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Original scientifi c article                                                                                           DOI 10.19233/ASHN.2017.11
Received: 2017-09-14
CORALLINE ALGAE ON BIOGENIC FORMATIONS IN MARINE WATERS 
OFF SLOVENIA (NORTHERN ADRIATIC SEA)
Martina ORLANDO-BONACA, Borut MAVRIČ & Lovrenc LIPEJ
Marine Biology Station, National Institute of Biology, SI-6330 Piran, Fornace 41, Slovenia
E-mail: martina.orlando@nib.si 
Sara KALEB & Annalisa FALACE 
Department of Life Sciences, University of Trieste, I-34127 Trieste, Via L. Giorgieri 10, Italy
ABSTRACT
Two major biogenic formations, composed mainly by dead corallites of the Mediterranean stony coral (Cladocora 
caespitosa), have been recently studied in Slovenian marine waters. The paper presents new data about the presence 
of coralline algae on the biogenic formation situated off Cape Ronek and off Cape Debeli rtič. Coralline algae are 
very important for the creation, development and maintenance of calcareous bio-concretions that offer new niches 
for many invertebrates and other algae. They are listed as important builders of the coralligenous biocoenosis in the 
“Draft Lists of coralligenous/maërl populations and of main species to be considered by the inventory and monitor-
ing” of the RAC-SPA, and should be further deeply studied and appropriately protected.
Key words: coralline algae, biogenic formations, circalittoral, northern Adriatic Sea
ALGHE CORALLINE DELLE FORMAZIONI BIOGENICHE IN ACQUE MARINE SLOVENE 
(ADRIATICO SETTENTRIONALE)
SINTESI
Due formazioni biogeniche, prevalentemente composte da coralliti morti della madrepora a cuscino (Cladocora 
caespitosa), sono state recentemente studiate nelle acque slovene. Nel presente lavoro vengono riportati nuovi 
dati relativi alle alghe coralline presenti al largo di Punta Ronco e Punta grossa. Le alghe coralline hanno un ruolo 
importante nello sviluppo e nel mantenimento delle concrezioni biogeniche, offrendo nicchie per invertebrati e altre 
alghe. Nel documento “Draft Lists of coralligenous/maërl populations and of main species to be considered by the 
inventory and monitoring” del RAC-SPA, le alghe coralline sono riportate come importanti organismi biocostruttori 
della biocenosi coralligena, meritevoli di ulteriori studi e di una appropriata protezione. 
Parole chiave: alghe coralline, formazioni biogeniche, circalitorale, Adriatico settentrionale
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Martina ORLANDO-BONACA et al.: CORALLINE ALGAE ON BIOGENIC FORMATIONS IN MARINE WATERS OFF SLOVENIA (NORTHERN ADRIATIC SEA), 89–96
INTRODUCTION
The shallow northern Adriatic area is dominated by 
muddy and sandy bottoms (Lipej et al., 2006) and for a 
long time it was believed that these are the only bottoms 
existing in this basin. More than 200 years ago Giuseppe 
Olivi (1792) was the fi rst to mention that in this part 
of the Adriatic Sea exist also rocky outcrops. Northern 
Adriatic fi shermen have been familiar with this kind of 
environments before marine scientists discovered them, 
since they are rich fi shing points, called tegnùe along 
the Venetian coast (Casellato et al., 2006), and trezze 
in the Gulf of Trieste. Around 250 such rocky outcrops, 
calcareous bio-concretions, have been counted in the 
Italian part of the Gulf of Trieste, derived from the build-
ing action of calcareous organisms on hard substrata of 
diverse geological origins (Falace et al., 2015). Similar 
formations were recently studied also in Slovenian 
marine waters (Lipej et al., 2016). Currently, two major 
biogenic formations are known for the Slovenian Sea, 
which were sampled within the Interreg project TREC-
ORALA. These biogenic formations are located off Cape 
Ronek and off Cape Debeli rtič. Both have substantially 
larger dimensions than trezze and are linked to the pres-
ence of Mediterranean stony coral (Cladocora caespi-
tosa), since they are formed entirely by dead corallites 
of this species. 
