Intersex in the clam Scrobicularia plana (Da Costa): Widespread occurrence in English Channel estuaries and surrounding areas

Abstract

Estuarine clams Scrobicularia plana were sampled from 108 intertidal locations around the English Channel and adjacent areas. Although S. plana is believed to be a strict gonochorist, 58% of the populations sampled included intersexed individuals (described as male clams exhibiting ovotestis).Over the entire region, on average, 8.6% of male clams exhibited intersex, although proportions of affected males ranged from 0% to 53% depending on location. The severity of intersex was assessed using a simple classification scale, with the majority of individuals showing low levels of impact. Sex ratios were significantly skewed at some sites. There were no significant relationships between the incidence and severity of intersex; or of associations with size or parasitism of individual clams.Intersex in S. plana is a useful tool to assess endocrine disruptive effects in estuaries, although mechanisms of impact and causative agents remain uncertain.

Gonadal Atresia, Estrogen-Responsive, and Apoptosis-Specific mRNA Expression in Marine Mussels from the East China Coast: A Preliminary Study

“…Many spent mussels were detected in July, prohibiting sex ratio calculations. No previous marine mussel sex ratio data is available for this region, though female sex ratio bias has been reported in mussels impacted by spilled oil in the Bay of Biscay (Ortiz-Zarragoitia et al 2011 ), and in clams, Scrobicularia plana , at selected sites from the English Channel (Pope et al 2015 ). A male bias has previously only been observed in S. plana from six locations in the English Channel region (Pope et al 2015 ) and following a > 36 week laboratory exposure using the bivalve Gomphina veneriformis to tributyltin (Park et al 2015 ).…”

Endocrine disruption and altered sexual development in aquatic organisms: an invertebrate perspective

“…Oocyte size was also higher in the Severn, notably at upstream sites (Langston et al, 2007a). Subsequently, an extensive survey of more than 100 sites along English and French Channel coastlines in 2009-2014 returned a similar range of frequency and severity figures (Pope et al, 2015); intersex was present in 58% of populations studied and proportions of affected males ranged from 0-53% (average 9%). The severity of intersex in Channel clams varied across the entire classification range (stages 1-6, Figure 4), though the majority of impacted individuals show only low severity (68% stage 1, 13% stage 2 and above).…”

“…Given this weight of evidence, not surprisingly, various measures of ‘endocrine disruption’ in molluscs, notably intersex, have been linked to sewage treatment works (WWTW) effluents (Moore & Stevenson, 1991; Chambers et al ., 1997; Gagné et al ., 2001; Gross et al ., 2001; Zulkosky et al ., 2002; Jobling et al ., 2003; Quinn et al ., 2004; Andrew-Priestley et al ., 2012), or known areas of anthropogenic contamination (Moore & Stevenson, 1991; Horiguchi et al ., 2000; Gagné et al ., 2002; Gauthier-Clerc et al ., 2002; Barbeau & Grecian, 2003; Lye et al ., 2005; Matozzo & Marin, 2007; Lee et al ., 2010).…”

“…The severity of intersex in Channel clams varied across the entire classification range (stages 1-6, Figure 4), though the majority of impacted individuals show only low severity (68% stage 1, 13% stage 2 and above). The overall mean M:F ratio was almost unity (1.007), indicating equal numbers of males and females, though sex ratios were significantly skewed at some sites: Nine populations were significantly biased towards females, six biased towards malesthe latter including sites known to be affected by TBT (Pope et al, 2015). Intersex frequencies varying between 1.5% and 71% have also been reported in S. plana from other estuarine locations in Europe, including Ireland (Raleigh & Keegan, 2006), Portugal (Gomes et al, 2009) and NW France (Tankoua et al, 2012).…”