Ecology and production of Heterocypris exigua and Plesiocypridopsis newtoni (Crustacea, Ostracoda) in an oligohaline hypertrophic shallow lake

Abstract

: The ostracod assemblage from the littoral zone of Santa-Olalla, a shallow hypertrophic lake (Donana National Park, Southwest Spain), was sampled monthly from March 1998 to November 1999. Five ostracod species inhabit the lake (Herpetocypris chevreuxi, Ilyocypris gibba, Limnocythere inopinata, Heterocypris exigua and Plesiocypridopsis newtoni), the last two being outstandingly dominant (> 98 % of total ostracod abundance with maximum densities of 220,000 ind/m 2 and 67,000 ind/m 2 , respectively). Populations of both species occur in the lake all the year around with a peak in late spring. Their sex-ratios were frequently biased towards females and shallower habitats (∼15 cm deep) were strongly and positively selected against less shallow ones (∼30 cm deep). We also explored the functional role of these species in the lake through estimates of their annual secondary production (28.7 and 4 g DW m -2 yr -1 for H. exigua and P. newtoni, respectively) and we related these production results with existing data for whole system productivity to examine the importance of ostracods in energy flux.