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  • Author: Martin Pfannkuchen x
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Tina Nenadović, Tena Šarčević, Hrvoje Čižmek, Jelena Godrijan, Daniela Marić Pfannkuchen, Martin Pfannkuchen and Zrinka Ljubešić

Abstract

The settling of diatoms as fouling organisms on a certain substrate is greatly influenced by substrate characteristics and the preferences of a diatom community and diatom species. A distinction among substrates can be made by analysing the specific abundance and composition of diatoms on different substrates. In this study, 11 different artificial substrates were exposed to a marine environment for a period of 30 days. Abundance and taxonomic composition of periphytic diatoms was determined on each of the substrates and on shoots of the marine seagrass Posidonia oceanica. The aim was to compare diatom community structure on different newly colonized surfaces. On all surfaces examined, periphytic diatoms were the pioneering organisms with differences in quantitative and qualitative composition on the different substrates. Taxonomic analysis of diatom communities on the substrates examined revealed 41 diatom taxa, with the dominant genera Cylindrotheca, Amphora, Nitzschia, Cocconeis and Navicula. Given that all the examined artificial substrates were solid materials, differences in the abundance and species composition of diatoms found between the materials point to the substrates’ physical and chemical characteristics as a major influence on the final settling of diatoms. Knowledge from investigating the settlement of fouling organisms on anthropogenic substrates can have future use in management of waste materials that end up in the marine environment.

Open access

Maja Mejdandžić, Tomislav Ivanković, Martin Pfannkuchen, Jelena Godrijan, Daniela Marić Pfannkuchen, Jasna Hrenović and Zrinka Ljubešić

Abstract

Every surface that is immersed in seawater becomes rapidly covered with an unavoidable biofilm. Such biofilm formation, also known as fouling, is a complex multistage process and not yet thoroughly investigated. In this study, the succession of diatoms and bacteria was investigated during a one month exposure on an artificial substrate of plexiglass (polymer of methyl methacrylate) mounted above the seafloor at a depth of 5 m. For biofilm analyses, the fouling was investigated using selective agar plates, epifluorescence, light and electronic microscopy, as well as high performance liquid chromatography (HPLC) pigment analysis. During biofilm development, the abundance of all biofilm components increased and reached maximum values after a one month exposure. In the bacterial community, heterotrophic marine bacteria were dominant and reached 1.96 ± 0.79 × 104 colony forming units (CFU) cm-2. Despite the fact that faecal coliforms and intestinal enterococci were detected in the water column, faecal coliforms were not detected in the biofilm and intestinal enterococci appeared after one month of exposure but in the negligible number of 60 ± 10 CFU cm-2. The phototrophic component of the biofilm was dominated by diatoms and reached a concentration of 6.10 × 105 cells cm-2, which was supported by pigment analysis with fucoxanthin as dominant pigment in a concentration up to 110 ng cm-2. The diatom community was dominated by Cylindrotheca closterium and other pennate benthic diatoms. A detailed taxonomic analysis by electronic microscopy revealed 30 different taxa of diatoms. The study confirmed that a plexiglass surface in a marine environment is susceptible to biofouling within 30 days of contact. Furthermore, the co lonization process sequence firstly involved bacteria and cyanobacteria, and secondly diatoms, which together formed a primary biofilm in the sea.