The Neogoniolithon brassica-florida - EQEL

Journal of Coastal Research
27
2
394–398
West Palm Beach, Florida
March 2011
The Neogoniolithon brassica-florida (Harvey) Setchell &
L.R. Mason (1943) Reef of Bahiret el Bibane Lagoon
(Southeastern Tunisia)
Habib Langar{, Meriem Bessibes{, Aslam Djellouli{, Christine Pergent-Martini1{{, and
Gérard Pergent{{
{
Institut National des Sciences
et Technologies de la Mer
(INSTM)
Laboratoire de Biodiversité et
des Biotechnologies Marines
28 rue du 2 mars 1934
2025 Salammbô, Tunisie
[email protected]
{
Faculté des Sciences de Tunis
Département de Biologie
Campus Universitaire el Manar
1002 Tunis, Tunisie
1
Regional Activity Center for
Specially Protected Areas
(RAC/SPA)
Boulevard du Leader Yasser
Arafat, BP 337
1080 Tunis cedex, Tunisie
www.cerf-jcr.org
{{
Université de Corse
UMR CNRS 6134
Faculté des Sciences et
Techniques
BP 52
20250 Corte, France
ABSTRACT
LANGAR, H.; BESSIBES, M.; DJELLOULI, A.; PERGENT-MARTINI, C., and PERGENT G., 2011. The Neogoniolithon
brassica-florida (Harvey) Setchell & L. R. Mason (1943) Reef of Bahiret el Bibane lagoon (southeastern Tunisia). Journal
of Coastal Research, 27(2), 394–398. West Palm Beach (Florida), ISSN 0749-0208.
Neogoniolithon brassica-florida (encrusting rhodobionta) is generally reported as a veneering coral community along the
wave-beaten rocky coast of the Mediterranean Sea. Its presence in the hyperhaline lagoon of Bahiret el Bibane, situated
in SE Tunisia, takes on particular importance because of its extension. It constitutes a reef formation 14 km long
developing on both sides of the sea inlet. The building of this ‘‘natural monument’’ seems to be the result of an
evolutionary series. The aim of this study was to investigate the current status of this reef, comparing it to 30 years ago.
The current extension of the Neogoniolithon brassica-florida reef appears to be much reduced from that reported 30 years
ago, indicating a regression of 26%. Four different phases leading to the reef building were also identified.
ADDITIONAL INDEX WORDS:
Coral reef, biogeography, status, evolutionary series.
INTRODUCTION
The encrusting rhodobionta, Neogoniolithon brassica-florida
(Harvey) Setchell & L.R. Mason (1943), is widely distributed,
mainly on the wave-beaten rocky coasts, both in tropical and
temperate habitats (John et al., 2004; Silva, Basson, and Moe,
1996; South and Skelton, 2003; Womersley, 1996) in the lower
mediolittoral zone (Giaccone et al., 1993; Molinier, 1960).
In the Mediterranean Sea, the Neogoniolithon brassicaflorida community appears in the European repertories for the
conservation of the biodiversity (EUNIS code: A1.232–Mediterranean Area) and in the list of habitats of interest for
conservation of the Barcelona Convention (CAR-ASP code:
II.4.2.8; PNUE-PAM-CAR/ASP, 2007).
In the hyperhaline lagoon of Bahiret el Bibane (southern
Tunisia), the Neogoniolithon brassica-florida builds a spectacular reef. Other localized and less-spectacular reefs have been
recorded in Greece and Turkey, but they cannot compare with
the reef of Bahiret el Bibane. This reef is unique, with no other
similar formation in the entire Mediterranean, and for this
reason, must be protected and gain the status of natural
monument (Boudouresque, 2004, and references therein).
DOI: 10.2112/JCOASTRES-D-10-00082.1 received 2 June 2010;
accepted in revision 26 August 2010.
Published Pre-print online 8 December 2010.
’ Coastal Education & Research Foundation 2011
The aim of this study was (i) to make an assessment about
the current extent of this reef, (ii) to determine its dynamics
during the past few decades, and (iii) to identify the phases
leading to the reef building.
