Hydrobiologia 375/376: 49–58, 1998.S. Baden, L. Pihl, R. Rosenberg, J.-O. Strömberg, I. Svane & P. Tiselius (eds),Recruitment, Colonization and Physical–Chemical Forcing in Marine Biological Systems.© 1998Kluwer Academic Publishers. Printed in Belgium.

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Regrowth of kelp and colonization of epiphyte and fauna community afterkelp trawling at the coast of Norway

Hartvig Christie1,∗, Stein Fredriksen2 & Eli Rinde3

1 Norwegian institute for nature research, P.O. Box 736, N-0105 Oslo, Norway2 Department of Biology, Section for Marine Botany, University of Oslo, P.O. Box 1069 Blindern, N-0316 Oslo,Norway3 Norwegian institute for nature research, P.O. Box 736, N-0105 Oslo, Norway∗ E-mail: hartvig.christie@ninaosl.ninaniku.no

Key words:kelp, kelp trawling, recovery, epiphytes, holdfast fauna

Abstract

The kelpLaminaria hyperboreais regularly harvested along the Norwegian coast. Kelp trawling is regulated byrestricting this to every 5th year in specified areas. The kelp plants form dense forests, 1–2 m high, and housea large number of epiphytes and associated invertebrates. Kelp, epiphytes, and holdfast (hapteron) fauna weresampled at two different regions in untrawled kelp forest and at sites trawled different number of years ago. Wehave examined the rate of kelp regrowth after trawling, and in what time scale the associated flora and faunacolonize the trawled areas. The trawl removed all adult kelp plants (the canopy plants), while small understoreykelp plants were left undisturbed. These recruits, given improved light conditions, made the new generation ofcanopy-forming kelp plants, exceeding a height of 1 m within 2–3 y. The recruitment pattern of the kelp ensuresmaintenance of kelp forest dominance despite repeated trawling. Both percent cover, abundance and number ofepiphytic species increased with time post trawling, but epiphytic communities were not totally re-establishedbefore the next trawling episode. Colonization of most species of fauna inhabiting the kelp holdfast were found asearly as one year after trawling, but increasing size of the habitat by age of kelp gave room for increasing numbersof both individuals and species. Slow colonization rate by some species might be due to low dispersal potential.Due to a higher maximum age and size of kelp plants in the northernmost region studied, restoration of both kelpand kelp forest community was slower there.

Introduction

Kelp dominate on rocky subtidal coasts of temper-ate waters (Mann, 1982), making diverse kelp for-est communities. The persistence of this communitywill depend on the stability properties of the kelp.Along European coasts, kelp forests are dominatedby Laminaria hyperborea(Gunn.) Foslie, and areknown as habitats for a diverse flora and fauna. Itsstiff and upright stipe provide substrate for a num-ber of macroalgae and sessile animals. More than 40species of epiphytic algae can be found, of which therhodophytes dominate (Sørlie, 1994). A rich fauna ofmobile invertebrates has also been found associated

with this kelp, and specially the fauna inhabiting theholdfasts (hapterons) have been studied (Jones, 1971;Moore, 1973, 1986; Schultze et al., 1990). The kelpis a resource exploited by alginate industries, and ca.170 000 tonnes are harvested (trawled) annually inNorway. The regrowth of kelp plants in trawled areasis obviously of interest to the alginate industry, andalso in an ecological context because the dynamics ofrecovery of the kelp forest ecosystem depend on therecovery of kelp as a keystone species. However, re-colonization of such disturbed systems will not onlydepend on recovery time of the habitat (kelp) itself,

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Table 1. Different sites sampled in the twoareas Rogaland and Smøla. –: not found.

Rogaland Smøla

Untrawled x x

Newly trawled x x

Trawled 1 year ago x x

Trawled 2 years ago x –

Trawled 3 years ago x x

Trawled 4 years ago x x

Trawled 6 years ago – x

but also depend on how the associated flora and faunaare able to colonize and re-establish the system.

