Biogeochemical Characteristics of Sediments Under the Canopy Of Invasive Alga Caulerpa racemosa var. cylindracea (Peljesac Peninsula, Adriatic Sea)

Sediments under the invasive alga Caulerpa racemosa var. cylindracea were investigated in the southern Adriatic Sea (Prijezba Cove, Peljesac Peninsula, Croatia). To identify the potential impact of Caulerpa racemosa var. cylindracea on granulometric composition, organic matter, organic carbon, total nitrogen, phosphorus content and redox potential, we investigated sites where the alga has developed the densest canopy in relation to sites unaffected with the alga. Vertical distribution of sediment particles along the cores showed highest variability in surface layers at invaded sites related to control that indicates changes in environmental conditions during the sedimentation. Prevailing coarse grains in surface sediments at invaded sites can be attributed to alga's capacity to trap sediment particles as well as to coastal weathering and transporting process. Organic carbon (C-ORG), total nitrogen (N-TOT) and total phosphorus content (TP) was also elevated in the surface sediment at invaded sites. C-ORG/N-TOT and C-ORG/TP ratios as well as negative redox-potential indicated the origin of the organic matter from marine sea-grasses captured by the canopies and its degradation under the anoxic conditions. Statistical analyses emphasized the differences between invaded and control sites in Prijezba Cove, and indicated gravel and sand contents, total phosphorus and redox-potential as the key parameters contributing to the presented differences.