Clearing the Name of Seaweed Suspects

Macroalgae, in recent years, have become a suspected reservoir of coral disease ever since the 2006 study where small corals placed in plastic containers had 100% mortality rates within 48 hours. After the din from the research, aquarium, and hobby community died down, people questioned if it was the methods in the experiment that killed the coral or the presence of the algae as the Smith group claimed.

Several field experiments have since taken place without replicating the drastic impact seen in the microcosm approach from 2006. PLOS One published today a follow-up paper that specifically looked at Caribbean Yellow Band Disease in Montastrea paired up with three native macroalga common to the area and/or suspected of harboring disease causing pathogens: Halimeda, Dictyota and Dictyosphaeria.

Interesting result? The researchers find no connection between the presence of these three algal species and the prevalence of CYBD infection in Montastrea. This joins results from other studies pointed out in the current paper:

Most similar studies, nearly all of which were performed in the field, have found only small or no effects on coral mortality, particularly when physical contact between corals and algae was precluded [39]–[41]. For example, a recent long-term field experiment found that in the absence of shading and abrasion, the presence of macroalgae had no effect on juvenile coral mortality [41]. This study also found that plastic algal mimics had the same deleterious effects as living macroalgae, indicating that the negative algal effects documented in natural settings are due to abrasion, shading, overgrowth and other related mechanisms, rather than allelochemicals or other algal exudates such as DOC [39].

While I would not say its back to the drawing board in the realm of coral disease and algal relationships – we do know that macroalga can harbor Vibrio and that they do leach allelopathic compounds and antifouling agents – its nice to have some water thrown on the fire that had been burning, particularly in the aquarium circles.