Oceans and Coasts

Reef fish responses to climate change

Understanding how fish communities in the Lakshadweep cope with change 

Tropical reefs have an uncertain future, and every coral mass mortality event further tests the resilience of these systems. While coral communities in many reefs in the Lakshadweep have shown a remarkable ability to withstand and recover from these events, how are its fish populations faring?

Fish play key roles in reef resilience

The role of fish communities in mediating reef resilience has long being recognized.  Top predators are often ecosystem keystones and their removal can lead to a range of flow-on consequences as the complex network of interactions they maintain unravel.  Their loss has been associated with declines of coral and the inability of reefs to recover from occasional disturbances.  Additionally, herbivore fish communities are also critical, playing much more direct roles in controlling algal growth in the aftermath of major bleaching events.  We have been tracking how fish communities respond to catastrophic coral die-offs in the Lakshadweep since 1998.  After the mass bleaching event of 1998, the worst affected reefs saw a major loss of fish species including top predators and coral feeding specialists.  In contrast, herbivore fish quickly dominated the community helping maintain reefs relatively free of algae and facilitating a rapid recovery of coral in many reefs.  Critically, the reefs of the Lakshadweep, were, until recently not heavily fished, a significant component of the native resilience of this archipelago.

Plasticity helps predators cope with changing reef

As the coral reefs of the Lakshadweep struggle to recover from large-scale mass-bleaching disturbances, our work so far shows that reef fish communities are steadily declining. In this general picture of overall decline however, there are a few species that appear to adapt to degraded reefs much better than others. 

Our work shows that benthic predatory fish (groupers) are at a serious disadvantage in degrading reefs because the loss of reef structure inhibits the ambush foraging strategy, and hence potentially limits a predator’s ability to forage efficiently. On the other hand, ‘widely-foraging’ predators that forage independently of reef structure are at an advantage in degrading reefs. In addition, we found that a few species of benthic predators like the commonly found peacock grouper (Cephalopholis argus), show the unique ability to forage flexibly using both the ambush and widely-foraging strategies, depending on the structural state of the habitat. More interestingly, this foraging flexibility enables the peacock grouper to maintain its specific diet even in degraded reefs. 

Our work suggests that behavioural plasticity not only enables species to survive in rapidly changing habitats but can also help preserve important specialist functions in degraded reefs. Moving forward, identifying and protecting such behaviourally plastic species within degrading habitats will be key in designing effective marine management strategies.