Benthic Macroalgae of Shark Bay, Western Australia · Benthic Macroalgae of Shark Bay, Western Australia G. A. Kendrick, J. M. Huisman* and D. I. Walker Botany Department, The University

Kendrick et al.: Shark Bay Algae 47

Botanica MarinaVol. 33, pp. 47-54, 1990

Benthic Macroalgae of Shark Bay, Western Australia

G. A. Kendrick, J. M. Huisman* and D. I. Walker

Botany Department, The University of Western Australia, Nedlands, 6009, Western Australia

* School of Biological and Environmental Sciences, Murdoch University, Murdoch, 6150, Western Australia

(Accepted 14 July 1989)

Abstract

One hundred and sixty one taxa of benthic macro-algae are reported from Shark Bay, Western Australia,growing either on subtidal rock platforms, on the extensive sandflats that dominate the bay, or as epiphyteson seagrasses and other algae. In addition many species survive as drift algae amongst the seagrass beds.Tropical taxa predominate. The Rhodophyta are represented by the greatest number of taxa, but these tendto be inconspicuous epiphytes. Members of the Chlorophyta are the most conspicuous in most areas, withPenicillus nodulosus and Polyphysa peniculus the most common species. Polyphysa peniculus dominates thehigh salinity areas south of the Faure Sill. The brown algae Hormophysa cuneiformis and Dictyota furcellatawere also common in high salinity areas. Benthic algal species richness was lower in areas of high salinity.

Introduction

Shark Bay, Western Australia, is a shallow sedimen-tary environment dominated by seagrass meadows[predominantly Amphibolis antarctica (Labill.) Sonderex Aschers.] which cover up to 30% of its subtidalsurface area (Walker et al. 1988). These extensivemeadows have formed shoals (Davies 1970) whichresult in restricted oceanic exchange. High evapora-tion and low precipitation in the area (Logan andCebulski 1970) result in a salinity gradient from 35%oin the northern reaches of Shark Bay to 70%o in theinner southern sections (Logan and Cebulski 1970,Smith and Atkinson 1983). The high salinities re-corded in the inner reaches of Shark Bay have pre-viously been found to be negatively correlated withproductivity of seagrass (Walker 1985), species rich-ness and community structure of macroalgal epirphytes (Kendrick et al. 1988) and percent cover,growth and development of encrusting epiphytic Cor-allinaceae (Harlin et al 1985).

The seagrass meadows host a large number of speciesof epiphytic algae (Harlin et al. 1985, Kendrick et al1988) which numerically dominate the algal flora of

the area. However, benthic macro-algae can also befound growing on occasional subtidal rock (lime-stone-sandstone) platforms and extensive sandflatswhich occur throughout the bay, and as drift withinseagrass meadows. This paper lists the benthic macro-algae collected from a variety of localities and habitatswithin Shark Bay, and concludes the series describingthe subtidal flora of the area (Harlin et al. 1985,Walker et al 1988, Kendrick et al 1988).

Material and Methods

Surveys throughout Shark Bay (26°S, 114Έ) weremade using SCUBA and snorkel during March, June,August, October and December 1982, August 1985,February and May 1986 and August 1988. Benthicalgae were sampled from the eleven locations shownin Figure 1. The distribution of benthic algae withinShark Bay is based on these locations only. Locations2, 6, 7, 8 and 9 (islands) were sampled during August1982. Transects were laid out perpendicular to theshore on rock substratum and species presence sam-

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and exposure were recorded. Voucher specimens ofall taxa collected were deposited in the herbaria atMurdoch University and The University of WesternAustralia.

Drift algae were observed throughout the bay andstudied in detail at Monkey Mia during June, Augustand October 1982. Biomass of dominant species ofdrift algae in subtidal seagrass communities was de-termined from 12 quadrats, each 0.1225 m2, sampledwithin seagrass beds.

Results

One hundred and sixty one taxa of algae are reportedfrom Shark Bay (Table I), including 30 taxa of Chlo-rophyta, 24 taxa of Phaeophyta and 107 taxa ofRhodophyta. The distribution of benthic algae deter-mined from the sampling locations shown in Figure

260 s l indicated that species richness decreased with in-creases in salinity within Shark Bay (Table I).

