Filamentous and mucilaginous algal blooms in a Corsican bay (Calvi-France)
In recent decades there have been profound changes in the benthic algal vegetation off the coast near Calvi (Corsica, France). These are probably linked to the disturbing effects of domestic sewage discharge which continually increase along with urbanization and tourism.
The Oceanographic Research Center "STARESO" is located in the bay of Calvi and provides excellent opportunity to carry out long term studies of algal vegetation. The first part of this study involved mapping the most important seaweeds of the bay (DEMOULIN & al., 1980; JANSSENS & al., 1993). The phenology, ecology and epiphytism of Cystoseira balearica Sauv. (the most common Fucoid in this part of the Mediterranean) were studied by CLARISSE (1984) and HOFFMANN & al. (1988). Other studies dealing with microscopic algae include WILMOTTE & al. (1988) who investigated the epiphytic Cyanophyceae and Bangiophyceae. In addition, WILMOTTE & DEMOULIN (1988) showed the influence of pollution on the distribution and ecology of some epiphytic Cyanophyceae. GOFFART (1982), LAMPROYE (1984) and DETIENNE (1988) studied the distribution of the Bangiophyceae in the bay of Revellata (near the bay of Calvi).
Before 1984, the rocky upper infralittoral zone of the Calvi bay was mainly populated by Cystoseira balearica settlements. Other Cystoseira species were present in the mediolittoral (C. compressa (Esper) Gerl. & Nizam. and C. stricta (Mont.) Sauv.) and medium infralittoral zones (C. spinosa Sauv.). Since 1984, the various species of Cystoseira and some other algae have shown a clear regression, while certain nitrophilous species (Cladophora prolifera (Roth) Ktz., Halopteris scoparia (L.) Sauv., Colpomenia sinuosa (Mertens ex Roth) Derbès & Solier and Enteromorpha sp.) tend to thrive. The Fucoid algae and more particularly the genus Cystoseira are known to exhibit a marked sensibility to organic wastes and gradually disappear from polluted sites (MUNDA, 1982). Now, other algal associations, including Halopteris scoparia, Dictyota sp. and Padina pavonica (L.) Thivy, have replaced or interrupted the Cystoseira stands in the bay of Calvi. In the North-Adriatic, these nitrophilous species are associated with moderately polluted sites (MUNDA, 1993).
In addition, since 1992, we have noted the extensive development of mucilaginous and filamentous aggregates in some parts of the bay.
In early spring, a large amount of filaments grow on rocks, macroalgae, gorgonians, and seagrass (Posidonia oceanica (L.) Delile). These new associations are found in all photophilic zones from 5 to 30 m with some preference for substrates with a southern exposure. The predominant species in these filamentous aggregates is Nematochrysopsis roscoffensis var. giganteus (Chrysophyceae). This species was first described in the bay as Tribonema marinum J. Feldmann (Xanthophyceae) by COPPEJANS & BOUDOURESQUE (1983). The morphology is unbranched and uniseriate with a cell wall constructed of " H-pieces ". The species Chrysonephos lewisii (Taylor) Taylor is also found in these associations. It is a tropical genus first described in the Mediterranean sea by SARTONI (1995).
In 1995, the first of these filamentous patches appeared near STARESO on March 15th (seawater temperature: 13.5 C) and on March 28th in 1996 (seawater temperature: 14.1 C). By mid-May, they could be found almost everywhere in Revellata bay. In some places, their development is very important and affects the growth of the rest of the vegetation by shading the water below and preventing photosynthesis. We have also observed growth of this filamentous association on artificial structures (i.e. metallic structures or ropes). At the "crique de l'égout", some filaments more than 2 m long grow on ropes vertically submerged. On uncovered substrates, a lack of competition with other species and fast growth in those filamentous forms seems to favor the development of new associations. The filamentous species preferably grow as epiphytes on Dictyota dichotoma or Cystoseira balearica where present, rather than on other macroalgae. D. dichotoma appears in various associations in early March. At the "la bibliothèque", the Cystoseira balearica association still exists is less healthy. During May 1996, the development of the filamentous associations was so prevelant that filaments could be found floating in the water column, free from any substrate. As a result, most of the macroalgae, and some Posidonia oceanica leaves are totally shaded and exhibit a markedly reduced growth.
