Algae on the reef: Gauging reef health by overlooked species

Image: Kristen Brown noting coral/algae interactions, and doing detailed taxonomic survey of all algae types


As I sit down to write on Day 9 of the expanded scientific Catlin Seaview Survey expedition, I honestly don’t know where to start, as we have had such a remarkable time in this country.


When not watching manta rays twirl up an imaginary spiral staircase from the depths, or admiring the flattest waters I have ever seen where the sky dissolves into the ocean, the Catlin Ocean Scholars have been afforded a unique and valuable opportunity to complete supplementary field for our PhD candidacies at The University of Queensland. 



Competition dynamics


I have come to the Maldives to record the abundance and diversity of macroalgal-coral interactions, one of the most significant competition dynamics that drive the structure and composition of the masterpiece we call coral reefs. The Maldives is a perfect place to study such a topic, as bleaching disturbances driven by global rising sea surface temperatures and ocean acidification have been increasing in severity and extent in recent years. These events can wipe whole reefs clean, giving larval recruits of many species a clean slate to settle on when competition for space is at its early stages. Now that the reef is recovering, when we drop down through the flawless cerulean waters, I find a coral community of indescribable swirls, mazes, petals, and stripes decorating the reef, in patterns intriguing and mystifying me day in and day out. My goal is to resolve these patterns. Identification is challenging, but ultimately fulfilling.



Overlooked species


Coral reefs are not just all about corals, they are also structured by the plants present – the algae. Particularly prevalent in the Maldives, coralline algae coat the reef like bubble gum, spreading in shades of cherry, rose, and burgundy. These algae are very important, as they provide a key settlement cue for coral larvae to colonize on, and they also have central roles in cementing the reef together.  As I take a preliminary look at the reefs we have seen thus far, I am happy to say the Maldives are not on the ‘slippery slope to slime’ (John Pandolfi et al, 2003), covered in slimy filamentous algae blanketing the corals, but rather seem to be pink with corallines and sprinkled with other calcifying species (calcareous algae), such as the emerald bushels of broccoli-like Halimeda. A total of 871 coral and algae interactions have been detailed thus far, dominated by these calcareous algae. However, where we have found branching species of corals (i.e. Acroporidae and Poritedae families) protruding off the reef, I have discovered a more diverse and complex fleshy algal community nestled in the spaces between the branches, presumably finding refuge from copious herbivores.


As a changing environment threatens this region again in 2015, we hope that the baseline surveying we are completing here will lend insight into how we might expect future reefs to appear.