Photosynthetic signatures of microbial colonies covering submerged hard surfaces as novel trophic status indicators: Baltic Sea studies

The study aimed to determine photosynthetic signatures, i.e. photosynthetic energy storage (ES) efficiency and photoacoustic spectra of pigment-containing biofilm communities attached to submerged solid substrates in relation to the temporal variability of the trophic state of natural water. Biofouling phenomenon signatures on artificial solid surfaces, deployed in the shallow Baltic Sea waters (Gulf of Gdańsk, Poland) for a specific period of time, were determined over a three-year period using improved photoacoustic spectroscopy apparatus based on closed cell geometry. Selected chemical parameters (oxygen, nitrogen and phosphorus concentrations) and biological productivity (primary production and Chlorophyll a; hereinafter abbreviated as Chl a) of the water body were obtained from the SatBałtyk System platform (http://satbaltyk.iopan.gda.pl) and used as comprehensive data. As a result, close cross-correlations between photosynthetic energy storage and PAS amplitude spectra and the seawater chemical parameters were demonstrated. As found, ES was negatively correlated with concentrations of biogenic elements (correlation coefficient R given in brackets): O (–0.67), P (–0.81), N (–0.76), and positively correlated with concentrations of Chl a (0.82) and primary production (0.39). As periphyton is believed to respond dynamically to water quality and environmental stresses, its photosynthetic system features can be used as novel, modern and robust indicators in marine bioassessment, in addition to traditional trophic state indices based on chemical analysis.