J. Antonio Raga

Living Together: The Parasites of Marine Mammals

The reader may wonder why, within a book of biology and conservation of marine mammals, a chapter should be devoted to their parasites. There are four fundamental reasons. First, parasites represent a substantial but neglected facet of biodiversity that still has to be evaluated in detail (Windsor, 1995; Hoberg, 1997; Brooks and Hoberg, 2000. Perception of parasites among the public are negative and, thus, it may be hard for politicians to justify expenditure in conservation programmes of such organisms. However, many of the reasons advanced for conserving biodiversity or saving individual species also apply to parasites (Marcogliese and Price, 1997; Gompper and Williams, 1998). One fundamental point from this conservation perspective is that the evolutionary fate of parasites is linked to that of their hosts (Stork and Lyal, 1993). For instance, the eventual extinction of the highly endangered Mediterranean monk seal Monachus monachus would also result in that of its host-specific sucking louse Lepidophthirus piriformis (Fig. 1b). Second, parasites cause disease, which may have considerable impact on marine mammal populations (Harwood and Hall, 1990). Scientists have come to realise this particularly after the recent die-offs caused by morbilliviruses (see Domingo et al., this volume). However, these epizootic outbreaks represent the most dramatic, but by no means the only, example of parasite-induced mortality in marine mammal populations (see Section 3 below).

CONSTRUCTIONAL MORPHOLOGY AND MODE OF ATTACHMENT OF THE TRUNK OF CORYNOSOMA CETACEUM (ACANTHOCEPHALA : POLYMORPHIDAE)

Dead specimens of Corynosoma cetaceum were used to describe the trunk musculature of this species and to infer the use of the trunk as a secondary holdfast. Inferences were based on trunk muscle arrangement, changes in trunk shape, size and distribution of spines, and geometry of tegument thickness. The foretrunk of C. cetaceum is swollen and forms a spiny disk that is bent ventrally. The disk is flattened by several groups of muscles not described previously, which seem able to finely adjust the disk surface over the substratum. Disk attachment appears to be accomplished by two dorsal neck retractor muscles specialized in pulling the anchored proboscis into the foretrunk. This mechanism has been described in other acanthocephalans, becoming surprisingly efficient when used with a flattened, armed foretrunk. The ventrally spined hindtrunk requires force to move downwards in order to attach. A single ventral neck retractor muscle seems specialized in pulling the posterior trunk forward, inducing a downward force due to the muscles precise points of insertion. This mechanism necessarily generates ventral wrinkling that needs to be eliminated for the spiny surface to be functional. The trunk ventral muscles are apparently arranged so as to concentrate the “excess” of the tegument into a single fold, optimizing the use of the remaining surface for attachment. The size and distribution of spines, as well as the geometry of tegumental thickness, conform to these observations. Morphological changes, seemingly simple, such as structural bending, may have triggered a cascade of subtle modifications and new functions during acanthocephalan evolution, reflecting how morphological integration and novelty interact. J. Morphol. 241:237–249, 1999.

Intestinal Helminth Fauna of Bottlenose Dolphin Tursiops truncatus and Common Dolphin Delphinus delphis from the Western Mediterranean

Abstract: We report on the intestinal helminth fauna of 15 bottlenose dolphins Tursiops truncatus and 6 short-beaked common dolphins Delphinus delphis from the western Mediterranean. Eight helminth species were found in bottlenose dolphin, i.e., the digeneans Synthesium tursionis, Brachycladium atlanticum, and Pholeter gastrophilus, the nematode Anisakis sp., and the cestodes Tetrabothrius forsteri, Diphyllobothrium sp., Strobilocephalus triangularis, and tetraphyllidean plerocercoids. Brachycladium atlanticum, S. triangularis, and tetraphyllidean plerocercoids are new host records. No T. forsteri had previously been reported in Mediterranean bottlenose dolphins. Three species of helminths were recorded in the common dolphin, i.e., the digenean Synthesium delamurei (which was a new host record), and the cestodes T. forsteri and tetraphyllidean plerocercoids. The intestinal helminth communities of bottlenose and common dolphins are depauperate, similar to that of other cetacean species, but those from bottlenose dolphins harbored a higher number of helminth species. This study supports the notion that oceanic cetaceans, such as common dolphins, have a comparatively poorer helminth fauna than that of neritic species, such as bottlenose dolphins, because the likelihood of parasite recruitment is decreased.

