Connectivity dynamics in Irish mudflats between microorganisms including Vibrio spp., common cockles Cerastoderma edule, and shorebirds

Shellfish, including the key species the common cockle Cerastoderma edule, living and feeding in waters contaminated by infectious agents can accumulate them within their tissues. It is unknown if microbial pathogens and microparasites can subsequently be transmitted via concomitant predation to their consumers, including shorebirds. The objective of this study was to assess if pathogens associated with C. edule could be detected seasonally in the faeces of shorebirds that feed on C. edule and in the physical environment (sediment) in which C. edule reside, along the Irish and Celtic Seas. Two potentially pathogenic global groups, Vibrio and Haplosporidia, were detected in C. edule. Although Haplosporidia were not detected in the bird faeces nor in the sediment, identical strains of Vibrio splendidus were detected in C. edule and bird faecal samples at sites where the oystercatcher Haematopus ostralegus and other waders were observed to be feeding on cockles. Vibrio spp. prevalence was seasonal and increased in C. edule and bird faecal samples during the warmer months, possibly due to higher seawater temperatures that promote the replication of this bacteria. The sediment samples showed an overall higher prevalence of Vibrio spp. than the bird faecal and C. edule samples, and its detection remained consistently high through the sites and throughout the seasons, which further supports the role of the sediment as a Vibrio reservoir. Our findings shed light on the fact that not all pathogen groups are transmitted from prey to predator via feeding but bacteria such as V. splendidus can be. As most of the wading birds observed in this study are migratory, the results also indicate the potential for this bacterium to be dispersed over greater geographic distances, which will have consequences for areas where it may be introduced.


Bird species Diet Status
Oystercatcher (Haematopus ostralegus) The main food resource includes the larger invertebrates, particularly mussels and cockles.
Resident and winter visitor from Iceland and the Faeroes.
Winter visitor to wetlands, as well breeding in small numbers in floodplains and boglands.

Bar-tailed godwit (Limosa lapponica)
Polychaete worms, particularly lugworms, form a large proportion of their diet. On the muddier estuaries, where lugworms may be absent, they take ragworms and bivalves.

Winter visitor to coastal estuaries from Russia and Scandinavia
Black-tailed godwit (Limosa limosa) Feed on a range of invertebrates, including bivalves, polychaete worms and shore crabs.
Winter visitor from Iceland.

Red knot (Calidris canutus)
Feed predominantly on small bivalves, especially mussels, clams and cockles, and also on crustaceans.
Winter visitor from northern Greenland and the Queen Elizabeth Islands of high Artic Canada west to Prince Patrick Island. In spring and light summer some breeding plumage birds can be spotted.

Dunlin (Calidris alpina)
Feed predominantly on small invertebrates of estuarine mudflats, particularly polychaete worms and small molluscs, including cockles 2 .
Summer visitor from NW Africa/SW Europe, winter visitor from Scandinavia to Siberia, passage migrant from Greenland (heading south to winter in Africa).
Resident, winter visitor from Iceland and passage migrant (from Scandinavia/the Baltic breeding areas to African wintering areas).

Common gull (Larus canus)
Feed on a wide range of terrestrial and aquatic insects and invertebrates, also fish, carrion and rubbish. In sandy and muddy shores molluscs, including cockles, can serve as food 3 .
Resident and winter visitor from Europe.

Black-headed gull (Chroicocephalus ridibundus)
Feed on mostly animal material, including a wide variety of insects, also earthworms, marine worms, molluscs, crustaceans, small fish and carrion. In sandy and muddy shores molluscs, including cockles, can serve as food 3 .
Resident along all Irish coasts, with significant numbers arriving from the Continent in winter.

Great black-backed gull (Larus marinus)
Diet includes carrion, fish, molluscs, crustaceans, marine worms, insects, rodents, berries, and the adults, young, and eggs of other birds. On mudflats, they follow the retreating tide to capture worms and small bivalves.
Resident along all Irish coasts.

Mediterranean gull (Larus melanocephalus)
Feed on terrestrial and aquatic insects, marine molluscs, including bivalves, and fish, also offal and carrion.
Breeds in small numbers in the southeast. Winter visitor from northwest France, Belgium and the Netherlands.

Sandwich tern (Sterna sandvicensis)
Feed mainly on surface-dwelling fish, taken from shallow dive.
Summer visitor to all Irish coasts. Winters in small numbers in Galway Bay and Strangford Lough.

Hooded crow (Corvus cornix)
Diet includes seeds, insects, carrion, young birds and eggs. In coastal areas, will take crabs, bivalve and gastropod molluscs.
Common resident throughout Ireland.

Raven (Corvus corax)
May feed on practically anything, but mostly on insects and their larvae, worms and other subterranean invertebrates, also berries, grain, small mammals and birds.
Widespread resident throughout Ireland, especially in upland areas.

Brent goose (Branta bernicla)
During the winter, it feeds mostly on eelgrass.
Winter migrant from high-Arctic Canada. This population winters almost entirely in Ireland, with small numbers in parts of Britain and France.

Little egret (Egretta garzetta)
Takes a wide variety of animals including small fish, frogs, snails and insects Resident along coasts and rivers throughout Ireland, but still scarce in the Midlands and the north-west. Grey heron (Ardea cinerea) Diet includes fish, amphibians, small mammals, insects and reptiles.
Common resident at wetlands, estuaries and along rivers throughout Ireland.