The adultL. hyperboreaplants form 1–2 m highkelp forests at the wave-exposed coasts of Norway(Kain, 1971a; Sjøtun et al., 1993). Kelp trawling iscarried out between 58◦ and 64◦ N where shallowrocky bottoms extend several km far out off the maincoastline. The trawling is regulated and decisions re-garding time interval of trawling is generally basedon unpublished data of kelp regrowth provided bythe kelp industry itself. However, newer independentreports have contributed to prolonging the trawlingintervals from 4 to 5 y in 1992 (Sivertsen, 1991;Rinde et al., 1992). The potential for dispersal andrecruitment ofL. hyperboreais high (Fredriksen et al.,1995) and a mature kelp forest normally contains anunderstorey vegetation of recruits ready to take overwhen adults are removed (Svendsen, 1972; Røv et al.,1990). According to industry capture records, thekelp forest recover in biomass by subsequent trawling.However, the restored kelp forest may differ in sizeand demography compared to untrawled kelp forests.Moreover, other macroalgae have played importantparts in the succession in kelp forest restoration afterdisturbances (e.g. Dayton et al., 1984, 1992; Os-hurkov & Ivanjushina, 1993). In Norwegian waters,Leinaas & Christie (1996) foundL. hyperboreatobe abundant first after 3–4 y in the succession of re-establishing kelp forest after removal of sea urchins inan overgrazed area.

Kelp trawling may affect the occurrence of theassociated flora and fauna in several ways. If the com-position of associated species depend on the size, ageand density of the host plants, kelp trawling may, bychanging the demography and size distribution of thekelp forest, indirectly affect the kelp forest commu-nity. The epiphytic algal composition have been found

Figure 1. Map of Norway showing the two sampling sites. The fig-ure also includes an illustration of how the coast line is divided intosectors (one nautical mile each), each permitted to trawling every5th year. Trawling is performed one year in sector A, next year insector B etc.

to be affected by age of plants (Whittick, 1983) andby shading (Harkin, 1981). Associated flora and faunacomposition may change with kelp species (Schultzeet al., 1990), and the proportion of other kelp speciesin the recovery process may thus affect the com-position of associated flora and fauna. Colonizationof the invertebrate species to the trawled plots willalso depend on the dispersal ability of the differentspecies. Species with pelagic larval dispersal (sup-ply side ecology, e.g. Roughgarden et al., 1987) mayhave advantages in colonizing the trawled areas com-pared to species with brooding or other forms of directdevelopment of juveniles.

Sjøtun et al. (1993) found that the kelp forest struc-ture (average age and size of population) vary withlatitude along the coastline. Thus, recovery patternsfound in one area may not be valid for the recovery atother parts of the coastal region.

In this study we focus on regrowth of the kelp for-est and the return of epiphytes and invertebrate faunain holdfasts in areas trawled a different number ofyears ago. For a study of possible latitudinal differ-ences, similar studies have been done in a southern andin a northern region where kelp trawling is permittedin Norway.

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Materials and methods

The sampling took part at a northern region; west ofSmøla island just north of 63◦ N, in August 1991,and at a southern region; in Rogaland just south of59◦ N, in August 1993 (Figure 1). Both areas havebeen important for kelp trawling for many years, andprovide neighbouring latitudinal sectors of 1 nauticalmile trawled at different years before any sampling(Figure 1). The regulation of trawling frequency ofevery 5th year give the opportunity to find samplingsites of newly trawled, tracks trawled different num-ber of years ago, as well as untrawled kelp forest, allwithin short distance.

All sampling were obtained by SCUBA diving. Fora comparison between the sampling sites, same waveexposure (strongly exposed, but some sheltered behindthe outermost skerries) and depth (5 m below low wa-ter level) was chosen. Due to difficulties by workingin the exposed waters off the Norwegian west coast,not all sampling was possible to fulfill according tothe planned design. Table 1 shows the kelp forest sitessampled in the two areas.

