A predator’s role in storing carbon

Publication specs

Title: Predators help protect carbon stocks in blue carbon ecosystems

Authors: Trisha B. Atwood, Rod M. Connolly, Euan G. Ritchie, Catherine E. Lovelock, Michael R. Heithaus, Graeme C. Hays, James W. Fourqurean, Peter I. Macreadie

Journal: Nature Climate Change

Year: 2015

When you think about carbon (C) storage in an ecosystem, you may think about a lush tropical forest sucking up carbon dioxide from the atmosphere. What isn’t considered as often is coastal marine ecosystems, which take up C 40 times faster than tropical forests. An estimated 25 billion tons of C is buried in vegetated coastal habitats like seagrass meadows, mangroves, and salt marshes, making them the most C rich environments in the world. Degrading these “blue carbon ecosystems” releases C into our atmosphere, fueling climate change. But did you know that losing predators like sharks within these environments also indirectly leads to the release of C?

One example of this comes from Western Australia where sharks influence how often herbivores like dugongs and sea turtles feed in a given time period. These grazers like to eat in places where there are very few tiger sharks waiting to attack them. In habitats where sharks are present, they spend more time watching their backs. This means that less seagrass is being consumed, and in some cases is only being cropped. In the areas where sharks are present and there are fewer grazers, the seagrasses are mostly slow growing species, which promotes the storage of C since it is not breaking down quickly. In other words, where the abundance and behavior of herbivores are being controlled by predators, growth of vegetation is enhanced, which leads to increased storage of C.

Scientists don’t know the total global area affected by the loss of predators. However, if only 1% of the vegetated coastal areas were to be affected, about 460 million tons of C would be released, equivalent to the emissions from 97 million cars. In order to protect these blue carbon ecosystems, balanced conservation efforts will need to occur where the habitat, predators, and herbivores are protected together.

How marine protected areas support healthy coral reefs

Publication specs

Title: Marine protected areas increase resilience among coral reef communities

Authors: Camille Mellin, M. Aaron MacNeil, Alistair J. Cheal, Michael J. Emslie, M. Julian Caley

Journal: Ecology Letters

Year: 2016

Many of our researchers are SCUBA divers, and we like to think that many of our followers also enjoy spending time under the sea or at the very least learning about it. It’s no wonder that we enjoy diving on vibrant reefs with a diversity of species. Of course, we also love getting the opportunity to see sharks and stingrays on our dives.

However, not all reefs are healthy. This has led scientists and advocates to push for more ocean protection. Marine protected areas (MPAs) are designed to support and protect the balance of life within them, making them valuable ocean conservation tools. Yet, their efficacy has been debated among scientists. 

Recently, a study was conducted using 20 years of data inside and outside marine protected areas of the Great Barrier Reef (GBR). A total of 46 locations were surveyed: 26 sites with fishing activity, and 20 sites without fishing activity. MPAs offered protection from natural disturbances like coral bleaching and disease, storms, and crown of thorn sea star outbreaks. On healthy reefs, crown of thorn sea stars feed on fast growing corals. However, outbreaks of these invertebrates can have devastating effects on the reef – crown of thorn sea stars accounted for 42% of coral loss from 1985 – 2012 on the GBR.

Researchers found that inside MPAs the effect of the disturbances was 30% lower and the recovery of the community was 20% faster than outside MPAs. On average, recovery time within MPAs took only six years compared to nine years outside these protected reefs. So why did reef sites in MPAs remain strong through disturbances and recover faster after disturbances? The study offered several potential explanations:        

  • Increased feeding on macroalgae, which allowed young coral to settle.





  • Increased predation on coral-eating fish like butterflyfish.



  • Lesser impact of crown of thorn sea stars resulting from more predation on them within MPAs.
  • Multiple species performing their ecological function together as a community.

Without these protected areas, researchers predicted that the recent loss of coral cover in the GBR might have been much worse. This study both recommended and demonstrated the value of MPAs that prohibit fishing.      

Dining in fear: the influence of predator and prey behavior on the health of coral reef ecosystems

Publication specs

Title: Reefscapes of fear: predation risk and reef heterogeneity interact to shape herbivore foraging behaviour
Authors: Laura B. Catano, Maria C. Rojas, Ryan J. Malossi, Joseph R. Peters, Michael R. Heithaus, James W. Fourqurean and Deron E. Burkepile
Journal: Journal of Animal Ecology
Year: 2015

Imagine: you’re quietly enjoying your breakfast when suddenly a lion barges through your front door. Do you continue eating? Run for cover? The answer for you, and other potential prey, is pretty clear. For small, plant-eating fish living on coral reefs, this is a constant threat. So much so that even just the fear of a potential predator, like sharks and grouper, can alter their behavior. While that may seem obvious, a recent study has revealed something not quite so intuitive – this fear is actually good for the entire coral reef ecosystem.

The findings of this study suggest something rather surprising – without predators, herbivorous fish cannot fulfill their normal function on the reef. Reefs come in a variety of structures and are comprised of a multitude of interdependent organisms. The feeding behavior of these fish, like surgeonfish and parrotfish, are influenced by both the structure of the reef and their predators. In the absence of predators, or in this case a grouper decoy, the fish ate almost two times more seagrass than when the decoy was present. In areas with and without complex reef structure, the fish did not eat as much when the grouper decoy was present.

Complex reef habitats don’t offer easy escape or shelter, which means that in areas with predators lurking, fish spend more time trying to find safe spaces rather than grazing. According to these findings, herbivorous fish concentrate their feeding to areas where they are less likely to encounter a roving predator, leaving more space for coral to settle, grow, and thrive. Reefs without predators encourage grazing across larger areas, leaving less open space for young coral to survive. This study suggests that this interplay – between predator, prey, and ecosystem – is crucial for healthy reefs.