Oblada Research Articles

Study of a Mediterranean reef fish assemblage. Comparisons of population distributions between depths in protected and unprotected areas over one decade

Differences in Mediterranean fish communities of two rocky coastal areas, one inside an integral marine reserve and the second outside the reserve, near Banyuls-sur-Mer, France, were compared using underwater visual census after a 12-year interval. In 1980, the community structure in and outside the marine reserve was studied at two depths (Bell, 1983). In 1992, We used the same methodology to assess if variations occurred in this fish community between these two samplings. In both 1980 and 1992, water depth affected the relative abundance of fish communities and the number of species was roughly maintained in both sites. However, there were several other important qualitative and quantitative variations in the fish fauna over this period: (1) The abundance of species has decreased in the integral reserve whereas it has been maintained outside the reserve; (2) Nine species are more abundant in the integral reserve and nine others are more abundant outside the reserve. Among the species vulnerable to fishing, such as Labrus merula, Symphodus tinca, Mullus surmuletus, Diplodus sargus, D. vulgaris, Scorpaena porcus, Oblada melanura, 6 of them are more abundant inside the integral reserve and 4 others are more abundant outside; (3) The demographic structure of vulnerable species inside the reserve has changed: only the proportion of large fish (30 to 40 cm length) compared to medium (15 to 30 cm) and small (0 to 15 cm) fishes was higher in the integral reserve. The prohibition of recreational and professional fisheries and scuba diving has the fish community in the integral marine reserve in 1992 enhanced less than in 1980. The impoverishment of the fish density in the integral reserve between these two periods is difficult to understand in regard to the stability of the fish density outside the reserve. These results stress the need for a more regular and more extensive survey of the fish assemblage in and around the marine reserve of Cerbère-Banyuls

Abundance/host size relationship in a fish trematode community.

The abundance of six species of trematodes: Aphanurus stossichi, Bacciger israelensis, Diphterostomum israelense, Plagioporus idoneus, Leprocreadium album and L. pegorchis, parasitic in the digestive tract of marine teleostei (Sparidae) collected near Jounieh (east Mediterranean), was analysed as a function of the host-size. In two parasite/host systems, infections were observed from the lowest size classes of the sample, with a clear tendency to an increase of abundance in older fish. In four others, parasites appear only above a rather high threshold class, young individuals never being infected. In the last three parasite/host systems, host invasion may occur early or late, but infection decreases above a well defined size class, old fishes rarely or never being infected. A given trematode species, when parasitizing several host species, shows similar abundance/host size relationships, e.g., P. idoneus in Diplodus vulgaris and Oblada melanura. When more than one species of trematode infects a single host species, curves can be markedly distinct; for instance, L. pegorchis was collected from Pagellus erythrinus below 15 cm. whereas D. israelense parasitized the same fish approximately above the same size. There is no evidence that such a replacement of one trematode by another in the course of host growth is a result of inter-specific competition.

Digenetic trematodes of Lebanese coast fishes: the species complexes Lepocreadium album (Stossich, 1890) and Lepocreadium pegorchis (Stossich, 1900) (Lepocreadiidae)

Trematodes belonging to the species Lepocreadium album (Stossich, 1890) and L. pegorchis (Stossich, 1900) were found in Spondyliosoma cantharus and Spicara smaris (their type-hosts, respectively) and other fishes in Lebanese waters. Morphometric variations in body-size, size and form of the pharynx, egg-size in relation to body-size, etc, according to host-species, are reported and commented upon. L. album obladae n. subsp. is erected for specimens from Oblada melanura.

The Opecoelidae (Digenea) of sparid fishes of the western Mediterranean. III. Macvicaria Gibson & Bray, 1982

Macvicaria obovata (Molin) n. comb. is redescribed from Sparus aurata off the Mediterranean coast of France and a neotype is designated. Specimens from Oblada melanura off Israel may belong to the same species. It is mainly characterized by the uterine extension between the ovary and the anterior testis and the lack of a vitelline confluence in the forebody. M. maillardi n. sp. is also described from Sparus aurata off the southern coast of France. Its uterus does not pass between ovary and testes and the vitelline fields are confluent in the forebody. M. crassigula (Linton) n. comb. is redescribed from Diplodus annularis, D. sargus, D. vulgaris, Pagellus erythrinus and Sparus pagrus off Corsica, Calamus bajonado off Bermuda, Spicara smaris, D. annularis off Yugoslavia, D. sargus off Israel, and D. cervinus, Sparodon durbanensis and Cheilodactylus fasciatus in the SW Indian Ocean. It is similar to M. maillardi, but differs in being smaller, having a greater sucker ratio and a larger pharynx. It may well be a species-complex. M. dubia (Stossich) n. comb. is redescribed from Oblada melanura off Corsica and Yugoslavia. It is similar to M. maillardi and M. crassigula, but has a more anteriorly situated genital pore.

Evidence of a chemical defence mechanism in the echiuran wormBonellia viridisRolando (Echiura: Bonelliidae)

Evidence for the existence of chemical defence in the echiuran Bonellia viridis is provided by investigating the palatability of Bonellia tissues to the shrimp Palaemon elegans, the teleosts Oblada melanura and Mugil labeo, and the anthozoan Anemonia sulcata. Bonellia tissues are shown to be highly distasteful to the shrimp. The results with the teleosts and the anthozoan are less clear‐cut though Bonellia extracts are shown to be distasteful also to these species.