Distribution of macroalgae and macroalgal communities in gradients ...

1

Hydrobiologia 333 : 1-17, 1996 . © 1996

Kluwer Academic Publishers . Printed in Belgium.

Distribution of macroalgae and macroalgal communities in gradients of physical conditions in Potter Cove, King George Island, Antarctica Heinz Kloser l , Maria Liliana Quartino 2

&

Christian Wiencke l

'Alfred- Wegener-Institutefor Polar and Marine Research, P .B . 120161, 27515 Bremerhaven, Germany 2 Instituto Antartico Argentino, Cerrito 1248, 1010 Buenos Aires, Argentina Received 4 July 1995 ; in revised form 6 February 1996 ; accepted 16 February 1996

Key words: macroalgae, distribution, sublittoral, exposition, communities, Antarctic

Abstract The vegetation of a small fjord and its adjacent open shore was documented by subaquatic video . The distribution of individual species of macroalgae and the composition of assemblages were compared with gradients of light availability, hydrography, slope inclination, substratum, and exposition to turbulence and ice . The sublittoral fringe is usually abraded by winterly ice floes and devoid of large, perennial algae . Below this zone, the upper sublittoral is dominated by Desmarestia menziesii on steep rock faces, where water movements become irregular, or by Ascoseira mirabilis and Palmaria decipiens on weakly inclined slopes with steady rolling water movements . In the central sublittoral above 15 m, where turbulence is still active, Desmarestia anceps is outcompeting all other species on solid substratum, However, the species is not able to persist on loose material under these conditions . Instead, Himantothallus grandifolius may occur . Deeper, where turbulence usually is negligible, Desmarestia anceps also covers loose material . The change of dominance to Himantothallus grandifolius in the deep sublittoral cannot completely be explained at present . Himantothallus grandifolius also prevails in a mixed assemblage under the influence of grounding icebergs . Most of the smaller algae are opportunists with different degrees of tolerance for turbulence, but some apparently need more stable microhabitats and thus are dependent from continuing suppression of competitive large phaeophytes . Introduction The sublittoral zonation of Antarctic macroalgae has frequently been described in a qualitative way (Skottsberg, 1941 ; Neushul, 1965 ; Deldpine, 1966 ; Zaneveld, 1966 ; Etcheverry, 1968 ; Price & Redfearn, 1968 ; McCain & Stout, 1969 ; Bellisio et al ., 1972 ; Dell, 1972 ; Arnaud, 1974 ; Lamb & Zimmerman, 1977 ; Zielinski, 1981 ; Furmanczyk & Zielinski, 1982 ; Etcheverry, 1983 ; Heywood & Whitaker, 1984 ; Picken, 1985 ; Dayton, 1990 ; Zielinski, 1990 ; Kloser et al ., 1994a ; Knox, 1994), but only few attempts at quantitative analysis have been performed (DeLaca, 1976 ; DeLaca & Lipps, 1976 ; Richardson, 1979 ; Amsler et al ., 1990 ; Miller & Pearse, 1991 ; Amsler et al ., 1995 ; * The present work is part of the Argentinian-German cooperation program RASCALS (Research on Antarctic shallow coastal and littoral systems).

Brouwer et al ., 1995) . The general pattern emerging from these descriptions includes an ice-abraded zone in shallow waters with several annual and pseudoperennial species, a central zone with dominant Desmarestia species, and a zone of Himantothallus grandifolius and several rhodophytes at greater depth . In detail, however, reports differ considerably . Particularly, the central Desmarestia belt may not be present . The southernmost locations (Zaneveld, 1966 ; Dayton et al ., 1970 ; Gruzov, 1977 ; Nakajima et al., 1982 ; Miller & Pearse, 1991 ; Cormaci et al ., 1992) are beyond the geographical distribution of the large phaeophytes Ascoseira mirabilis, Desmarestia menziesii, Desmarestia anceps, Himantothallus grandifolius, Cystosphaera jacquinotii . Their scarcity in other parts of the Antarctic (Neushul, 1965 ; Castellanos, 1973 ; DeLaca & Lipps, 1976 ; Zamorano, 1983 ; Kirkwood & Burton, 1988), however, must be explained by other causes .

2 To improve our understanding of the ecology of the Antarctic sublittoral vegetation, a detailed analysis of the macroalgal zonation under contrasting exposure to ice impact and turbulence was performed in Potter Cove, King George Island, as part of the ArgentinianGerman RASCALS program . The general ecological situation was already described by Kloser et al . (1993, 1994a, 1994b) and Schloss et al . (1995) .

Material and methods In the vicinity of the Scientific Base "Jubany" in Potter Cove, King George Island (62'14'S, 58°40'W: Figure 1), 14 subaquatic video profiles from the waterline down to around 35 m have been performed by SCUBA diving from September 1993 to February 1994, using a Sony High8 Camcorder CCD-V800E in a MPK-VX1 housing . Usually a series of dives was necessary to complete a profile . While recording, the camera was held vertically at a distance of approximately 1 m from the bottom. At intervals, the profile was interrupted for recording panorama overviews . In addition, reference specimens of all relevant organisms were collected for taxonomical identification . After the dives, the depth of the investigated profiles were recorded by echo sounding (Figure 2) . The video profiles first were used for a general qualitative survey . Information available from dives performed for other tasks was also included . Then, the two most contrasting profiles with regard to exposure (Profiles 3 and 13 : Figure 1, Figure 2) were selected for detailed analysis : Profile 3 showed the densest macroalgal cover found within the investigation area, and on profile 13 most groundings of icebergs were observed (Kloser et al ., 1994a) . For analysis, the fixed image option of the camcorder was used : the playback of the video tape was stopped, and coverage of macroalgae and substratum types was estimated on a monitor screen with an overlay of a 20 rectangle grid, each rectangle representing 5% of the visible area. Five grades were recognized : 0 = not observed, 1 = less than 5% of the visible area covered ; 2 = between 5 and 25% of the visible area covered ; 3 = 25 to 50% of the visible area covered ; 4 = 50 to 75% of the visible area covered ; 5 = 75% to 100% of the visible area covered . Then, the tape was moved to proceed until the upper margin of the former fixed image touched the lower margin of the screen, and the tape was stopped again . In this way, continu-

