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Martin Hing says that the Gobiodon populations forming a group may have rebounded after the first cyclone, they showed no signs of recovery after being hit by a second cyclone the following year. Credit: Paul Jones
Climate change poses a number of threats to the long-term sustainability of the Great Barrier Reef and the species that live there. Although the damage caused by more frequent bleaching of corals is well documented, the impact of tropical cyclones is less well studied because of their short duration and unpredictability.
As in the case of coral bleaching, climate change models predict that tropical cyclones of high intensity will occur more frequently as the planet warms up.
In an article published in the journal PLOS ONE On September 5th, researchers at the University of Wollongong (UOW) studied the effects of two successive Category 4 cyclones – Cyclone Ita in April 2014 and Cyclone Nathan in March 2015 – on the social structure of the coral reef fishes. Lizard Island.
Lead author of the study, Dr. Martin Hing of the Center for Sustainable Ecosystem Solutions of the School of Biological Sciences at UOW, said that cyclones can devastate the physical structure of coral reefs and the abundance and distribution of animals.
However, scientists know relatively little about how cyclones affect the social structures of species living on the reef or how different social strategies affect a species' ability to cope with disturbances.
"For social species, social organization is a key factor in terms of elements such as the foraging efficiency and reproduction of this particular species – things that contribute to their survival "said Mr. Hing.
"If this is interrupted, if their social structure is changed, their feed efficiency may decrease and they will have lower survival rates."
The researchers sampled the group size and coral size of five species forming groups and eight species of Gobiodon fish (aka coral gobies) before and after cyclones Ita and Nathan.
The group sizes of the species forming groups decreased after each cyclone, but showed signs of recovery four months after the first cyclone (Ita). A similar increase in group size was not evident in species forming groups after the second cyclone (Nathan). On the other hand, there was no change in the average size of the group forming the pair after one or other of the cyclones.
"We found that the species forming groups decreased in the size of their group after each cyclone, while the pair-forming species did not increase or decrease at all in their group size," M said. Hing.
"Between the two cyclones, the group species recovered slightly and began to retreat to larger group sizes, which was rather unexpected because the average size of corals was much smaller and fish.
"Then, when the second hurricane arrived, they further decreased in group size."
"We sampled about 10 months after the second cyclone and the size of their group was still very small.After an isolated incident, the population could probably rebound, but it seems that multiple impacts have more lasting effects on them.
"As the frequency of more intense cyclones is expected to increase in the near future, this could lead to population declines and even local extinctions of coral gobies forming groups."
One of the reasons why the impact of repeated tropical cyclones on reef inhabitants is less well known is the difficulty of knowing when and where cyclones will hit. For this study, the UOW team was at Lizard Island before and after the two cyclones.
"This study was highly opportunistic and probably unique – we were trying to conduct a longer-term study on the sociality of these fish, but the cyclones had different plans for us," Hing said.
"Essentially, we started an experiment, then the cyclone passed and we thought," Okay, let's go back and see what we can find. "
"During the first trip, we tagged about 600 fish and we went to see if these same individuals were still in their original corals or if they were moved to other corals around the place. 'found only 11 of the 600 fish we tagged, so it was quite devastating.'
"However, we collected the data we collected and could compare it before and after the cyclones, which happened two years in a row.
"We were actually at Cairns airport when the second hurricane came in. We made a trip to the planned Lizard Island but we went back."
Explore more:
Coral reefs protect coastlines from strong storms
More information:
Martin L. Hing et al. Repeated cyclones reveal potential causes of sociality in Gobiodon fish living in corals. PLOS ONE (2018). DOI: 10.1371 / journal.pone.0202407
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