Influence of disseminated neoplasia, trematode infections and gametogenesis on surfacing and mortality in the cockle Cerastoderma edule

Abstract

Cerastoderma edule is a widely distributed bivalve mollusc, commercially exploited throughout Europe and is also an important food source for birds and crustaceans. Recently, mass surfacing and mortalities of cockles have been observed and reported at sites in Ireland and elsewhere, particularly in the summer months. One such site is Flaxfort Strand, Courtmacsherry Bay, County Cork, Ireland, an important feeding area used by many seabirds during the summer months. For the past few years large numbers of surfaced cockles have been observed at the site in a moribund condition. Samples of cockles from this area were collected over the summer months and their health status assessed. Cockles that had surfaced (moribund) and those still buried in the sediment were quantified and screened: sex, gonadal maturity and size class of cockles were also determined. Disseminated neoplasia and trematodes were observed in screened cockles. The most significant finding during the study was that mortalities and surfacing of cockles was related to a greater incidence of disseminated neoplasia. No neoplasia was observed in the smallest and largest size classes. There was a significantly higher prevalence of neoplasia in moribund cockles than in buried cockles, whereas in both groups a similar concentration of trematode metacercariae was observed in the screened tissues. Also, most of the cockles that had surfaced were either in the process of spawning or were spent. Overall a much larger percentage of moribund cockles exhibited both trematode infections plus neoplasia compared with buried cockles. A combination of the presence of neoplasia and trematodes, along with stress related to spawning, may immunocompromise the cockless, causing the animals to surface and become moribund. KEY WORDS: Cerastoderma edule · Disseminated neoplasia · Trematodes · Surfacing · Gametogenesis Resale or republication not permitted without written consent of the publisherDis Aquat Org 98: [73][74][75][76][77][78][79][80][81][82][83][84] 2012 cockles peaked in 1987 when 106 494 tonnes of cockles were harvested, but decreased to 11 809 tonnes in 2009, the last year for which statistics are available (www.fao.org/fishery/species/3535/en; accessed 6 Sep 2011). Declines in yields can be attributed, in part, to the ban of mechanical cockle fishing in the Wadden Sea (The Netherlands) since 1 January 2005, and to further restrictions on other sand flats such as the Oosterschelde (www.seaonscreen.org/ vleet/content/eng/cockle-fisheries.htm). Yields for cultured C. edule have been variable in the past (www. fao.org/fishery/species/3535/en; accessed 6 Sep 2011).Sexual maturity is usually reached when cockles are 18 mo old or when shell length reaches 15 to 20 mm (Seed & Brown 1977). Seed & Brown (1977) reported that cockles overwinter in a spent condition, but gametogenesis from late autumn/early winter has also been described (Twomey 1987). Gonadal development occurs rapidly once initiated in the spring and spawning begins in late spring/early summe...

Neoplastic diseases of marine bivalves

“…There is a not clear pattern regarding sex and occurrence of DN. Some studies reported no association between sex and DN prevalence in softshell clams M. arenaria (Brown et al, 1979;Potts, 1996), in mussels M. trossulus (Cosson-Mannevy et al, 1984) and in cockles C. edule (Iglesias, 2006;Morgan et al, 2012). Nevertheless, Brousseau and Baglivo (1994) found that female clams had a significantly lower occurrence of DN than male clams in three populations of M. arenaria from Connecticut.…”

“…DN was described at consistently high prevalence (>20%, but frequently over 40% in some samples) in cockles C. edule from the European Atlantic coast, sometimes associated with abnormal mortalities Ordás and Figueras, 2005). DN in cockles was reported in southern Ireland, in different locations of County Cork at an overall prevalence of 22% (range: 0-72%) Mulcahy, 1984, 1988b;Morgan et al, 2012). In France, cockles from Brittany had an overall prevalence of 4% (range: 2-46%) ) and from Arcachon Bay, monthly prevalence ranged from 2.2% to 13.6% (Le Grand et al, 2010).…”

“…These threshold sizes coincide with the size at which these species reach their first maturity: 25-39 mm in M. arenaria (Porter, 1974;Brousseau, 1978;Rosenblum and Niesen, 1985), and 15-20 mm in C. edule (Seed and Brown, 1977). Onset of reproduction is a physiologically stressful time which may render bivalves more susceptible to the development of diseases such as DN (Morgan et al, 2012;Böttger et al, 2013;Taraska and Böttger, 2013). The lower prevalence of DN in the older classes reported in some studies could be due to death of larger, older diseased bivalves (Brousseau and Baglivo, 1994;Potts, 1996;Böttger et al, 2013) or maybe older clams had developed some resistance to the disease (Taraska and Böttger, 2013).…”

“…Iglesias (2006) reported higher prevalence of DN in Galician adult cockles of 28-40 mm of shell length (1-2 years old) than in juvenile cockles of 10-21 mm of shell length (<1 year old). Morgan et al (2012) detected DN in Irish cockles ranging from 12 to 33 mm, but neoplasia occurred most often in intermediate size cockles (18-21 mm). The occurrence of DN in flat oysters, O. edulis, from France was significantly higher in oysters >2.5 years old (Balouet et al, 1986).…”

Withdrawn: “A health status survey of clams, Mya arenaria and Ensis siliqua, in the Irish Sea”

“…No parasites, pathogenic states or disease were found in any of the soft shell clams sampled in either of the two sites in the current study, despite a heavy prevalence of trematodes, neoplasia and Nematopsis spp. in Cerastoderma edule within the same area (Morgan et al, 2012), and Ostreid Herpes Virus previously identified in Crassostrea gigas in Bannow Bay .…”