ous, complete profiles could be achieved as a series of fixed images . The identification of species on the video tapes could be performed with unexpected accuracy . Only two pairs of species could not be separated : Gigartina skottsbergii differs macroscopically from Sarcothalia papillosa only in the umbilicate or basal attachment of the rhizoid, not visible in the video . Notophycus fimbriatus and Iridaea cordata are too similar macroscopically to allow a safe identification on the video . Please note that the sum of coverage percentages of all macroalgae can exceed 100% . This is partly due to overlapping thalli, but also to a certain, unavoidable overestimation in such arborescent species, which do not completely cover the occupied area . Coverage percentages of substratum type are given irrespective of macroalgal coverages .

Results General survey Overall, 43 species of macroscopically identifiable macroalgae were found, most with generally ample distribution within the investigation area (Table 1) . Soft bottom of the inner cove (Figure 3) was devoid of macroalgae (Profiles 8-11 : Table 1 ; Figure 1) . A notable exception are boulders and stones of moraine deposits, which occur down to about 9 m depth in front of glacier cliffs north of the cove . Here Himantothallus grandifolius was dominant (Profiles 6 and 7 : Table 1 ; Figure 3) . On the southern beach of Potter Cove, some scattered dropstones in the upper 6 m carried Phyllophora appendiculata and some other macroalgae (Profiles 9 and 10 : Table 1) . The bottom of the outer Potter Cove and the adjacent open coasts consists of hard substrata (rock, boulders, stones, gravel, pebbles, coarse sand) with a macroalgal vegetation of changing density (Figure 3) . The sublittoral slopes of Barton Peninsula are comparatively steep, with alternating promontories and inlets (Figure 2) . These slopes are largely sheltered from iceberg groundings, because they lie on leeward side with regard to prevailing currents, which come from northwest and bend into the cove . A dense belt of Desmarestia anceps is present, ranging from 5 m/10 m down to 15 m/25 m (Figure 3), except at a vertical rock face, which drops beyond diving limits and carries curtains of Himantothallus grandifolius (Profile 2: Figure 1) . At Potter Peninsula, an extended sublittoral platform



3 Table 1 . Presence of sublittoral macroalgae in the investigated profiles . Profiles 8 and 11 were devoid of macroalgae .

Macroalgae in Profile 9 and 10 were restricted to some dropstones near the shore . Profiles 1 and 2 as well as 4 and 5 were lumped because of their proximity Species/Profiles

1/2

3

4/5

x

X

6

9

10

12

13

14

X

X

X

X

x

x

Chrysophyta Antarctosaccion applanatum (Gain)Delepine 1970 Bacillariophyta Parlibellus delognei (VanHeurck) Cox 1988 Parlibellus schefterae (Lobban) Cox 1988 Chlorophyta Lambia antarctica (Skottsberg)Delepine 1967 Monostroma hariorii Gain 1911 Phaeophyta Adenocystis utricularis (Bory) Skottberg 1907 Ascoseira mirabilis Skottsberg 1907 Cystosphaera jacquinotii (Montagne) Skottsberg 1907 Desmarestia anceps Montague 1942 Desmarestia antarctica Moe et Silva 1989 Desmarestia menziesii J. Agardh 1848 Elachista antarctica Skottsberg 1953 Geminocarpus geminatus (Hooker fil . et Harvey) Skottsberg 1907 Halopteris obovata (Hooker et Harvey) Sauvageau 1904 Himantothallus grandifolius (A . et E. S . Gepp) Zinova 1959 Phaeurus antarcticus

x

x

x

x

x x

x

x

x

X

X

X

X

X

x

x

x

x

X

x

x

x

x

X

x

x

x

x

x

x

x

x

x

x

x x

x

1

*2

x

*3

x

X

*

x

X

x

x

x

X

X

X

X

X

X

X

X

X

X

x

x

x

X

x

x

x

x

x

x

x

X

X

x

x

x

x

x

x

x

x

x

x

x x

x

x

* 4 X

* 5 x

x

x

x

x

x

x

Skottsberg 1907 Rhodophyta Antarcticathamnion palysporum Moe et Silva 1979 Ballia callitricha (C . Agardh) Kiitzing 1843 Callophyllis sp . Curdiea racovitzae Hariot in De Wildeman 1900 Delesseria lancifolia (Hooker fil .) Agardh 1872

x

x

x

X

X

x

x

X

x

x

* 6

x

x

x

X

X

x

x

X

X

X

x

x

X

X

X

X



4

Table 1 . (continued) Species/Profiles

1/2

3

Delesseria salicifolia Reinsch 1888 Georgiella confluens (Reinsch) Kylin 1956

4/5

6

7

9

10

12

13

14

x x

x

x

x

x

x

Gigartina skottsbergii x x Setchell et Gardner 1936 and/or Sarcothalia papillosa (Bory) Leister 1993 Gymnogongrus antarcticus X

