The sponges of the intertidal zone of Charente-Maritime rocky shore

Charente-Maritime shores are located on coasts of France between Loire and Gironde estuaries (Fig. 1). This 46°N latitude situation is responsible for temperate climate and this coastal position pulls oceanic conditions. Rocky shore represented 20% of the seashore (i.e. 88 Km versus 440 Km) of the total Charente-Maritime shores (IFEN, 1997). Furthermore, intertidal shore is influenced by Atlantic oceanic tides with two daily periods, moony and seasonal variations. At the equinox tide, the variations of water height can reach approximately 6.5 m (macrotidal shore).

Fig. 1 : Situation of Pertuis Charentais Sea and the Charente Maritime seashore (France insert) in the Biscay Bay on the West coast of France (Borja & Collins, 2009).

The total biodiversity of sponges is estimated has approximately 15,000 species, in which about 7000 are well known (Hooper et al., 2002 ; Fromont et al., 2006 ). In North-Atlantic marine water 337 sponges species has been found (van Soest et al., 2000). In the Pertuis Charentais Sea, 19 species have been reported since 18th century (Montaudouin (de) & Sauriau, 2000). However sponges are considered to be taxonomically difficult and consequently poorly documented in many regions of the world (Hooper et al., 2002). That is why our study which took placed on rocky shore in the intertidal zone at low tide (Fig. 2) from 2001 to 2011 reported 23 species including 13 that have never been described in the Pertuis Charentais Sea.  It confirms what Montaudouin (de) and Sauriau (2000) have announced that whole zoological phylum have been neglected in previous studies and specially the sponges phylum (or Porifera Grant, 1836).

Fig. 2 : Main rocky site of the Pertuis Charentais Sea sampled from 2001 to 2011 in intertidal zone of Charente-Maritime seashore (sampling sites 1-12 and La Rochelle Bay insert).

Sponge is among the oldest known metazoan organisms wishes ever leaved (Hooper et al., 2002). The oldest sponges fossils were dating from the late Precambrian. From the Palaeozoic to the late Mesozoic Era they have been major contributors to reef formation (UCMP, 2015). Since the Tertiary Era, three sponges classes remain:

• Demospongia (or "siliceous sponges") are composed of spongin fibbers and/or siliceous spicules. It represent 95% of the known living sponges (20 species on 23 showing in this Web site).
• Calcarea or "calcareous sponges" have spicules composed of calcium carbonate. They are predominantly living on near-shore shallow waters (3 species on the 23 common species living on Charente-Maritime rocky shore).
• Hexactinellida or "glass sponges" thus named due to the thinness of the spicules network. They are characterized by siliceous spicules consisting on six rays. In our time, they are living in deeper waters and polar area (UCMP, 2015).

Today, researches on sponges consist to extract many actives diseases substances of their tissues. For example, in the fifties antivirus molecules were extracted from Caribbean sponge (Bergmann & Feeney, 1951). Some ten years later, synthesis of antitumour compound (ARA-C) against lymphoid tumorale disease and another drug against Herpes virus (Ara-A) were possible (Thakur & Müller, 2004). In New-Zeeland, another antitumorale molecule (halichondin B) extracted from several sponges lead to preclinical tests. In Seychelles sponge species another substance with antifungal properties was isolated to take care AIDS patient from several opportunistic diseases. The first sponge secondary metabolite output in a bioreactor with successful lead to avarol molecule, a potential antiviral, antitumorale and anti-inflammatory compound (Müller et al., 2000).

For their ability to filter great amount of marine water (432L per individual sponge), their resistance to various pathogens wishes leave on rocky shore for several hundred million years, to accumulate and tolerate various pollutants, sponges still unrecognized for many peoples, could bring many compounds to the whole humanity as a matter of a many others organisms wishes colonized marine world and composed marine biodiversity (Séguignes & Lagrange, 2010).

Acknowledgements:

 I am vary grateful to Michel Séguignes my course Master, for his attention, his framework about me and his aid in the sampling of the rocky shore biodiversity of Charente-Maritime coasts. Furthermore I wish to thank La Rochelle University and l'ILE (Environnemental Littoral Institute) of Charente-Maritime for their approval to access at their magnifying glass (Leika DMIRB) for the sponge spicules identification and the picture purchase by Olympus digital camera.

References:

Anonymous : http://www.ucmp.berkeley.edu/porifera/porifera.html in 23/07/2015.

Bergmann, W. & Feeney, R. J., (1951) J. Org. Chem., 16, pp. 981-987.

Borja, A. & Collins, M., (2009) Regional Seas integrative studies, as a basis for an ecosystem-based approach to management: The case of the Bay of Biscay, Continental Shelf Research, 29, (8), pp. 951-956.

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Séguignes, M. G. & Lagrange, C., (2010) Prise en compte des études de la biodiversité intertidale dans une approche de développement durable, liris.cnrs.fr/cnriut10/actes/articles.

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