P. L. Pascoe

The use of the dog-whelk, Nucella lapillus , as an indicator of tributyltin (TBT) contamination

The term ‘imposex’ was coined by Smith (1971) to describe the superimposition of male characters onto unparasitized and parasitized females of gonochoristic gastropods. In Nassarius obsoletus (Say) the development of imposex results in the female having one or more of the following characters: (1) a penis with a duct leading to (2) a vas deferens which passes back to the ventral channel of the capsule gland and (3) convolution of the normally straight gonadial oviduct (Smith, 1980). Imposex in the similarly gonochoristic Nucella lapillus (L.) was first noted by Blaber (1970) who found females with penis-like outgrowths in Plymouth Sound populations. Subsequent studies (Bryan et al. 1986; Gibbs & Bryan, 1986) have demonstrated that the incidence and intensity of imposex have since increased markedly in the same populations and that the phenomenon is widespread around south-west England.

Sex Change in the Female Dog-Whelk, Nucella Lapillus , Induced by Tributyltin from Antifouling Paints

Imposex, the development of a penis and vas deferens in the female (Smith, 1971) is known to occur in over 30 species of marine gastropods but, to date, in only one species has this syndrome been demonstrated to have a serious deleterious effect. This species is the dog-whelk, Nucella lapillus L. Both field and laboratory observations have provided conclusive evidence that imposex in N. lapillus is initiated by tributyltin (TBT), used as a biocide in antifouling paints, at concentrations in water of less than 1 ng Sn/1. This feature is manifest in the widespread occurrence of imposex even in areas far removed from centres of boating activity (see Bryan et al. 1986). Imposex appears to have little effect on the reproductive biology of N. lapillus until this syndrome is developed to its fullest extent when it sterilises the female because the pallial oviduct becomes occluded by vas deferens tissue thus preventing expulsion of the egg capsules (Gibbs & Bryan, 1986). Laboratory experiments have indicated that this condition, found in females close to harbours and marinas, may prevail after prolonged exposure during the first few years of life to TBT levels as low as 2 ng Sn/1 (Gibbs et al. 1987). Of six organotin compounds tested by Bryan, Gibbs & Burt (1988), tributyltin chloride proved the most effective in promoting imposex in N. lapillus .

TBT-induced imposex in the dogwhelk, Nucella lapillus: Geographical uniformity of the response and effects

The imposex response of the dogwhelk, Nucella lapillus, to tributyltin (TBT) pollution has been investigated in adults taken from four UK populations geographically separated over 10° of latitude. Exposure to TBT water concentrations of c.1 and 17 ng Sn/litre over a period of 12 weeks resulted in similar levels of accumulation of TBT within the body tissues and similar increases in female penis length in all four populations. The features are imposex in N. lapillus populations in south-west Brittany are described; they follow the same pattern as found in earlier surveys of the southern England coast, including sterilisation of females, population decline and disappearance of the species close to TBT sources. The evidence of these two investigations indicates that the level of sensitivity and development of imposex as a response to TBT pollution is uniform in N. lapillus throughout its distributional range.

Nassarius reticulatus (Nassariidae: Gastropoda) as an indicator of tributyltin pollution before and after TBT restrictions

Between 1984 and 1993, levels of imposex (the induction of male characters including a penis on females) were measured in gastropods Nassarius (Hinia) reticulatus (L.) at localities in south-west England. Since tributyltin (TBT) was thought to cause imposex, concentrations in tissues and sea-water were also determined. Measurements made prior to the restriction of TBT usage in 1987 showed that intensities of imposex were related to TBT levels in females. Tissue concentrations were also related to those of sea-water and concentration factors (dry tissue/water) were approximately 30,000 at 10 ng Sn I -1 and 75,000 at 1 ng Sn I -1 . Penis development in females was initiated at about 1 ng Sn I -1 and in this respect JV. reticulatus appears less sensitive to TBT than the dog-whelk Nucella lapillus . As result of the TBT restrictions, concentrations in sea-water and tissues at some of the more polluted sites decreased by factors of 5–10 times between 1987 and 1993. However, population imposex declined very slowly. This was attributed to the longevity of the snails, the slow decline of penis-length in older females and the limited recruitment of less-affected females. It was concluded that N. reticulatus is a useful alternative to N. lapillus as an imposex-based TBT indicator at contaminated sites. However, when environmental TBT concentrations are declining fairly rapidly, analysis of N. reticulatus tissues provides a far better indication of change than measurements of population imposex.

Tributyltin-induced imposex in stenoglossan gastropods: Pathological effects on the female reproductive system

Abstract 1. 1. The imposition of male sex organs on female stenoglossan gastropods—“imposex”—is a worldwide phenomenon now known to be associated with the usage of marine antifouling paints containing tributyltin (TBT) compounds. 2. 2. The effect of the imposex response on the female reproductive system varies according to species: in some, breeding appears unaffected, whilst in others the anatomy of the oviduct may be so modified that the female is effectively sterilised. 3. 3. New evidence suggests that TBT interrupts steroid metabolism, notably the conversion of testosterone to oestradiol 17β.