x

x

x

x

x

x

x

x

X

X

X

X

X

x

x

x

x

x

x

x

x

X

X

Skottsberg 1953 Hymenocladiopsis crustigena Moe 1986 Iridaea cordata (Turner) Bory 1826 and/or Notophycus fimbriatus Moe 1986 Kallymenia antarctica Hariot 1907 Myriogramme manginii (Gain) Skottsberg 1953 Myriogramme smithii (Hooker f it . et Harvey) Kylin 1924 Palmaria decipiens (Reinsch) Ricker 1987

x

* 8

X

X

x

x

X

X

x

x

x

x

x

x

x

x

x

X

x

x

x

x

Pantoneura plocamioides Kylin 1919 Phycodrys antarctica (Skottsberg) Skottsberg 1923

x

x

x

x

x

x

x

x

x

X

X

Phycodrys austrogeorgica Skottsberg 1923

X

X

X

X

Phycodrys yuercifolia (Bory) Skottsberg 1923 Phyllophora appendiculata Skottsberg in Kylin et Skottsberg 1919 Picconiella plumosa (Kylin) De Toni 1936 Plocamium cartilagineum (Linnaeus) Dixon 1967 Porphyra plocamiestris Ricker 1987 Rhodymenia subantarctica Ricker 1987 Sarcodia montagneana (Hooker f it . et Harvey) J . Agardh 1872

x X

x

x

x

x

x

x

x

x

x

x

x

x

x

x X

x

x

x

x

X

x

x

x x

x

x

x

x

x x

x x

#

x

* 9

x * 10

Remarks : * 1 - early summer epiphyte of Plocamium cartilagineum; * 2 - rare on denuded rock in the sublittoral fringe; * 3 - able to grow on mud, but also under overhanging rock ; * 4 - occasional patches in the upper sublittoral ; * 5 - on flanks of boulders in open Himantothallus communities ; * 6 - in small caverns and on flanks of boulders ; * 7 - on pepples in -10 m to -25 m in clear water; * 8 - scattered occurrence in open Desmarestia stands ; * 9 - late summer epiphyte on Plocamium cartilagineum ; * 10 - scattered occurrence in large furrows of exposed rocks ; # - as Anisocladella serratodentata (Skottsberg) Skottsberg 1923 in Kloser et al . (1994a)

5

68”W64”W 6o”W Antarctic - 6’“s

Peninsula

- 64% 4

- 65%

Maxwell

Bay

Figure

I. Map of the investigation

arm. Positions

exists (Figure 1, Figure 2). Here, the vegetation of the central sublittoral is sparse without an obvious belt of Desmarestia anceps. Fields of sand interrupt the scattered macroalgal cover further (Figure 3).

of all video profiles

m indicated

Profile 3 (Barton Peninsula: Figure 4) To a large extent, the big phaeophytes (Ascoseira mirabilis, Desmarestia menziesii, Desmarestia anceps, Himantothallus grandifolius, Cystosphaera jacquinotii) achieve a cover of 100%. Himantothallus grandifolius is dominant on gravel, pepple and cobble in a depth of 33 m to 18 m, with some scattered plants of

6

Depth (m)

Figure 2 . Echosounding records of Profiles 3 and 13, providing correct depth profiles for comparison with diving profiles in Figures 4, 5 and 6 .

Desmarestia anceps and Cystosphaera jacquinotii . At 18 m, Desmarestia anceps takes over in an abrupt transition without any significant change in the substratum . From 15 m upwards, Desmarestia anceps occurs only on solid rock . It is replaced by Desmarestia menziesii on an emerging ridge in 9 m to 7 m depth, and again on an almost vertical rock face starting in 7 m depth . On the latter, the cover with Desmarestia menziesii is less dense, and some individuals of Ascoseira mirabilis occur. The uppermost 3 m are essentially devoid of big phaeophytes . Due to the general preponderance of the large phaeophytes, few other macroalgae were abundant on this profile. The uppermost 3 m as well as clearings between Desmarestia menziesii down to 5 m were preferred by Phaeurus antarcticus, Myriogramme manginii, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus . Besides, this group could appear scatteredly in vegetation gaps down to 15 m . Larger vegetation gaps between 10 and 15 m were predominantly occupied by Desmarestia antarctica, Palmaria decipiens and Monostroma hariotii . The large rhodophytes Gigartina skottsbergii and/or Sar-

cothalia papillosa showed a similar occurrence like Ascoseira mirabilis . They essentially occupy open spaces between Desmarestia menziesii on the steep rock face below 5 m . Further, the dense growth of Ballia callitricha in open spaces in the Himantothallus fields between 18 and 25 m is noteworthy. This was not found elsewhere. Profile 13 (Potter Peninsula, outward of Em Rock : Figure 5) Outward of Em Rock (Figure 2), the cover with big phaeophytes is rather sparse ., The ranges of occurrence still mirror preferred zones of the individual species, i .e . Ascoseira mirabilis and Desmarestia menziesii occupy the highest, Desmarestia anceps intermediate, and Himantothallus grandifolius the lowermost parts (Figure 5a, b) . However, Himantothallus grandifolius as well as Desmarestia menziesii and Ascoseira mirabilis spread out into the central zone, which was the exclusive domaine of Demarestia anceps in Profile 3 . The overall prevailing species in this mixed assemblage is Himantothallus grandifolius . Below 30 m,

,

m

m

II

l”l

I””

“‘“y””

..,u

I

is\&eira mirabilis and Palmaria decipiens Dense vegetation of Desmarestia anceps Communities with dominant Himantothallus grandifolius Open communities of variable composition, mostly with Himantothallus grandifolius