Hadwenius tursionis (Marchi, 1873) n. comb. (Digenea, Campulidae) from the bottlenose dolphin Tursiops truncatus (Montagu, 1821) in the western Mediterranean

The taxonomic position of Synthesium tursionis (Marchi, 1873) (Digenea, Campulidae) is revised, based on material from 147 worms from four bottlenose dolphins Tursiops truncatus stranded off the Comunidad Valenciana (Spanish western Mediterranean). The species is transferred to Hadwenius, as H. tursionis n. comb., and characterised by a high length/width ratio of the body, spinose cirrus and unarmed metraterm. Synthesium, a monotypic genus, becomes a synonym of Hadwenius. The intraspecific variation of some morphological traits is briefly discussed.

Diphyllobothriids (Cestoda: Pseudophyllidea) from the long-finned pilot whale Globicephala melas (Traill, 1809) off the Faroe Islands, with comments on the taxonomy of Diphyllobothrium Cobbold, 1858 species from cetaceans

The taxonomy of marine species of the genus Diphyllobothrium, particularly those parasitic in cetaceans, is rather confused. During parasitological investigations of long-finned pilot whales Globicephala melas from waters off the Faroe Islands, five diphyllobothriid species were detected: Diphyllobothrium sp. (possibly D. polyrugosum), D. stemmacephalum, Diphyllobothrium sp. A, Diphyllobothrium sp. B and Diphyllobothriidae sp. D. stemmacephalum is reported for the first time from G. melas. The stituation regarding the taxonomy of Diphylobothrium species from cetaceans is briefly reviewed. It is concluded that the recent development of genetic techniques may be of great value in relation to clarifying the taxonomy of this group.

Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) (Copepoda: Harpacticoida) from loggerhead sea turtles, Caretta caretta, from Japan and the Western Mediterranean: amended description and geographical comparison.

Abstract The ectoparasitic harpacticoid copepod, Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) (syn. Balaenophilus umigamecolus Ogawa, Matsuzaki and Misaki, 1997), has been reported on 3 species of marine turtles from the Pacific and the Mediterranean and from the West Indian manatee off Cuba in the Caribbean. The 3 available descriptions of this species were made using light microscopy. In this paper, we provide an amended description of B. manatorum using scanning electronic microscopy (SEM) for specimens in the collection from which B. umigamecolus was originally described. This material was collected from 1 loggerhead sea turtle, Caretta caretta, from Japan. The use of SEM allowed us to add several new microcharacters to the original description but, more importantly, allowed us to correct a number of the traits originally described. Some of the corrections could affect the interpretation of putative homology and variability of characters among populations of B. manatorum. A SEM comparison of specimens of B. manatorum from loggerheads from Japan and the western Mediterranean suggested the existence of morphological stasis between these populations. However, there were apparent meristic differences with a recently published description of this species from olive ridleys, Lepidochelys olivacea, in Mexico. Although B. manatorum is currently considered as a single, widespread taxon, the possibility that it actually represents a species complex deserves further attention.

Cestodes from Hector's Beaked Whale (Mesoplodon hectori) and Spectacled Porpoise (Phocoena dioptrica) from Argentinean Waters

