There is a multitude of microbes to be found in non-square, non-pants-wearing, non-kitchen sponges. Many of these microbes are symbiotic, photosyntheticly active cynaobacteria (used to be blue-green algae). Cyanobacteria can provide the sponge with organic carbon (think sugar). This relationship is similar to dinoflagellates and corals. In “Complex interactions between marine sponges and their symbiotic microbial communities” Christopher J. Freeman and Robert W. Thacker inform us that the amount of organic carbon provided to the sponge from the symbionts varies from species to species. They also mention a previous observation by Thacker that not all sponge species have the same symbionts. They leave use with the question of whether the variation in symbiont organic carbon contribution is due to differences in sponge species (ie. the sponges’ ability to take up dissolved organic carbon) or the photosynthetic activity of the symbionts.
To investigate the importance of symbiont-derived nutrition to host sponges, we coupled manipulative shading experiments with stable isotope analyses of isolated symbiont and host cell fractions. Experiments were conducted with four common reef sponges: Aplysina cauliformis, A. fulva, Neopetrosia subtriangularis, and Niphates erecta. The sponge N. erecta lacks photosymbionts, had a higher growth rate under shaded conditions, and displayed no difference in chlorophyll a (Chl a) concentrations across treatments. Isotope values suggested that this sponge obtains nutrition from particulate organic matter in the water column. In contrast, sponges hosting cyanobacterial symbionts (Aplysina spp. and Neopetrosia) had lower growth rates and lower Chl a concentrations under shaded conditions, suggesting that these hosts rely on photosymbiont nutrition. d15N and d13C values of sponge and microbial cell fractions demonstrated that, while both carbon and nitrogen are transferred from symbionts to host cells in A. cauliformis, only carbon is transferred in N. subtriangularis, and only nitrogen is transferred in A. fulva. Under shaded conditions, shifts in symbiont d13C values were coupled to shifts in host d13C values in some, but not all, host species, suggesting that the stability of these interactions varies across host species. Symbiont-derived nutrients are transferred to the cells of host sponges, and the variability observed among host species indicates that these interactions are more complex than originally hypothesized.
I know there are no protists, but I liked the paper.