths below thehalocline. The great correspondence between mping the habitat quality of Havstensfjord by succes-sional stages and apparent RPD suggests that appar-ent RPD alone may be a rather accurate and easyparameter to use for such an assessment. A similarcorrelation with the use of profile images has earlierbeen demonstrated for Narragansett Bay, Rhode Is-land, USA, an area partly disturbed by anthropogenicinput (Valente et al., 1992). In another similar studyin New Yersey, USA, rizzle and Penniman ( I99 1concluded that the apparent RPD in sediment profileimages compared well with probe measurements.Thus, apparent RPD may be a good integrator ofinfaunal activity and habitat quality. Grizzle andPenniman ( 199 1) also made a detailed comparison ofdata obtained through traditional benthic communityanalysis with that interpreted from sediment profileimages collected in the same area. They concludedihat data from sediment profile images were as use-ful as traditional data in delimiting spatial extent ofpollution-impacted benthos. The SPI technique is,therefore, recommended as a powerful tool in moni-toring marine benthic areas and may be an improve-ment on traditional benthic fauna1 monitoring pro-grammes, Advantages of the SPI technique is that itis ardcrs of l~~~gnitndescheaper and quicker, com-pared to quantification and identification of mac-robenthic infauna, to detect spatial and temporalchanges in benthic habitat quality (R hoads and G er-mano , 1 982; OC onnor et al., 1989; Valente et al.,1992).

5. ConclusionSuccessional models show that benthic infauna is

structurally and functionally distributed along gradi-ents of environmental stress such as declining oxy-gen. The infaunal distribution is related to sedimentgeochemistry and habitat quality. It is shown thatsediment profile imaging (SPI) is a rapid techniqueto statistically assess differences in benthic habitatquality. Parameterization of sediment and animalfeatures in the images is quickly and accuratelymade by digital analysis.. A benthic habitat quality(BHQ) index is easily calculated, which is related to


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Dr. Linda Schaffner and three anonymous referee;are acknowledged for coimprove this manuscript.by the Giiteborg and Bo

Anon., 1992, 1993, 1994. Giiteborgs och Bohus IZnsvattenvirdsfdrbund, Arsammanfattning. Cou nty of Gateb orgsoch Bohus tin (in Swedish).

Axelsson, R. and Ryd berg, L., 1 993. UtvHrdering av Bohusl;insKustvatten-kon trollprogram fdr Pcrioden C90-92. Hydrografioch Ntiingsgmnen. Dep. Oceanogr., Gn aborg Univ., RadaSer., 19, 17 pp. (in Swedish).

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Benthic Habitat Quality Assessment of an Oxygen Stressed

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