Centennial Changes in the Near‐Shore Mysid Fauna of the Gulf of Naples (Mediterranean Sea), with Description of Heteromysis riedli sp. n. (Crustacea, Mysidacea)

Abstract

Abstract. The marine mysid fauna of the Gulf of Naples is the best known in the Mediterranean, dating back to faunal lists and revisions given by founder authors in 1877 – 1929. Up to 1930, a total of 21 (currently valid) benthopelagic and benthic coastal species were recorded. The new census in 1975 – 2000 yielded no species in brackish and freshwaters (salinity range 0 – 30), only one species in mixoeuhaline waters (30 – 39), and 39 species in fully marine near‐shore waters (36 – 38). Most species were restricted to islands and submarine banks as hotspots of biodiversity, while only four species were also found along the more intensively urbanized continental coasts of the gulf. Compared with the situation in the 19th century, two marine species, Acanthomysis longicornis and Mysidopsis angusta, have disappeared from the Gulf of Naples, while still present in the less urbanized and largely oligotrophic Gulf of Salerno. The numbers of known euthalassobiontic species decreased in the ‘continental’ Gulf of Naples, but increased in the ‘insular’ gulf.Local population extinctions are related mainly to human impact on freshwater input into shallow coastal waters. Urbanization processes favoured the disappearance of brackish and freshwaters from the surface (through drainage and canalization) and the deterioration (through urban and industrial pollution) of the remaining ones, resulting in eutrophication of coastal waters and in impoverishment of the benthos, such as the visible regression of seagrasses. Increased species numbers in the ‘insular’ gulf reflect the lower degree of urbanization in the less polluted peripheral zones and the increased use of more specific sampling methods in combination with improved knowledge of mysid biology.With the use of epibenthic nets during the day and at night, Heteromysis (Heteromysis) riedli sp. n. was sampled from Posidonia oceanica meadows on the Island of ­Ischia. The males of the new species are exceptional in having a pair of modified, backwards‐oriented, flagellate setae terminally on the antennular trunc, while the females show only the usual forwards‐oriented, smooth setae in this position.