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A subtidal transect in Jervis Bay, New South Wales

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A subtidal transect in Jervis Bay, New South Wales
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   ustralian Journal  o Ecology  1981) 6,439-457   subtidal transect in Jervis Bay, New South Wales VALERIE MAY National  Herbarium of New South Wales, Royal Botanic  Gardens, Sydney,  Australia 2000 A. W. D. LARKUM School of  Biological  Sciences,  Macleay  Building, University  of Sydney,  Australia 2006  bstract Long-term  variations  in the  intertidal algal flora of  the  entire rock platform at  Plantation  Point,Jervis Bay, are described by May 1981). Thestudy now reported presents similar long-termchanges in the flora of a subtidal  region  of the same  headland observed within  the same period of time.This first  detailed report  of  subtidal macroalgal communities in New South Wales describes a several year  study of the benthic communities along a transect in the  upper  sublittoral region  of a rocky headland  at  Plantation  Point Jervis  Bay. Eighty nine species  of  algae were  recorded fiveof which were previously unrecorded for NewSouth Wales.The area studied is dominated by the largebrown algae  Ecklonia radiata  and  Phyllosporacomosa,  large areas of which were cleared periodically  by storms.  Turf shade and  crustosecoralline algal communities also were  present. Storms, seasonal variation and longer termchanges all affected the abundance and distri-bution of the algal species growing along the transect  and  hence  the  floristic composition  ofthearea.  ntroduction Changes in the intertidal algal flora of the entirerock platform at Plantation Point, Jervis Bay,are described by May (1981). It was consideredthat additional information on changes in theflora of a subtidal region of the same headland,observed within the same period, could yieldvaluable additional information. Hence serialobservations were begun concurrently on anunderwater transect. The transect was chosen,on practical grounds, to include a variety ofcommunities and to exhibit gradual changes insuch factors as slope, depth, light, exposure towave action and kind of substrate. It was also inthe general region of  a  planned sewer outfall.This paper  gives  the results of  a  study of part  of the benthic algal flora of Jervis Bay and presentsthe first report for New South Wales of a whollysubtidal transect. The only other work publishedon subtidal communities of Australia is that ofShepherd & Womersley (1970, 1971, 1976)which relates solely to South Australia.The present work was begun in September1974 as part of a systematic survey of theintertidal and subtidal algae of Plantation Point,Jervis Bay, in response to plans to site a seweroutfall there. The outfall was placed in closeproximity to the study site in August 1976, 23months after the beginning of the study.Sampling continued until 1979. The presentpaper deals entirely with the subtidal algae. Theintertidal algae, including a separate study ofthose occurring near the sewerage outfall, arethe subject of separate communications. Location Plantation Point (35°04' S, 150°42' E) is asiltstone (shale) headland within Jervis Bay,which lies on the warm temperate east coast ofAustralia. The characteristics of this bay havebeen discussed previously (May, Collins & 0307-692X/81/120O-O439 02.00 © 1981 Blackwell Scientific Publications  440  alerie  May and  A W D Larkum Collett 1978). The Point is exposed to a certainamount of  w ve  action, but this  is  much less thanon the adjacent open ocean coast.A transect was located near the eastern tip ofPlantation Point and ran seaward in a southerlydirection for some 50 m Fig. 1). Seven samplingstations A-G) were marked along this transectand were chosen so that they would include themajor vegetational and topographic zones alongthe transect. Station A was at an angle to the RockplatformPlantationpoint   Km \noi23 Verticalprofile oftransectockplatform 4 3 2 m I I I I I Shallowsubmergedrocks 1 2 m L  I I Submergedrocky outcrop FIG. 1. Details ofthe transect site.a. Map of Plantation Point and the rock platform showing Transect region and sewerage outlet marked X). b.  Mapof JervisBay.c. Map of the transect area.d. Profile of transect.  Subtidal  transect in Jervis  Bay  441other transect stations and was a gully con-necting directly to the site of the sewer outfall.The sampling region was approximately 10 mwide.  ethods Collecting was carried out by SCUBA diving.Samples of representative algae were collectedby hand and placed in plastic  bags.  Small chips  of rock were also taken for identification of smalleralgae. To avoid disturbance to the vegetation ofthe stations, collecting was carried out over awide but prescribed area, which was chosenaccording to the size and characteristics of eachstation. It is considered that sampling by thistechnique had a negligible effect on the flora,especially in comparison with the effects ofstorms and seasonal changes. The algae wereidentified in the laboratory by one of  us  V.M.).The study area was first investigated in June1973 and on several subsequent occasions, butcollecting along the transect did not begin untilSeptember 1974. Collections were made on 24separate occasions from 1974 to 1979 see Table 4a).  The collection of April 1975 was lost andonly a photographic record of forty colouredslides remained so that the list of speciescompiled from the photographs for that date islikely to be incomplete, particularly for smallerspecies. However both this with twenty species)and the next collection in July, in which twenty-nine species were recorded, followed closelyupon storms which denuded many rock surfacesin the transect area of their algae. Forcomparison with other collections see Table 4a.  esults General description  of  the algal  communities of the area The sublittoral algal communities of PlantationPoint have been described briefly by Larkum  1973).  