The effect of substratum type, orientation and depth on the development of bacterial deep-sea biofilm communities grown on artificial substrata deployed in the Eastern Mediterranean.

An increasing number of deep-sea studies have highlighted the importance of deep-sea biofouling, especially in relation to the protection of deep-sea instruments. In this study, the microbial communities developed on different substrata (titanium, aluminum, limestone, shale and neutrino telescope glass) exposed for 155 days at different depths (1500 m, 2500 m, 3500 m and 4500 m) and positions (vertical and horizontal) in the Eastern Mediterranean Deep Sea were compared. Replicated biofilm samples were analyzed using a Terminal Restriction Fragment Length Polymorphisms (T-RFLP) method. The restriction enzymes CfoI and RsaI produced similar total numbers (94, 93) of different T-RFLP peaks (T-RFs) along the vertical transect. In contrast, the mean total T-RF number between each sample according to substratum type and depth was higher in more samples when CfoI was used. The total species richness (S) of the bacterial communities differed significantly between the substrata, and depended on the orientation of each substratum within one depth and throughout the water column (ANOVA). T-RFLP analyses using the Jaccard similarity index showed that within one depth layer, the composition of microbial communities on different substrata was different and highly altered among communities developed on the same substratum but exposed to fouling at different depths. Based on Multidimensional Scaling Analyses (MDS), the study suggests that depth plays an important role in the composition of deep-sea biofouling communities, while substratum type and orientation of substrata throughout the water column are less important. To the authors' knowledge, this is the first study of biofilm development in deep waters, in relation to the effects of substratum type, orientation and depth.

Cycling of carbon and oxygen in layers of marine microphytes; a simulation model and its eco-physiological implications.

A mathematical simulation model was used to ascertain the relation between the diffusion of oxygen and inorganic carbon into layers of marine microphytes and the carbon metabolism of these microphytes. The simulation model included physiological and physico-chemical parameters and was validated using the few data available from the literature on production determinations, on oxygen and pH values, and on growth dynamics of natural populations. The model was tested with various modifications to mimic experiments with suspended algae and algal films on inert substrates, and also to simulate microphytobenthos in sediment cores with or without grazing. The simulated variations in oxygen concentrations and pH values over time scales of min and days were consistent with field and experimental observations. The model predicted upper limits of primary production and biomass observed in well developed natural populations; these limits are caused by a combination of oxygen accumulation and depletion of inorganic carbon resulting from diffusion limitations and the recirculation of organic carbon in photosynthetic, respiratory and excretory processes. The model calculations were used to check on the adequacy of the various methods used to determine the primary production of benthic microphytes.