For a description of kelp vegetation structure, a1×1 m frame was dropped randomly above the kelpcanopy, and the number of plants were counted in 6replicate frames. The plants were grouped in canopyforming and understorey plants. The canopy formingplants in three of the six quadrates were harvestedfor individual measurements of stipes length and agedetermination (method from Kain, 1963).

Of the harvested plants from each site, 5 (Smøla) or15 (Rogaland) were randomly picked out for analysisof epiphytes. The harvested plants were analysed onland soon after sampling (for visually occurring epi-phytes). The epiphytes generally start to colonize thebasal part of the stipes (the oldest part) and with timedevelop an increasing coherent cover upwards. Theproportion of epiphytic cover of the stipes was mea-sured. The stipes were then divided into three equalparts, the upper, middle, and lower stipe. Epiphyticmacroalgae and macroinvertebrates were identifiedand semiquantitatively recorded for abundance (1 –present, 2 – common, 3 – dominating) on each part ofthe stipe and on the holdfast. The abundance recordswere added up for each plant, giving a possibility forcomparison of relative abundance of epiphytes, andalso illustrating the amount (volume) of the epiphytes.

Samples of 20 (Smøla) and 15 (Rogaland) ran-domly chosen kelp holdfasts were collected by firstcutting off the stipe, then carefully loosening the hold-

Figure 2. Kelp forest structure different number of years post trawl-ing compared to untrawled forest at the two investigated sitesRogaland and Smøla (where untrawled kelp forest had an averageage of 7 and 10 y respectively). Mean values are given with 95%confidence limits. A. Number of canopy plants per m2, B. Canopyheight (stipes length), C. Holdfast volume of canopy plants.

fast using a knife and sealing each holdfast in a plasticbag. The holdfast volumes were measured accordingto Jones (1971), cut to pieces, washed and sieved(250µm) for retaining associated fauna. A total quan-titative and qualitative analysis of macrofauna is verytime consuming, and only three replicate holdfastsfrom selected sites were analyzed. Holdfasts from un-trawled kelp forest and from one year after trawlingwere chosen from each area, and holdfasts from 4 and6 y after trawling from Smøla and 3 y after trawlingfrom Rogaland were also analyzed. The invertebrateswere individually counted and identified to species orhigher taxonomic groups.

This study included two independent samplings, in1991 from Smøla and in 1993 from Rogaland. The

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Figure 3. Age frequency distribution of canopy forming kelp plants in trawled and untrawled areas from the Rogaland and Smøla sites.

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Table 2. Mean density of understorey plants (no/m2±one standard error) in the trawled sites at Smølaand Rogaland. – no data from this site.

Years after trawling 1 2 3 4 Untrawled

Smøla 46(38) – 71(25) 52(29) 83 (11)

Rogaland 23(7) 47(25) 9(7) 25(9) 34 (4)

aim was to draw a comparison between the two ar-eas, and thus the second study was designed similar tothe first with respect to exposure, depth and parame-ters sampled. However, some variations were includedfor the purpose of making improvements (more repli-cate plants for analysis of epiphytes), and for reducingdiving time (a reduction to 15 holdfasts). Our ob-servations showed that the four year old kelp forestat Rogaland were very similar to the untrawled kelpforest (in contrast to Smøla), and thus holdfast faunaanalysis was decided to be taken from the 3 y old forestrather than from the 4 y old as done for the Smølastudy. Also holdfasts from a 6 y old forest at Smølawere analysed for fauna, due to the observed largesize difference between plants from this forest and theuntrawled kelp forest in this region.

Differences in kelp structure and demography anddifferences in epiphytes and holdfast fauna betweenuntrawled and trawled tracks were tested by t-testsand one way ANOVAs (significance level,a= 0.05).Recolonization patterns were also analyzed by linearregression.

