ANNALES • Ser. hist. nat. ■ 10 - 2000 • 2 (21)
original scientific paper	UDC 574.5(267-14)
received: 1. 2000
CALCAREOUS STRUCTURES BUILT BY THE CORALLINE ALGA PNEOPHYLLUM CONFERViCOLA (KUTZINC) CHAMBERLAIN (CORALLINALES, RHODOPHYTA) IN A MARINE CAVE IN THE GULF OF OMAN
Jože ŠTIRN 5Î-6230 Portorož, Fizine fi
Cuido BRESSAN, Lia Angela GHIRARDELLt & Lorenza BAB BIN I □¡partimento di Biología cfell'Università degli studi di Trieste, IT-341 27 Trieste, Via L. Ciorgiuri 10
e-mail: ghirardl@ur>iv.trieste.U
ABSTRACT
A peculiar marine ecosystem has been discovered in a karst cave system, popularly named the Tiwi Sinkhole, which is located in the south-western coastal zone of the Gulf of Oman, Indian Ocean. This small, isolated ecosystem comprises a very unusual benthic community occupying the sinkhole's sunlit walls. Its components occur in the form of calcareous layers enveloping the primary bedrock and sometimes forming bulk concretions produced apparently only by one prolific population of a crustose coralline species. The results of microscopical analyses and other taxonomical examinations of numerous typical specimens demonstrate that all the structures are produced just by one species, identified as Pneophyllum confervicola (Kutzing) Chamberlain.
Key words: bioconstruction, coralline alga, Pneophyllum confervicola, marine- cave
STRUTTURE CALCAREE COSTRUITE DALL'ALCA CORALLINA PNEOPHYLLUM CONFER VICO LA {K Ü TZ1N C) CHAMBERLAIN (CORALLINALES, RHODOPHYTA) IN UNA
GROTTA MARÍN A NEL GOLFO DI OMAN
SI NT ESI
Un peculiars ecosistema marino <? stato rinvenuto in un sistema di grolte carsiche, popolarmente cluamato Tiwi Sinkhole, localizzato sulla costa sitd-occidentale del Coito di Oman, nell'Oceano Indiano. Questo piccolo, ecosistema isolato, comprende un'inusuale comunita bentonica che occupa le pared soleggiate della cavita. Le sue componenti si presentano in forma di strati calcatei ricoprenti il substrato di base e, a volte, in forma di grandi conciezioni, prodotte apparentemente da da una popotazione di un'unica specie corallina crostosa, prolifica. i risultati deile analisi microscopiche e di a It re indagini tassonomiche di numerosi esemplari tipici dimostrano che tutte le strutture vengono prodotte da una sola specie, identificara come Pneophyllum confervicola (Kutzing) Chamberlain.
Parole chiave: biocostruzione, alga corallina, Pneophyllum confervicola, grotta marina
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ANNALES • Ser. hist. nat. ■ 10 - 2000 • 2 (21)
jo» Stirn calcareous structures built by the cquauine alga pneophyu um coNrmncoi* (Kützinq, 219-236
INTRODUCTION
Occurring throughout the world's oceans in photic benthic zones of hard bottoms, and often on detrited soft bottoms as well, the many genera ami species of the Corallinales are important builders of several types of calcareous concretions and structures. Apart from ubiquitous encrustations enveloping primary rock-substrata, detrited rubble and living sessile organisms (epiphytes), there are quite massive and extensive calcareous structures that many ciustose corallines are able to produce. For many coastal ecosystems these structures are of great importance, particularly in the tropical areas. For example, ciustose species, belonging mainly to lite genera Porolithon, Lithophyllum and Neogonlolithon, are, in addition to stony corals, the second most important framework builders, framework cementers and infilled elements of all coral reefs to which they contribute up to 35% of carbonate material (Adey, 1998). In temperate and subtropical environments, however, some ciustose species built extensive framework structures, which are almost entirely composed of coralline material
such as the reef-like formations found in the Mediterranean Sea and the adjacent N!i. Atlantic: upper-littoral "trottoirs" of Tenarea tortuosa (Fsper) Lemoine and deep-littoral coralligenous platforms built by a number of species belonging to the genera Mesophylluni, Lithophyllum, Uthothamnium etc. (Margalef, 1985).
It is the deep-littoral platform that is remarkably similar, by its structure, to the one evolved in a peculiar marine ecosystem discovered in a karst cave system, popularly named the liwi Sinkhole, located in the south-western coastal 2one of the Cult of Oman (Indian Ocean).
