Feminisation of male clams Scrobicularia plana from estuaries in Southwest UK and its induction by endocrine-disrupting chemicals

Abstract

The risk of endocrine disruption in the marine environment is unclear and is often overlooked in invertebrates. We show that disruption to the 'normal' gonadal development of male estuarine clams Scrobicularia plana is occurring extensively at sites in Southwest UK, with populations exhibiting varying degrees of intersex (ovotestis). This is one of the few studies to have examined the extent of the condition in mollusc populations. Intersex was present in more than two-thirds of the populations screened from the Avon, Southampton Water, Bristol Channel/Severn, Erme, Plym, Fal, Tamar and Lynher Estuaries; severity varied, with between 0 and 60% of males exhibiting the condition. Prevalence of intersex tended to peak as gonads reached maturity in July, and was highest in clams from the Bristol Channel and Severn Estuary, coinciding with an increase in oocyte size in both the female gonad and in the ovotestis of affected males. Experimental exposures to sediment spiked with mixtures of 17β-oestradiol (E2), 17α-ethinyloestradiol (EE2), octylphenol (OP) and nonylphenol (NP) indicated that (xeno)estrogens could be a contributory factor in the induction of intersex and increased oocyte size. It is plausible, therefore, that the incidence of ovotestis may be linked to urban, industrial and agricultural influences, or a combination thereof, although the relative importance of these sources has yet to be determined. S. plana offers potential as a sentinel species for screening and investigation of endocrine disruption in the estuarine environment, helping to focus remediatory strategy where it would be most beneficial. KEY WORDS: Endocrine disruption · Intersex · Ovotestis · Scrobicularia plana · EstuariesResale or republication not permitted without written consent of the publisher

Latitudinal gradients in Scrobicularia plana reproduction patterns, population dynamics, growth, and secondary production

“…Moreover, this species is an important link in the food chains of these ecosystems, playing an important role in the diet of wading birds, crabs and benthic fish (Hughes 1969, 1970b, Bachelet 1982, Guelorget & Mazoyer-Mayère 1983, Casagranda & Boudouresque 2005, Langston et al 2007). There is increasing commercial interest in it as a human food resource with potential economic and social value (Rodríguez-Rúa et al 2003, Langston et al 2007.…”

“…There is increasing commercial interest in it as a human food resource with potential economic and social value (Rodríguez-Rúa et al 2003, Langston et al 2007.…”

Recovery from TBT pollution in English Channel environments: A problem solved?

“…However, analysis of sex ratios in Poole and Southampton clams in 2009 indicated deviation from the expected ratio of unity present in 'normal' populations (Langston et al, 2007). At sites in Poole and Southampton where TBT concentrations in sediments were highest there was a significant bias towards males (2:1, p<0.05, Fischer Exact test), compared with the Channel average of 1:1 (Fig.…”

“…Furthermore, exposure of S. plana to (xeno)oestrogens (17β oestradiol, nonylphenol) can induce intersex (ovotestis) in males, implying that this species is susceptible to endocrine-disrupting chemicals, albeit that the mechanisms are unknown and may not involve the conventional receptors and steroid pathways associated with endocrine disruption in vertebrates (Langston et al, 2007;Pope et al, Rotchell et al, this volume). Identification of the severity and mode of action of such chemicals, in ecologically-important indicators such as S. plana, are clearly pertinent goals to improve the evaluation and management of future contaminant threats to the Channel environment.…”

Site-specific distribution of the bivalve Scrobicularia plana along the European coast

“…The species is an important food source for shorebirds and fish (e.g. Hughes 1970, Moreira 1997, and economically valuable, especially in southern Portugal and Spain (Langston et al 2007). The species is present along the NE Atlantic coast, from the Norwegian and Baltic Seas in the north to Senegal in the south, and in the Mediterranean Sea (Tebble 1976).…”