Results

Figures 2 & 3 and Table 2 show a common pattern ofadultL. hyperboreain densities of about 10 plants perm2 and high number of small plants in the understoreyin both regions. However, considerable differences inuntrawled kelp forest structure and demography be-tween the two regions (Smøla and Rogaland) werefound. The adult kelp plants at Smøla were signifi-cantly older and higher than those at Rogaland and aregional difference could also be reflected in the dif-ference in plant densities, suggesting Smøla as mostoptimal for growth ofL. hyperborea. In the followingpresentation, the data from trawled tracks are pre-sented asX years after trawling (X year old forest), andthe untrawled sites are given as average age of canopyplants; 7 y for Rogaland and 10 y for Smøla.

Figure 4. Occurrence of epiphytes on examined canopy plants fromdifferent trawled tracks compared to untrawled forest in the twoinvestigated sites Rogaland and Smøla. Mean values are givenwith 95% confidence limits. A. Percentage cover of epiphytes, B.Relative abundance of epiphytes, C. Number of epiphytic algalspecies.

The pattern of restoration of the kelp forest struc-ture is illustrated by comparing plant density and sizeat the different trawled areas with the untrawled sites(Figure 2). The kelp trawl removed all large plants,and at both regions the new canopy layer in the newlytrawled tracks consisted of a high density (Figure 2A)

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Figure 5. Macrofauna in holdfasts from canopy plants from differ-ent trawled tracks compared to untrawled forest in the two investi-gated sites Rogaland and Smøla. Mean values are given with 95%confidence limits. A. Number of macrofauna species per holdfast,B. Macrofauna abundance per holdfast.

of recruits of small size (< 25 cm, Figure 2B). Thenumber of plants were strongly reduced during thefirst 2–3 y after trawling to a number not significantdifferent from the density of canopy forming plants inan untrawled kelp forest. The recruits grew initially bysimilar growth rate at the two regions (although localvariations were found), and within 2–3 y after trawlingthe plants have exceeded a height of 1 m. At this stagethe kelp forest size had recovered at Rogaland (no sig-nificant difference in height between plants from 2 and4 y old forest and untrawled, while 3 y was signifi-cantly higher). More than 6 y was needed for recoveryof plant size at Smøla (plants from 6 y old forest wassignificantly smaller than plants from untrawled). Thegrowth of the kelp holdfasts (Figure 2C) showed asimilar pattern of recovery as the stipe length. Hold-fast volume at Rogaland recovered after 4 y, but atSmøla the holdfasts from the 6 y old forest were stillsignificant smaller than at untrawled.

Table 2 shows that kelp recruits established anunderstorey vegetation (<25 cm in height, c.f. Fig-ure 2B) below the new canopy as soon as one yearafter trawling and every year thereafter.

The age composition of the canopy forming kelpplants in the different trawled tracks (Figure 3) show

Figure 6. Colonization rate of holdfast fauna given as increase peryear in number of individuals of different macrofauna groups in thetwo investigated sites Rogaland and Smøla. A. increase in numberof individuals per holdfast per year. Mean value of slope with 95%confidence limits is given, based on linear regression analysis offauna abundance from kelp of different years. B. estimates of in-crease in number of individuals per m2 per year. (see text for furtherdescription of estimates).

that the new generations of plants have settled duringmore than one year prior to trawling. The age structureof this kelp forest is, however, less heterogeneous 4 yafter trawling compared to the untrawled area com-posed of six or seven year classes. The 6 y old kelpforest at Smøla consisted of six year classes, but wasdominated by 7 y old plants.