This small, isolated ecosystem whose habitats are briefly described below, also comprises a very unusual benthic community, which occupies the sinkhole's sunlit walls. All its macro-components, i.e. few non-crustose algae and faunal species, are mainly attached to the secondary hard substrata that occur in the form of calcareous layers enveloping the primary bedrock or forming bulky concretions, produced apparently only by one prolific, population of the crustose coralline species this paper is dealing with
PLAN
TIWISINKHOLE
A Marine Cave in Oman
ELEVATION a~â
0 -10 -
NXARABIAV^	
\\ Cave-	^ ps G ulf of
	) Oman
	INDIAN
	OCEAN
Land surface
70 Lm
Fig. 1: Diagrammatic topography of the Tim Sinkhole cave-system (based on the survey by R. Hill and the Oman Cave Divers; Anon., 1995), also showing characteristic water masses (Štirn, 1996), of which only the "lake's" brackish and oxk layer (F) supports macroalgae and benthic macrofauna, whereas the deep, anoxic and H2S-bearing layers (S, N and D) are inhabited only by suspended sulphur bacteria (S) and peculiar bacterial macroaggregates (B). Marked with L is the dry land of the rockpile evolved when the roof of the cave have collapsed, P indicates pyriie sediments and X a possible connection to the sea. See also table 1. Si. 1: Shematična topografija jamskega sistema ponorja Tiwi (izdelana na osnovi raziskav R. Hilla in omanskih potapljačev; Anon., 1995), ki ponazarja tudi značilne vode mase (Štirn, 7 996), med katerimi le "jezerska" brakična in oksična plast (F) zagotavlja razmere za rast makroalg in bentoške makrofavne, medtem ko globoke, anoksične plasti in plasti s HoS (S, N in D) naseljujejo le suspendirane tveplcne bakterije (S) in nenavadni bakterijski makroagregati (B). Črka L označuje del kopnega (gmoto skal), nastalega po zrušitvi stropa jame, P piritne sedimente, X pa možno povezavo z morjem. Glej tudi tabelo 1.
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Join ST»K «af.: CAICARFOUS STRUCTUMS B(JHT HVTHF CO RAIL Is--1 L A1.CA PMOPHniUM CONfiRWCOlA (KU7ZING). 2*9-2»
Habitat and Community Description
The Tiwi Sinkhole and the large cave system beneath developed in tertiary limestones, along the fissure in a Pleistocene marine terrace, which is now some 20-25 m above the sea level. The sinkhole is the only known entrance into the cave, and is located inland, nearly 900 m from the sea shore of tire south-western Gulf of Oman between Muscat and the village of Tiwi, its geographical position being roughly 23°OT N and SO'W F. This vertical (15-25 m deep) and to the surface open shaft is actually the upper part of a large and at least 64 m deep cave whose roof apparently collapsed (Figs. 1, 2). Consequently, almost half of the sinkhole's bottom surface is dry land (a rockpile of rubble and boulders), whereas the rest is occupied by the ILlake" (Figs, t, 2). This 4-7 m deep water body is actually the surface layer of a large water mass that occupies the main, completely submerged cave below, which obviously has a hydraulic connection with the sea (Fig. 1), for the "lake" shows clear, but for some 907o reduced, tidaf oscillations (Tab. 1).
Unlike the deep water mass, which is constantly anoxic and whose salinity and temperature values are invariably high (-35 psu; >29°C). the "lake" water is moderately brackish and shows rather important seasonal variations of salinity and temperature values (ranges of 19-25 psu and 22-33°C, respectively with lower values during winter conditions) and is as a rule quite well oxygenated. Therefore, receiving enough solar light for at least sciapbiiic algae to grow on its walls, this unusual habitat provides quite specific conditions for the tlour-shing productivity of the above mentioned corallines {Fig. 3), and the rest of a relatively rich benthic community {Fig. 4) composed mainly of the following niac-rocomponents:

Fig. 2: The Sinkhole photographed from its upper edge showing the "lake" surface and the rockpile of the collapsed roof of the cave. Note at the left horizon, the adjacent coastal sea. (Photo: /. Štirn) SI. 2: Ponor Tiwi, fotografiran z njegovega gornjega roba, z "jezersko" površino in gmoto skal zrušenega jamskega stropa. Na levem horizontu je lepo videti dotikajoče se oba/no morje. (Foto: /. Štirn}
PARAMETERS	EUPHOTIC/F Depth: 0-7 m	SULPHURETUM/S Depth: 7-17 m	DEPTH/N+D N: 18-24 m D > 25 m
TEMP CC)	22-33	28-31	29-30
SAL (psu)	19-25	30-31	34-35
OXYGEN' (ml H)	3-6	± 0	0.1-1.5
H-)S (mg H)	0	- 180	0
NITRATE-N immoi I ')	0.1-17	0.1-0.4	0.1-0,5
PHOSPHATt-P (mmol H)	0.02-0.30	0.10-1.50	0.30-0.60
VIS (m)	1-25	<1	>25
Tab. 1: Physical and chemical characteristics of habitats in the studied area.