The Influence of an Electric Light on the Capture of Deep-Sea Animals by a Midwater Trawl

For centuries man has used lights to attract and concentrate fishes near the sea surface to aid their capture by nets or hooks (Ben-Yami, 1982). Underwater lights lowered into shallow seas are now regularly used to lure fish into set nets, large nets suspended beneath ships or into the vicinity of powerful pumps (Sidelnicov, 1981; Andreev, 1962; Nikonorov, 1969). Usually lights of more than 1 kw are used and such power requires a surface generator and strong insulated cable from the surface to the light. Although we know from these applications that some fish species are attracted by lights, the use of lights on trawls has not been developed for commercial exploitation or for research sampling. Perhaps such development has been discouraged by the safety problem and technical difficulties of providing electrical power on deck and handling heavily insulated conducting cable between the trawl and the generator. Lights have been used on commercial trawls with television in experiments to study fish reaction to trawls but such experiments were not concerned with finding the effect that lights might have on the quantity of fish caught and catches have not been analysed (A. Maclntyre, personal communication).

Cephalopod Species in the Diet of a Sperm Whale ( Physeter Catodon ) Stranded at Penzance, Cornwall

Stomach contents from an adult male sperm whale ( Physeter catodori ) stranded at Penzance, Cornwall, included a total of 125 upper and 110 lower beaks (mandibles) of cephalopods. All but two of the cephalopod species represented by lower beaks were oceanic squid belonging to four species in four families comprising: Histioteuthis spp. (44·5% by number and 10·7% by estimated wet weight); Architeuthis spp. (42·7% by number, 82·2% by weight); Todarodes sagittatus (7·3% by number, 6·0% by weight); Galiteuthis sp. (0·9% by number, 0·02% by weight); an oceanic octopod, Haliphron atlanticus (3·6% by number, 0·9% by weight) and one neritic species, Loligoforbesi (0·9% by number and 0·1% by weight). Mantle lengths of the squid were estimated to vary from 126 to 1056 mm.

The influence of artificial light on the capture of deep-water demersal fish by bottom trawling

Lights were attached to the headline of a bottom trawl during a series of tows at 1000 m depth in the Rockall Trough (north-east Atlantic). There was no significant difference in the overall numerical abundance of demersal fish between the trawl catches with light and the controls with no light. A principal components analysis based on the total fish catch between the experimental and the control stations showed no segregation. At the individual species level significant differences in catch rate were found for eight species. These are discussed in relation to the small amount of available information on the visual systems of deep-sea demersal fish and their diet.

The Influence of an Electric Light on the Capture of Oceanic Cephalopods by a Midwater Trawl

A total of 57 comparative hauls using a rectangular midwater trawl with a fishing mouth area of 50 m2 (RMT 50) were carried out along the sides of an imaginary triangle south of Madeira in 1986. A total of 1258 cephalopods were caught, giving a mean of 22 per haul with a range from 0 to 67. The nets were used with a divers light on the top bar which was either switched off or was operated with a 20, 70 or 150 W bulb, powered by a car battery. A significantly greater number of individuals per haul was caught with lights on than without lights, increasing from a mean of 13·5–25·1, a factor of 1·8. Similarly, the number of species caught was increased from a mean of 7 to 10·4, a factor of 1·5 and the volume of cephalopods was increased from a mean of 41·1–162·3ml, a factor of 3·9. Similar comparisons made for catches during day or night separately and on the three courses separately also showed marked increases with the lights. Samples show that increase in power of the lights increased the total number of cephalopod individuals caught. In the 12 species with more than ten individuals, in 33 of the 36 comparisons (of number of individuals, species and volumes) there is an increase with the light. The most influenced species was Taonius pavo which increased in numbers by a mean factor of 3·9 times with 20W, 4·0 times with 70W and 6·1 times with 150W when compared with the numbers caught with no light.

Karyotypic differences between two species of Pomatoceros, P. triqueter and P. lamarckii (Polychaeta : Serpulidae)

Consistent with most other closely-related polychaete species which have been analysed cytogenetically to-date, Pomatoceros triqueter and P. lamarckii share an identical chromosome number (2n=24) and have a number of other karyotypic features in common. However, commensurate with their separate species status, their karyotypes differ at least in four chromosome positions as a result of structural chromosomal rearrangements. With a rDNA probe using the FISH technique, we have been able to demonstrate that the nucleolar organizer region (NOR) occurs at the same site on the same pair of chromosomes in the two species, which indicates that an inversion event is unlikely to have been the cause of the species variation in this particular case. Taken together, these karyotypic differences may be indicative of a chromosomal barrier to the formation of fertile offspring; an important feature for maintaining species integrity where the two forms occur sympatrically, such as in parts of south-west England.