Biodiversity of the meiobenthos of sandy beaches in Ecuador with emphasis on free-living marine nematodes

T his thesis is part of a VLIR-ESPOL project, being a co-operation between the University of Gent (Belgium) and ESPOL (Escuela Superior Politécnica del Litoral, Ecuador). During August 1999, meiofauna was collected from the intertidal Ecuadorian sandy beaches in five stations along of Guayas province. This thesis is the first scientific contribution to the study of the meiobenthos from that area. The work includes the study of the structure of the meiofauna communities, especially on the most dominant taxon: Nematoda. The composition and diversity of nematodes and their relationship with environmental factors was examined and discussed. The sampling was made during low tidal and three replicate cores were taken to meiofauna identification and one to granulometric analysis (10 cm2 surface). The meiofauna samples were immediately fixed in hot (60 °C), 4% formaldehyde solution. In the laboratory a series of sieving, decantation and centrifugation were done to separate the meiofauna from the sand and detritus. Five meiofauna taxa were identified and quantified, the densities ranged between 349-2544 ind./10 cm2. Nematoda was the most dominant taxon with 87.1% of the meiofauna, second dominant taxon was Gastrotricha with 8.2 %, which is one of the highest densities ever recorded for marine sediments. The nematode composition showed that most dominant genus were: Metadesmolaimus (28.5%), second most dominant was Metachromadora (22.8%), followed by Paracyatholaimus (17.1%) and Daptonema (10.4%). The following genus represented less of 10%: Anoplostoma, Bathylaimus, Ceramonema, Enoplolaimus, Gonionchus, Halalaimus, Neochromadora, Odontanticoma, Odontophora, Omicronema, Paradontophora, Rhynchonema, Sinonchyella, Sabatiera and Viscosia. A total of 19 genera belonging to 14 families were identified. Non-selective deposit feeders (1B) were the most abundant feeding group, mainly at Playas and Salinas I stations which reflects the high concentration of Metadesmolaimus at these stations. The second abundant feeding group was the predators (2B), represented by two genus: Metachromadora and Paracyatholaimus. The selective deposit-feeders (1A) and epistratum-feeders (2A), both were not highly incident. In our study two of the five stations (Salinas and Playas) are beaches under strong anthropogenic pressure, which had substantial impact on the interstitial life and beach ecosystem functioning. The diversity index did not show great variability, only Playas (B) site exhibit a highest diversity (14 genus), followed by Cenaim (B) station (12 genus). TWINSPAN and PCA analyses revealed that the density distribution of nematodes displayed a significant correlation with biogenic factors such as chlorophyll a, POM and SPM principally, but not happened it with median of sediment grain size and percentage of sand and silt. The result of the present study was discussed in comparison with other areas of worldwide meiobenthos studies