psu = practical salinity unit - approx. ppt; VIS = horizontal UV visibility as estimated by divers; euphotic - for plant growth adequately illuminated habitat; hypoxic - low oxygen environment, arbitrarily <7ml O2 l~7; H?S ~ toxic hydrogen sulphide (rotten-egg-gas); sulphuretum = aquatic community dominated by sulphur hacteria. See figure I for explanation.
Tab. 1: Fizikalne in kemične značilnosti habitatov raziskovanega obinočja.
psu = praktična enota slanosti = pribl. ppt; VIS - horizontalna UV vidljivost po oceni potapljačev; evfotičen - za rast rastlin zadovoljivo osvetljen habitat; hipoksičen - okolje z majhno količino kisika, in sicer <Jml O2 I'1; H2S ~ strupen vodikov sulfid (plin gnilih jajc); sulfuretum = vodna združba s prevladujočimi žveplenimi bakterijami. Clcj sliko 1 za pojasnilo.
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lože STIRN <?! a!.: CALCAREOUS STRUCTURES IfUHT HY Tl i; CORAI
Fig. 3: Crustose envelopes and massive calcareous structures built by the coralline Pneophyllum confervi-cola on the hard bottom of the Sinkhole "lake", here in the dept of 2 m. (UV macrophotograph; by }. Štirn). SI. 3: Skorjasti ovoji in masivne apnenčaste strukture, ki jih na trdem dnu - tu v globini 2 m - gradijo koralinske alge Pneophyllum confervicola. (UV makrofotografija; J. Štirn)
-	non-crustose macroalgae: Celidielia rigidiscula (Feldmann) Fcidmann & Hamef, Valonta aegagropilta C. Agardh, Rhizoclonium ripariurrt (Roth) Kiitzing ex Harvey and Cbdophora sp. (Sara & Bavestrello, 1995; Stirn, 1996)
-	sessile filter ■ feeders: sponges Haliclona and Suberites spp. and Tethya omartensis Sara &■ Bavestrello rs.sp. (Sara & Bavestrello, 1995), tubeworm Leodora knightjonesi and the ascidian Polycarpa colled;
■ grazing snails Pirenella doriae Hornung & Mermod and Planaxis sulcatus Born, and omnivorous euryhaline fish Aphanius dispar Rueppel (Stirn, 1995, 1996).
MATERIAL AND METHODS
Samples of coralline material needed for this study were collected during 1995-199? from the walls of the Sinkhole, manually at the surface and by divers at deeper positions down to the depth of 3 m. Some samples were preserved in 2% formaldehyde sea water and other ones as dry samples. For the taxonomic purposes these were morphologically examined in the outer layers as well as deep inside of concretions. Specimens for fight microscopy were decalcified in Tellyesniczky solution (acetic acid 5 ml, potassium dichromate 3 g to 100 ml with distilled water) and sectioned by means of microtome, whereas the preparations for SEM were fixed in 4% glutaraldehyde in 0.6 M phosphate buffer, dehydrated in a graded ethanol series, critical point dried and gold-coated. Leica Stereoscan 430i was used for SEM examination. Taxonomic identifications were based
IH-Jl ALGA WWiOUW CONmviCOLA (K0TZING), J19-226
Fig. 4: Benthic community in the Sinkhole "lake" composed here of the bushy red alga Celidiella rigidiscula, purple and yellow sponges Haliclona and Clathrlna spp. and the orange ascidian Polycarpa colleti. (UV macro-photograph, approx. surface 1 dm2; by J. Štirn) SI. 4: Bentoška združba v ponornem "jezeru", ki se tu sestoji iz košatih rdečih alg Gelidiella rigidiscula, vijoličastih in rumenih spužv Haliclona and Clathrina spp. in oranžnih kozolnjakov Polycarpa colleti. (VV makrofotografija, površina okoli 1 dm1;). Štirn)
upon the following sources: Chamberlain, 1994; Hamei & Lemoine, 1952; Silva eta!., 1996 and Suneson, 1943 for coralline algae; Gallardo et ai, 1993; Giaccone et al., 1994; Sara & Bavestrello, 1995 and Štirn, 1996 for non-coralline algae and animals.
