Meiofauna and sedimentary organic matter off Central Chile: response to changes caused by the 1997–1998 El Niño

Abstract

Quantitative surveys of metazoan meiofauna were carried out in an upwelling region off Central Chile (36ºS). During May 1997 and May 1998, coinciding with the onset and end of El Niño, five benthic stations (respectively 27, 34, 64, 88, and 120 m depth), from the middle of Concepción Bay to the edge of the adjacent continental shelf, were sampled. The sedimentary organic matter biopolymeric fraction (proteins, carbohydrates and lipids) and chloroplastic pigments were also assessed. Total meiofauna abundance and biomass increased significantly between sampling dates at the mid-bay and inner shelf sites, from 1474 ± 354 to 5035 ± 291 individuals 10 cm-2 and from 2618 ± 332 to 5241 ± 903 individuals 10 cm-2 , respectively. The relative importance of copepods in the top 2 cm increased at all sites (except in the bay mouth). During May 1998, meiofauna, especially nematodes, penetrated deeper in the bay, as well as in the inner and middle shelf sediments. Changes observed in meiobenthos structure among sites and periods were attributed to the higher oxygenation of bottom waters during the summer of 1998 (i.e. El Niño conditions). This was most evident at sites such as the mid bay, where during non-El Niño years, oxygen-deficient conditions prevail. A decrease of organic matter quantity and quality, related to low primary productivity conditions in 1998 (El Niño), apparently caused few changes in meiofauna structure. A positive correlation between Thioploca and the meiofauna biomass was observed in May 1997, whereas in May 1998 no relationship was found. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Méiofaune et matière organique du sédiment sur les côtes du Chili central : réponses aux changements causés par « El Niño », 1997-1998. Des mesures quantitatives de la méiofaune ont été réalisées dans une région côtière du Chili central (36°S). Pendant les périodes de mai 1997 et de mai 1998, qui coïncident avec l'apparition et la disparition d'El Niño, cinq stations (27, 34, 64, 88, 120 m de profondeur), comprises entre le milieu de la baie de Concepción et le bord du plateau continental, ont été examinées. La fraction de matières organiques sédimentaires (protéines, hydrates de carbone et lipides) ainsi que les pigments chloroplastiques ont été déterminés. L'abondance de la méiofaune et sa biomasse augmentent significativement : dans le milieu de la baie, de 1474 ± 354 à 5035 ± 291 individus pour 10 cm-2 , dans les sites intérieurs du plateau, de 2618 ± 332 à 5241 ± 903 individus pour 10 cm-2. L'importance relative des copépodes dans les 2 cm supérieurs augmente dans presque tous les sites, à l'exception de l'entrée de la baie. En mai 1998, la méiofaune, en particulier les nématodes, pénètre plus profondément dans les sédiments de la baie que dans ceux de l'intérieur et du centre du plateau. Les changements de la structure du méiobenthos, sont attribués à la haute oxygénation de l'été 1998 (El Niño). Ceci est plus évident dans les sites où, pendant les années sans El Niño, des conditions...

Diatoms, protein and carbohydrate sediment content as proxies for coastal eutrophication in Montevideo, Rio de la Plata Estuary, Uruguay

“…For example, in Italy, in a harbor area of the Southern Adriatic Sea, maximum protein and carbohydrate concentrations of 13.99 mg g-1 and 11.99 mg g-1 respectively, were observed (DELL´ANNO et al, 2002). The values reported here are in the same range as those of the north-western Mediterranean coastal zone (ROSSI et al, 2003) and upwelling areas of Chile (NEIRA et al, 2001). We have observed higher protein and lower carbohydrate content than those observed by Pusceddu et al (2003) in transitional ecosystems of the west coast of Sicily.…”

Is the meiofauna a good indicator for climate change and anthropogenic impacts?

“…El Niño has led to increased oxygenation of the central Chilean shelf, an area associated with an OMZ, as well as an increase in the supply of organic matter (Neira et al 2001;Levin 2003). The 1997-1998 El Niño events caused changes in meiofaunal community in an upwelling region off Central Chile: harpacticoid copepod densities were nine times higher than during the previous year, but total meiofaunal densities were 42 % lower (Neira et al 2001).…”

Coastal hypoxia and sediment biogeochemistry

“…Mountford, 1977). However, commonly small macrofauna and meiofauna will persist (Levin, 2003;Neira et al, 2001;Sellanes et al, 2003;Sellanes and Neira, 2006;Sellanes et al, 2007); often these are opportunistic taxa with short generation times (Dauer et al, 1992). Under severe dysoxia or anoxia, filamentous, mat-forming bacteria (Jørgensen and Gallardo, 1999), calcareous foraminifera, nematodes and branchiate, and soft-bodied annelids are typically favored (reviewed in Levin, 2003;Guttierez et al, 2008).…”