Epiphytic diatom assemblages on invasive Caulerpa taxifolia and autochthonous Halimeda tuna and Padina sp. seaweeds in the Adriatic Sea – summer/autumn aspect

Abstract

This study focuses on the taxonomy of epiphytic diatoms in the area of invasive macroalgae from the genus Caulerpa. Caulerpa species are characterized by the presence of secondary metabolites, such as caulerpenyne (CYN), the main function of which is a chemical defense mechanism against herbivores and epiphytes. Epiphytic diatoms were studied on fronds of Caulerpa taxifolia (“killer seaweed”) and, for comparison, on autochthonous macroalgae Padina sp. and Halimeda tuna at the eastern Adriatic Sea coast (Island of Hvar) in the summer and autumn of 2010. The qualitative analysis was performed with the use of light and scanning electron microscopy. The Shannon–Wiener Diversity Index determined for Caulerpa taxifolia showed a wide range of values (3.11–4.88), with a maximum in August and a minimum in October. While the number of taxa on Caulerpa taxifolia fronds increased from June (41) to August (88), it declined in autumn due to the high relative abundance of Cocconeis caulerpacola, which is a diatom typical for Caulerpa. On the other hand, the largest number of taxa on Padina sp. was observed in September (82). The detailed composition of epiphytic diatoms and seasonal dynamics in the area affected by the invasive macroalga Caulerpa taxifolia have been determined for the first time.

Group II intron and repeat-rich red algal mitochondrial genomes demonstrate the dynamic recent history of autocatalytic RNAs

“…A study of group II introns in other diatom species shows their transfer between non-diatom ( Chattonella , Raphidophyceae) and diatom species [ 45 , 46 ]. There are many reports of epiphytic diatoms inhabiting the surface of diverse algae (Rhodophyta, Chlorophyta, and Streptophyta) [ 47 – 49 ], where they exchange various substances such as inorganic nutrients [ 50 ]. The driving force of gene transfer between different species can be a plasmid or a virus.…”

Understanding the Role of Macroalgal Complexity and Allelochemicals Production in Invasive and Non-Invasive Macroalgae in the North-Western Adriatic Sea: Effect on the Associated Communities

“…Conversely, in Porto variations were due to the abundance of motile forms (i.e., Navicula spp., Pseudo-nitzschia spp., and Nitzschia spp. ), which are able to move in response to a multitude of factors (e.g., light, hydrodynamics, tides, nutrient) and perhaps as a defence strategy against grazing or other stressors [63,64]. Similarly, a previous study [65] performed in the Adriatic Sea reported that the dominant taxa on the fronds of the invasive green alga Caulerpa taxifolia were characterized by high motility (e.g., Navicula and Nitzschia spp.…”