Dogwhelk Populations Research Articles

AFLPs reveal different population genetic structure under contrasting environments in the marine snail Nucella lapillus L.

Dispersal has received growing attention in marine ecology, particularly since evidence obtained with up-to-date techniques challenged the traditional view. The dogwhelk Nucella lapillus L., a sedentary gastropod with direct development, is a good example: dispersal was traditionally assumed to be limited until studies with microsatellites disputed this idea. To shed some light on this controversy, the genetic structure of dogwhelk populations in northwest Spain was investigated with highly polymorphic AFLP markers giving special attention to the influence of hydrodynamic stress. In agreement with the expectations for a poor disperser, our results show a significant genetic structure at regional (<200 km) and areal scales (<15 km). However, the spatial genetic structure varied with wave-exposure in the present case study: IBD was evident under sheltered conditions but absent from the exposed area where genetic differentiation was stronger. Our results provide evidence that differences in wave-exposure can exert a detectable influence on the genetic structure of coastal organisms, even in species without a planktonic larva.

Genetic and morphological diversity in populations of Nucella lapillus (L.; neogastropoda) in response to tributyltin contamination

During the past three decades, North Atlantic populations of dogwhelks have been severely reduced in numbers, due to imposex and female sterility caused by TBT. We examined the relationship between the known history of female sterility and the present genetic diversity (measured by five allozyme-loci) and phenotypic variance (measured by nine quantitative characters) in six populations of Nucella lapillus along the coast of Norway. The environment of one of the populations was severely polluted with a vas deferens sequence index (VDSI) of 4.31, resulting in 24% sterile females. The environment of four of the other five populations was moderately polluted (VDSI 3.31–3.97, 0–1.6% sterile females), while the last population was unpolluted (VDSI 0.02, 0% sterile females). The six populations did not differ significantly with respect to genetic diversity. However, the population from the most polluted area had greater phenotypic variation in shell size, compared to all other populations. The results indicate that although TBT has had severe local negative effects on N. lapillus populations, it has not caused a reduction in long-term adaptive potential.

Rapid recovery of genetic diversity of dogwhelk (Nucella lapillus L.) populations after local extinction and recolonization contradicts predictions from life‐history characteristics

The dogwhelk Nucella lapillus is a predatory marine gastropod populating North Atlantic rocky shores. As with many other gastropod species, N. lapillus was affected by tributyltin (TBT) pollution during the 1970s and 1980s, when local populations became extinct. After a partial ban on TBT in the United Kingdom in 1987, vacant sites have been recolonized. N. lapillus lacks a planktonic larval stage and is therefore expected to have limited dispersal ability. Relatively fast recolonization of some sites, however, contradicts this assumption. We compared levels of genetic diversity and genetic structuring between recolonized sites and sites that showed continuous population at three localities across the British Isles. No significant genetic effects of extinction/recolonization events were observed in SW Scotland and NE England. In SW England we observed a decrease in genetic diversity and an increase in genetic structure in recolonized populations. This last result could be an artefact, however, due to the superposition of other local factors influencing the genetic structuring of dogwhelk populations. We conclude that recolonization of vacant sites was accomplished by a relatively high number of individuals originating from several source populations (the 'migrant-pool' model of recolonization), implying that movements are more widespread than expected on the basis of development mode alone. Comparison with published data on genetic structure of marine organisms with contrasted larval dispersal supports this hypothesis. Our results also stress the importance of local factors (geographical or ecological) in determining genetic structure of dogwhelk populations.

Endocrine active industrial chemicals: Release and occurrence in the environment

Of the xenobiotic endocrine active substances (EASs), tributyltin (TBT) has had the clearest link to an impact on aquatic ecology. Its release from marine antifouling paints had a drastic impact on dogwhelk populations in polluted harbors due to a masculization effect. 4-tert-nonylphenol is seen as the most significant of the industrial xenobiotic estrogen mimics, being implicated as the dominant endocrine disruptor in certain industrialized river reaches. Apart from hot spots associated with particular industries, the estrogenic alkylphenols, phthalates, and bisphenol A are present in effluent and receiving water at concentrations below that which would give cause for concern. Other more bioaccumulative compounds such as polybrominated flame retardants, dioxins, furans may possess some endocrine active properties. The possibility of additivity effects may yet mean that low concentrations of xenobiotic EASs will need careful consideration. It is noted that considerable quantities of many of these compounds are often found in sewage sludge and sediments.

