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The Mediterranean region under climate change

 | 
Jean-Paul Moatti
, 
Stéphane Thiébault

Part 2. Vulnerability and impacts

Sub-chapter 2.2.3. The sea level rise and the collapse of a Mediterranean ecosystem, the Lithophyllum byssoides algal rim

Aurélie Blanfuné, Charles François Boudouresque, Thierry Thibaut et Marc Verlaque

Texte intégral

1The Mediterranean is a hot-spot of marine and terrestrial epsilon species diversity (Boudouresque, 2004; Blondel and Médail, 2009; Coll et al. 2010). The Mediterranean Sea also harbors a wide range of ecosystems, some of whose structure and functioning are unique in the world. These ecosystems include midlittoral Lithophyllum byssoides rims, shallow vermetid platforms, the Posidonia oceanica seagrass meadow, the Cystoseira seaweed forest and the coralligene (e.g. Pérès and Picard, 1964; Laborel, 1987; Hereu Fina, 2004; Ballesteros, 2006; Boudouresque et al., 2014; Personnic et al., 2014).

2Lithophyllum byssoides is a calcified cushion-like red alga (Rhodobionta, kingdom Archaeplastida), which, as the result of coalescence, stacking, and persistence of the individuals, results in formations that are as hard as stone, and are highly resistant to waves and storms. In ancient publications, the species was known as Tenarea tortuosa, Lithophyllum tortuosum and L. lichenoides, which are not legitimate names. Lithophyllum byssoides thrives in rocky and shady habitats, in semi-exposed and exposed conditions, just above the mean sea level, in a zone characterized by the oscillation of the waves and tide, the lower mid-littoral zone (Fig. 1; Pérès and Picard, 1964; Laborel, 1987; Laborel et al. 1994; Boudouresque, 2004). L. byssoides bioconstructions are known as algal rims or ‘trottoirs and can reach a width of 2 m (Fig. 1; Bianconi et al. 1987; Laborel, 1987). L. byssoides is the autogenic ecosystem engineer of a unique ecosystem characteristic of the Mediterranean Sea. Although it belongs to the marine realm, this ecosystem forms a frontier between the marine and terrestrial realms: it harbors both typically marine taxa, such as the encrusting coralline red alga Neogoniolithon brassica-florida and typically terrestrial taxa such as the arachnid Mizaga racovitzai (Pérès and Picard, 1964).

Figure 1
The Cala Litizia Lithophyllum byssoides rim in Scàndula Natural Reserve, Corsica, in 1983. Its width can reach 2 m.
© J.-G. Harmelin (courtesy of the author).

3The bioconstruction of L. byssoides algal rims is only possible when the sea level is stable or a slightly rising (Laborel, 1987; Faivre et al. 2013). After the Last Glacial Maximum (LGM), ~ 20 ka ago), when the sea level was 120-130 m below the current sea level (Lambeck and Bard, 2000), the sea level rose steadily at a speed of up to 3.7 m/century (Collina-Girard, 2003). The current algal rims correspond to the LIA (Little Ice Age; 13th through 19th centuries CE), when the polar ice sheets stopped melting and Alpine glaciers advanced, more or less stabilizing the sea level. Former algal rims, which today are submerged and increasingly bioeroded by sea urchins (Paracentrotus lividus), date mussels (Lithophaga lithophaga), boring sponges (e.g. Cliona sp.) and Cyanobacteria, were constructed during the DACP (Dark Age Cold Period, ca. 2nd through 8th centuries CE) and in earlier cold periods (Fig. 2).

4By the end of the LIA (mid-19th century), the sea level had resumed its rise. The rise was at first slow (0.4 mm/a) but, due to the human-induced amplification of climate warming, the sea level rise subsequently accelerated. It has now reached 3.4 mm/year (Nicholls and Cazenave, 2010). By the end of the 21st century, the rise will probably be within the range 26-82 cm, but a much greater rise in sea level cannot be ruled out. This rise should continue since at the end of three out of the last four interglacial periods, the maximum sea level was probably several meters above the current sea level (Waelbroeck et al. 2002).

Figure 2
Profile of a limestone cliff at La Ciotat (near Marseilles, Provence, France), showing the structure of the present Lithophyllum byssoides rim (LIA and post-LIA) and the remains of the previous submersed rims that are gradually disappearing under the influence of sublittoral bioerosion. From Laborel and Laborel-Deguen (1994, 1996), redrawn and simplified.