F$ure

3. Map of the investigation

arca providing

it forms a denser vegetation, to which well developed specimens of Cystosphaera jacquinotii are confined. The only somewhat denser stand of Desmarestia anceps is found around 15 m behind a shallow rampart. Demarestia menziesii covers two ridges of large boulders in 11 and 13 m densely (Figure 5b), while only few individuals grow on the vertical rock face of Em Rock. Ascoseira mirabilis is not well represented on that rock either. Like Desmarestia menziesii, it rather grows in scattered stands down to about 20 m. The ample space between the large phaeophytes is colonized by a whealth of other, mostly small species. Most of them fit into groups of common distribution patterns. One group (Additional species I) includes Phaeurus antarcticus, Gymnogongrus antarcticus, Phyllophora appendiculata, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus and occupies the vertical rock face of Em Rock,particularly the parts closest to the waterline and the more exposed parts. Further down it is scarce. The next group (Additional species II) of Myriogramme manginii, Palmaria decipiens, Plocamium cartilagineum, Delesseria lanczfolia and Georgiella confluens also colonizes the ver-

the distribution

of sublittornl

assemblages

of macroalgae.

tical rock face but prefers crevices and the lower part of the rock. Contrary to the preceding group, the latter is abundant also in greater depth, disappearing not before approximately 25 m. Gigartina skottsbergii and/orSarcothaliapapillosa, Kallymenia antarctica, Pantoneura plocamioides, Hymenocladiopsis crustigena and Picconiellaplumosa form a group, which is almost absent from the rock face, but is very abundant from 11 to at lest 39 m (Additional species III). A last group (Additional species IV) neither occurs above 10 m nor below 25 m. It contains Rhodymenia subantarctica, Phycodzys austrogeorgica, Phycodrys antarctica, Myriogramme smithii and Ballia callitricha. Three other species did not fit into one of these groups: Desmarestia antarctica, Monostroma hariotii and the frond-forming diatom Parlibellus schefterae. Parlibellus schefterae was abundant on pebbles and bivalve shell fragments in sandfields with signs of erosion as well as on a barren rock shoulder emerging from the sand between 24 m and 32 m (Figure 5a). A second center of abundance existed at the foot of Em Rock (Figure 5b). Monostroma hariotii had a particular habitat on stones with some sand in the interstices.



Depth ( ) Diving profile 10 20 30 40

Percentage of coverage MR,IRIOR 'CUM

40

;y.;;

•;

:4r 3 0

Grades of coverage

Ascoselra mlrabills

b3 2 1 b

a 3 2 1

Desmarestia anceps

b, al 3{

1tAl

A

+

.

Y+

liamlimill

111

Himantothallus grandifolius

I

ii 1

f

Cystosphaera ]acquinotii

b

a

Species of the sublittoral fringe

Species of sublittoral gaps

1. b

II

a

Y YIN Gigartina skottsbergii and/or Sarcothalla papillosa

1.

3 1

Plocamlum cartilagineum

b

Pantoneura plocamioldes

Ballia callitricha

b 3 2 .1

JL

Dominance of Himantothallus grandifollus

lil Dominance of Desmarestia anceps j

Gap ;

f

Gap

Ridge Stand Vertical S with D. of ; rock with F D. men- D.an- ; ziesil ceps ; menzlesli

Figure 4. Profile 3 . The upper bar gives the diving profile, which refers to the position of the diver regardless true distances or slope inclinations ; the true depth profile is given in Figure 2 . The second bar gives types of substratum (for graphic key, please refer to Figure 6) . The other bars indicate coverage grades of species or species groups : 0 = not observed, 1 = less than 5% of the visible area covered ; 2 = between 5 and 25% of the visible area covered; 3 = 25 to 50% of the visible area covered ; 4 = 50 to 75% of the visible area covered ; 5 = 75% to 100% of the visible area covered. Species of the sublittoral fringe include Phaeurus antarcticus, Myriogramme manginii, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus . Species of sublittoral gaps include Desmarestia antarctica, Monostroma hariotii and Palmaria decipiens . Species, which have been omitted due to the minor importance and inconclusive distribution patterns, are: Hymenocladiopsis crustigena, Callophyllis spec ., Phyllophora appendiculata, Kallymenia untarctica, Georgiella confluens, Gymnogongrus antarcticus and Geminocarpus geminatus . Note gap in the dense vegetation of Desmarestia anceps above 15 m coinciding with loose substratum .



D

pth (m) Diving profile

~

O

ercentage of coverage

N

A

Bottom composition

Trades of coverage Ascoselra mkabllls

Desmarestla menziesii

1 Desmarestla anceps

I

I

II

I

Himantothallus grandifolius

u

II .

l

III

I i i A ~ Cystosphaera jacquinotli

II

I

~ I.

I Parlibellus schefterae

Monostroma hariotii

I Desmarestla antarctica

IL . .. 1W

.IIA

Additional species I

Additional species 11 i I

JUL .LL L

I

l . I

.1 . Additional species III

11 I I Additional species IV

1 .1111 w

IAL . Lu

Dominance of H. grandifollus

Heavily eroded mixed substratum

Sand barrens

Ill . I

_

11

1L .~IIr,

1111

.. . _

Open mixed communities

Figure 5a . Profile 13, seaward side of Em Rock, 39 m to 20 m . Arrangement like Figure 4 . The species groups are composed as follows :

Additional species I : Phaeurus antarcticus, Gymnogongrus antarcticus, Phyllophora appendiculata, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus ; Additional species II : Myriogramme manginii, Palmaria decipiens, Plocamium cartilagineum, Delesseria lancifolia and Georgiella confluens ; Additional species III: Gigartina skottsbergii and/or Sarcothalia papillosa ; Kallymenia antarctica; Pantoneura plocamioides, Hymenocladiopsis crustigena and Picconiella plumosa ; Additional species IV : Rhodymenia subantarctica, Phycodrys austrogeorgica, Phycodrys antarctica, Myriogramme smithii and Ballia callitricha. Species, which have been omitted due to minor importance and inconclusive distribution patterns, are : Sarcodia montagneana, Callophyllis spec . and Geminocarpus geminatus .