Recovery of polluted ecosystems: the case for long-term studies

Recovery of marine ecosystems from pollution has tended to receive less attention than the study of new or continuing impacts, but such studies are important in charting recovery from acute incidents and following legislation to deal with chronic contamination. Recovery is inevitably a long-term process, and where such studies have been made they are often too short-lived. Interest quickly wanes following an acute incident and governmental bodies rapidly switch to new legislative priorities for chronic inputs. We review three case studies: recovery of dogwhelk populations after local extinction by tributyl tin leachates from antifouling paints; recovery of rocky shore communities from oil spills; and recovery of estuarine ecosystems from industrial and urban development. We then make some generalisations about recovery processes before making a plea for long-term studies of polluted areas.

Imposex in populations of dogwhelks Thais spp. in relation to shipping intensity and mariculture activity in east Asia

Summary Imposex was recorded in samples of dogwhelks Thais spp. from each of the sites surveyed in Hong Kong and Singapore, and the majority of those in Phuket and Penang. There was no imposex in samples from Langkawi. The most advanced symptoms were those from shores close to commercial harbours, marinas and mariculture sites, suggesting that tributyltin (TBT) is a primary cause of the condition. All females were categorised as sterile from four sites on Hong Kong. In these cases recruitment has probably occurred as a result of the dispersal of larvae from fecund populations elsewhere. However, severe imposex was surprisingly localised, even in Hong Kong. There was evidence of decreasing symptoms of imposex with increasing distance from centres of shipping activity.

The use of imposex to assess tributyltin contamination in coastal waters and open seas

Imposex in muricid gastropods has been used to monitor tributyltin (TBT) contamination worldwide. Pollution was severe during the 1980s but regulations prohibiting the use of TBT-based antifoulants on vessels <25 m in length have been highly effective in reducing TBT levels in coastal waters. Large vessels are still sources of TBT and major ports, especially those with dry docking and repair facilities, continue to be hot-spots of contamination. Measures of imposex suggest that severe pollution is normally localised to within a few kilometres of them. Mild imposex, possibly as a result of TBT pollution (although other causes have not been ruled out), has been described in whelks Buccinum undatum from offshore waters of the southern and central North Sea. However, the species is still abundant there and the occurrence of imposex does not seem to have affected its breeding performance. Imposex was mild or absent in populations of dogwhelks from open oceanic sites around the north Atlantic Ocean, suggesting that the oceans are free of contamination at biologically significant levels.

TBT or not TBT?: That is the question

The benefits which have accrued from the development of TBT‐based antifouling paints, and their use on boat hulls and mariculture cages, must be assessed against environmental costs. High concentrations of tributyltin (TBT) occurred in some coastal waters in areas of intensive shipping (or ship‐related) activity or mariculture during the period of unregulated use of TBT‐based paints, and there is evidence that they were harmful to marine life. For example, they were held responsible for the near collapse of oyster farming in France and declines in the populations of dogwhelks in British waters. However, regulations, which were introduced by many countries a decade or so ago, restricting the use of these antifoulants to vessels > 25 m in length, have been highly effective in reducing TBT contamination. Predictions that TBT was likely to have catastrophic effects on some marine life have not been fulfilled and the problem of serious pollution is now restricted largely to centres of commercial shipping activity, such as major ports and shipyards. Severe impact is even localised in Hong Kong, which is one of the busiest ports in the world, and where regulations are said to be ignored. The International Maritime Organisation (IMO) is currently considering draft regulations which will ban the application of TBT‐based antifoulants from the year 2003. TBT coatings will not be allowed on ships from 2008 onwards. It is argued that the introduction of these regulations is premature and should be delayed until a proven safe alternative is available. Additional regulations could reduce the ambient concentrations of TBT in the environment still further, as could the development of new technologies relating to, for example, waste water treatment, port facilities and the properties of paints.