The age of kelp is important for epiphytic (total al-gal and faunal) cover (Figure 4A), relative abundance

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of epiphytes (Figure 4B), and number of epiphytic al-gal species (Figure 4C). The proportion of the stipesfouled by epiphytes was significantly lower in trawledtracks the first three years after trawling in both re-gions. Epiphytic growth can vary from encrustingalgae or bryozoans to a luxuriant vegetation of volu-minous red algae. The latter is characteristic on thestipes at untrawled sites, and this kind of epiphyticrecovery is best illustrated by the relative abundance(Figure 4B) which shows that epiphytes needs morethan four years at Rogaland and more than six years atSmøla for significant restoration. The relative rate ofabundance recovery was slower at Smøla. The estab-lishment of the different epiphytic algal species wasalso a slow process at Smøla compared to Rogaland.Total number of species did not differ significantly be-tween two and four years after trawling and untrawledat Rogaland (an exception was the three year old forestthat differed from the recovery trend in other ways).In contrast, the number of species gradually increasedat Smøla, and still 6 y after trawling the number ofepiphytic species was significantly lower than at un-trawled areas. The increase at Smøla fitted a linearmodel (95% confidence limits: 1.1–1.5;r2 = 0.89).

The macrofauna (sessile epiphytes as bryozoanswas not included) found in the holdfasts are character-ized by high variation within replicates both concern-ing number of species (taxa) per holdfast (Figure 5A)and number of individuals per holdfast (Figure 5B).In contrast to the epiphytic species, a high numberof species settled one year after trawling (Figure 5A).Average number of species increased slowly by in-creasing age of kelp at both regions. t-tests show nosignificant difference in the number of species be-tween 3 y and untrawled at Rogaland and between6 y and untrawled at Smøla. One way ANOVA rejectsthe hypothesis of equal means (p< 0.001) for bothRogaland and Smøla. The linear regression analysisshowed significant trends of increase by 5 (Rogaland)and 2.5 (Smøla) new species per year (p< 0.0001,r2 = 0.92; p<0.0001, r2 = 0.83, respectively). The95% confidence limits of the slopes are 3.8–6.5 and1.4–2.7.

The total number of macrofauna individuals perholdfast was low during the 3 or 4 y after trawlingat Rogaland and Smøla respectively. The number ofindividuals increased significantly approaching the un-trawled (Rogaland) and the 6 y old forest (Smøla)(Figure 5B). After 6 y, no further increase in faunaabundance was found at Smøla although average hold-fast volume in untrawled areas was significantly larger

than holdfasts in the 6 y forest. To quantify changesin abundance of holdfast fauna during the years af-ter trawling, we performed linear regression modelsof number of individuals within the four importantspecies groups; polychaets, isopods, gastropods andamphipods (for Smøla only up to 6 y). The slopes(increase in numbers per year) with 95% confidencelimits are presented in Figure 6A. All species groups,except for polychaets at Smøla, showed significantincrease in number of individuals per holdfast withincreasing time after trawling (the confidence limit donot cross the x-axis). Within each species group, therewere no significant difference in the rate of increasebetween the two regions. Figure 6 also show highestmean colonization rate by amphipods.

The re-establishment of holdfast fauna abundancemay be considered not as number of individuals perholdfast, but rather number of individuals per unit areaof kelp forest. One year after trawling, a total of 750individuals per holdfast and 40 plants per m2 resultsin a fauna density of 30 000 per m2. In untrawled kelpforest 5000 individuals per holdfast gives an estimateof 50 000 individuals per m2 (10 canopy plants perm2). Such estimates are tentative due to high varia-tions in both plant densities and fauna abundance perholdfast (thus no error bars are given in Figure 6B).However, data on individual density of the differentfauna groups may provide examples on differences incolonization patterns. The estimates on number of in-dividuals per m2 (density) of amphipods and isopodsstill showed a strong increase with kelp age at both re-gions, while the increase of polychaets and gastropodswere less pronounced (Figure 6B). This implies thatpolychaets and gastropods colonize in densities closeto their maximum density during the first year aftertrawling, while isopods and amphipods need longertime to reach maximum density.