During a scientifi c meeting on the coralligenous 
environment, which took place at the Marine Biology 
Station in Piran in March 2011, the Italian, Croatian 
and Slovenian researchers suggested that the northern 
Adriatic forms of coralligenous environment, such as 
trezze, tegnùe, the precoralligenous in the infralittoral 
belt and biogenic formations of Mediterranean stony 
coral C. caespitosa (Linnaeus, 1767), should be recog-
nized as a specifi c element within the Mediterranean 
coralligenous biocoenosis. The expression “biogenic 
formation” refers to any formations that are the result 
of limestone loading by some marine organisms, 
known as bioconstructors, during their lifetime. Among 
Fig. 1: Locations with Mediterranean stony coral (Cladocora caespitosa) colonies in the Slovenian coastal sea. 
Legend: 1 - Biogenic formation at Debeli rtič; 2 - Cape Debeli rtič; 3 - Cape Strunjan; 4 – Cape Ronek; 5 – Piranček; 
6 – Pacug; 7 – Bernardin; 8 - Biogenic formation at Ronek. 
Sl. 1: Lokalitete s kolonijami sredozemske kamene korale (Cladocora caespitosa) v slovenskem morju. Legenda: 
1 – Biogena formacija pred Debelim rtičem; 2 - Debeli rtič; 3 - rt Strunjan; 4 – rt Ronek; 5 – Piranček; 6 – Pacug; 
7 – Bernardin; 8 – biogena formacija pred rtom Ronek. 
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Martina ORLANDO-BONACA et al.: CORALLINE ALGAE ON BIOGENIC FORMATIONS IN MARINE WATERS OFF SLOVENIA (NORTHERN ADRIATIC SEA), 89–96
invertebrates the most well known bioconstructors are 
corals (Anthozoa), hydrozoans (Hydrozoa) and marine 
tube worms (Polychaeta Sedentaria) (Lipej et al., 2016). 
However, the precoralligenous and the coralligenous 
are primarily built by coralline algae (Laborel, 1961; 
Sartoretto, 1996). Among the eight action plans adopted 
by the Contracting Parties of the Barcelona Conven-
tion, one is devoted to the coralligenous habitat: the 
Action plan for the conservation of the coralligenous 
and other calcareous bio-concretions in the Mediter-
ranean Sea, UNEPMAP-RAC/SPA (Ballesteros, 2008). 
Within this document, the coralligenous formations 
are considered a typical Mediterranean underwater 
seascape, comprising coralline algal frameworks that 
grow in dim light conditions and in relatively calm 
waters (Ballesteros, 2006).
Coralline algae are very important for the creation, 
development and maintenance of new niches for many 
invertebrates and other algae. Their habitat-building 
capacity is associated with the mechanism of minerali-
zation of the cell wall with calcium and, to a lesser ex-
tent, magnesium carbonate. In red algae (Rhodophyta) 
from the family Corallinaceae, the carbonate is present 
in the crystalline calcite form mainly, while in red algae 
from the family Peyssonneliaceae and in green algae 
(Chlorophyta) from the family Halimedaceae it pre-
cipitates as aragonite. The occurrence of calcifi cation 
helps to balance the carbon dioxide defi cit in water, 
which is due to photosynthesis, and thus contributes to 
the maintenance of the alkaline potential in sea water 
(Andreoli et al., 2010). 
Falace et al. (2011) reported on the presence of cor-
alline algae in the Slovenian circalittoral belt, including 
the biogenic formation off Cape Ronek. The aim of the 
current paper is to report the fi rst available data about 
the presence of coralline algal species on the biogenic 
formation located off cape Debeli rtič, and new data 
about their occurrence at Cape Ronek.
MATERIAL AND METHODS
Study area
The biogenic formation at Cape Debeli rtič (Figs. 1 
and 2) is more or less of triangular shape with a rounded 
plateau, which looks like a knob. On the reef there is 
a relatively steep step where the coastal sandy-rocky 
bottom sweeps into muddy sediment, which happens 
very quickly in comparison with the near surroundings. 
The biogenic formation is mostly covered by a thin 
layer of mud and, therefore, the accurate assessment 
of its borders was very diffi cult. It starts at about 10 m 
of depth and sweeps down to 17.5 m. This biogenic 
formation is mainly composed of dead Mediterranean 
stony coral corallites, with only a few living colonies 
(Lipej et al., 2016). 
