Protozoi ed Elminti parassiti dei molluschi cefalopodi delle acque circostanti la Sardegna. Morfologia, sistematica, epidemiologia, possibile utilizzo dei parassiti come indicatori bioecologici

Abstract

Cephalopods are marine organisms which play a crucial role in the food webs of all the world oceans both as preys and predators. They are also actively exploited in many areas, with a rapid increase of their commercial value in the last decades. Despite this, the knowledge on the role of cephalopods in the host-parasite relationships is partial and frammentary, particularly in the Mediterranean Sea. This doctoral thesis was aimed to analyze the parasite fauna of 15 species and the orders Octopoda, Sepiida, Sepiolida, Myopsida, and Oegopsida, collected during research programs from the seas surrounding Sardinia (Geographic Sub-Area 11, code: GSA11). Some of the collected octopuses and squids are of commercial interest while other have only ecological importance, and/or are very rare in western Mediterranean. Techniques of light microscopy were mostly used for morphologic analyses and the parasites were examined as fresh mounts. Histological sections of infected organs were also examined, to find evidences of pathological effects. Furthermore, SEM microscopy for details of external morphology, and molecular tools to determine the species of Anisakis spp. third-stage larvae were used. The host-parasite complexes were also epidemiologically investigated, highlighting the relationships between levels of infections and sex, maturity, size, or geographic area of sampling. Among protozoans, five associations between the coccidian genus Aggregata and cephalopods were observed: Aggregata octopiana in the common octopus; A. sagittata in T. sagittatus, as a new geographical record; a probably new species in Histioteuthidae, here described in detail; and two cases in A. lichtensteinii and R. macrosoma. To date, only two species of these coccidians were known in the Mediterranean Sea. The helminth parasite fauna collected were dominated by third-stage larvae of anisakid nematodes of the species Anisakis pegreffii, A. physeteris and Lappetascaris sp. Type A (sensu Nagasawa and Moravec, 2002). With only one exception (one larva in E. cirrhosa), these roundworms were all found in Oegopsida. The same is valid for the digenean metacercariae of the family Didymozoidae, observed only in flying squids. Among Cestoda, plerocercoid larvae of Tetraphyllidea were the only harboured by octopods, even with infection indices lower than those observed in oegopsid squids. Trypanorhyncha plerocercoids of the genus Nybelinia were exclusively detected in Todarodes sagittatus. Regarding Anisakis species is important to remark the high values of infection of these zoonotic agents observed in commercial squids as Illex coindetii, T. sagittatus and Todaropsis eblanae. These data should provide basic information in the planning of food safety related to the consumption of raw or undercooked cephalopods. Histological observations of the lesions highlited the typical inflammatory response of molluscs to protozoan and metazoan infections, e.g. cystic encapsulation of parasites, hemocytic infiltration and distension of tissues. One interesting question deals with how the impact of such environmental biotic stressors as parasitic diseases may affect the dynamics of cephalopod populations, also since positive correlations were generally observed between prevalence and intensity of infections and the size and sexual maturity of hosts. Possible reasons include the increased feeding that occurs with growth and a change in diet with growth. Host sex-related preference were not markedly seen, although females are slightly more involved as hosts than males. The centrality of cephalopods in the oceanic food web is strongly confirmed by their role as intermediate and paratenic hosts for anisakids, didymozoids and cestodes which exploit their mobility to reach their definitive hosts in different levels of the water column. This indicates that squids in particular are prey items of primary importance for large marine top predators as cetaceans, scombrids, and elasmobranchs rispectively. A decrease in the abundance of parasites relatively to depth of trawl samplings was observed, excepted for that of Lappetascaris sp. Type A whose this infection index was very higher in lower bottoms. Given also the fact that the intermediate hosts of Aggregata spp. are usually benthic crustaceans, the findings of these parasites in neritic cephalopod hosts suggest that their feeding habits include a substantial component of predation in the seabed of the continental slope. Moreover, it seems to indicate that the still unknown definitive host for Lappetascaris sp. Type A may be a large demersal teleost. Data collected allowed to evaluate the potential use of some taxa of parasites as biological indicators of ecology and biology of cephalopod hosts, particularly concerning their trophic links with predators and preys, and the variations in diet depending on size or depth. These informations may represent a contribute to an holistic and multidisciplinary approach in the study on marine biocenosis including resources which need accurate management and prediction models for exploitation