Collections of epiphytes were made on the pneuma-tophores of the mangrove Avicennia marina during1986. Ulvaria oxysperma, Caloglossa leprieurii, Spyr-idia filamentosa, Bostrichia moritziana, B. radicansand B. tenella ssp. flagellifera were identified fromthese collections.

Fig. 1. Map of Shark Bay, W. A. showing sampling locationsand haloclines (in %o): 1-South Passage; 2-Egg Island; 3-SandyPoint; 4-Monkey Mia; 5-Herald Bight; 6-Charlie Island; 7-Double Island; 8-White Island; 9-Salutation Island; 10-Glad-stone Inlet; 11-Hamelin Pool.

Five species dominated the drift algal flora: Laurenciamajuscula, Laurencia filiformis, Vidalia spiralis, Di-genia simplex and Eucheuma speciosum. Distributionof drift algae was patchy. Mean biomass (+ standarddeviation) was 152.5 (± 248.5) and 223 (± 357) g dryweight m~2 in Amphibolis antarctica and Posidoniaaustralis beds respectively.

pled at intervals of 0.5m with 0.1255m2 quadrats.Locations 4, 5, 10 and 11 were sampled during 1982,1985 and 1988 both quantitatively using haphazardlyplaced 0.1225m2 quadrats and with qualitative sur-veys. Locations 1 and 3 were surveyed during 1988.Because of the variety of sampling techniques em-ployed locations were grouped into geographical re-gions representing regions with different salinity re-gimes. Some taxa were not present at any of the elevenlocations sampled intensively, but nonetheless wererecorded from Shark Bay and therefore are includedin the species list. All samples of algae were preservedin 6% formalin in seawater, salinity was measured atevery survey location and observations on substra-tum, depth, current regime, depositional environment

Discussion

The benthic algae of Shark Bay were not predomi-nantly temperate as was the case with the seagrasses(Walker et al 1988) and seagrass epiphytes (Kendricket al. 1988). The majority of taxa are either of tropical(e.g. Digenia simplex, Galaxaura rugosa, Portieriahornemannioides, Dictyopteris plagiogramma, all Cau-lerpa spp. and Halimeda spp.) or cosmopolitan dis-tributions (e. g. Enteromorpha intestinalis, Solieria ro-busta, Anotrichium tenue). Certain species previouslythought to be restricted to the south-west of WesternAustralia are also present (e.g. Cryptonemia kally-menioides) but their apparent localized distributionprior to the present survey was no doubt due to thelack of collections from north-western Australia.

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Eighty of the taxa of algae found in Shark Bay wereepiphytic on the seagrass Amphibolis antarctica. Ofthese, over half (43 Taxa) have been reported both asepiphytes and as benthic algae. Ballantine and Humm(1975) and May et al (1978) noted that epiphytecommunities on seagrasses can include organismswhich also occur on hard substratum but are foundas epiphytes when available substratum is a limitedresource. Thirty seven taxa were only found as epi-phytes, 36 being Rhodophyta.Algal distributions within the bay appear to corre-spond to a combination of salinity tolerance andsubstratum availability. Within the hypersaline areasouth of Faure Sill, Polyphysa peniculus is the domi-nant species, forming 'collars' around the stromato-lites in Hamelin Pool. Hormophysa cuneiformis andDictyota furcellata are also regularly present, but theother species recorded (Caulerpa lentillifera, Agla-othamnion cordalum, Crouania capricornica) occurredsporadically, and are probably at the extremities oftheir range. The low species richness in high salinityareas would seem to implicate salinity as a limitingfactor. High salinities in Shark Bay have also beencorrelated with decreases in above-ground productiv-ity of Amphibolis antarctica (Walker 1985), slow ratesof growth and development of epiphytic crustose cor-alline algae (Harlin et al. 1985), and decreases inspecies richness of epiphytic algal communities onstems of A. antarctica (Kendrick et al. 1988). Whilesalinity is a measure of total salts (grams of salts perkilogram of solution), it also describes biologicallysignificant aspects of the physics and chemistry ofwater including total osmo-concentration (osmoticpressure), ion composition and density of water. Highsalinities have been shown to decrease growth (Munnset al. 1983), photosynthesis (Gordon et al. 1980, Lehn-berg 1978) and respiration rates (Lehnberg 1978).More research as to the cause of the patterns indistribution and growth of the primary producers inrelation to salinity within Shark Bay is needed.

