Descriptive study of the vertical structure of floating algal mats in the Maple River, Cheboygan Co., MI.

Abstract

Flabs (floating algal benthos; also referred to as floating algal mats) are present in several streams and bodies of water of northern Michigan. They are formed at the benthic surface until an accumulation of oxygen due to photosynthesis and other external forces dislodges them from the bottom and make them float at the surface. Flabs have ecological importance since they serve as microhabitas for different fauna, such as insect larvae, crustaceans, bacteria, etc., and for different algal taxa that might grow better in the conditions provided by the mat (e.g., blue-green filaments like Oscillatoria). They act also as refuges for several organisms in periods of dry downs or adverse conditions, and serve as a food source for the fauna that lives inside them, as well as other animals, such as macroinvertebrates or even fish. They have also been used as indicators of eutrophicatin in some systems since it is this phenomenon that enhances the occurrence of floating algal mats. Several types of floating algal mats have been described for marine and freshwater habitats, and it has been suggested that the flab-forming organisms are blue-green algae. Nevertheless, some other algal taxa, such as diatoms or green algae, have also been observed in the flabs. Since the flabs are cohesively kept together as a separate entity, it should be of interest to assess if any vertical structuring exists in these flabs, such as different algal taxa occupying different layers or zones of the algal mat. Some studies have looked at stratification in algal mats regarding physical parameters such as pH, light, temperature, and oxygen and hydrogen sulfide concentration at microscales. Only a few studies though, have analyzed the vertical structure of species composition in flabs. It is important to realize that the microhabitat that flabs create is a whole microecosystem in its own, and since flabs are dynamic microenvironments capable of supporting a whole array of interactions, much information can be gained by assessing profiles of algal mats.