Nature is full of surprises! One recent example came from a new United States study that suggests that some fish that are coral predators can actually promote the well-being of these reefs… and it’s all down to their excrement.
Coral is essential to the protection of marine ecosystems, but its health is threatened by various factors, including being eaten by other species. However, some corallivorous fish, until now exclusively seen as coral predators that weaken reefs, could actually make a key contribution to their survival.
For example, that’s the case of the butterflyfish and the parrotfish. Curiously, these species do bite the coral and potentially harm them, but they also provide these reefs with substances that promote their health. How? Through their poo!
That’s right, the faecal deposits left by these fish are a source of “good” bacteria that become part of a cycle that enables the coral to thrive. Meanwhile, fish that eat algae and detritus spread faeces with pathogenic bacteria that can be harmful to the reefs.
This was the conclusion reached by US-based scientists, whose work was published this month in the journal “Frontiers in Marine Science”.
“Animal waste products are an important component of nutrient cycles and result in the trophic transmission of diverse microorganisms. There is growing recognition that the faeces of consumers, such as predators, may impact resource species, their prey, via physical effects and/or microbial activity,” the study outlines.
The researchers conducted laboratory tests using faecal samples from several reef fish species. The scientists also wanted to verify if the “fresh” faeces and those sterilised by heat produced the same amount of bacteria.
The analyses showed that in the case of algae and detritus-eating fish, fresh faeces caused 4.2 times greater lesions on corals, compared with those from sterilised faeces. The microbial activity found in colliavore faeces caused fewer and smaller lesions.
“Testing how faeces derived from animal species affect cohabiting organisms can inform agriculture, ecosystem management, and restoration,” the authors conclude.
While they emphasise the beneficial effect of corallivorous species, they note that more research is needed to better understand how the feeding behaviours of these fish can affect coral health.