The biogenic formation at Cape Ronek is located 
outside in the waters off Strunjan Nature Reserve (Fig. 
1). Its shape is elliptical, with the longest axis in the 
west-east direction, and the shortest in the north-south 
direction (Fig. 3). The highest point of the biogenic 
formation is at 12.4 m depth, and it extends down to 
21 m, where it shifts into a muddy bottom. It is entirely 
composed of dead, broken corallites of Mediterranean 
stony coral. This solitary structure is surrounded on 
all sides by a muddy bottom, signifi cantly less rich in 
biodiversity (Lipej et al., 2016). This formation is not 
covered by a surface layer of mud, with the density of 
living colonies of Mediterranean stony coral consider-
ably higher than in other areas of the Slovenian Sea 
(see Tab. 1). 
Fieldwork and laboratory work
The surveys of coralline algae at biogenic formations 
were done in July 2013. Algae were randomly manually 
collected from the sea bottom, scraped when they were 
found attached, on a transect in a depth range from 10 
m to 13 m at Cape Debeli rtič, and from 13 m to 16 m at 
Cape Ronek (Figs. 2 and 3). Samples were collected in 
plastic bags and all the material was transported to the 
laboratory of the Marine Biology Station of the National 
Institute of Biology. Algal samples were sorted in labora-
tory and fragments of material were air dried, mounted 
on aluminium stubs with acrylic adhesive and then 
analysed by scanning electron microscopy (SEM). Stubs 
were sonicated with a Vitec sonicator to remove sedi-
ments and diatoms and then coated with gold/palladium 
(with S150 Sputter Coater, Edwards) prior to viewing in a 
LEICA Steroscan 430i at 20 kV.
Tab. 1: Density of Mediterranean stony coral colonies in 
various areas of the Slovenian Sea (adopted from Lipej 
et al., 2016).
Tab. 1: Gostota sredozemske kamene korale v različnih 
predelih slovenskega morja (prirejeno po Lipej in sod., 
2016).
Locality
Density of C. caespitosa 
colonies (n/100m2)
Biogenic formation at 
Debeli rtič
3 (2-4)
Cape Debeli rtič 83 (70-96)
Cape Strunjan 85 (66-105)
Cape Ronek 108
Piranček 160 (128-192)
Pacug 186
Bernardin 285 (263-306)
Biogenic formation at 
Ronek
652 (498-806)
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RESULTS AND DISCUSSION
Over the surveys performed in 2013, six species of 
coralline algae were found at the biogenic formation of 
Cape Debeli rtič, while seven were found at Cape Ronek 
(Table 2). In samples collected in 2010 by Falace et al. 
(2011) at the biogenic formation of Cape Ronek, Neogo-
niolithon brassica-fl orida (Harvey) Setchell & L.R. Mason 
and Titanoderma pustulatum (J.V. Lamouroux) Nägeli 
were missing. However, in those samples they recorded 
Lithothamnion philippii Foslie, Pneophyllum confervi-
cola (Kützing) Y.M. Chamberlain and Pneophyllum fragile 
Kützing that were not found at Cape Ronek in 2013. 
During the present study, encrusting thalli of 
Lithothamnion sonderi Hauck, N. brassica-fl orida and 
Phymatolithon lenormandii (Areschoug) W.H.Adey were 
collected at both biogenic formations. P. fragile was found 
as an epiphyte on dead Mediterranean stony coral coral-
lites only at Cape Debeli rtič, where also few encrust-
ing thalli of P. confervicola were collected. Conversely, 
Lithophyllum racemus (Lamarck) Foslie, Lithothamnion 
minervae Basso and T. pustulatum were found only at the 
biogenic formation of Cape Ronek; the fi rst only as non 
living sub-globular thalli (rhodoliths), the second both as 
encrusting form and live rhodoliths, and the third only as 
encrusting thalli. The term “rhodolith” includes all bio-
genic excrescences where calcareous red algae represent 
at least 50% of the nodule, which consists of the coralline 
alga together with the substrate/core (Bressan & Babbini, 
2003). The fact that thalli of L. minervae were found alive 
on all sides of the rhodolith proves that the structure is 
occasionally rolled by marine currents, representatives of 
the vagile fauna and/or anthropogenic activities such as 
fi sheries, diving and anchorage.
