Influence of a freshwater runoff on temporal variations ofan intertidal meiofauna assemblage

Abstract

An intertidal meiofaunal assemblage in Los Cristianos Bay,Tenerife, Canary Islands, Spain was sampled monthly at one location from May 2000 through April 2001, at mean low tide. Nematodes dominated meiofauna assemblage, ranging from 73% in November to 98% in February and March. Turbellarialogy,ns and harpacticoid copepods were the second and the third most abundant groups, respectively. During November 2000 at times of heavy rainfall, freshwater runoff from a ravine (temporary river) affected the intertidal location. Meiofaunal densities drastically decreased, particularly nematodes, during November and December 2000 and January 2001. Nematodes recovered to pre-disturbance densities in February 2001, while copepods recovered the second fortnight of November 2000, indicating the high mobility of this meiobenthic group. The most abundant species were the nematodes Odontophora aff. wieseri, Theristus sp. and Daptonema hirsutum that made up 88% of the overall meiofauna density, showing significant differences in their abundances throughout the study period (May 2000April 2001). Odontophora aff wieseri showed its lowest densities during run-off period (November) and recovered gradually from December to March. Theristus sp. almost disappeared in the run-off period (November) and obtained highest abundances in summer months (June-August). Daptonema hirsutum was absent in November and in summer months (May-August). Significant differences were found in univariate parameters (abundance, species richness and Shannon's diversity). Multivariate analysis distinguished the freshwater runoff period (November) from the remaining months of the year, as well as throughout the study period.