10

Des

fq

lest!

Himantotha

"

Additional species I

Additional species 11

Additional species Ill

Additional species IV

0 ~mixed vpmmumuvo

Recent Iceberg ~~~:1 ; scar COMM .

Abundant and H. grandifollus

Open mixed COMM .

~

~

Boulder ridges with

i

Barren stones Vertical "^ w S rock F !

D. menziesil

Figure5b- Profile 13, seaward side of Em Rock, 20 m to low tide waterline . For explanations, refer to legend to Figure 5a. Note that above 15 in both Desmarestia species are confined to large boulders or rock.

11 Desmarestia antarctica was abundant as proliferating young growth around 23 m and around 17 m, while old plants were found only above 15 m . Profile 13 (Potter Peninsula, between Em Rock and shore (Figure 6) No information is available from the back side of Em Rock itself . Otherwise, the shallows between Em Rock and the shore were covered mainly by Ascoseira mirabilis and Desmarestia menziesii, Ascoseira mirabilis being dominant in the basin formed by a subaquatic reef and the shore (Figure 6) . Of the other big phaeophytes, only a single plant of Desmarestia anceps was present. The leftover space was filled by profusive growth of Palmaria decipiens . Although less abundant, Myriogramme manginii, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus showed a similar distribution as Palmaria decipiens . In contrast, Phaeurus antarcticus was restricted to the top of the reef and to the embankment of the shore . The largest gap inside the basin was colonized by the otherwise scattered Monostroma hariotii and Adenocystis utricularis . Gymnogongrus antarcticus, Plocamium cartilagineum, Gigartina skottsbergii and/or Sarcothalia papillosa and Desmarestia antarctica occurred in all smaller gaps and were slightly more important outside the basin . Unlike the other mentioned species, however, Desmarestia antarctica was lacking on the top of the reef. Epiphytic Geminocarpus geminatus densely covered plants of Desmarestia menziesii in the central parts of the basin .

Discussion Desmarestia menziesii versus Ascoseira mirabilis Ascoseira mirabilis has been reported to grow in large quantities on exposed rocks under turbulent conditions (Neushul, 1965 ; DeLaca & Lipps, 1976 ; Lamb & Zimmerman, 1977) . In our study, however, it has been scarce in such sites . Instead, it dominated in flat rock platforms and weakly inclined cobble and shingle beaches (Figure 3, Figure 6), together with Palmaria decipiens, which is discussed below. It is surely important, in which manner turbulence acts : the steady movements of surge waves rolling to the beach may be tolerated by Ascoseira mirabilis and Palmaria decipiens, while the unpredictable move-

ments of breakers battering against steep rock faces may not . Under the latter conditions, Desmarestia menziesii appears to be more successful . Potentially, the perennials Ascoseira mirabilis and Desmarestia menziesii may closely approach the low tide waterline, but this is realized only in parts of the shore, which are exceptionally well protected against winterly ice floes (Figure 6) . Desmarestia anceps versus Desmarestia menziesii In contrast to the circumantarctic Desmarestia menziesii, the geographical distribution of Desmarestia anceps seems to be restricted to the South Orkney Islands, the South Shetland Islands, and the northern part of the Antarctic Peninsula (Skottsberg, 1907 ; Papenfuss, 1964 ; Moe & DeLaca, 1976 ; Lamb & Zimmerman, 1977) . Its general depth range extends to greater depth than the one of Desmarestia menziesii (Delepine, 1966 ; Furmanczyk & Zielinski, 1982 ; Zielinski, 1990) . Unfortunately, in most earlier zonation studies from this area, Desmarestia anceps was lumped with Desmarestia menziesii or confused with other species (Skottsberg, 1941 ; Neushul, 1965 ; Richardson, 1979 ; Amsler et al ., 1990 ; Chung, 1994 ; Kloser et al ., 1994a ; Amsler et al ., 1995) . At its southern distributional limit, Desmarestia anceps only forms mixed stands with Desmarestia menziesii below an upper zone purely dominated by the latter species (Melchior Island : Delepine, 1966 ; Arthur Harbor : DeLaca & Lipps, 1976) . Also at the northern distributional limit at Signy Island, both species were mixed, with Desmarestia anceps prevailing in a deeper zone than Desmarestia menziesii (Brouwer et al ., 1995) . In our study area at the centre of the geographical distribution of Desmarestia anceps, the two species clearly occupy distinct habitats (Table 2) . It was already stated, that Desmarestia anceps and/or Desmarestia menziesii outcompete all other species under conditions optimal for seaweeds, i .e . stable substrate, sheltered from ice, ample light, moderate to low turbulence (Kloser et al ., 1994a) . Profile 3 demonstrates clearly (Figure 4), that the less exposed central sublittoral is the almost exclusive domaine of Desmarestia anceps . Desmarestia menziesii, which occupies the complete upper and central sublittoral in other regions of the Antarctic, is confined to severely wave-exposed rock faces in our study area (Figure 4) . The competitive dominance in optimal conditions of Desmarestia anceps is further confirmed by the fact, that the other big phaeophytes readily enter the central sublittoral



12 Depth (m) Divln prof lie A 30

Bottom type : rock ® Boulders > im diameter Boulders 50 -100cm diameter Stones 20 - 50cm diameter ® Pebbles 5-20cm diameter ® Gravel 2-5cm diameter Gravel < 2cm diameter Sand ® Fragmented empty clam shells (Laternula ellipticaKing at Broderip 1831)

Bottom com osition

M Solid

Desmarestla 3 Z ,

A

11~lili 1 ~ .~1~~ ICI ~l u

k11inl

111I-

Desmarestla anceps z

I

S.