At the end of spring, mucilaginous aggregates also begin to grow in high densities. The first globules were observed on May 29th 1996 (seawater temperature: 19.5 C) at Punta Revellata, "la bibliothèque", and in the STARESO area. They mainly contain Chrysophyceae, Pulvinaria giraudii (Derbs et Solier) Bourrelly 1957 (= Tetraspora giraudyi, Phaeocystis giraudyi, Pulvinaria feldmannii). This species can be found on macroalgae and on seagrasses, but is most commonly observed on uncovered rocks in small streams. Concurrently we noticed patches of blue-green algae and Diatomophyceae developing on the macroalgae. The blue-green algae are mostly Hydrocoleum sp. and Pseudanabaena sp. Due to the lack of competition with other macrophytes, these blue-green algae can develop in the upper infralittoral zone during the summer. Often the layer of blue-green algal filaments trap bubbles of oxygen from photosynthesis and are lifted to the sea surface.
The development of these aggregates is a peculiar phenomenon that changes benthic associations that are of potentially great importance when considering the general ecology of the bay.
These changes often involve the occurrence of new and rare algal species which is indicative of the need for further taxonomic and ecological studies.
Acknowledgements:
This work was supported by a grant from the Research Oceanographic Center; STARESO. I would like to also thank Jaimie Alonzo for his good english advices.
Literature cited:
CLARISSE, S., 1984. - Apport de différentes techniques cartographiques à la connaissance de l'autoécologie de Cystoseira balearica Sauvageau, macroalgue marine dominante dans la région de Calvi. Lejeunia, 113: 1-24.
COPPEJANS, E. & BOUDOURESQUE, C.-F., 1983. - Végétation marine de la Corse (Méditerranée). VI. Documents pour la flore des algues. Botanica Marina, XXVI: 457-470.
DEMOULIN, V., JANSSEN, M.-P. & LICOT, M., 1980. - Mise au point d'une méthode de cartographie des macroalgues marines. Application à la région de Calvi (Corse). Lejeunia, 102: 68 pp.
DETIENNE, X., 1988. - Comportement des Bangiophycées épiphytes de la région de Calvi en relation avec la qualité des eaux - Approche expérimentale et in situ. Mémoire de Licence en Sciences Botaniques de l'Université de Liège, 110 pp.
GOFFART, A., 1982. - Systématique et écologie des bangiophycées épiphytes dans la baie de Calvi (Corse). Mémoire de Licence en Sciences Botaniques de l'Université de Liège, 165 pp.
HOFFMANN, L., CLARISSE, S., DETIENNE, X., GOFFART, A., RENARD, R. & DEMOULIN, V., 1988. - Evolution of the population of Cystoseira balearica (Phaeophyceae) and epiphytic bangiophyceae in the bay of Calvi (Corsica) in the last eight years. Bull. Soc. Roy. Liège, 4-5: 263-273.
JANSSENS, M., HOFFMANN, L. & DEMOULIN, V., 1993 . - Cartographie des macroalgues dans la région de Calvi (Corse): Comparaison après 12 ans (1978-79, 1990-91). Lejeunia, 141: 1-62.
LAMPROYE, A., 1984. - Contribution à la taxonomie des Bangiophycées spécialement des espèces épiphytes de la région de Calvi (Corse). Mémoire de Licence en Sciences Botaniques de l'Université de Liège, 138 pp.
MUNDA, I.M., 1982. - The effects of organic pollution on the distribution of fucoid algae from the Istrian coast (vicinity of Rovinj). Acta Adriat., 23 (1/2): 329-337.
MUNDA, I.M., 1993. - Changes and degradation of seaweed stands in the Northern Adriatic. Hydrobiologia, 260/261: 239-253.
SARTONI, G., BODDI, S. & HASS, J., 1995. - Chrysonephos lewisii (Sarcinochrysidales, Chrysophyceae), a new record for the Mediterranean algal flora. Botanica Marina, 38: 121-125.
WILMOTTE, A., GOFFART, A. & DEMOULIN, V., 1988. - - Studies of marine epiphytic algae, Calvi, Corsica. I. Determination of minimal sampling areas for microscopic algal epiphytes. Br. Phycol. J., 23: 251-258.
WILMOTTE, A. & DEMOULIN, V., 1988. - Studies of marine epiphytic algae, Calvi, Corsica. II. Seasonal variations in the populations of epiphytic blue-green algae in three harbours with different pollution loads. Br. Phycol. J., 23: 259-266.
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