RESULTS
Diving observations, supplemented by underwater photography and macroscopic examinations of numerous samples, revealed that crustose corallines cover the entire surface of the upper hard bottom zone of the Sinkhole from the water surface down to the depth of about 3 m. On the north-western walls, which are relatively well illuminated, the corallines produce rather simple but quite thick crusts (4-26 mm), whereas in the shade of deeper sites (2-3 m) they build massive, up to 34 cm thick concretions that occur as two typical varieties: one is bright purple, compact and built in a form similar to the flowstone (Fig. 5), while the other one has a dark red-brown colour, and a porous, travertine-like structure (Fig. 6). This is clearly the result; of corallines enveloping and cementing the subfossil and recent aggregates composed of calcareous tubes of the polychaet worm Leodora knightjonesi, which are attached directly to the primary rock substrate
One of these constructions is illustrated on figures 5 and 6. The outer part, faced towards the outside (Fig. 5), shows a compact pink form, while the inner part (Fig, 6), which envelops the aggregates where it is attached, is porous, vermiculate and dark, quite black.
ANNALES • Ser. hist. nat. ■ 10 • 2000 • 2 (21)
Sllifcv st :>!. CAICAKEOI 'S STRUCT UKR GUI! T P.Y 111 r COEALUNL AtuA miOHIYUUMCOKFCKVICOlA. IKOTZIMGil 219-2M
Figs. 5, 6: Macrophotography of the compact (Fig. 5) and the porous (Fig. 6) part of the bioconstniction. Bar 1 cm.
Typically, this encrusting species is forming, in the Sinkhole and elsewhere; small ihalli with creeping filaments, which vary from partially (fig. 7) to entirely unconsolidated forms (fig. 8). Generally, the thaili are composed of rather small cclJs (10-16 ¡mi x 20 pm) whose shape, observed in surface view, is squarish and isodiametric (Fig. 8), among them intercalary trichocytes are rare (Fig. 9). There are also epithailial cells for which SUM observations show pits and actual holes where the calcified wails seem to be much thinner (Fig. 8). In section the thaili appear monostromatic and unistratified, except in places were the epithailial cells are visible.
The conceptades observed by SEM (Fig. 10) in surface view are clearly uniporate, hemispheric and measure 90 urn x 60-70 ¡.¡m, whereas the light microscopy showed that they are tetra/bisporangial.
Based upon the above-mentioned morphological variability, there were the folfowing two taxonomic forms previously recognised for this species as f. typica and f. lacunosa,. (jotme? f, rninutula; Chamberlain, 198,-i). The f. typica is a compact form with consolidated filaments (Figs. 8, 11), while the f. lacunosa often shows a partially unconsolidated thai I us (Fig. 7). The very sur-
Sl. 5, 6: Makrofotografija kompaktnega (SI. 5) in poroznega (SI. 6) dela hiokonstrukcije. Merilo 1 cm.
face of the Sinkhole's specimens is almost always dominated by the f. typica.
DISCUSSION
The results of microscopical analyses (the germination disc wiili 8 central ceils, intercalary trichocytes, uniporate conceptades) and other taxonomrcal examinations of numerous typical specimens demonstrate a rather surprising fact that, despite such a great variability, all above structures are produced just by one species only, identified as Pneophyllum confervicola (Kutzing) Chamberlain (Chamberlain, 1983).
The coralline P. confervicola is obviously a very tolerant, euryoecic species, which has a wide geographic distribution from the boreal Atlantic Ocean to the Mediterranean Sea, in the Pacific and the Indian Ocean.
However, in ail other records it es reported only as an epiphyte growing on a wide range oi macroalgal species (Irvine & Chamberlain, 1994).
The only known exception is the Sinkhole's population whose generations overgrow on previously deposited layers of the same algae, which causes the forma-
2 23
ANNALES • Ser. hist. nat. ■ 10 - 2000 • 2 (21)
loa? Stirn a.a. calcareous structures euitt sv tme coralline alga pNtoa-nuuM cowfRvtcoiA (kütz»ng>, 22b
m
Fig. 7: Detail of the bioconstruction with thalli characterised by creeping filaments. Bar 100 pm. SI. 7: Detajl biokonstrukcije S steljkami, ki jih označujejo plazeča se vlakna. Merilo 100 pm.
i., -'¿cä
j® * t, ,< " JsP ' "■ ' . -
šmštmnm iMVa m-
.fet® šm
V ■?. i a msM-. s ■ r	, , -
, „	C'
, - .v
Si
Fig. 9: Detail of the thallus showing an intercalary trichocvte and the monostromatic structure. Bar 10 pm.
