Ecology of intertidal microbial biofilms: mechanisms, patterns and future research needs

There is a continual struggle in ecology to improve our understanding of the complex interactions that take place between organisms and their surroundings at the genetic, species, community and ecosystem level. These interactions, and the transfer of material and energy that they support, drive the functional capacity of any ecosystem (Solan et al., 2012). Intertidal soft-sediments of temperate estuaries and shallow coastal lagoons are ranked among the most productive marine ecosystems (Heip et al., 1995) and are critical habitats in determining the sediment transport balance between the terrestrial and marine realm. On intertidal sand and mudflats, microbial biofilms, that are complex agglomerates of prokaryotes and microbial eukaryotes like diatoms, protozoa and fungi (Decho, 2000), are instrumental to both processes by affecting sediment stability through the secretion of extracellular polymeric substances (EPS) (Underwood and Paterson, 2003) and by regulating the energy transfer through the benthic food web as a major food source for herbivore consumers (Herman et al., 2000). Autotrophic diatoms are major components of the biofilms and contribute significantly to estuarine primary production (i.e. 29–314 g C m− 2·yr− 1; Underwood and Kromkamp, 1999), thereby supplying energy resources to biofilm consumers and their predators, while the heterotrophic prokaryotes are the primary remineralizers of organic matter. The exposure to highly variable and often extreme conditions is a regulating feature of estuarine conditions that determines biofilm properties. For example, UV radiation (Mouget et al., 2008 and Waring et al., 2007), dessication and change in temperature and salinity (Coelho et al., 2009 and Rijstenbil, 2005) during emersion; and hydrodynamic forces and sediment transport associated with currents and waves during submersion (Van Colen et al., 2010a and Widdows et al., 2004), have survival implications for the structure and functioning of biofilms and therefore require adaptation mechanisms such as the vertical migration exhibited by diatoms (Brotas et al., 2003, Consalvey et al., 2004 and Jesus et al., 2006).