2.6 Mixotrophy & Energy

Mixotrophy in Corals

• Mixotrophs - organisms that use multiple energetic strategies

  • Dicot carnivores - plant autotrophs that also carnivorize animals

    • carnivorous plants,

  • Anthozoan photosynthesizer - heterotrophic organism that integrates chloroplasts into its body

    • nudibranchs, aphids

  • Symbiotic mixotrophs - heterotrophs with endosymbionts that produce autotrophic energy

    • Cnidarians, sponges, giant clams, salamanders

  • Carnivorous Algae - photosynthesizing algae can consume microbes,

See symbiosis for more info on energy flow

References

Houlbreque 2009

This paper is a review of coral heterotrophy. They summarize what types of matter and plankton are ingested through heterotrophy, which provide C, N and P nutrients, and how increased feeding alters coral physiology. They reported that feeding increases proteins, lipids, photosynthesis, symbiont density, growth rate (calcification, branch extension etc.) and tissue thickness.

Hoogenboom 2015

Conducted a feeding experiment on a few species with different colony morphologies, and measured feeding rates, photosynthesis, respiration, chl, sym counts, protein and isotopes. They found that feeding strongly affected protein, affected chl and sym density in some species, and did not affect photosynthesis, micro-skeletal morphology, or growth rate. They created models of coral assemblages to evaluate C uptake at reef-scales. They found that branching corals sequestered larger amounts of C than laminar/encrusting species.

Fox 2018

This meta-analysis compared δ13C and δ15N values from around the world with sea surface primary productivity (chl values) from satellite data. They found that δ15N generally did not vary with any sea surface conditions, but that chl affected the ∆C host-sym, that δ13C was constrained by species and site, and that depth was associated with lower δ13C values.

Teece 2011

Conducted CSIA on fatty acids in a few coral species. I didn't find this paper to be super useful but I think it was one of the first CSIA studies on corals. They found that fatty acids were primarily translocated from symbionts to coral but that heterotrophic feeding can be an important source of specific essential fatty acids.

Ferrier-pages 2011

A Mediterranean temperate coral was collected from nearby turbid and clear-water sites for SIA. Chl, protein, δ13C and symbiotic state did not change much based on site conditions, whereas δ15N did change a lot. A more δ13C depleted in winter indicates higher reliance on heterotrophic C sources. C/N plots show that host and sym values are closer to the three food values in winter than in summer, indicating a different energy source in summer

Burmester 2018

Feeding and wound recovery study on the temperate coral A. poculata. The authors tracked wound recovery, growth rate, chl, PAM, and polyp behavior in apo- and symbiotic, fed and unfed colonies. Results were as expected with well fed, symbiotic colonies having the best wound recovery. However, some factors like colony growth did not all follow the same pattern. This study indicates that temperate corals may be allocating different nutritional sources to different metabolic or physiological needs.

Palardy 2008

For bleached and unbleached corals along a depth gradient, the authors investigated the size and assemblage of zooplankton feeding, and the contribution of heterotrophy to the energy budget. They found that responses were very species specific but that heterotrophy contributed enough to view corals on a continuum from auto- to heterotrophic.