5L. byssoides algal rims have begun to be submersed throughout the Mediterranean Sea. While they formerly belonged to the lower mid-littoral zone, they have progressively ‘shifted’ to the infra-littoral zone (in fact, it is the infra-littoral zone that has ‘shifted’ upwards). The calcareous red alga L. byssoides then dies and is subsequently covered by infra-littoral species, such as soft red algae and articulated corallines (e.g. Corallina caespitosa). Simultaneously, the dead, ‘fossil’ algal rim is bioeroded by endolithic photosynthetic and non-photosynthetic borers and by grazers. The rim is perforated by holes of increasing size (Fig. 3), and its width and thickness decrease. Its total destruction may require five millennia. Under exposed conditions, the algal rim is protrudes higher above the mean sea level than under semi-exposed conditions; consequently, L. byssoides algal rims that thrive under semi-exposed conditions are more sensitive to the ongoing sea level rise (unpublished data).

6Popular media and scientists often rightly draw the attention of the public to the flooding of Pacific atolls and the states that are affected as a result. Here, we draw attention to the fate of the Mediterranean algal rims and to the first forecast collapse of a marine ecosystem as the indirect result of global warming, through the sea level rise: the current rate of sea level rise appears to be too fast and L. byssoides rims thus appear to be condemned (Faivre et al. 2013; Thibaut et al. 2013).

Figure 3
A dead, highly bioeroded, Lithophyllum byssoides rim, at Punta Palazzu (Natural Reserve of Scàndula, western Corsica).
© T. Thibaut.

Bibliographie

References

Ballesteros E., 2006
Mediterranean coralligenous assemblages: a synthesis of present knowledge. Oceanogr. Mar. Biol.: Ann. Rev., 44: 123-195.

Bianconi C.H., Boudouresque C.F., Meinesz A., Di Santo F., 1987
Cartographie de la répartition de Lithophyllum lichenoides (Rhodophyta) dans la Réserve Naturelle de Scandola (côte occidentale de Corse, Méditerranée). Trav. Sci. Parc Nat. Rég. Rés. Nat. Corse, 13: 39-63.

Blondel J., Médail J., 2009
Biodiversity and conservation. In: Woodward J.C. (ed.), The physical geography of the Mediterranean. Oxford University Press, Oxford: 615-650.

Boudouresque C.F., 2004
Marine biodiversity in the Mediterranean: status of species, populations and communities. Sci. Rep. Port-Cros Natl. Park, 20: 97-146.

Boudouresque C.F., Ruitton S., Bianchi C.N., Chevaldonné P., Fernandez C., Harmelin-vivien M., Ourgaud M., Pasqualini V., Perez T., Pergent G., Thibaut T., Verlaque M., 2014
Terrestrial versus marine diversity of ecosystems. And the winner is: the marine realm. In: Proceedings of the 5th Mediterranean Symposium on Marine Vegetation (Portorož, Slovenia, 27-28 October 2014). Langar H., Bouafif C., Ouerghi A. (eds.), RAC/SPA publ., Tunis: 11-25.

Coll M., Piroddi C., Steenback J., Kaschner K., Ben Rais Lasram F., Aguzzi J., Ballesteros E., Bianchi C.N., Corbera J., Dailianis T., et al. 2010.
The biodiversity of the Mediterranean Sea: Estimates, patterns and threats. PlosOne, 5 (8): 1-334 (e11842).

Collina-Girard J., 2003
La transgression finiglaciaire, l’archéologie et les textes (exemple de la grotte Cosquer et du mythe de l’Atlantide). In: Human records of recent geological evolution in the Mediterranean basin–historical and archeological evidence. CIESM Workshop monographs 24, CIESM publ., Monaco: 63-70.

Faivre S., Bakran-Petricioli T., Horvatinčić N, Sironič A., 2013
Distinct phases of relative sea level changes in the central Adriatic during the last 1500 years–influence of climatic variations? Palaeogeogr., Palaeoclim., Palaeoecol., 369: 163-174.

Hereu Fina B., 2004
The role of trophic interactions between fishes, sea urchins and algae in the northwestern Mediterranean rocky infralittoral. Tesi Doctoral, Univ. Barcelona: i-xii + 1-237.

Lambeck K., Bard E., 2000
Sea-level change along the French Mediterranean coast for the past 30 000 years. Earth Planetary Science Letters, 175: 203-222.

