Assessing the role of canopy cover on the colonization of phytotelmata by aquatic invertebrates: an experiment with the tank-bromeliad Aechmea lingulata

The presence of canopy cover may influence the amount of organic detritus and stored water in bromeliad tanks and, consequently, the colonization of these ecosystems by aquatic invertebrates. The aim of this study was to determine the effects of canopy cover on the colonization of the tank-bromeliad Aechmea lingulata in the restinga, an ecosystem composed of a variety of plant communities in the sandy coastal plains of Brazil. We hypothesized that the taxonomic composition of invertebrate communities would differ between bromeliads covered and not covered by a dense canopy (shaded and unshaded bromeliads). Prior to the beginning of the experiment, bromeliads of similar size were carefully washed to remove all organisms and organic detritus, and their tanks were filled with 1.0 L of spring water. On days 7, 14, 21, 30, 45, 60 and 90, four bromeliad tanks of each shade treatment were sampled to determine invertebrate communities, stored water and organic detritus. Average daily values of water temperature and light intensity were higher in unshaded than in shaded bromeliads. The amount of fine particulate organic matter (FPOM) and stored water did not differ between treatments, but the amount of coarse particulate organic matter (CPOM) was higher in shaded bromeliads. Ostracoda, Hydracarina and Oligochaeta were the most abundant taxa in bromeliad tanks. Among insects, Culicidae, Chironomidae and Ceratopogonidae were the most representative. Invertebrate colonization occurred quickly and values of abundance were higher in unshaded bromeliads compared to shaded bromeliads. The values for biomass and richness did not differ between treatments or colonization times, and the taxonomic composition of invertebrate communities was similar throughout the experiment. Our results showed that canopy cover had a small influence on the colonization of tanks of A. lingulata in restinga, not corroborating the proposed hypothesis. These findings were likely due to the lack of variation in environmental conditions that are relevant to the colonization process, such as stored water and FPOM. However, because the amounts of CPOM were higher in shaded bromeliads, the taxonomic composition of invertebrate communities could have differed if typical shredders were present.