Sustratum availability also plays a role in benthicalgal distribution within Shark Bay. 'Hard ground',a diagenic feature of hypersaline basins, is commonin the more saline areas of the Faure Sill and HamelinPool (Logan and Cubulski 1970), but did not supportany benthic algae. On the seaward side of Faure Sill,where salinities are comparatively lower, algal speciesrichness increases. Some of these areas are dominatedby sandy substrata and where they are not colonizedby seagrasses, sand colonising algae (rhizobenthos),most comniorily Penicillus nodulosus, dominate. Lo-calised rocky outcrops are restricted in area withinShark Bay. Intertidal and subtidal outcrops of thePeron sandstone occur in the channel off Monkey

Mia, along Dirk Hartog Island and in the FreycinetEstuary. These areas support a diverse array of algae,suggesting that sustratum availability, rather than sal-inity, limits benthic algal distributions within SharkBay. The most oceanic sampling locations, SouthPassage, Egg Island and Sandy Point, have a tropicalflora, dominated by taxa such as Galaxaura rugosa,Asparagopsis taxiformis, Laurencia spp"., Lobophoravariegata, and Hydroclathrus clathratus.Drift algae also play an important role as primaryproducers within seagrass beds. Virnstein and Car-bonara (1985) found drift algal biomass to be greaterthan 3 times that of above ground biomass of sea-grasses in the Indian River lagoon, Florida. They alsofound drift algae to be more important locally interms of habitat, nutrient dynamics and primary pro-duction than the seagrasses. In Shark Bay, drift algaewere abundant but patchy within seagrass beds. Driftalgal biomass was only 34% and 26% of the meanabove ground biomass of Amphibolis antarctica andPosidonia australis respectively (Walker and McComb1988). All the drift algae collected were also found asepiphytes.Although seagrasses are the most visually dominantorganisms found in Shark Bay (Walker et al. 1988),macroalgae are a significant component within thesystem, occurring as epiphytes, drift algae associatedwith the seagrasses, occupying relatively rare rockysubstrata or as rhizobenthos. These macroalgae showtropical biogeographical affinities and their local dis-tribution within Shark Bay is correlated with salinity.However, the roles that these algae play, their contri-bution to production and nutrient cycling, and thefactors controlling their distributions require furtherinvestigation.

Acknowledgements

This paper presents work carried out as part of TheUniversity of Western Australia Shark Bay Program(supported by the University Development Fund), theCommonwealth of Australia Marine Science andTechnology Grant Scheme, and the French Bicenten-ary Shark Bay program. Thanks are expressed toSeaton Korner, Master, R/V Uniwest; Wilf and HazelMason, Monkey Mia Caravan Park; and C. Patulloand the captains and crews of the M/V 'Cape Don'.We also wish to thank Dr R. King for allowing us toinclude species growing on the pneumatophores ofmangroves which he identified. Gary Kendrick andDi Walker would like to thank Assoc. Professor Ar-thur J. McComb for his guidance. John Huismangratefully acknowledges the enthusiasm and supportof Dr M. Borowitzka and the A. R. C. for financialsupport.



54 Kendrick et al:. Shark Bay Algae

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Anclote Estuary: Epiphytes on seagrass leaves. Florida Sei.38: 144-149.

Davies, G. R. 1970. Carbonate bank sedimentation, easternShark Bay, Western Australia. Am. Assoc. Petr. Geol. Mem.75:85-168.

Gordon, D. M., P. B. Birch and A. J. McComb. 1980. Theeffect to light, temperature and salinity on photosyntheticrates of an estuarine Cladophora. Bot. Mar. 23: 749—755.

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Documents

Benthic Macroalgae of Shark Bay, Western Australia · Benthic Macroalgae of Shark Bay, Western Australia G. A. Kendrick, J. M. Huisman* and D. I. Walker Botany Department, The University