Ecology and population structure of the hyperbenthic copepod Mesaiokeras hurei Kršinić, 2003 (Calanoida: Mesaiokeratidae) from an isolated marine lake (Mljet island, Southern Adriatic Sea, Croatia)

Abstract

The monogeneric family Mesaiokeratidae (Copepoda: Calanoida) is exclusively bentho-pelagic and comprises nine small hyperbenthic species. Previous knowledge of these species has been limited to the description of their morphology and habitat. We provide new information about the ecology of Mesaiokeras hurei Kršinić, 2003, one of the small-size species of the family and found only in an isolated marine lake on the southern Adriatic island of Mljet (Croatia). Genetic markers were used to investigate its phylogenetic relationships with other copepods. The abundance of M. hurei abundance was highly variable over the years and seasons sampled. Densities were higher in spring and autumn. It was particularly abundant in 2011, averaging 629 ± 800 individuals/m3, and with a maximum of 1971 individuals m-3 in November, but averaged 74 ± 71 individuals/m3 and 66 ± 71 individuals/m3 in 2001 and 2008, respectively. Specimens were found in a range of temperatures, from 10.5°C to 18.3°C, but a majority of individuals (67%) was found in the 12-14°C layer. In addition to temperature, oxygen was a significant predictor (p<0.001) of the vertical micro-distribution of M. hurei. The DNA barcode sequence for the species is reported here for the first time. Analysis of the nuclear small subunit rRNA gene fragment (18S) showed a genetic similarity with representatives of the superfamily Clausocalanoidea.