Abstract Single individuals of 2 little-known cetacean species, Mesoplodon hectori and Phocoena dioptrica, stranded and died on the coast of Argentina (Buenos Aires and Chubut provinces, respectively) and were studied for the presence of helminths. The cestodes found were described and illustrated using light microscopy. The following cestode taxa were recovered: Tetrabothrius (Tetrabothrius) hobergi n. sp. (several fragmented specimens, at least 1 gravid) and Tetrabothrius (s.l.) sp. 1 (several fragmented immature specimens) from M. hectori, and Tetrabothrius (s.l.) sp. 2 (single fragmented immature specimen) and 2 morphotypes of tetraphyllidean larvae from P. dioptrica. Tetrabothrius (T.) hobergi n. sp. can be distinguished from Tetrabothrius (T.) forsteri by the greater number of testes and larger eggs and oncospheres, from Tetrabothrius (T.) curilensis by the smaller testes and vitellarium, the shape and size of the ovary, and the larger oncospheres and longer embryonic hooks, and from Tetrabothrius (T.) sp. from Ziphius cavirostris by the narrower strobila, smaller scolex, and smaller number of testes. The generic designations of Tetrabothrius (s.l.) sp. 1 and Tetrabothrius (s.l.) sp. 2 were based on the scolex morphology. Tetrabothrius (s.l.) sp. 1 is closest to Tetrabothrius (T.) forsteri and Tetrabothrius (Biamniculus) innominatus based on the number of testes, while the scolex size of Tetrabothrius (Tetrabothrius) sp. 2 is within the variability range reported for Tetrabothrius (T.) forsteri. More definite identification of the 2 species was not possible due to the condition of the available material. The present study provides the first descriptions of cestodes from M. hectori and P. dioptrica, thus enriching the knowledge regarding the helminths of insufficiently studied marine mammals.

Comparison of a Manual and an Automated Method to Estimate the Number of Uterine Eggs in Anisakid Nematodes: To Coulter or Not to Coulter. Is That the Question?

Studies reporting numbers of eggs in vagina and utero in nematodes often give little information of the technique used for the estimations. This situation hampers comparison among studies, because, so far, differences in estimations provided by different techniques have not been assessed. This note examines whether a manual method based on visual counts in aliquots and an automated method using a Coulter counter yield equivalent estimations of egg numbers in vagina and utero of 3 anisakid nematode species (Anisakis simplex, Pseudoterranova decipiens, and Contracaecum osculatum). The number of eggs from 50 females per nematode species was estimated using both techniques. The automated and manual methods yielded similar egg counts (correlation coefficients >0.9 in the 3 species), but the methods were not always statistically equivalent. The automated method was more precise and seemed less dependent on egg density, whereas the manual method was less time-consuming (contrary to previous perceptions) and less expensive. Despite the higher precision of automated counts, the manual technique seemed to produce similar estimates; thus, it may be particularly useful in developing countries where nematode parasitism is prevalent in humans and domestic animals, but scientific resources are limited.

Establishing the relative importance of sympatric definitive hosts in the transmission of the sealworm, Pseudoterranova decipiens : a host-community approach

The importance of a given host to a particular parasite can be determined according to three different criteria: host preference, host physiological suitability and host contribution to transmission. Most studies on the sealworm Pseudoterranova decipiens have focussed on the latter factor, but few attempts have been made to develop a quantitative transmission model evaluating the relative importance of each host. The purpose of this study was to propose a flow-chart model to study sealworm transmission within a seal community. The model was applied to hypothetical data of four seal species acting as definitive hosts of P. decipiens sensu stricto in eastern Canada: harp seal Phoca groenlandica , harbour seal P. vitulina , grey seal Halichoerus grypus and hooded seal Cystophora cristata . The dynamics of the model was studied using population estimates from 1990 to 1996. To illustrate the interrelationship of the seal populations in the flow dynamics, the model’s behaviour was explored by manipulation of the harp seal population size. The results showed that grey seals accounted by far for most transmission from and to the seals. The harbour seal population also sustained a biologically significant proportion of the flow, whereas the role of hooded and harp seals seemed negligible despite their large population sizes. The hypothetical removal of the harp seal population resulted in small increases in the relative flows to the other seals. These results conform to previous qualitative assessments on the relative importance of these seal species in sealworm transmission. The model provided some heuristic rules useful to understand transmission patterns. The data suggested that the harbour seal population should be about twice that of the grey seals to account for a larger share of transmission than grey seals. Although this is unlikely to occur at a large geographic scale, harbour seals outnumber grey seals in some areas and, therefore, the role of each host may change locally. To make this approach more realistic, further work should seek accurate estimates of parasite population parameters, better definition of the host community boundaries (at a local scale) and improved control of confounding variables.