MATERIALS AND METHODS
Study Area
This work was carried out in Bahiret el Bibane, a hyperhaline lagoon of SE Tunisia (Keer, 1976; Medhioub, 1979)
(Figure 1). This lagoon, which has an area of about 230 km2,
is separated from the sea by a fossil Tyrrhenian oolitic
limestone offshore bar (Medhioub, 1979). The central part of
this offshore bar is split at approximately 2.5 km into a series of
nine small islands separated by passes. On the largest of these
islands (1 ha), surrounded by the two deepest passes (the
lagoon sea inlet), a fishing company is in charge of managing
fishing within the lagoon. Low stone walls, submerged during
high-sea levels, block all other passes. The Development
Company of Bahiret el Bibane recently built a hotel with 12
bungalows on one of the nine small islands at the entrance of
the lagoon (Ramsar, 2007).
With a maximum depth of 6 m, the lagoon is characterized by
increasing salinity from the sea inlet to the enclosed extremities, reaching more than 50% during the summer (Guelorget,
Frisoni, and Perthuisot, 1982; Medhioub, 1979). The bottom of
Neogoniolithon brassica-florida Reef of Bahiret el Bibane Lagoon
Table 1.
Figure 1.
Geographical location of Bahiret el Bibane lagoon.
the central part of this lagoon is covered by a vast meadow of
Cymodocea nodosa (Ucria) Ascherson (1869), mixed locally
with the chlorobionta Caulerpa prolifera (Forsskål) Lamouroux (1809) (Zaouali, 1982); the surface is covered by a mixed
meadow that is estimated at 19,546 ha, i.e., 84% of the lagoon
(Vela et al., 2008). Neogoniolithon brassica-florida, reported in
the lagoon since 1929 (Seurat, 1929), develops in the northern
part of the lagoon on both sides of the sea inlet, where it
establishes a reef parallel to the coast. The reef is about 30 km
long, which is comparable to a small fringing reef (Thornton,
Pilkey, and Lynts, 1978).
Field Activities and Data Analysis
In a previous study (Vela et al., 2008), 459 field data points
were obtained from the surface of the lagoon using a diving
mask, when the depth and turbidity allowed it, or by scuba
diving to cover the various types of benthic features represented in the lagoon. These data enabled the identification of
bottom types and seabed types in the el Bibane lagoon and the
approximate location of a thinly scattered Neogoniolithon
brassica-florida reef platform lining the north coast of the
lagoon. The limits of this reef were located in this study using a
Global Positioning System (GPS) Garmin 276C (accuracy
estimated between 5 and 10 m). Reef size, shape, distance
from the coast, and vertical structure were investigated by
snorkeling. The main reef builders (both algal and animal)
were also identified, documenting their vertical position in the
reef. Samples of macrophytes were also collected on the reef to
produce an inventory of the main species of the benthic
multicellular marine algae living on the reef.
For different subtidal and intertidal Mediterranean macro-
395
Braun-Blanquet cover-abundance scale.
Braun-Blanquet Score
Range of Cover (%)
5
4
3
2
1
+
75–100
50–75
25–50
5–25
,5; numerous individuals
,5; few individuals
phyte assemblages, the qualitative minimum sampling area
was previously determined to be between 64 and 200 cm2
(Ballesteros, 1992; Boudouresque, 1974; Boudouresque and
Belsher, 1979a, 1979b; Cinelli et al., 1977a, 1977b; Coppejans,
1980). In the present study, samples were collected in three
replicates within 400 cm2 (20 cm 3 20 cm) metal frame and
preserved in a 4% formalin–seawater solution (commercial
37% formaldehyde 5 100%). Identification of algal species was
based on microscope studies of formalin-preserved specimens.
An exhaustive species list was drawn up. Taxonomic nomenclature was aligned with the nomenclature used in the
Algaebase database (Guiry and Guiry, 2009).
Dominance and abundance of each species was visually
estimated in situ, using the Braun-Blanquet cover-abundance
scale (Braun-Blanquet, 1932, 1964), as shown in Table 1,
developed for terrestrial phytosociological studies but also
being applied by phycologists, especially those working in the
Mediterranean (e.g., Boudouresque, 1971a, 1971b). Areas used
for estimating dominance and abundance were those selected
for sampling macrophytes.