Discussion

The results show that kelp trawling efficiently harvestall the adult canopy formingL. hyperboreaplants,and leave a high density of recruits behind. This poolof L. hyperborearecruits start to grow by given im-proved light conditions, resulting in a new generationof plants maintaining the kelp forest. This recruitmentpattern ensure persistence of a kelp forest dominatedby L. hyperboreathroughout the whole recovery (suc-cession) period after any trawling disturbance, andnot giving space for alternative kelp species (as have

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been found by Dayton et al., 1984; Reed & Foster,1984). Intraspecific competition leads to reduction ofthe canopy plant density of the new generation ap-proaching untrawled kelp forest size and density after2 to 4 y. During this time, settlement of sporelings andnew establishment of understorey kelp recruits ensurethe potential for continuation of the kelp forest by thenext trawling episode. Thus,L. hyperboreahave theability to resist the disturbance of repeated trawling(and probably other disturbances like storms etc.), animportant property of stability (c.f. Connell & Sousa,1983).

The age distribution of canopy plants from trawledtracks showed that the young kelp plants found af-ter trawling were composed by more than one yearclass. This indicates that kelp recruits have the abil-ity to persist as small understorey recruits for severalyears. Thus regrowth of kelp after trawling does notdepend solely on the recruitment success in the yearof trawling. The ubiquity of kelp recruits of differentyear classes gives this species an advantage in the suc-cession after any trawling, regardless of season whentrawling is performed. This is a further trait of theL.hyperboreaspecies to maintain the dominant role inthe system by a competitive advantage compared toother species.

During the first years after trawling, plant growthrate and development of kelp forest structure wasfound to be similar at the two regions investigated.Despite these similarities, the restoration of the kelpforest was different between the regions due to dif-ferences in maximum plant age and size. Thus, plantsize recovered prior to subsequent trawling at Roga-land, but needed longer time for recovery at Smøla.Local differences were also seen, even though similarsampling sites were chosen to eliminate differences inphysical factors that could introduce such differences.Three years after trawling the kelp forest at Rogalandhad reached a significantly higher plant size than thefour year and untrawled sites, and was composed of ahigh density of plants. An explanation of this may bemore favorable growth conditions at this site than theneighbouring sites. The structure of the three year for-est at Rogaland underline that disturbances like kelptrawling might lead to regrowth of a very dense andhomogenous kelp forest.

The re-establishment of epiphytes on the kelpstipes was a slower process than the regrowth of kelpplants. Even though a high percentage of the stipeswas covered by a number of species of epiphytesduring 2–3 y, the relative abundance showed that epi-

phytes did not recover before next trawling at eitherof the two regions. Even when most of the stipeswere fouled and most of the species were established,the abundance, or three dimensional structure of theepiphytes had not recovered. As for the kelp itself, epi-phytes showed a generally slower recovery at Smølathan at Rogaland. Since age is of importance for epi-phytic growth (Whittick, 1983; this study), a fieldsubjected to repeated trawling will probably neverrecover in epiphytic abundance and diversity.

Another inhibiting factor for the development ofepiphytic algal growth is shading (Harkin, 1981). Thecanopy forming plants can reduce the light penetrationto the bottom by as much as 90% (Norton et al., 1977).The dense canopy of the homogenous new kelp gen-eration in trawled tracks will inhibit light penetrationmore efficiently than the heterogeneous plant struc-ture of the untrawled forests. This might be illustratedby the low number of species established in the threeyear forest at Rogaland, where population density washigher than at the two and four years old forest.