Phaeurus antarct/cus

Adenocystis utricularls and Monostroma harlot!! 5

;:1.1 I I : S Scattered species , 9

1111,

I .I- . .

l

I J . . I

U! 1 1

arvaurarva:la 8n}arCtlca

Il 111

~ 1 1 1 I IIW

S.

Z

Geminocarpus geminatus

I ∎ Outward R slope T

II 1IIi l1 1

Dominance of Ascoseira mlrabilis

S F

Gap Gap Figure 6. Profile 13, inshore of Em Rock. Arrangement like Figure 4. Species of the same group as Palmaria decipiens are: Myriogramme manginii, Curdiea racovitzae and Iridaea cordata and/or Notophycus fimbriatus: Scattered species are: Gymnogongrus antarcticus; Plocamium cartilagineum and Gigartina skottsbergii and/or Sarcothalia papillosa . Species, which have been omitted due to minor importance and inconclusive distribution patterns, are : Elachista antarctica, Phyllophora appendiculata, Kallymenia antarctica, Sarcodia montagneana, Georgiella confluens, Delesseria lancifolia and Ballia callitricha. Note that no ice-abraded sublittoral fringe is present due to protection of this part of the shore against ice by numerous rock islets (compare with Figure 1).

of Profile 13, where Desmarestia anceps is reduced (Figure 5) . As these two species of Desmarestia are similar in size and morphology, it is not easy to explain, why Desmarestia anceps is able to outcompete Desmarestia menziesii . A possible explanation may be the selec-

Live feeding of the fish Notothenia neglecta Nybelin 1951, which is abundant in the Desmarestia stands (Richardson, 1975 ; Zukowski, 1980 ; Barrera-Oro & Caseaux, 1990 ; Caseaux et al ., 1990) . It was found, that this fish feeds preferentially on Desmarestia menziesii, but seems to avoid Desmarestia anceps (Iken,



13 Table 2. Schematic presentation of dominating seaweeds in different combinations of substratum, slope inclination and turbulence . Modification by ice impact is neglected. The scheme is valid in the upper and central sublittoral Turbulence calm

moderate

strong

Himantothallus grandifolius

Himantothallus

Desmarestia

grandifolius

menziesii

Sloping

Desmarestia anceps

Desmarestia anceps

Desmarestia menziesii

Horizontal

Desmarestia anceps

Desmarestia

Ascoseira

anceps

mirabilis

Inclination

a) Rock and boulders Vertical

b) Pebbles and gravel Sloping

Desmarestia anceps

Himantothallus grandifolius

none

Horizontal

Desmarestia

Himantothallus

none

anceps

grandifolius

1995) . The dominance of Desmarestia menziesii on wave-exposed rock may then be considered as being partially the result of a higher turbulence resistence of this species compared to Desmarestia anceps, but also partially of reduced grazing, as Notothenia neglecta prefers sheltered sites . Desmarestia species versus Himantothallus grandifolius In Profile 3, Desmarestia anceps gives way to Himantothallus grandifolius in a depth of 18 m (Figure 4), where ambient light exceeds about 4 times the minimum light requirement of Desmarestia anceps during its main growth period (Kloser et al ., 1993 ; Wiencke et al ., 1993 ; Kloser et al ., 1994a) . Accordingly, light limitation alone is unlikely as an explanation for this replacement . This is confirmed by the scattered occurrence of Desmarestia anceps below 25 m (Figure 4) and similar general depth ranges of the two species (Zielinski, 1990) . This is difficult to explain, if not again selective herbivory is assumed to be a crucial factor. As losses by grazing have to be replenished by growth, this factor should be increasingly important with greater depth, where reduced light availability slows down algal growth . Himantothallus grandifolius so far was never reported to be consumed

(Reichard & Dieckmann, 1985 ; Iken, 1994, 1995) . In contrast, Desmarestia species are readily taken by a variety of animals (Richardson, 1975 ; DeLaca & Lipps, 1976 ; Brand, 1980 ; Iken, 1994, 1995) and particularly seem to constitute a major portion of the food of the sea urchin Sterechinus neumayeri (Meissner, 1900) Mortensen, 1903 (Brand, 1980) . On a dive outside of our proper investigation area at Ardley Island, inner Maxwell Bay, we found a sheltered, weakly inclined slope of solid rock in approximately 5 m depth, which would be a perfect substrate for Desmarestia anceps ; but was completely devoid of this species . Instead, some individuals of Himantothallus grandifolius and extraordinarily great numbers of sea urchins were found (Kloser, unpublished) . Unfortunately we cannot exclude, that this is just a coincidence, as the two species of Desmarestia have not been differentiated in the study of Brand . Thus it must remain open at present, whether Sterechinus neumayeri really reduces Desmarestia anceps . Neither we do know how important such assumed selective grazing pressure may be in quantitative terms . Attempts have been made to explain the prevalence of Desmarestia species versus Himantothallus grandifolius with specific substratum affinities, attributing Desmarestia species to solid substratum, and Himantothallus grandifolius to smaller grained substrata (Richardson, 1979 ; Kloser et al ., 1994a ; Brouwer et al ., 1995) . However, settling algal propagules cannot distinguish between substratum types and establish themselves on any available space . Thus, specific substratum affinities must result from additional modifying factors like turbulence : above 15 m, the bushy Desmarestia anceps cannot persist on loose substrata (Figure 4, Figure 5), because it would not be sufficiently anchored during storms, while Himantothallus grandifolius may remain (Kloser et al ., 1994a ; Profile 6 and 7 of this study), possibly due to lesser drag on its smooth, ribbon-like thalli . At greater depth, Desmarestia anceps is able to persist on stones of smaller dimensions in both profiles (Figure 4, Figure 5) . Obviously, this deeper part is only occasionally subject to strong turbulence, as indicated by the presence of Cystosphaera jacquinotii (Figure 4) . Having gas-filled bladders, Cystosphaera jacquinotii is the only large seaweed of the region, which is growing upright . Thus this species is extremely sensible to strong water movements (Neushul, 1965 ; Lamb & Zimmerman, 1977 ; Zielinski, 1981 ; own observations) .

