Mangroves Build Coastlines and Maintain a Healthy Marine Life Habitat in Singapore
When most foreigners think of Singapore they picture a modern and densely populated city-state with skyscrapers. As one of Asia’s largest financial and economic centers, it is easy to overlook Singapore’s existing tropical vegetation and its nature reserves. However, for visitors who explore the city’s outskirts and the northern coastal areas, they will encounter fragments of pristine landscapes that were once historically present throughout the island.
This past summer, during my stay at the National University of Singapore (NUS), I studied the seeds of Mangrove Apple (Sonneratia alba), a pioneering mangrove species that is present throughout the Indo-West Pacific region. Pioneering plant species are the first to establish after a major disturbance to the landscape (e.g. hurricanes), they create the optimal conditions necessary for later successional species of mangroves to subsequently establish and thrive. These mangroves help stabilize sediment and create an environment where degraded coastal systems can regenerate.
|Photo: An opportunity to work in the mud while I collected ripe fruit from the Mangrove Apple trees.|
Mangroves are salt tolerant trees that grow along coastlines and within swamps. These forests provide habitat and shelter for marine life; they serve as nursery areas for a wide variety of tropical fish, birds, crabs and sea snails. In Singapore, approximately 97% of mangrove forests have been lost since the arrival of colonial settlers to the island in the early 19th century. Urban development is one of the major contributors to the loss of these ecosystems. In addition, the building of dams and other freshwater deviation projects throughout the mainland has led to changes in the natural discharge of rivers and creeks into these dynamic coastal systems. As a result of these hydrological changes, the number of trees throughout the coast has decreased and subsequently the understory habitat for marine life has also been reduced. Today, restoration efforts are underway along the northern coast near the existing wetland reserve at Sungei Buloh. Yet, the future success of this and other future coastal management plans will largely depend on the mangrove species selected to jump start these disturbed systems.
As an ecologist, I was interested in examining how the seeds of Mangrove Apple respond to the highly variable environments present along the coastlines. Until now information available about this particular species has been limited, but if we ever attempt to re-plant these trees into degraded sites as part of a restoration plan, it is crucial that we know the optimal conditions for its growth. This study was a part of a broader research project at NUS that aims to quantify how vegetation and sediment deposition influences changes in coastal elevation.
Early in the mornings, when the tides were low, you could find me along the coastal mud flats collecting ripe Mangrove Apple fruit that had fallen onto the mud. Since my work was unconventional and I relied completely on public transportation to get to the field sites, my commute trips were always an adventure. On my two hour ride back into the city, while most of the travelers on the bus and metro were dressed in business attire, my muddy field clothes would draw the attention and curiosity of local Singaporeans. This gave me many opportunities to meet and talk to them about my research project. They would give me recommendations as well as share their own personal experiences visiting the mangroves. They were always surprised to find out that foreigners were conducting research at those remote swamps. For them, these places were inconveniently located and were to be avoided. Instead they would try to convince me to visit the newest shopping centers or clubs downtown. Without fail every conversation would end with a warning, to watch out for the snakes and crocodiles. I followed their advice.
After visiting my field sites I returned to the lab to begin classifying the fruit and preparing them for greenhouse experiments. During my first round of lab experiments, I tested the viability of the Mangrove Apple seeds, in order to determine the percentage of seeds that would sprout from each fruit. Each fruit contained over 100 seeds. I later began adding other variables to the original germination study; they included soil type, salinity, and seed burial depth within the growing containers. All of these variables could be influencing the current loss of seedling and sapling throughout the coastal areas.
A few weeks into my project, I faced a few challenges that required immediate attention. The number of fruits available diminished significantly when the trees began producing less fruit, and during extremely hot days the seeds used in the experiments began drying rapidly within the containers. I was unsure how to proceed from these unexpected obstacles. The water that would keep the seeds and soil moist would evaporate quickly during the hottest part of the day, and I knew I needed to find a way to keep them at least partially moist. That is when I turned to local nursery experts who were familiar with growing other varieties of mangroves. While they did not specialize in growing Mangrove Apple, they did provide me with important recommendations and expressed interest in my project. To keep the mangrove seeds moist and to partially recreate field conditions in a greenhouse setting, a mud/clay blend was mixed with coconut husk mulch. The mulch serves as sponge that keeps the seeds in a moist environment. These field experiences allowed me to see firsthand the techniques local gardeners use to keep the seedlings alive after they germinated. I took those lessons back to the university and applied similar techniques to my own experiments. I began using a cotton base fibrous material to line the growing containers, this change in technique allowed me to keep the seeds moist throughout the day and to continue with the experiments on the right track. I am very thankful for their guidance and willingness to help.
|Photo: At the NUS campus, I set up experimental plots examining different variables
(e.g. soil type, salinity, and seed depth).
From the experiments, I was able to conclude that in a controlled greenhouse setting, the seeds from Mangrove Apple require a moist environment with low salinity in order to germinate. The findings from this research provide insight in to the early live cycle of this pioneering mangrove species. This work was shared with the Applied Plant Ecology (APE) Laboratory, supervised by my host Dr. Edward Webb at NUS. When I first started this research project, the existing research team was interested in finding a method to grow Mangrove Apple seedlings. Some prior efforts had not been successful. However in order to move forward with other lab experiments, they required a significant number of this particular seedling species. The seedlings were needed to examine the impact of tides on the displacement of coastal vegetation, the findings from that ongoing research project will be valuable to land managers who choose to restore this threaten habitat.
I truly enjoyed working and living in South East Asia. A few years ago, I never imagined I would have an opportunity to live in that part of the world. I am also grateful to have had the chance to put my skills as a field ecologist to the test, especially at this early stage in my career. This collaborative project was made possible with the support of the National Science Foundation (NSF) through a grant from the East Asia Pacific Summer Institute (EAPSI) Fellowship Program. I plan to bring these experiences back to the classroom and into my future projects as restoration ecologist. If I had the chance to do go back and work with mangroves once again, I would go back in a heartbeat.
Gabriela Sosa is a Ph.D. student at Texas A&M University, she is completing a doctoral program in the Department of Ecosystem Science and Management. She plans to pursue a career as a professor and practitioner of restoration ecology. Gabriela grew up in Brownsville, Texas and graduated with a B.S. in Environmental Science from the University of Texas at San Antonio. Her Ph.D. program is supported by the Alfred P. Sloan Foundation. At Texas A&M she is the current President of the Hispanic Latino Graduate Student Association and is the former Chief Student Leader of the Society for Ecological Restoration-Student Guild.
A special thanks to everyone at the Applied Plant Ecology (APE) Lab at NUS and to my wonderful EAPSI roommates, Liz and Dominic.