Survey of imposex in dogwhelks (Nucella lapillus) from North Sea coasts

Following a North Sea Task Force (NSTF) initiative in 1991, and funding from the Department of Environment (DOE), The Scottish Office Agriculture, Environment and Fisheries Department Marine Laboratory (SOAEFD), Aberdeen, was awarded a contract to assess the impact of tributyltin compounds in dogwhelks in all North Sea coastal waters. These waters were surveyed in 1991 and 1992 to evaluate the distribution and effects of tributylin (TBT) compounds on the common dogwhelk, Nucella lapillus. Wild and, where necessary, transplanted dogwhelks were analysed for imposex. Historical records indicate that Nucella lapillus was once present, on suitable substrates, around the whole of the North Sea coastline. Wild dogwhelks could be collected in all countries except Belgium and Germany, where the species is present only on Helgoland (in numbers too small to be sampled). All wild populations of dogwhelks showed imposex. Near sites of intense boating activity, all populations examined contained some sterile females. At all sites where transplants were recovered, the dogwhelks were affected by TBT. Prolonged survival of dogwhelks at any of these sites would not be expected, except perhaps at Torsminde in Denmark. All sites studied were categorized with reference to their potential for the maintenance of self-sustaining Nucella populations. All sites in the southern part of the North Sea (i.e. the coastlines of Belgium, The Netherlands, Germany and southern Denmark) were placed in Category C (reduced egg capsule production) or D (adult females expected to be sterile). In Norway, sites near large harbours had only sterile females in the population (Category D), whilst those further from harbours probably had reduced egg capsule production (Category C). In Sweden, all wild sites were affected but probably had no reduction in egg capsule production (Category B). In France and the UK, sites near large harbours or areas of small-boat activity probably had reduced egg capsule production (Category C). Sites further from sources of TBT contamination probably do not have reduced egg capsule production ( Category B). One site on the north east coast of Scotland shows effects consistent with an area distant from a source of TBT pollution (Category A). Copyright © 1999 Crown Copyright

The recovery of populations of dogwhelks suffering from imposex in the Firth of Forth 1987–1997/98

The impact of tributyltin (TBT) contamination on dogwhelk (Nucella lapillus) populations was assessed at 33 sites in the Firth of Forth, UK, during spring 1997 and summer 1998. The sex ratio of the animals; the ratio of juveniles to adults; the degree of imposex, as determined by the relative penis size index (RPSI); and the total tin concentration in a sample of dogwhelk tissue were used as measurements of TBT impact on dogwhelk populations. These data were compared with data from a similar survey carried out at the same sites in the Firth of Forth in 1987 (Bailey, S.K., Davies, I.M., 1988. Tributyltin contamination in the Firth of Forth (1975–1987). Science of the Total Environment 76, 185–192.) before restrictions were introduced on the use of TBT. The results demonstrate a general recovery in dogwhelk populations from the impact of TBT at the majority of the sites studied, although at six of the sites, the RPSI value remains high enough to suggest breeding problems in the population. It is suggested that large vessels are responsible for localised cases of imposex within the Firth of Forth.

Quantification of organotin compounds and determination of imposex in populations of dogwhelks ( Nucella lapillus) from Norway

Unintentional effects of the antifouling agent tributyltin (TBT) have been discovered in marine gastropods as the induction of male sex characters in females, known as imposex. The occurrence of imposex in dogwhelks ( Nucella lapillus) was investigated in 41 populations sampled in 1993–1995 along the Norwegian coast. A method for quantification of organotin species using gas chromatography and atomic emission detection (GC-AED) was developed. Some degree of imposex occurred in almost all populations of dogwhelks studied, except in four from Northern Norway. The concentration of organotin compounds in the gastropods from the unaffected populations was below the detection limit (7 ng Sn/g d.w.). The concentration of TBT in dogwhelks from affected populations was in the range 48–1096 ng Sn/g d.w. A positive relation between the concentration of TBT in dogwhelks and the degree of imposex was found.

Selective decline in imposex levels in the dogwhelk Lepsiella scobina following a ban on the use of TBT antifoulants in New Zealand

The level of imposex, the imposition of male characters in female gastropods, was compared in populations of dogwhelks before and after restrictions were introduced on the use of organotin antifouling paints in New Zealand. In one area subject only to pleasure craft there has been a significant decline in the percentage of imposex and in the relative penis size index (RPSI) in female dogwhelks. In a harbour area subject to both pleasure craft and commercial vessels there has been no decline in the percentage of imposex, but a significant decline in the RPSI.

