The first record of Gammarus aequicauda (Martynov, 1931) (Amphipoda, Gammaridea) in the estuary of the river Jadro (Adriatic Sea, Croatia)

Abstract

Gammarus aequicauda (Martynov, 1931) (Amphipoda, Gammaridea) is known as an euryhaline and euryvalent species in warm temperate waters, including lagoon systems and shallow coastal waters. The estuary of the River Jadro is a part of Kastela Bay (Adriatic Sea), and after construction works on the downstream watercourse of the river, some ecological conditions have changed. A concrete barrier that was built decreases the influence of fresh water, which resulted in an increased salinity and a raised level of dissolved organic compounds. Such conditions were favourable for macroalgae, especially Enteromorpha sp., thus overgrowing riversides and providing amphipods with food and protection against predators. There are no earlier published data confirming the presence of G. aequicauda in Kastela Bay. This is the first record of G. aequicauda from the River Jadro estuary as well as the first record of the species for Croatian rivers in general.