Evaluations of recovery of invertebrate fauna con-nected to the holdfasts are more difficult to make dueto the high variations of fauna abundance betweenholdfasts of same age and size. As the kelp plantsgrow during the years after trawling, the holdfastsincrease gradually in size (volume). This gives moreroom and probably also more niches to animals, and anincreasing number of individuals and species per hold-fast would be expected. This was found at Rogaland,and at Smøla of samples up to 6 y. The unexpectedlack of further increase in fauna abundance at Smøla(mean value was lower at untrawled than at 6 y af-ter trawling although holdfast size was about doubled)may be due to the possibility that these large holdfastsgave room for larger predatory polychaets, crustaceansand echinoderms contributing to a reduction of thenumerous herbivores and detritivores. The increasein number of individuals of invertebrates per hold-fast as the holdfast volume increase by age, may beof minor importance in a fauna abundance restorationcontext, the main objective being the restoration offauna density per unit area. Due to the decrease inkelp plant population density with increasing numberof years after trawling, estimates of recolonization perunit area showed population density of early invadersto be re-established after one year, while other speciesincreased in density by increasing age of kelp forest.Animals with pelagic larval settlement, polychaets andgastropods, established densities approaching maxi-mum density one year after trawling, while isopods

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and amphipods showed increasing density throughoutthe period of kelp forest restoration. The latter speciesrecruit by brooding, and colonization into disturbedhabitats might be by crawling or swimming. Due tothe lack of a dispersal phase, these animals may havelimited dispersal ability (e.g. Lessios et al., 1994).Differences in dispersal may be an explanation of theobserved differences in colonization rates, in whichcase isopod and amphipod recovery might be morevulnerable if larger kelp areas are disturbed.

A relatively high number of both species and indi-viduals of invertebrates colonized the small holdfastsone year after trawling, and a diverse community of as-sociated flora and fauna were established subsequentlytrawling (5 y) at both regions. However, those specieswith stronger demands to habitat heterogeneity andthose with highly reduced dispersal patterns contributeto a community not totally recovered by next trawling.As the kelp plants form a habitat of limited duration(maximum 10 y found at Rogaland and 14 y at Smøla),the flora and fauna of this community must be adaptedto a regular colonization of new kelp plants. Thus,a kelp forest community may be recovered during aperiod of approximately one kelp generation.

More recent reports (Christie, 1995) have foundhigh numbers of invertebrate species inhabiting thestipes epiphytes, and strongly increasing abundancewith increasing epiphytic volumes. The reduced epi-phyte abundance in the trawled tracks will thus con-tribute strongly to an additional retarded recovery offauna abundance and diversity due to kelp trawling.This factor also contribute to the longer time of faunarestitution at Smøla.

Mean size and age of the kelpL. hyperboreavaries by latitude within the area of distribution (Kain,1971b) and within the restricted area of kelp trawlingactivity along the west coast of Norway (Kain, 1971a;Sjøtun et al., 1995). Our data on differences betweenRogaland and Smøla support these observations. Bothrecovery of kelp demography and structure, as well asrestoration of the flora and fauna community associ-ated with kelp forest took longer time at Smøla whereuntrawled kelp forest consists of larger and olderplants. The process of community change followingkelp trawling at Rogaland was similar to the pattern ofmarine invertebrates found by Dean & Connell (1987)where species richness and abundance showed largestincrease up to middle successional stages. The patternof kelp forest community recovery at Smøla was fol-lowing the model of continously increase during thesuccession or process of recovery (c.f. Odum, 1969).

The results from this study may be utilized in the man-agement of kelp resources. A time interval of trawlingof 5 y for both regions may be questioned, and differ-ences in intervals between latitudinal regions may besuggested.

This study is an introductory elucidation to the un-derstanding of patterns of community recovery of kelpforest after trawling, and thus leave a number of ques-tions. Kelp trawling, according to our observations,fragments the kelp forest by tracks rather than totallyclear larger areas. The recolonisation and recovery ofkelp plants and kelp forest community reported in thisstudy is only valid for the processes within the trawledtracks. The larger ecological consequences may de-pend on the dynamics formed by the proportion anddistribution of trawled and untrawled kelp forest.

Acknowledgements

This study was funded by the Norwegian Directoratefor Nature Management. We are grateful to ArnfinnSkadsheim, Arne Sivertsen, and the kelp trawlingindustry for help and information, and we thank Mo-hammed Abdullah for corrections to the manuscript.

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