So far 31 species of coralline algae were reported for 
the Slovenian sea (Falace et al., 2011). Among the 10 
species collected in 2013 (Table 2), four were found for 
the fi rst time in this coastal area in 2010: Lithothamnion 
minervae Basso, L. philippii, Lithothamnion sonderi and 
N. brassica-fl orida (Falace et al., 2011). However, all of 
them were previously recorded in the Italian part of the 
Gulf of Trieste. Several species of coralline algae found 
in Slovenian marine waters are listed as important build-
ers of the coralligenous biocoenosis in the “Draft Lists 
of coralligenous/maërl populations and of main species 
to be considered by the inventory and monitoring” of 
the RAC-SPA (UNEP(DEPI)/MED WG.362/3, 2011). In 
the Mediterranean Sea, the coralligenous biocoenosis 
comprises at least 315 algal species (Boudouresque, 
1973; Ballesteros, 2006). Among them, some species 
are bioconstructors (coralline algae), others bore holes 
into hard structures (particularly certain green algae 
Fig. 2: Image of biogenic formation at Cape Debeli rtič generated from multi-beam 
ecosounder data (photo: E. Gordini). Coralline algae were collected along the red 
transect. 
Sl. 2: Slika biogene formacije pred Debelim rtičem, narejena na podlagi podatkov 
iz ehosonderja (avtor E. Gordini). Koraligene alge so bile nabrane vzdolž transekta, 
označenega z rdečo črto.  
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Martina ORLANDO-BONACA et al.: CORALLINE ALGAE ON BIOGENIC FORMATIONS IN MARINE WATERS OFF SLOVENIA (NORTHERN ADRIATIC SEA), 89–96
and blue-green algae (Cyanobacteria)), and some are 
accompanying species, which include a number of 
exotic and invasive taxa (Andreoli et al., 2010). The 
genus Lithophyllum is known to be the most species-
diverse genus of coralline algae in the Mediterranean 
Sea and plays a key role in the formation of several 
widespread bioconstructions (Falace et al., 2016). These 
taxa contribute with their growth to the construction of 
organogenic formations also in shallow northern Adri-
atic Sea (Bressan & Babbini, 2003; Bressan et al., 2009; 
Giaccone et al., 2009; Falace et al., 2016). Among the 
25 species of coralline algae reported for the northern 
Adriatic calcareous bio-concretions, Lithophyllum 
incrustans Philippi is one of the most important biocon-
structors, in particular at the outcrops located at a depth 
of 23–25 m and at a distance 10 km from the coast 
(Falace et al., 2015). Even though L. incrustans has been 
reported for the Slovenian area (Falace et al., 2011) it 
was not observed at the biogenic formations near Cape 
Debeli rtič and Cape Ronek. Therefore, on the basis of 
the recent fi ndings of coralline algae on biogenic forma-
tions in Slovenian waters, it is reasonable to expect that 
future researches in the area will reveal new species 
among algae and benthic invertebrates, as well.
In the light of the current (limited) knowledge about 
coralline algae, biogenic formations, and other infralit-
toral and circalittoral coralligenous environments in the 
Slovenian Sea, some recommendations can be made, 
according to Ballesteros (2003), for their conservation: 
a) prohibition of trawling in areas with coralligenous 
forms and their vicinity, to avoid both the physical dam-
age of trawling and also the indirect effects due to in-
creased turbidity and sedimentation rates; b) prohibition 
of other anthropogenic activities that lead to increased 
water turbidity and/or sediment removal (e.g. coastline 
modifi cations) in the vicinity of coralligenous forms; c) 
no waste water discharge in these areas; d) implementa-
tion of the management of traditional and recreational 
fi sheries  in order to prevent stock depletion of target 
species; e) controlled recreational diving pressures; f) 
urgent need for a protection law of coralligenous envi-
ronments; g) further scientifi c research to increase the 
knowledge about biology and ecology of taxa inhabiting 
the coralligenous biocoenosis, to give a more accurate 
estimation of the coralligenous biodiversity. 