14 Furthermore, steep to vertical rock faces with dominant Himantothallus grandifolius were observed in the central sublittoral (Neushul, 1965 ; Chung et al ., 1994 ; this study : vertical rock face in Profile 2, Figure 1, Table 2) . A possible explanation might be that in vertical arrangement the bushy plants of Desmarestia self-shade too much, while the hanging curtains of Himantothallus grandifolius do not . Vertical rock faces in the upper sublittoral, however, are the domaine of Desmarestia menziesii (Figure 4, Figure 5, Table 2) which may escape self-shading effects because the bushy thalli constantly move back and forth with the waves . Consequently, the suggested affinity of Himantothallus grandifolius to loose substrata may be an impression, which primarily results from the fact that solid rock is rarely available in the deep sublittoral, to which Himantothallus grandifolius usually is confined by interspecific competion on well-vegetated slopes . Equally, a suggested sensibility of Himantothallus grandifolius to turbulence (DeLaca & Lipps, 1976 ; Moe & DeLaca, 1976 ; Dayton, 1990) may be feigned by interspecific competition : at exposed outlying sites, turbulence as well as light reach deeper than in inshore localities, causing the belt of Desmarestia anceps to shift to greater depth, where Himantothallus grandifolius then is ousted, while Desmarestia menziesii occupies the additional turbulence-influenced space on the usually steep rocks . In localities with weakly inclined slopes, however, Himantothallus grandifolius may well appear in the uppermost meters (McCain & Stout, 1969 ; Arnaud, 1974 ; Zamorano, 1983 ; Picken, 1985 ; Kl6ser et al ., 1994a; Brouwer et al ., 1995) and even in tidepools (Moe, 1980) . Modifications due to ice impact The main agent creating open space in the otherwise dense seaweed vegetation is ice, with ice floes and icebergs acting in different ways . Unlike High Antarctic conditions (Dayton et al ., 1970 ; Gruzov, 1977 ; Dayton, 1989), the effect of anchor ice is negligible in the Antarctic Peninsula region (DeLaca & Lipps, 1976 ; Richardson, 1979 ; Rauschert, 1984) . Drifting sheets of sea ice tend to ride up the beach, if they are pressed against a shore with little inclination (Kovacs & Sodhi, 1980), harming only the sublittoral fringe of a few meters depth . At steeply inclined obstacles like rock islets or promontories, they will be pushed up . Without support by a shallow bottom, the weight of the accumulated ice will press a great

portion under water, as is similarly the case in freely floating pressure ridges (Kovacs & Sodhi, 1980) . By this process, a much more extended zone than on less inclined shores will be abraded . This explains, why Desmarestia menziesii may completely cover protruding rock ledges and ridges, which do not reach the water surface, but is strongly reduced on sublittoral slopes of surfacing cliffs (Figure 4, Figure 5b) . The smaller species found in the sublittoral fringe and the upper, denuded sublittoral coincide with those recorded by other authors (Neushul, 1965 ; Castellanos, 1973 ; DeLaca & Lipps, 1976 ; Zamorano, 1983 ; Chung et al ., 1994) . These species are not uniform ecologically, but clearly belong to two species groups (see below) . Grounding icebergs, on contrast, may touch the bottom down to a depth of several hundred meters and rather influence weakly inclined slopes than steep ones (Belderson et al ., 1973 ; Heine, 1989) . On steep slopes, the iceberg may only touch the bottom with a corner, tearing open limited gaps like the one present at 25 m in the dense vegetation of Profile 3 (Figure 4) . On weakly inclined slopes, they can firmly run aground with the whole underside resting on the bottom . By melting and/or fragmenting, the iceberg becomes smaller and usually is pushed higher up by the waves, thus scouring the whole depth range up to the shore (Neushul, 1965 ; Klaser et al ., I994a) . As a consequence, the central belt of Desmarestia anceps is largely suppressed in Profile 13 (Figure 5) . Direct observations have shown that Himantothallus grandifolius is able to withstand this impact better by its potential to inhabit loose substrata (Klaser et al ., 1994a) . However, since Desmarestia anceps may equally occur on such substrata in the deeper sublittoral (Figure 4, Figure 5), this is not sufficient to explain why Himantothallus grandifolius becomes prevailing now. Perhaps, the much branched, bushy thalli of Desmarestia anceps get easily entangled in projections of the icebergs and are dragged away, while the smooth ribbons of Himantothallus grandifolius slip off. The habitats of additional species Parlibellus schefterae, a diatom of macroalgal growth habit (Lobban, 1986), and Monostroma hariotii colonize the most severely denuded parts of Profile 13 (Figure 5) . Their role may be interpreted as that of pioneers substituting proper macroalgae in disturbed habitats, being replaced by these species in the course of recolonization .

