Description: Temperature, Salinity, pH, oxygen and chlorophyll data was collected with a Hydrolab HL7 multi parameter sonde installed on an oyster table in the Oddewatt oyster reef in Königshafen, Sylt, Germany (55.028483, 8.433876). The table and sonde surface during low tide.

Description: Temperature, Salinity, pH, oxygen and chlorophyll data was collected with a Hydrolab HL7 multi parameter sonde installed on an oyster table in the Oddewatt oyster reef in Königshafen, Sylt, Germany (55.028483, 8.433876). The table and sonde surface during low tide.

Description: In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. We collected the data in a laboratory experiment. Here, snails (Littorina littorea) infected with a parasite (Himasthla elongata) were kept in two different treatments (with predation risk and control). Subsequently, the excreted cercariae were collected as data. The experiments were conducted at the Wadden Sea Station of the Alfred Wegener Institute in List, Sylt, Germany. We sampled the snails at the the Danish coast of the Baltic Sea (Jütland, Arosund; 55*15'45.8'N 9*42'39.2'E). Snails had a shell height of 14-18mm corresponding to an age of two years. Infection status were screened at the laboratory. The crabs for the predation cue were sampled at the Oddewatt, List Sylt (German, Wadden Sea). Only male crabs with a size og 20-30mm catapace width were sampled. The blue mussels were sampled at the west coast of Sylt (Wenningstedt beach) were trematode infection do not occur naturally (confirmed by screening 50 mussels). Mussel shell length wars 25-30mm. Sampling of the experimental organisms: Mytilus edulis (latitude:54.937.600, longitude: 8.312.915); Littorina littorea (latitude55.262.722:longitude:9.710.889 ) and Hemigrapsus takanoi (latitude:55.028.713longitude:8.434.260 ).

Description: In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. We collected the data in a laboratory experiment. Here, snails (Littorina littorea) infected with a parasite (Himasthla elongata) were kept in two different treatments (with predation risk and control). Subsequently, the excreted cercariae were collected as data. The experiments were conducted at the Wadden Sea Station of the Alfred Wegener Institute in List, Sylt, Germany. We sampled the snails at the the Danish coast of the Baltic Sea (Jütland, Arosund; 55*15'45.8'N 9*42'39.2'E). Snails had a shell height of 14-18mm corresponding to an age of two years. Infection status were screened at the laboratory. The crabs for the predation cue were sampled at the Oddewatt, List Sylt (German, Wadden Sea). Only male crabs with a size og 20-30mm catapace width were sampled. The blue mussels were sampled at the west coast of Sylt (Wenningstedt beach) were trematode infection do not occur naturally (confirmed by screening 50 mussels). Mussel shell length wars 25-30mm.

Description: In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. We collected the data in a laboratory experiment. Here, snails (Littorina littorea) infected with a parasite (Himasthla elongata) were kept in two different treatments (with predation risk and control). Subsequently, the excreted cercariae were collected as data. The experiments were conducted at the Wadden Sea Station of the Alfred Wegener Institute in List, Sylt, Germany. We sampled the snails at the the Danish coast of the Baltic Sea (Jütland, Arosund; 55*15'45.8'N 9*42'39.2'E). Snails had a shell height of 14-18mm corresponding to an age of two years. Infection status were screened at the laboratory. The crabs for the predation cue were sampled at the Oddewatt, List Sylt (German, Wadden Sea). Only male crabs with a size og 20-30mm catapace width were sampled. The blue mussels were sampled at the west coast of Sylt (Wenningstedt beach) were trematode infection do not occur naturally (confirmed by screening 50 mussels).

Description: In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. We collected the data in a laboratory experiment. Here, snails (Littorina littorea) infected with a parasite (Himasthla elongata) were kept in two different treatments (with predation risk and control). Subsequently, the excreted cercariae were collected as data. The experiments were conducted at the Wadden Sea Station of the Alfred Wegener Institute in List, Sylt, Germany. We sampled the snails at the the Danish coast of the Baltic Sea (Jütland, Arosund; 55*15'45.8'N 9*42'39.2'E). Snails had a shell height of 14-18mm corresponding to an age of two years. Infection status were screened at the laboratory. The crabs for the predation cue were sampled at the Oddewatt, List Sylt (German, Wadden Sea). Only male crabs with a size og 20-30mm catapace width were sampled. The blue mussels were sampled at the west coast of Sylt (Wenningstedt beach) were trematode infection do not occur naturally (confirmed by screening 50 mussels). Mussel shell length wars 25-30mm.

Description: Temperature, Salinity, pH, oxygen and chlorophyll data was collected with a Hydrolab HL7 multi parameter sonde installed on an oyster table in the Oddewatt oyster reef in Königshafen, Sylt, Germany (55.028483, 8.433876). The table and sonde surface during low tide.

Description: Predators can affect parasite–host interactions when directly preying on hosts or their parasites. However, predators may also have non-consumptive indirect effects on parasite–host interactions when hosts adjust their behaviour or physiology in response to predator presence. In this study, we examined how chemical cues from a predatory marine crab affect the transmission of a parasitic trematode from its first (periwinkle) to its second (mussel) intermediate host. Laboratory experiments revealed that chemical cues from crabs lead to a threefold increase in the release of trematode cercariae from periwinkles as a result of increased periwinkle activity. This positive effect on transmission was contrasted by a 10-fold reduction in cercarial infection rates in the second intermediate host when we experimentally exposed mussels to cercariae and predator cues. The low infection rates were caused by a substantial reduction in mussel filtration activity in the presence of predator cues, preventing cercariae from entering the mussels. To assess the combined net effect of both processes, we conducted a transmission experiment between infected periwinkles and uninfected mussels. Infection levels of mussels in the treatments with crab cues were sevenfold lower than in mussels without crab chemical cues. This suggests that predation risk effects on mussel susceptibility can counteract the elevated parasite release from first intermediate hosts, with negative net effects on parasite transmission. These experiments highlight that predation risk effects on parasite transmission can have opposing directions at different stages of the parasite's life cycle. Such complex non-consumptive predation risk effects on parasite transmission may constitute an important indirect mechanism affecting prevalence and distribution patterns of parasites in different hosts across their life cycle.

Description: With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea (Magallana) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri, a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.