Ecological zonation of benthic foraminifera in the lower Guadiana Estuary (southeastern Portugal)

Abstract

The present study analyzes the spatial distribution and seasonal distribution of live benthic foraminiferal communities in the estuary of Guadiana, the fourth largest river on the Iberian Peninsula, and establishes, through statistical analysis, their relationships with a series of environmental parameters. Forty-four superficial sediment samples were collected along distance-to-sea and elevation gradients in the winter and summer of 2010. Fiftythree foraminifera species were identified along the intertidal margins of the estuary. Foraminiferal distribution reflected seasonal variation of environmental factors, whose relative importance varied according to species tolerances. Elevation in relation to mean sea level appeared to be the most important parameter controlling foraminiferal distribution, probably because it combines the effects of a series of other variables (i.e. organic matter, sediment texture, pH and temperature). In the highest marsh areas, where environmental conditions approach survival thresholds, only some agglutinated species are able to survive. In the lower intertidal zone, where subaerial exposure is diminished and environmental conditions are generally less variable, more diverse faunas, mainly composed of calcareous species, prevail. During winter, when fluvial discharge peaks, agglutinated species represent more than 80% of the total individuals. In summer, when marine conditions prevail, calcareous species become more competitive, increase their densities and expand into higher marsh zones and estuarine upper reaches. In the estuary, three different foraminiferal assemblages are distinguished: i) Miliammina fusca assemblage, which dominates in unvegetated areas of the lower marsh and tidal flats of the mid-upper estuary; ii) Jadammina macrescens assemblage, which dominates in the highest marsh areas in the lower estuary; and iii) Ammonia aberdoveyensis assemblage, which dominates the areas of low marsh and tidal flats of the lower estuary.

Taxonomy, ecology and biogeographical trends of dominant benthic foraminifera species from an Atlantic-Mediterranean estuary (the Guadiana, southeast Portugal)

“…In order to address these knowledge gaps, this study presents a photographic and systematic compendium of almost all species found in the estuary and provides preliminary genetic information on two of the most important taxa. These data, along with the ecology and bio-geography of the main species, are expected to complement the previous study by Camacho et al (2015) and contribute to a more robust taxonomic basis for foraminiferal identification.…”

“…Seasonal species distribution within the estuary was studied in detail in Camacho et al (2015). Here we synthesize the main findings in that work with new observations on species distribution patterns and major environmental forcing parameters.…”

“…Redundancy Analysis (RDA) (a constrained form of the linear ordination method of PCA) was chosen to analyse the relationships between the dominant species and elevation and distance-tosea, which were the two most important environmental variables in living foraminiferal distribution in Guadiana River Estuary (Camacho et al, 2015). In the present work, RDA was performed with a focus on inter-species correlations, where abundances of individual dominant species are transformed to a comparable scale.…”

“…Whenever possible, 100 to 300 living individuals were counted. Due to low numbers of stained individuals in some samples, an exceptional threshold of 48 living individuals was adopted for the purpose of statistical significance (see details in Camacho et al, 2015). Samples with fewer than 48 living individuals were not analyzed statistically (in grey in Tables 2 and 3, Appendix).…”

“…Nevertheless, the resulting taxonomic data are very limited, with little systematic study and no molecular analysis. Recently, the seasonal and spatial patterns of live benthic foraminifera in intertidal margins of the Guadiana Estuary were studied (Camacho et al, 2015). That analysis lacked detailed taxonomical information and genetic data.…”