During the period of the present studyboth  Ecklonia  radiata  and  Phyllospora comosa occurred, sometimes intermixed, on rock sur-faces around the Point. However, in theshallower region west of the Point where theexposed rock platform grades into a shallowlyshelving bottom of shale, sand and shells thesetwo algae were replaced by smaller brown algae such as  Sargassum  spp. and  Caulocystiscephalornithos and many turf algae;  aulerpa cactoides  also occurred frequently there. In thedeeper water  1-3  m) of  this  area there were bedsof the seagrass  Posidonia  australis  growing insand. However, these beds did not occur on thesouthern side of the Point.On the southern side ofthe Point the  Ecklonia radiata  and  Fhyllospora comosa  were patchilydistributed. They were interspersed with com-munities of crustose coralline algae, turf algaeand, on overhanging rocks, of shade algae andsponges.The transect site crossed algal communitiesrepresentative of those found in the sublittoralregion on the eastern and southern sides of therock platform. Algae found  in transect Eighty-nine species of algae were found duringthis study see Appendix).Five species of algae in the study have notpreviously been recorded for New South Walesalthough they are known for adjoining states.These species are as follows: 1)  Cladophora feredayi  Harv., known fromVictoria Womersley 1956). 2)  Glossophora nigricans  J. Ag.) Wom.,known from Victoria Womersley 1967). 3)  Lophosiphonia prostrata  Harv.) Falk.,known from Queensland Cribb 1956). Asrecorded previously, this prostrate speciesoccurred epiphytic on members of theZonarieae, here mostly on  Lobophora  variegata and  Zonaria turneriana.  4)  Lophosiphonia reptabunda  Suhr) Cribb,previously known from Queensland Cribb 1956).  5)  Stypopodium zonale  Lamour.) Pap.,reported from Queensland Bailey 1912).Specimens of these and other species of algaerecorded from Plantation Point, including thetransect, are stored at the National Herbarium ofNew South Wales, Royal Botanic Gardens,Sydney NSW).Table 2 lists the occurrences and distributionof the species which were common  in  the transectduring this study and Table 6 gives similarinformation for the rare species.  442  Valerie  May and A. W. D. Larkum FIG. 2. Photo of Station   showing uniform turf flora. Stations of  transect The flora of the gully Station A) was veryheterogeneous, often with mixed  Eckloniaradiata  and  hyllospora comosa  on the sides and E. radiata  and turf algae on rock slabs on thefloor. The rock slabs on the floor, some measur-ing up to several cubic metres in volume, wereoverturned on several occasions by severestorms, which kept the vegetation at a youngstage of growth.The next station of the transect Station B), ahorizontal  shelf had a uniform turf flora Fig. 2)with no large plants of  E. radiata P. comosa  or Sargassum  spp.; breaking  wave  action at this siteseems to have been too severe for large algae.This station and Station D were probably subjectto the heaviest wave action occurring in thetransect.Station C consisted of the sides of a deeperchannel flanked by submerged overhanging rocks.  There was no visible growth in the channelbottom which was composed of loose shells andboulders. There was some water surge. Thisstation appears to be distinctive from otherstations of the transect because of its low lightintensity, as shown in Table 1. It had a uniformflora of shade algae, crustose or small creepingreds and occasional small brown and green algae Table 2). TABLE 1. A representative series of underwater irradianee readings forStations A-F X). Measurements were taken on a clear day in mid-summer January) when above-water reading in direct sunlight was 2.150Readings were taken at low tideStation A 900-1200 B 900-1200 C 50-75 D 940-1240 Underneathkelp approx.100) E 450-700 F 350-700  Subtidal  transect in Jervis  Bay  443 FIG. 3. Photo of Station D stiowing the overlay by  Phyllospora comosa  on the turf algae. Station D was towards the outer weather)edge of a submerged rock outcrop exposed toheavy breaking wave-action. The vegetation onthis outcrop changed in a distance of 10 m fromcrustose coralline algae through turf algae onthe seaward side) to a mixed stand of  Ecklonia radiata  and particularly  Phyllospora comosa  onthe shoreward side). The latter species some-times overlaid the adjacent turf of small algae asshown in Fig. 3.Station E was a small site at the base of therock outcrop of Station D, on a subhorizontalledge. It was a deep site 4 m—see Fig. 1) andwas shaded by the rock outcrop so that theirradiance was much less than at other sites,apart from Stations C and F. Wave action wasusually less than in preceding stations, but thesite was subject to storm-generated abrasiveaction of small rocks and gravel from theadjacent site F. The commonest algae at this sitewere filamentous or small terete or foliosealgae.Station F included the deepest site  3  to  4 5  m)and consisted of  a  fairly flat seabed covered withsand, gravel, shells and semi-mobile  rocks.  Manyhairy mussels  Trichomya  hirsute were presentand these consolidated a large part of substrate.A number of crustose and articulate corallinealgae were also common and these too helped toconsolidate the substrate. Nevertheless thesevere storms that took place during the studymobilized much of the area and the resultantabrasion had a severe detrimental effect on themussels and the algal flora. Large plants of Ecklonia  radiata  and  Phyllospora  comosa  wereabsent from this area except on some largeboulders near the outer extremity.  Sargassum spp.,  Cystophora moniliformis  and  Clado-stephus verticillatus  were common.  Deliseapulchra  was also common at this station and atStation G but  was  absent or  very rare  elsewhere.Station G was situated on a large shallowsubmerged rock outcrop some 50 m offshore.This station was the least disturbed by watermovement. Extensive patches of large plants of Ecklonia  radiata  occurred in this area before thegreat storm of June 1973 see below) and thesehad largely become re-established by late 1978.However, there were many large patches withcrustose coralline algae, turf algae or 5flrgflS5u/ri spp.  Caulerpa cactoides,  common in 1974, wasnoted to be covered with crustose coralline algaein April 1975 following storms in February-March. After further storms from June 27-29,plants of  C cactoides  at Station G were observedin July 1975 to be almost white and this was thelast time that this species was observed in thetransect or near it, although a specimen wasobserved in a protected gully in deeper waternear to Station G in November 1978.
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