Food composition of the shrimp Palaemon adspersus Rathke, 1837 (Crustacea Decapoda, Palaemonidae) in Karkinitsky Bay of the Black Sea in September 2016

Abstract

Palaemon adspersus is an inhabitant of the upper shelf (0–30 m) in temperate and subtropical zones of the East Atlantic, the northern limit of range reaching 60°N (Norway coast) and its southern limit being Atlantic waters of Morocco coast. The food of this species was studied at different times in different parts of its range, but it is described here for the first time for the Black Sea population. Stomach contents of 218 adult P. adspersus (74 of them had some food in the stomach, and 30 stomachs were full) were investigated. Samples were collected in September 2016 from commercial trap net near the Swan Islands in Karkinitsky Bay at the depth not exceeding 1.5 m. There was a small number of stomachs with food. It was due to a long stay of the shrimp in the trap net before their sampling. The shrimp had a body length (from the anterior edge of the orbits to the end of the telson) of 31.5–58.1 mm (males – 33.9–44.1 mm with a mode of 37 mm). The sex ratio was approximately 1 : 8 (11.7 % of males and 82.3 % of females). Females were represented by two groups. The first one had ovaries in maturity stage II and a modal size of 37 mm. The second group with the ovaries in maturity stage III had a modal size of 47 mm. Therefore, in September most of the females were mating, molting, and in their ovaries vitellogenesis began. By food composition, P. adspersus is a benthic feeder – euryphagous. Its food spectrum includes a wide range of food items from detritus and plant residues to gastropods, higher crustaceans, including shrimp, and fish. P. adspersus is primarily a gatherer detritophagous and macrophages, 70 % of its virtual food lump consisted of detritus and corpses of higher crustaceans. However, in relation to polychaetes it behaves as attacking predator while to gastropods it behaves as a grazing one. The comparison of the food composition of P. adspersus in Karkinitsky Bay (2016) with that in the Baltic Sea (1977), in the waters of Atlantic (1987) and Mediterranean (1993–1994) coasts of Spain reveals its spatial and temporal quasi-stability. Based on the totality of available data on food composition of P. adspersus, it should be attributed to sublittoral predators-opportunists.