Si 9: Detajl steljke z vrinjenim trihocitom in monos-tromatično strukturo. Merilo 10 pm.

¿WW

ÊmMMMMMmiê
ÄiW , i * i ■ ' >
ggs p a ♦ ** *
«■TOB «Î g	pill
: Ï1 ,■ j > ■ -i.V fell



Fig. $: Young thallus of P. confervicola in which the epithallial cells are clearly visible. Bar 20 pm. SI. b: Mlada steljka koralinske alge P. confervicola z lepo vidnimi epitalialnimi celicami. Merilo 20 pm.
tion of massive calcareous structures described above (Figs. 5, 6). from a biological point of view, it seems indeed that it is the overgrowing capacity (Figs. 7, 11) of the thalli of this species on itself that generate the bioconstructions.
The dominance and the richness of P. confervicola in these bioconstructions, probably dLte to a considerable viability of the species, seems to fully accord with what occLirs for at least another species of this genus: Pneophyllum conicum (Dawson) Keats, Chamberlain & Baba, the only non-geniculate coralline that has been observed to regularly anil commonly overgrow and kill corals, especially taxa with small polyps and relatively smooth colonies (Keats et at., 1997).
Also in the case of the bioconcretion of Tiwi, the construction examined seems to have been produced by the overgrowing of a multitude of thalli present under the form of extremely small scales (Figs. 7, 11).
This leads us to believe thar the above forms art' more likely the ecotypes evolved through a morphic
224
ANNALES Ser. his», nat. • 10 2000 2 (21)
¡Oie S i IRN tt ai.. C.ALCARtOL/S STRUCTURÉS null T BY THF. COKAUiHC AI CA PHUOPHYLiUM CONFERVICOlA (KUTZINGI, 219-226
Fig. 10: Uniporafe conceptacle. Bar 20 pin. Si. 10: Enoporni konceptakel. Merilo 20 pm.
process adaptation to small-scale differences in the ranges of environmental factors, among which the illumination intensity probably are the most crucial. Moreover, the total absence of any type of disturbance in such a particular biotope (lack of wind, current and limited tide range) seems to have contributed to tlie building of these formations. The adaptation ability of this euryoecic specics seems justified by the relative structural simplicity of its thai lus.
Fig. 11: Overgrowing thalli of P. confervicola. Bar 100 pm.
Si 11: Razraščajoče se steljke ko ta finske alge P. confervicola. Merilo 100 p m.
ACKNOWLEDGMENTS
We are very grateful to the Oman Cave Divers, guided by R. Hill, to Miss 8. Troian for her assistance during SEM observation, and to Mrs. M. Attilio for the revision of the English text.
APNENČASTE STRUKTURE, KIJIH GRADIJO KORALINSKE ALG F PNEOPHVLLUM CONFERVICOLA (KUTZING) CHAMBERLAIN (CORALLINALES, RHODOPHVTA) V ENI IZMED MORSKIH JAM V OMANSKEM ZALIVU
jože ŠTIRN Si-6230 Portorož, Fiziiie 8
Guido BRESSAN. Lia Angela GHIRAROELU & i.oren za BABBiNi Oddelek za biologijo. Univerza v Trstu. IT-34127 Trst, Via L.. Giorgieri 10 e-niail: gliifsrdl@univ.trieste.it
POVZETEK
V jugozahodnem obalnem pasu Omanskega zaliva v- Indijskem oceanu je bil v nekem kraškem jamskem sistemu, ki mu domačini pravijo ponor (liwi), odkrit prav poseben morski ekosistem. Ta mali, izolirani ekosistem zajema zelo nenavadno bentoško združbo, ki živi na ponorjevih steniih, obsijanih s soncem. Njegove komponente se pojavljajo v obliki apnenčastih plasti, ki obdajajo matični substrat ter tu in tam oblikujejo zrastke. ki jih očitno gradi zelo plodna populacija skorja ne koralinske vrste. Rezultati mikroskopskih analiz in drugih taksonomskih raziskav številnih značilnih osebkov so pokazali, da vse strukture gradi ena sama vrsta, identificirana kot Pneophyllum confervicoia (Kutzing) Chamberlain.
Ključne besede: biokonstrukci ja, koral inske alge, Pneophyllum confervicola, morska jama
ANNALES • Ser. hist. nat. ■ 10 - 2000 • 2 (21)
Jote STIRN i-í al: CAI CAKEOUS STRUCTURES BUILT RY THE CORALLINE ALCA PNÍOlllYLt ÜM CONFERViCOL* (KOTZINGí. 2i9-226
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