Spatial distribution of copepod abundance in the epipelagic layer of the south Adriatic Sea

Zooplankton has a non-random distribution in the pelagic community and exhibits various levels of patchiness (HAURY et al., 1978). Recently, particular attention has been focused on investigating the small-scale vertical and horizontal distribution of zooplankton assemblages which are important for monitoring marine processes and disturbances to marine ecosystems (PAFFENAn investigation into the spatial distribution of copepod abundance, using an “Adriatic Trap”, in the epipelagic layer of the south Adriatic Sea, was performed during 4 cruises at 5 stations from April 1993 to June 1994. Samples were collected at 1, 5, 10, 20, 50, 75, and 100 meter depths. Nauplii were the most abundant identified at all stations and depths, corresponding to an average of 69-81% of all copepod individuals. With respect to the total number of postnaupliar copepods, the 0-50 m layer was dominated by specimens of calanoids (49.7%), while in the 50-100 m layer, the most abundant taxa were cyclopoida-oncaeids (31.5%), cyclopoida-oithonids (23.5%) and harpacticoids (6.7%). Our research also clearly indicates that copepodites and small adult copepods, such as calanoids, Paracalanus parvus, Clausocalanus paululus, oithonids Oithona similis, Paroithona parvula, oncaeids Monothula subtilis, Oncaea zernovi, Spinoncaea ivlevi and harpacticoids Microsetella norvegica, M. rosea, were particularly dominant in the euphotic zone. Consequently, the problem of loss of small and undeveloped copepods through standard plankton nets requires that other quantitative methods must be utilised for an objective evaluation of total copepod population.