No abstract

Biotic remains have been used in paleoecological studies to provide information on past environmental conditions. Death assemblages can be used to make inferences about past environmental conditions if modern optima and ranges of taxa are known. Gaps in knowledge about historical biotic changes often stem from a paucity of information regarding species distributions, community species richness and evenness, community structure, ecological interactions, and possible factors that caused past biotic shifts. We studied mollusc assemblages in sediment cores from Río Lagartos coastal lagoon (Mexico) and compared them to present-day mollusc communities to gain insights into environmental changes that occurred in the lagoon throughout the last century. A total of 18,779 mollusc specimens, representing 20 bivalve and 45 gastropod species, and belonging to 32 families and 48 genera, were identified in three short sediment cores collected from the coastal lagoon in 2017. Molluscs in the sediment cores were compared to an inventory of modern fauna from the lagoon, which was collected along a salinity gradient in 2017 and 2018 to link species distributions with environmental variables. Mollusc communities from the sediment cores and present-day datasets possess the same ubiquitous species and feeding guilds. Nearly twice as many species, however, were identified in the sediment cores as in the present-day inventory. We report differences in mollusc abundance and taxonomic composition in the cores across space and time, which may be related to the salinity gradient in the lagoon, temporal shift in salinity, and recent human-mediated modifications of the nearby terrestrial environment. Biotic changes driven by shifts in salinity could have been reduced salinity. Such inputs may have been driven by hurricanes, along with associated high wind velocities and geomorphologic transformations. This paleobiology study will be of use for future conservation efforts in the coastal lagoon.

No abstract

In the Port of Santa Bárbara de Samana, chemical residues, organic matter and heavy metals from domestic activities are deposited together in the waters and sediments. The analysis of the sediments by X-ray fluorescence of four extracted and sectioned cores showed that concentrations of trace metals such as Nickel, Chromium, Lead and Mercury were present at various depths, exceeding Limits of Toxicity (PEL) for marine sediments according to National Oceanic and Atmospheric Administration (NOAA) and Canadian Council of Ministers of the Environment (CCME). Cadmium presented values above the toxicity threshold (TEL) in its minimum values and in its maximum values they exceeded the PEL value. While the Zinc and Copper values were low in all sections and lower than TEL. The analysis of the loss by ignition and the dating with lead 210 due to excess of the C4 core, showed a sudden change in the organic matter content and sedimentation rate. The superficial sediments show that unlike the deeper ones, the heavy metal content is lower, as well as that they do not represent a risk to the ecosystem by not exceeding toxicity levels.