ACKNOWLEDGEMENTS
The authors would like to thank dr. Emiliano Gor-
dini, Milijan Šiško, Tihomir Makovec, Nicola Bettoso, 
Valentina Pitacco, Jernej Uhan and Marko Tadejević for 
their help during fi eldwork. Special thanks are due to dr. 
Fig. 3: Image of biogenic formation at Cape Ronek generated from multi-beam 
ecosounder data (photo: E. Gordini). Coralline algae were collected along the green 
transect.  
Sl. 3: Slika biogene formacije pred rtom Ronek, narejena na podlagi podatkov iz 
ehosonderja (avtor E. Gordini). Koraligene alge so bile nabrane vzdolž transekta, 
označenega z zeleno črto.  
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Emiliano Gordini and Milijan Šiško also for the prepara-
tion of fi gures. The surveys were carried out under the 
TRECORALA project (TREzze e CORalligeno dell’ALto 
Adriatico: valorizzazione e gestione sostenibile nel 
Golfo di Trieste), funded from the “Italy - Slovenia 
Cross-border Cooperation Operational Programme 
2007-2013” – Programme under the European Territo-
rial Cooperation Objective, co-funded by the European 
Regional Development Fund (ERDF) and by national 
funds (fi nancial support from the Slovenian Research 
Agency (research core funding No. P1-0237)). 
Tab. 2: Coralline algae found at biogenic formations at 
Cape Debeli rtič and Cape Ronek (* alive thalli, ** dead 
thalli). Data from 2010 were published in Falace et al. 
(2011).
Tab. 2: Koraligene alge, najdene na biogenih formacijah 
pred Debelim rtičem in rtom Ronek (* žive steljke, ** 
mrtve steljke). Podatki iz leta 2010 so bili objavljeni v 
delu Falace in sod. (2011).
Location 
Biogenic 
formation 
Cape 
Debeli 
rtič 
Biogenic 
formation 
Cape 
Ronek 
Biogenic 
formation 
Cape 
Ronek 
Taxa/             Year 2013 2013 2010
Lithophyllum 
racemus 
** **
Lithothamnion 
minervae 
* *
Lithothamnion 
sonderi 
* * *
Lithothamnion sp. * *
Lithothamnion 
philippii 
*
Neogoniolithon 
brassica-fl orida 
* *
Phymatolithon 
lenormandii 
* * *
Pneophyllum 
confervicola 
* *
Pneophyllum 
fragile 
* *
Titanoderma 
pustulatum 
*
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KORALIGENE ALGE NA BIOGENIH FORMACIJAH V SLOVENSKIH MORSKIH VODAH 
(SEVERNI JADRAN)
Martina ORLANDO-BONACA, Borut MAVRIČ & Lovrenc LIPEJ
Morska biološka postaja, Nacionalni Inštitut za biologijo, SI-6330 Piran, Fornace 41, Slovenija
E-mail: martina.orlando@nib.si 
Sara KALEB & Annalisa FALACE 
Department of Life Sciences, University of Trieste, I-34127 Trieste, Via L. Giorgieri 10, Italy
POVZETEK
Pred kratkim so raziskovalci v slovenskem morju pričeli z raziskavami dveh velikih biogenih formacij, ki jih 
sestavljajo mrtvi koraliti sredozemske kamene korale (Cladocora caespitosa). Avtorji poročajo o novih podatkih 
o navzočnosti koraligenih alg na biogeni formaciji pri Ronku in biogeni formaciji pred Debelim rtičem. Koraligene 
alge so zelo pomembne pri ustvarjanju, razvoju in ohranjanju apnenčastih tvorb in nudijo življenjske niše za mnoge 
nevretenčarje in druge alge. So pomembni gradniki koraligene biocenoze, navedene tudi v seznamu populacij 
koraligenih/maërl alg, ki jih je potrebno popisati in redno spremljati na podlagi priporočil RAC-SPA, zato bi jih bilo 
potrebno natančno raziskati in primerno zavarovati.
Ključne besede: koraligene alge, biogene formacije, cirkalitoral, severni Jadran
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