Uncovering mollusk diversity in mangrove forests

Tricia C. Goulding

Onchidiidae slug

Pennsylvania State University
Department of Biology

2nd place winner of the best student presentation award at the 

American Malacological Society

This past week I joined other mollusk researchers to exchange ideas, discuss challenges in the field, and learn from each other’s research at the annual meeting of the American Malacological Society. I was able to attend to present my dissertation research on mangrove gastropods in the Indo-West Pacific. I enjoyed meeting many eminent malacologists, as well as the other students, during our week of activities.

The snails and slugs I study live in tropical mangrove forests, a threatened estuarine habitat. Mangrove forests are cut down across the Indo-West Pacific to produce shrimp ponds, or for firewood and building materials. The loss of mangroves leaves coastlines vulnerable to storms, and results in declining habitats for fish and shellfish which support wild fisheries. Gastropods are an important component of mangrove ecosystems, but the species diversity across the Indo-West Pacific is still poorly known. In order to better understand the species diversity in mangroves, I have explored hundreds of mangroves with collaborators from 10 countries and collected samples of snails and slugs. I extracted DNA from these samples and sequenced a fragment of DNA known as a “DNA barcode,” which is useful in many groups of animals to differentiate species. I used this data to get a better understanding of species richness across the Indo-Pacific. Specifically, I have estimated that the area with the highest number of mangrove gastropod species is found in a region commonly called the Coral Triangle (a region encompassing Indonesia and the Philippines). Interestingly, this data also shows that the South China Sea (between Singapore, Sumatra, Borneo and Vietnam) is also a significant hotspot for diversity in mangrove gastropods, and that many of the species in this region are unique from the fauna of the Coral Triangle.

After estimating species richness, the next step to understanding mangrove ecosystems is to identify the species and to describe the new species. I have been working on re-describing the onchidiid slugs and classifying the species into genera using modern microscopy and DNA sequences. Most of the diversity within the family Onchidiidae is in the tropical Indo-West Pacific (from eastern Africa to the Pacific Islands). However, original species descriptions, mostly from the 1800s to 1930s, often did not include information on the habitat of these slugs or their appearance when alive, which are important characteristics used for identification. In addition, museum collections contain very few of these slugs because mangroves have rarely been explored (possibly because of the other fauna in mangroves: mosquitos, snakes and crocodiles!).

 
By collecting new samples from across the Indo-West Pacific, our lab has been able to record important natural history information, photograph live animals in the field, and preserve tissue samples for DNA analysis. These new collections have been invaluable in studying the diversity of this group, and have resulted in the identification of 40 new species of slugs! Onchidiid slugs are very abundant in intertidal ecosystems, and it is only after we have identified the species present and their distribution that other researchers will be able to study their role in mangrove ecosystems.