RESULTS
The Neogoniolithon brassica-florida reef extends 12.5 km to
the west and for about 1.5 km to the east of the sea inlet
(Figure 2). This reef is 0.5 m to 2.0 m wide and is continuous in
the western side of the sea inlet and delimits a small channel
parallel to the coast (Figure 3), whereas on the eastern side, it
is discontinuous and less developed (Figure 4). The reef
distance to the coast varies between 1 m on each side and
nearly 20 m in the central part, especially along the western
coast.
Taking into account the reef vertical structure, the upper
part is composed of the rhodobionta Neogoniolithon brassicaflorida, whereas the lower part was composed of Sabellariidae.
This latter part, bioconstructed by the Sabellariidae, is more
fragile than the rhodobionta section and has tended to
deteriorate with time (bioerosion) generating structures like
mushroom (Figure 5) or overhanging along the reef (Figure 6).
On the Sabellariidae, several macrophytes are observed
(Table 2). Between the reef and the coast, other structures
bioconstructed by the Sabellariidae (platforms) and covered by
a few macrophytes and some individuals of Neogoniolithon
brassica-florida were also observed.
Samples of macrophytes taken from the base of the reef and
from the bioconstructed platforms were very homogeneous
from a specific point of view. However, the relative abundance
of each species was variable between the sampling from the
base of the reef and that of the bioconstructed platforms.
Journal of Coastal Research, Vol. 27, No. 2, 2011
396
Langar et al.
Figure 2. Extension of the Neogoniolithon brassica-florida reef in the
Bahiret el Bibane lagoon.
The main species of macrophytes recorded at the base of
Neogoniolithon brassica-florida reef includes 6 Heterokontophyta (class Phaeophyceae), 3 Chlorophyta (2 Ulvophyceae and
1 Bryopsidophyceae), and 5 Rhodophyta (class Florideophyceae). The most abundant species was Cystoseira compressa,
and the least abundant one was Padina pavonica. On
the bioconstructed platforms, the most abundant species
was Padina pavonica, and all other species were weakly
represented.
DISCUSSION
The current extension of the Neogoniolithon brassica-florida
reef (14 km) appears much reduced from that last reported in
1978 (31 km) by Thornton, Pilkey, and Lynts (1978). However,
the less-detailed method adopted by Thornton, Pilkey, and
Lynts (1978) to estimate the extension differed from that used
in this work (measuring the coastal line); using our method on
the 1978 observations would reduce the last extension of the
reef to approximately 19 km.
Figure 3.
Neogoniolithon brassica-florida reef, continuous appearance.
Figure 4.
Neogoniolithon brassica-florida reef, discontinuous appearance.
Despite this correction, regression of the coral reef seems to
have occurred during the past 30 years, primarily affecting the
areas located on both sides of the sea inlet, where the
hydrodynamism is the most important in the lagoon (Medhioub, 1979). To the east of the sea inlet, the totality of the reef
observed in 1978 seems to have disappeared, and a new reef,
with a discontinuous appearance, is now observed more to the
east (Figure 2). However, because the fastest growth rate
reported for any of the corals is the staghorn species Acropora
cervicornis (Roth, 1979), with a maximum growth rate of
264 mm/y (Lewis et al., 1968), it seems unlikely that our
observations correspond to a new bioconstructed structure,
achieved during the past 30 years, but they could correspond to
what remains of the previously described reef. Our current
method of geolocation, being more precise than that of
yesteryear, we can consider that our geographical location is
more accurate. The regression observed on both sides of the sea
inlet, therefore, concerns nearly 5 km (26% of the reef extent),
according to our method of measurement.
Figure 5. Vertical structure of the mushroom-like Neogoniolithon
brassica-florida reef.
Journal of Coastal Research, Vol. 27, No. 2, 2011
Neogoniolithon brassica-florida Reef of Bahiret el Bibane Lagoon
397
Table 2. Main macrophytes present at the base of Neogoniolithon
brassica-florida reef and on the bioconstructed platforms and their
respective affected Braun-Blanquet score according to Table 1.