Laborel J., 1987
Marine biogenic constructions in the Mediterranean, a review. Sci. Rep. Port-Cros Natl. Park, 13: 97-126.

Laborel J., Boudouresque C.F., Laborel-Deguen F., 1994.
Les bioconcrétionnements littoraux de Méditerranée. In: Les biocénoses marines et littorales de Méditerranée, synthèse, menaces et perspectives, Bellan-Santini D., Lacaze J.C., Poizat C. (eds.), MNHN publ. Paris: 88-97.

Laborel J., Laborel-deguen F., 1996
Biological indicators of Holocene sea-level and climatic variations on rocky coasts of tropical and subtropical regions. Quaternary International, 31: 53-60.

Nicholls R.J., Cazenave A., 2010
Sea-level rise and its impact on coastal zones. Science, 328: 1517-1520.

Personnic S., Boudouresque C.F., Astruch P., Ballesteros E., Blouet S., Bellan-Santini D., Bonhomme P., Thibault-Botha D., Feunteun E., Harmelin-Vivien M., Pergent G., Pergent-Martini C., Pastor J., Poggiale J.C., Renaud F., Thibaut T., Ruitton S., 2014
An ecosystem-based approach to assess the status of a Mediterranean ecosystem, the Posidonia oceanica seagrass meadow. PlosOne, 9 (6): 1-17 (e98994).

Pérès J.M., Picard J., 1964.
Nouveau manuel de bionomie benthique de la mer Méditerranée. Rec. Trav. Stat. Mar. Endoume, 31 (47): 3-137.

Thibaut T., Blanfuné A., Verlaque M., 2013
Mediterranean Lithophyllum byssoides (Lamarck) Foslie rims: chronicle of a death foretold. Rapp. Comm. Int. Mer Médit., 40: 656.

Waelbroeck C., Labeyrie L., Michel E., Duplessy J.C., Mcmanus J.F., Lambeck K., Balbon E., Labracherie M., 2002
Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. Quaternary Sci. Reviews, 21: 295-305.

Table des illustrations

Légende Figure 1The Cala Litizia Lithophyllum byssoides rim in Scàndula Natural Reserve, Corsica, in 1983. Its width can reach 2 m.© J.-G. Harmelin (courtesy of the author).
URL http://books.openedition.org/irdeditions/docannexe/image/23472/img-1.jpg
Fichier image/jpeg, 181k
Légende Figure 2Profile of a limestone cliff at La Ciotat (near Marseilles, Provence, France), showing the structure of the present Lithophyllum byssoides rim (LIA and post-LIA) and the remains of the previous submersed rims that are gradually disappearing under the influence of sublittoral bioerosion. From Laborel and Laborel-Deguen (1994, 1996), redrawn and simplified.
URL http://books.openedition.org/irdeditions/docannexe/image/23472/img-2.jpg
Fichier image/jpeg, 157k
Légende Figure 3A dead, highly bioeroded, Lithophyllum byssoides rim, at Punta Palazzu (Natural Reserve of Scàndula, western Corsica).© T. Thibaut.
URL http://books.openedition.org/irdeditions/docannexe/image/23472/img-3.jpg
Fichier image/jpeg, 113k

Auteurs

Aix-Marseille University, CNRS/INSU, UMR MIO, France
Marine algae, Aix-Marseille University, CNRS/INSU, Toulon University, IRD, OSU Pythéas, Mediterranean Institute of Oceanography (MIO), UM 110
aurelie.blanfune@mio.osupytheas.fr

Aix-Marseille University, CNRS/INSU, UMR MIO, France
Marine ecologis, Aix-Marseille University and Toulon University, OSU Pytheas, Mediterranean Institute of Oceanography (UMR MIO), Marseille, France
charles-francois.boudouresque@mio.osupytheas.fr

Aix-Marseille University, CNRS/INSU, UMR MIO, France
Marine ecology, Aix-Marseille University, CNRS/INSU, Toulon University, IRD, OSU Pythéas, Mediterranean Institute of Oceanography (MIO), UM 110
thierry.thibaut@mio.osupytheas.fr

Aix-Marseille University, CNRS/INSU, UMR MIO, France
Marine ecologist, Aix-Marseille University and Toulon University, OSU Pytheas, Mediterranean Institute of Oceanography (UMR MIO), Marseille, France
marc.verlaque@mio.osupytheas.fr

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