Rocky shores monitoring programme

SynopsisRocky shores in Sullom Voe were first surveyed in 1976 and, apart from a break of two years (1982–83), have been surveyed annually since. The aim of the surveys is to monitor the health of the rocky shore communities by identifying any major changes in the abundance of the fauna and flora and distinguishing anthropogenic effects from natural fluctuations. The 23 primary sites are spread around Sullom Voe, from Mavis Grind, at the head, to Mioness, just outside the entrance. A belt transect method is employed, and categorical abundances of conspicuous species on a checklist are recorded. Graphical analysis of the data for selected species and sites is presented to illustrate the most important changes that have been observed.The rocky shore communities in Sullom Voe are dynamically stable, except where physical disturbance has not allowed them to reach a state of long-term stability. The effects of, and the recovery from, the 1979 Esso Bernicia oil spill and its clean-up are described. While recovery of communities was rapid on shores where no clean-up was attempted, the communities on shores which were mechanically cleaned were showing continued effects in 1993. The deterioration of dogwhelk populations affected by the antifouling paint additive tributyltin (TBT) has been followed in recent years. Dogwhelk populations close to the terminal jetties are very small and are dominated by adults. Natural fluctuations in abundances of barnacles, dogwhelks, limpets, fucoid algae and littorinid gastropods over the period 1976 to 1992 are also described.

Recovery of dogwhelk populations on the Isle of Cumbrae, Scotland following legislation limiting the use of TBT as an antifoulant

There is evidence of recovery from symptoms of imposex in populations of dogwhelks Nucella lapillus (L.) from study sites on the Isle of Cumbrae (Scotland) and, in particular, on shores adjacent to the town of Millport. RPSI scores and the numbers of ‘penisbearing’ females have decreased, and the numbers of dogwhelks on the shore have increased, between 1988 and 1993. Dogwhelks were not found at all at one site at Millport in 1988 but were abundant there by 1992–1993.

Assessment of imposex in the dogwhelkNucella lapillus(L.) and tributyltin along the northeast coast of England

Summary Concentrations of tributyltin (TBT) less than 5 ng/l were recorded in most coastal water samples taken from a series of sites in north-east England during autumn 1991. Levels in the industrialized Tyne estuary still exceeded the Environmental Quality Standard (EQS) in 1991 but had fallen from values recorded in 1989–90. Coastal dogwhelk Nucella lapillus (L.) samples taken in 1991 had low concentrations of <0.01–0.03 μg TBT/g wet tissue. Dogwhelk populations were suffering from severe imposex when they were sampled in 1986, but there was clear evidence of recovery by 1991/92. Relative Penis Size Index scores declined between 1986 and 1991/92; two populations which were not breeding in 1986 (as evidenced by lack of juvenile recruitment) reproduced successfully in the years preceding 1991; and dogwhelk abundance on the shore increased over the study period.

Recovery in populations of dogwhelks Nucella lapillus (L.) suffering from imposex

Populations of dogwhelks Nucella lapillus in areas of high boating activity on the Northumbrian coast had severe symptoms of imposex when they were sampled in 1986. They had high RPSI scores, male-biased sex ratios (probably due to high female mortality) and poor reproductive performance. There has however been marked recovery of these populations since the partial ban on the use of anti-fouling paints containing triorganotin compounds in 1987. RPSI values are lower, recruitment has improved and there is evidence of better survivorship of females.

Variation in Foraging Behaviour Among Individuals and Populations of Dogwhelks, Nucella lapillus: Natural Constraints on Energy Intake