Braun-Blanquet Score
Class, Order, and Species
At the
base of the
reef
On the
platform
Florideophyceae
Figure 6.
Neogoniolithon brassica-florida reef overhanging structure.
Ceramiales
Laurencia obtusa (Hudson) Lamouroux 1813
Corallinales
Jania rubens (Linnaeus) Lamouroux 1816
Gigartinales
Hypnea musciformis (Wulfen) Lamouroux
1813
Peyssonnelia dubyi Crouan & Crouan 1844
Peyssonnelia squamaria (Gmelin) Decaisne
1842
3
+
2
1
2
1
2
+
1
+
1
+
1
+
1
+
2
+
2
+
2
2
1
+
+
2
4
+
Bryopsidophyceae
The observed macrophytes species are typical of lagoonal
environments (Djellouli, Verlaque, and Rais, 2000; Pérez-Ruzafa
et al., 2008). Their presence on the reef and on its base suggests
that the reef constitutes a favorable substratum for the installation of an algal assemblage dominated by Cystoseira compressa
and combining several species of the upper infralittoral.
It is difficult to identify exactly the phases leading to the reef
building, but it is possible to propose the following hypothesis:
Phase 1: Installation of Sabellariidae on shell debris,
creating small patches of hard substrate
Phase 2: Development of a colony of Sabellariidae, which is
at the origin of the bioconstruction of platforms on which
an association with Cystoseira compressa builds on.
Phase 3: Individuals of Neogoniolithon brassica-florida
settle on the platforms and start to develop both
horizontally and vertically.
Phase 4: Isolated colonies of Neogoniolithon brassicaflorida join and form the reef.
The vertical structure of the Neogoniolithon brassica-florida
formation shows this superposition, with a ‘‘layer’’ of Sabellariidae at the base, on which the macrophytes grow, surmounted
by the encrusting rhodobionta (Figure 5).
CONCLUSION
The decline of the Neogoniolithon brassica-florida reef in the
past few decades and the recent construction of infrastructures
on the small islands located at the entrance of the lagoon, which
are likely to degrade the environmental quality, justify
implementation of measures allowing for the preservation of
this natural monument. The inclusion of the lagoon on the list
of sensitive sites in Tunisia, by the Coastal Protection and
Planning Agency (APAL) (Decree No. 98-2092 of October 28,
1998) and its recent inclusion in 2007 on the Ramsar List of
Wetlands of International Importance (Ramsar site No. 1697)
(Ramsar–Iran, February 2, 1971, United Nations Treaty Series
No. 14583) are first steps in this direction and should be
continued.
Bryopsidales
Halimeda tuna (J. Ellis & Solander) J.V.
Lamouroux 1816
Ulvophyceae
Cladophorales
Anadyomene stellata (Wulfen ) C. Agardh
1823
Dasycladales
Acetabularia acetabulum (Linnaeus) P. C.
Silva 1952
Phaeophyceae
Cutleriales
Cutleria multifida (Turner) Greville 1830
Dictyotales
Dictyota dichotoma (Hudson) Lamouroux
1809
Dictyota dichotoma var. intricata
(C. Agardh) Greville 1830
Dilophus fasciola (Roth) M.A. Howe 1914
Padina pavonica (Linnaeus) Thivy in W.R.
Taylor 1960
Fucales
Cystoseira compressa (Esper) Gerloff &
Nizamuddin 1975
ACKNOWLEDGMENTS
This work was carried out and funded through the
framework of the decentralized cooperation program between
the territorial collectivity of Corsica (France) and the
Medenine governorate (Tunisia), which brings together the
University of Corsica, the I.N.S.T.M. (National Institute of
Science and Technology of the Sea), and the University of
Tunis. We also thank Dr. Marc Verlaque from the Université
de la Méditerranée (Marseille, France) for his help in
Neogoniolithon brassica-florida determination, and anonymous reviewers for their valuable comments and suggestions
that helped to improve the manuscript.
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