Effects of Nematode Parasites and Staghorn Sculpins on Burrowing Shrimp in US West Coast Estuaries: Implications for Shellfish Aquaculture

Pacific staghorn sculpins (Leptocottus armatus) are recognized generalist predators that feed on ghost shrimp (Neotrypaea californiensis) in estuaries along the US West coast where these burrowing shrimp cause substantial losses to oyster aquaculture. Ghost shrimp have been shown to harbor the third larval stage of a nematode parasite Ascarophis sp. but adult nematodes have not been described nor have the final hosts been identified. We designed surveys to discover whether staghorn sculpins serve as final hosts and whether this nematode and host regulate burrowing shrimp abundance on oyster aquaculture beds. Larval nematodes identified as Ascarophis (Ascarophis) sp. A were found in several populations of ghost shrimp in four US West coast estuaries. Mean nematode abundance varied by sampling site, but not season, and was 29% higher on oyster beds versus adjacent shrimp beds. Subsequent surveys of staghorn sculpins revealed that though they preyed on shrimp, they were not hosts of adult Ascarophis (Ascarophis) sp. A, suggesting that some other final fish host is responsible for the presence of this larval Ascarophis nematode in shrimp. Sculpin catch did not differ by habitat, but 10% more sculpins preyed on shrimp in shrimp beds outside oyster aquaculture where shrimp were more abundant. Larval Ascarophis nematodes were only found in large shrimp (> 12 mm CL) and the proportion of large shrimp was similar between habitats, which suggests that these trophically transmitted nematode parasites were not responsible for size selective mortality or predation pressure by habitat and unlikely to enhance natural biological control of shrimp on oyster beds.