Predicting coastal change depends upon our knowledge of postglacial relative sea-level variability, partly controlled by glacio-isostatic responses to ice-sheet melting. Here, we reconstruct the postglacial relative sea-level changes along the Caribbean and Pacific coasts of northwestern South America by numerically solving the sea-level equation with two scenarios of mantle viscosity: global standard average and high viscosity. Our results with the standard model (applicable to the Pacific coast) agree with earlier studies by indicating a mid-Northgrippian high stand of ~2 m. The high-viscosity simulation (relevant to the Caribbean coast) shows that the transition from far- to intermediate-field influence of the Laurentide Ice Sheet occurs between Manzanillo del Mar and the Gulf of Morrosquillo. South of this location, the Colombian Caribbean coast has exhibited a still stand with a nearly constant Holocene relative sea level. By analyzing our simulations considering sea-level indicators, we argue that tectonics is more prominent than previously assumed, especially along the Caribbean coast. This influence prevents a simplified view of regional relative sea-level changes on the northwestern South American coast.

The north-eastern region of Venezuela includes some of the most productive marine ecosystems of the country, sustaining high abundances of fisheries resources. This feature, coupled with the high diversity of coastal ecosystems, increases the interest for the development of conservation policies to prevent and/or mitigate negative environmental impacts associated with human interventions at the area. However, previous malacological assessments made in the Araya Peninsula are mainly restricted to epibiotic molluscs associated with bivalve banks. In this vein, we performed three different surveys for soft-bottom molluscs in the intertidal (using a stainless steel corer), shallow subtidal (Eckman dredge) and subtidal (Arca zebra dredge) areas of Araya Peninsula. We found 41 species including Bivalvia, Gastropoda, one Cephalopoda and one Scaphopoda, although according to sample-based rarefaction techniques there may be several more undetected species. Since there is an ongoing project aiming to construct a shipping terminal on Araya Peninsula that could adversely affect coastal marine biodiversity in the region, the knowledge about the molluscan assemblage in the area is a key requirement for designing conservation measures.