Parasite community study of the undulate ray Raja undulata in the Ria of Muros (Galicia, northwest Spain)

The parasites present in 75 undulate rays (Raja undulata Lacepede, 1802) ca ptured in the Ria of Muros, a coastal embayment (ria) in northwest Spain we re studied. A total of five species of cestodes (Onchobotlrrinm uncinatum, Phyllobothrium lactuca, Echeneibothrium beauchampi, Acanthobothrium beneden i and Grillotia sp.), three species of nematodes (Schulmanela [Piscicapilla ria] sp., Pseudanisakis rotundata and Cystidicolidae gen. sp.) and one acan thocephalan (Acanthocephaloides propinquus) were detected. All species were elasmobranch-specific except Cystidicolidae sp. and Acan. propinquus, whic h can both be considered accidental in this host. Species diversity peaked over the period April-September (Shannon-Wiener di versity = 1.9-2.2; Pielou evenness = 0.8-0.9). The dominant species were ce stodes, notably O. uncinatum (present in 73 of the 75 hosts, and accounting for 45% of all parasites detected), followed by A. benedeni, P. lactuca an d Grillotia sp., all of which were present in more than 30% of the host ind ividuals. All species detected were autogenous, and all individuals except those of Cystidicolidae gen. sp. were adults. The five species of cestodes were present in hosts of all sizes, though sin gle-host species richness, single-host species diversity and overall intens ity of infection increased with increasing host size. Nematodes appeared in larger individuals (body length > 33 cm). Larval Cystidicolidae gen. sp. a ppeared only in the largest size class (> 33 cm), probably because only ray s of this size are capable of ingesting relatively large demersal fish, the usual intermediate hosts in this area. Analysis of the species compositions of single-host parasite communities, c onsidering cestodes only, suggests that negative interspecific interactions do not occur, despite the typically large size and abundance of the parasi tes. and their spatial concentration in the spiral valve. (C) 2000 Elsevier Science B.V. All rights reserved.