Phytholiths in pellets and coprolites, posterior redistribución in associated soils and taphonomic implications

OSTERRIETH, M.; M. F. ÁLVAREZ; R. VIOLANTE; T. LUPPI; E. ROVERE; V. BERNAVA LABORDE; M. TOMÁS

Mar del Plata, Argentina

Otro; 7th International Meeting on Phytolith Research – 4th Southamerican Meeting on Phytolith Research; 2008

The first results of silicophytholiths in goat pellets in saline soils in Llancanelo, Mendoza and crab pellets in sodic-saline soils in Mar Chiquita, Buenos Aires will be presented. There are no precise definitions of the nomination coprolites and pellets in relation to the different fields that approach them; sometimes they are differentiated according to size, others according to their origin in vertebrates or invertebrates, independently from their size. In the goat coprolites that were analyzed, 2 predominant shapes were observed: the elliptical ones, of a size of 0.6 x 1mm and an average weight of 0.6 g. and the spheric ones of an average weight of 0.9g. Most coprolites have a rough surface and, under a binocular magnifying glass, remains of plants (stems, seeds, etc.) may be observed. Some have very smooth surfaces due to the great concentration of salts from the environment. They were quantified per surface unit in order to establish the relation between area occupied by the coprolites/ average weight / weight of phytoliths per coprolite. The crab pellets analyzed belong to Neohelice granulata; it is a crab that lives in the south-western Atlantic, the northern distribution limit of the species is Río de Janeiro (22º 57’ S - 42º 49’ W) and the southern distribution limit is the Riacho San José (42º 24’ S - 64º 36’ W). Its distribution is discontinuous because its population is found in lagoons, estuaries and bays with marshes, with different proportions of non-vegetated tide plains and marshes. The conditions of salinity, soil composition and flora may vary both latitudinally and locally. It is a intertidal digger crab, that builds semipermanent caves and feeds on detritus deposits and Spartina spp.; the characteristics of the caves and the type of food depends on the area in which the crab lives. It is a key element in these environments; it is considered an ecosystemic engineer due to its ability to modify the environment; it can turn over between 2.5 kg and 6 kg of sediments/day*m2. In addition, they are considered one of the main producers of detritus deposits in these environments. To obtain the feces, male crabs from the tide plains and marshes of the Lagoon of Mar Chiquita were collected (37º 32’ S - 57º 19’ W). They were taken to the laboratory immediately and they were placed in individual receptacles. During 8 hours and at intervals of 1 hour, all the feces produced by each crab were collected with a pipette; they were placed in Eppendorf tubes and preserved in alcohol. In the goat coprolites, bilobates predominate, especially Stipa type ones, followed by panicoids. Rondels are abundant and elongates are very abundant, especially with smooth surface. There is a considerable amount of indefinite ones. Their state of preservation is generally good. The content estimated enables the estimation of the contribution of phytoliths by goat coprolites which will be incorporated to the soil dominated by salicorns and other halophytes which are not generally carriers of phytoliths. The crab pellets generally have more than 60% of phytoliths, 8% of diatoms, scarce poripherans and carbons and 20% of minerals. Bilobates and rondels are the dominant morphotyes, as well as tabulars, papilates and abundant indefinites. Considering their production, the high population density and the high production of phytoliths, these pellets are also contributors of more phytoliths apart from the ones originated by the degradation of these soils’ vegetation. To sum up, crab pellets and goat coprolites in saline and sodic soils contribute further amounts of phytoliths to the system. This taxonimical aspect must be taken into account in the environmental and paleoenvironmental evaluations and associated vegetation in the aforementioned environments and the past.