The shell of Hexaplex (Trunculariopsis) trunculus (Gastropoda : Muricidae) as a mobile hard substratum for epibiotic polychaetes (Annelida : Polychaeta) in the Ria Formosa (Algarve coast-southern Portugal)

This work reports and illustrates secondary colonisation of Hexaplex (Trunculariopsis) trunculus shells by polychaetes in the Ria Formosa lagoon (Algarve coast-southern Portugal). Information is presented in terms of qualitative and quantitative data on epibiotic polychaetes, fouling frequency, degree of epibiosis, preferential areas for colonisation and incidence of shell damages. A total of 2,880 polychaetes belonging to 10 families were identified. Besides Spirorbidae (not quantified), the most abundant families were Serpulidae (67.5%), Sabellidae (10.2%), Sabellariidae (9.6%) and Cirratulidae (8.5%). From a total of 2,264 T. trunculus individuals analysed for epibiosis, 28.4% were non-fouled, 66.8% were intermediately fouled and 4.8% were heavily fouled. The fouling frequency, degree of epibiosis and incidence of damages in the shell spire increased markedly with T. trunculus shell length. Some epibiotic polychaetes were located preferentially on/or nearby particular features of T. trunculus shells, which probably facilitate settlement and tube construction, in addition to provide some protection against tube damage. The main consequences of epibiosis (benefits and disadvantages) for the gastropod basibiont (T. trunculus) are discussed. The present study apparently indicates that besides burrowing into soft bottom substrates, sporadic inter-tidal exposure and mutual predation on epibiosis, T. trunculus lacks other typical antifouling defence adaptations.