15 The other small species predominantly occur on open spaces among the scattered large phaeophytes and in the sublittoral fringe . Additional species I (Figure 5) represent species particularly tolerant to the harsh conditions of the sublittoral fringe and are largely restricted to the shallower sublittoral . Additional species II (Figure 5) are more sensitive, dwelling in crevices in the sublittoral fringe, but are abundant in open sites down to about 25 m . Additional species III avoid completely shallow parts on the outward side of Em-Rock, but go down at least to 39 m (Figure 5) . Gigartina skottsbergii and/or Sarcothalia papillosa, however, also grow in the shallower sublittoral inshore of Em Rock and in Profile 3 (Figure 4, Figure 6), which are more sheltered . Apparently, the three groups mirror an increasing degree of sensibility to turbulence . In Profile 3 (Figure 4), this differentiation is not resolvable due to the strong preponderance of the large phaeophytes . Additional species IV were restricted to a depth range which in more protected parts of the coast would completely be overgrown by Desmarestia anceps . Except Ballia callitricha, these species were rare in other profiles than Profile 13 and 14, and Myriogramme smithii did not occur in other profiles at all (Table 1) . This may indicate, that these species are dependent from stable microhabitats in a generally unstable environment of frequent mechanical disturbance, which continuously keeps away the large phaeophytes .

Conclusions Four principal zones instead of the classical three ones (ice-abraded sublittoral fringe, Desmarestia zone and Himantothallus zone) are present in the study area : a sublittoral fringe, an upper sublittoral with Desmarestia menziesii and Ascoseira mirabilis under strong turbulence, a central sublittoral with Desmarestia anceps under moderate turbulence, and a calm deeper sublittoral with Himantothallus grandifolius . This zonation is strongly modified by the impact of grounding icebergs . Especially the belt of Desmarestia anceps is suppressed in the central sublittoral of Potter Peninsula and replaced by a unique mixed assemblage of macroalgae with prevailing Himantothallus grandifolius. Although similar observations have been made earlier, not much attention was payed to these records . We believe that our present understanding of Antarctic macroalgal zonation patterns is biased towards sheltered conditions : work had to be done where facilities allowed, and Antarctic bases, for obvious reasons,

are established preferably in well protected bays and fjords .

Acknowledgements We gratefully acknowledge help and friendship of all our scientific and non-scientific companions in the field during three seasons on the base "Jubany" . Equally, we thank the logistic personal in the Instituto Antarctico Argentino, in the Alfred Wegener Institute, and on board "Polarstern" and "Almirante Irizar" . They provided excellent support during the preparational phase of the expeditions and en route to our Antarctic destination, respectively . Special thanks go to the Netherlands Institute of Ecology (Yerseke, Netherlands) which helped with a position for the first author during a critical phase of the project . References Amsler, C . D ., D. R . Laur, L. B . Quetin, R . J . Rowley, R . M. Ross & M. Neushul, 1990. Quantitative analysis of the vertical distribution of overstory macroalgae near Anvers Island, Antarctica. Antarct. J . US 25 : 201-203 . Amsler, C. D ., R . J . Rowley, D. R. Laur, L . B . Quetin & R . M . Ross, 1995 . Vertical distribution of Antarctic peninsular macroalgae : cover, biomass and species composition . Phycologia 34 : 424430 . Arnaud, P. M., 1974 . Contribution a la bionomie marine benthique des regions Antarctiques et Subantarctiques. Tethys 6: 465-653. Barrera-Oro, E . R . & R. J . Casaux, 1990. Feeding selectivity in Notothenia neglecta Nybelin, from Potter Cove, South Shetland Islands, Antarctica . Antarct. Sci . 2 : 207-213 . Belderson, R . H ., N. H . Kenyon & J . B . Wilson, 1973 . Iceberg plough marks in the northeastern Atlantic . Paleogeography, Palaeoclimatology, Palaeoecology 13 : 215-224. Bellisio, N. B ., R . B . Lopez & A . P. Tomo, 1972 . Distribucidn vertical de la fauna bentdnicaen tres localidades Antarticas : Bahia Esperanza, Isla Petermann y Archipielago Melchior. Contr. Inst. Antart . Arg. 142: 1-87. Brand, T. E ., 1980 . Trophic interactions and community ecology of the shallow marine benthos along the Antarctic Peninsula . Ph.D . thesis . Univ. Davis, California . Brouwer, P. E . M ., E . F. M . Geilen, N. J. M. Gremmen & F. van Lent, 1995. Biomass, cover and zonation pattern of sublittoral macroalgae at Signy Island, South Orkney Islands, Antarctica . Bot. Mar. 38 : 259-270 . Casaux, R. J ., A . Mazotta & E. R . Barrera-Oro, 1990. Seasonal aspects of the biology and diet of nearshore notothenioid fish at Potter Cove, South Shetland Islands, Antarctica . Polar Biol. 11 : 63-72 . Castellanos, Z. J. A ., 1973 . Estratificacion del complejo bentonico de invertebrados en Puerto Paraiso (Antartida) . Contr. Inst. Antart. Arg . 164 : 1-30. Chung, H ., Y. S . Oh, I. K. Lee & D. Y. Kim, 1994. Macroalgal vegetation of Maxwell Bay in King George Island, Antarctica . Korean J . Phycol . 9 : 47-58 .

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Zielinski, K ., 1990 . Bottom macroalgae of the Admiralty Bay (King George Island, Antarctica) . Pol . Polar Res . 11 : 95-131 . Zukowski, C., 1980 . Catches of fishes of the genus Notothenia and Trematomus at Admiralty Bay (King George Island, South Shetland Islands) in the winter-spring season, 1977 . Pol. Polar Res . 1 :163-167 .