SUMMARY (1) The behaviour of dogwhelks, Nucella lapillus (L.), predatory gastropods of rocky shores, was quantified by tracking populations of tagged individuals at two sites over three periods of 4-6 weeks. The dogwhelks fed upon mussels, Mytilus edulis L., or barnacles, Semibalanus balanoides (L.). Prey consumption and use of refuges by individuals were recorded on each daytime low tide. Variation among diets thus characterized was analysed to determine the effects on foraging behaviour of locality and previous experience of prey, and to compare observed behaviour with predictions of Optimal Foraging Theory. (2) Path analysis allowed the largest source of variation among individuals to be traced to the predominant species of prey in the diet, largely reflecting availability at specific sites. Dogwhelks transplanted between sites retained a slight preference for their original prey type. (3) Diets comprised largely of mussels included fewer, larger prey and provided a greater energy intake than diets comprised largely of barnacles. Dogwhelks feeding on barnacles spent a greater proportion of time foraging and were more likely to engage in extended bouts of sequential attacks. (4) Larger dogwhelks tended to include a greater proportion of mussels in their diet and to take more, larger prey of either type, resulting in greater energy intake. Larger dogwhelks were also more likely to engage in longer foraging bouts. (5) Differences in time-budgets between individuals taking smaller, less profitable prey and those taking larger, more profitable prey are consistent with the idea of a digestion-rate constraint or the miximization of absorption rate, given an optimal rate of gut processing. Further reduction in the time spent foraging is due to sheltering in refuges during harsh conditions. Dogwhelks thus appear to be able to integrate characteristics of their internal state with those of the environment (prey availability and mortality risk) when making foraging decisions.

Organotins in lake sediment

Organotin compounds are entering the aquatic environment due to their use in antifouling paints on boats and from municipal and industrial wastewaters [1]. Tributyltin (TBT) is highly toxic to aquatic life, particularly to marine molluscs (oysters) [2] and gastropods, leading to observed declines of dog-whelk populations on various coasts [3]. Chronic toxic effects on these organisms occur at aqueous concentrations of a few ng/1. TBT, dibutyltin (DBT), and monobutyltin (MBT) have been detected in the aquatic environment. Increased concentrations of TBT in water, sediment, and biota have been linked primarily to pleasure boating activities. In the water column, TBT concentrations were reported to lie in the high ng/1 range for marinas, and in the low to medium ng/1 range for open waters [4, 5]. TBT residues in sediments were found to be considerably higher, typically in the high /~g/kg range [4 6], and total butyltin concentration was shown to decrease with depth in sediment cores [7]. In the water column, TBT is biodegraded by successive dealkylation reactions leading to DBT as the principal degradation product with lesser amounts of MBT [6, 8]. In sediments, degradation was reported to be much slower with half-lives of 4 to 5.5 months [6 8]. To date, little is known about the occurrence and persistence of organotin compounds in sediments. Here, we report on the vertical distribution of a series of butyltins and phenyltins in the sediment of freshwater marinas of Lake Lucerne, Switzerland. The occurrence of phenyltin residues has not been previously reported. By using radiocesium isotopes in the sediment, we derive geochronological data. Con-

Continuing impact of TBT, previously used in mariculture, on dogwhelk (Nucella lapillus L.) populations in a Scottish Sea Loch

Abstract The degree of development of a penis and vas deferens in adult female dogwhelks as a result of exposure to tributyltin (TBT) compounds, and concentrations of total tin in homogenised soft parts of these individuals, have been investigated for three consecutive years (1986–1988) in a Scottish sea loch where TBT anti-foulants were used in mariculture until 1987. Results of these surveys, which included the examination of sub-adults and juveniles, and of adults transplanted from a site with low imposex levels to two sites within Loch Laxford, have indicated that, even though the use of TBT paints in mariculture was prohibited in the UK in 1987, low residual concentrations of TBT were still present in the loch during 1988–1989. A mathematical model describing the penis-length-shell-length relationships in individuals of all size ranges, from selected populations in 1987 and 1988, has shown that penis growth was stimulated in males, as well as females, in response to exposure to TBT; and that there was a smaller degree of imposex development in the sub-adult and juvenile dogwhelks in 1988, than in 1987. The decrease in imposex development suggests that although TBT was present in 1988, the concentrations were lower than in the previous year, suggesting that the 1987 legislation curtailing the use of TBT in mariculture was beginning to be reflected in the imposex condition of dogwhelk populations.

Variation in Growth and Consumption Among Individuals and Populations of Dogwhelks, Nucella lapillus: A Link Between Foraging Behaviour and Fitness

Variation in Growth and Consumption Among Individuals and Populations of Dogwhelks, Nucella lapillus: A Link Between Foraging Behaviour and Fitness