Zooplankton communities across a hydroperiod gradient of temporary ponds in the doñana national park (sw spain)

We studied the influence of hydroperiod on the composition and richness of the zooplankton community in 19 freshwater temporary ponds of the Doñana National Park (SW Spain) at different spatial and temporal scales. The study ponds were assigned to three hydroperiod categories (long, intermediate, and short) according to previous hydrologic records. During the study period (October 1996––September 1998), wet phases ranged from 56%% to 100%% of the study period in the five long-hydroperiod ponds, from 25%% to 47%% in the 10 intermediate-hydroperiod ponds, and from 5%% to 21%% in the four short-hydroperiod ponds. A total of 56 crustacean species (27 cladocerans, 11 cyclopoids, 5 diaptomids, 1 harpacticoid, 1 notostracan, 1 anostracan, 1 diplostracan) and 47 rotifer taxa were identified from the 19 ponds. Most zooplankton taxa were widely distributed in the ponds. However, Dapnia longispina was restricted to the long-hydroperiod ponds and Metacyclops minutus to the short-hydroperiod ponds. There was a significant (P<0.01) positive correlation between the number of zooplankton taxa collected in each pond over the entire study period (or cumulative richness) and the pond wet-phase length (r== 0.790 for crustaceans and r==0.862 for rotifers, log-transformed data). However, single collection richness (or number of taxa registered in each pond at each sampling date) was not significantly different among hydroperiod categories (Kruskal-Wallis test, P>0.05) for either crustaceans or rotifers. On average, single collection richness represented between 30%% and 48%% of the cumulative richness, and this percentage was significantly lower in the long- than in the short-hydroperiod ponds (Mann-Whitney tests) for crustaceans (P<0.05) and rotifers (P<0.01). Our data showed that the effect of hydrologic variability on zooplankton taxon richness depended on the temporal scale of observation; it was weakly affected at a momentary scale and strongly affected in the long-term. A longer hydroperiod implied more chance for change in these fluctuating environments.