Of butterflyfish and angelfish and their distribution

In our recent paper, just out of the oven, we make a case that latitude and live coral independently determine the species richness of butterflyfish and angelfish communities in the Andaman & Nicobar Islands.

Cabra Island_Nicobar_Vardhan Patankar.JPG
Vibrant coral reef at Cabra island

The idea for this paper started in the year 2015 when an intern Sowjanya Chandrasekhar started exploring the huge dataset, that my colleague Elrika D’Souza and I had collected in 2012 & 2013. Though we had collected data on all reef species, Sowjanya picked only two groups for their aesthetic elegance and their overall importance to the coral reef ecosystem. The butterflyfish are known as indicators of the health of coral reef ecosystem, whereas angelfish are dependent on reef habitat for structure. The initial plan was just to make a checklist of butterflyfish and angelfish. After the painstaking task of going through thousands of pictures, field guides and monographs, Sowjanya identified 30 species of butterflyfish belonging to four genera and 13 species of angelfish from 9 genera.

The idea further developed after a conversation with Aniruddha Marathe, my colleague and flatmate in Bangalore. Aniruddha works on how elevation gradients impact distribution on ant species in Arunachal Pradesh. Though there are no direct similarities in ants and fish, commonalities of distribution gradients in elevation and latitude were a good enough reason for us to work together. Meanwhile, Sowjanya was accepted for the James Cook University Master’s programme, whereas I left for the field and spent most of my time in the Andaman and Nicobar Islands to collect 2016 bleaching related data.

After exploratory analysis, a few questions that piqued our curiosity were: Why certain species are found only in some areas? Why is the distribution of some species patchy? Is species richness higher in the islands that are closer to the Centre of origin of the coral reefs? And most importantly, how do natural disturbances alter the patterns of species distribution? The fact that the Andaman and Nicobar Islands have 6 to 13 ° latitudinal gradient was a good enough reason for us to follow-up on these questions. With scattered information of a dataset spread across 75 sites and 51 islands, we explored the relationship between 1) species richness and latitude,  2) species richness and important benthic variables i.e., live coral, dead coral, algae, 3) species diversity and latitude, and 4) species diversity and benthic variables for butterflyfish and angelfish.

The initial findings were interesting and the results met most of our predictions. We found that live coral cover and latitude were the best predictors for explaining variation in the distribution of these fish communities across the A & N archipelago. This is probably because of the high dependence of these two fish groups on the live coral cover and Nicobar’s geographical proximity to the Coral Triangle, which is considered to be the centre of origin of coral reefs and supports high biodiversity.

While it is great news that these fish groups are surviving despite repeated catastrophic disturbances, loss of coral structure or habitat is still the greatest threat to these species. Yellow teardrop butterflyfish, with two sightings in the Central Nicobar region and North Andaman region and Three-spot angelfish, with one sighting in the South Andaman region, are especially vulnerable as they were observed only at select locations. Our results show that despite the high dependence of butterflyfish and angelfish on live coral cover, reduction of live coral cover due to series of disturbances (tsunami, bleaching) events had limited influence on species richness of these two fish groups, indicating that broad geographical trends are important in explaining variation in species richness for butterflyfish and angelfish groups.

The manuscript writing took almost six months. After lots of discussions, debates, and endless arguments over coffee, we submitted the manuscript to the journal Coral Reefs.  We were relieved when we got to know that the manuscript is in a review. Unfortunately, the decision of the editor, Dr. Michel Berumen was to ‘reject’ the paper, but the suggestions and feedback we received were very useful. We incorporated all the changes and then sent out the paper to the journal Marine Biodiversity as per the suggestion by Dr. Berumen.

To our dismay, the paper was rejected once again. However, this time the journal was keen on receiving a fresh draft after addressing all the comments. We quickly got our acts together, and addressed all the possible comments raised by the reviewers and provided an explanation for the few comments that we were unable to address. Finally, after several iterations, the paper that came out of this collaboration is rather interesting, especially in times when more corals are being damaged due to global climate change and human impacts. This paper is a rare example of practising geographical ecology in marine systems.

Angelfish_Vardhan Patankar
Emperor angelfish, (Pomacanthus imperator)

We look forward to your criticisms, comments and perspectives on this work. Thank you for taking time to read the paper and a blog post!





Published by Vardhan Patankar

Email: vardhanpatankar@gmail.com