Abstract
With the aim of analyzing the trophic dynamics of deep-sea shrimp over the central Algerian slope, stomach contents of 219 individuals of Parapenaeus longirostris and 263 Aristeus antennatus were collected at night at depths between 200 and 400 m on a seasonal scale in 2007. Fullness ( f ), which is a measure of feeding intensity, showed significant seasonal changes in Aristeus antennatus , and the highest f was found in pre-reproductive periods (3.3% in January; 3.0% in April) before the beginning of gonad maturation (April-September in the area). This trend was coupled with the period of high surface productivity off the central Algerian coast (November-April). In that pre-reproductive period A. antennatus consumed more crustaceans (e.g. large decapods such as Processa sp.) with a high energetic value. These kinds of seasonal oscillations in f were not found in P. longirostris , probably because it was distributed shallower than A. antennatus and does not have a single marked peak in its reproductive cycle. The dietary composition of P. longirostris and A. antennatus was clearly segregated in the MDS analysis, which suggests there is good resource partitioning between the two species. Foraminiferans, bivalves and polychaetes were the most frequent prey in the diet of both P. longirostris and A. antennatus . Small micro and mesoplankton prey (radiolarians, tintinnids, copepods and pteropods) were more important in the diet of P. longirostris , while A. antennatus fed more on benthos. Planktonic prey found in the diet of the two shrimp were more frequent in January-February and April-May, e.g. in periods of higher water homogeneity coupled with periods of higher surface production. The large contribution of zooplankton to the diet of the deep-water shrimp over Algerian slopes is probably due to the importance of eddies in the area, which may enhance water column production locally. The high surface temperature (lowest T in January of 15.2°C) may accelerate the degradation of the organic matter that reaches Algerian slope bottoms, thus reducing the biomass of macrobenthos. We hypothesized that this low availability of benthic food resources may favour night time migratory movements by benthopelagic shrimp off the Algerian coast in search of more productive, shallow bottoms.
Highlights
Trophic relationships and the study of deep-sea trophic webs have been the focus of a number of studies in the deep Mediterranean and neighbouring areas, with special emphasis on the trophic role of decapod crustaceans (Lagardère, 1972; Cartes, 1994, 1995; Labropoulou and Kostikas, 1999; Kapiris et al, 2000; Cartes et al, 2008)
In A. antennatus we studied the diet of males, and for females we distinguished between small females (CL
Aristeus antennatus showed the lowest V in April and the highest in July 2007
Summary
Trophic relationships and the study of deep-sea trophic webs have been the focus of a number of studies in the deep Mediterranean and neighbouring areas, with special emphasis on the trophic role of decapod crustaceans (Lagardère, 1972; Cartes, 1994, 1995; Labropoulou and Kostikas, 1999; Kapiris et al, 2000; Cartes et al, 2008). The most commercially interesting decapod species are: Aristeus antennatus (Risso, 1816), Aristaeomorpha foliacea (Risso, 1827), and Parapenaeus longirostris (Lucas, 1846). Trophic factors such as prey availability and interspecific competition are especially important in a physically stable environment such as the deep Mediterranean (Cartes and Carrassón, 2004), and influence both the depth distribution and the local abundance of species. Ecological information from wide areas of the Mediterranean, such as the continental slope of North African countries (e.g. off the Algerian coast; Mouffok et al, 2008) is still very scattered and fragmentary
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