World Seagrass Association Blog

Every fortnight we feature a seagrass meadow from around the world. This week, Marjolijn Christianen shares her experiences working in the beautiful tropical island of Derawan in Indonesia. Marjolijn is currently a PhD student at Radboud University in The Netherlands. She has a blog detailing her experiences working with turtles and seagrass.

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by Marjolijn Christianen

The Derawan Archipelago, is a hotspot of biodiversity and located in front of the Berau River on the mainland of East Kalimantan, Indonesia. In recent decades the once pristine rainforest and mangroves have been quickly transformed into palm oil plantations, coal mines and shrimp farms. Since all this activity is concentrated around the rivers it expected that the adjacent estuary will experience great effects of the increasing sediment and nutrient loads that will negatively affect the marine life & biodiversity of the adjacent estuary. So what is the effect of this on the seagrasses here?

(a) Map of the a Indo-Pacific Ocean with (b) The Derawan Archipelago and the (c) location of the exclosures on Derawan Island (d) Leaves are intensively grazed by green turtles, and a detritus layer is absent.

Following a pilot expedition of a Dutch group of marine biologists in 2003, we started with a 5 year PhD project in cooperation with the Indonesian Institute of Sciences (LIPI) and based ourselves on the small & beautiful Island of Derawan. The island is surrounded by a large shallow area (light-blue in picture c above) which is dominated by a mono species Halodule univervis meadow. On the other islands of the archipelago you can also find other species like Cymodocea rotundata, Cymodocea serrulata, Halophyla ovalis (with very rare dugong tracks), Enhalus acoroides, Thalassia hemprichii, Syringodium isoetifolium.

We found that the effect of increasing nutrient loads proved to be much less than the effect of the local grazers. Directly after arrival I was amazed by the extremely shortly grazed leaved, that were also very thin. It just looks like there is someone mowing the underwater seagrass lawns every day. And the extremely high densities of green turtles (Chelonia mydas) were found responsible for this. In our latest paper (Christianen et al. 2011, Journal of Ecology, link http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01900.x/citedby) we estimated that these hungry grazers graze 100% of the daily primairy production of the seagrass meadow.While populations of green turtle have dramatically declined at most other places, green turtle hotspots like Derawan could teach us about the historical role of the role of these megaherbivores. The green turtle not only drives structure and functioning of their foraging ground but also increases the tolerance of seagrass ecosystems to eutrophication (Christianen et al. 2011).

It is not difficult to spot green turtles grazing around the island

The majority of our fieldwork on Derawan focuses on unraveling the interactions between seagrasses, turtle grazing and increasing nutrient loads. A fancy fieldwork station is lacking but this stimulates to interact a lot with the (families of the) local fisherman that have a lot of knowledge about the ecosystems.

On a small island with 1500 people we always have enough attention from the local kids (left). Daily fieldwork life, working on exclosures 400 meters offshore of the island (right)

Working on such a remote island is amazing because you are surrounded by marine life such as green turtles, mantas, dolphins, frog fish, and (my favorite) the robust ghost pipefish (looks like a Thalassia leaf). But on the other hand you also have to plan your experiment well and buy your materials a full day travelling away, or even further. And don’t step in a stingray like I did because this will definitely slow down your fieldwork.

180 degrees panorama from the Telkom tower

Every fortnight we feature a seagrass meadow from around the world. This week, Ria Tan takes us on a tour of Cyrene Reef in Singapore. Ria is an avid naturalist and runs the wildsingapore webpage. In addition to hanging out in seagrass meadows, she enjoys exploring new intertidal reefs and has recently taken to trudging around in mangroves.

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People normally assume that the best seagrass meadows are found in shallow, sheltered, clear waters far away from human impact and industry. That’s not the case in Singapore, a small island nation sitting at the tip of the Malayan Peninsular. One of Singapore’s best seagrass meadows is surrounded by massive petrochemical industries, a world class container terminal and major shipping lanes in one of the world’s busiest ports. Cyrene Reef is a 1km by 500m submerged reef with astonishing marine biodiversity!

http://www.flickr.com/photos/wildsingapore/3722430121/
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On one side of the Triangle is Pulau Bukom, the site of Singapore’s first oil refinery, set up in 1961 by Shell. Today, the 500,000 barrels-per-day Bukom Refinery is the largest Shell refinery in the world, in terms of crude distillation capacity. On another side of the Triangle are the massive heavy industries on Jurong Island encompassing a wide variety of installations. Some industrial activities that can potentially impact marine life include flaring. Developed in 1974, the Pasir Panjang Container Terminal is the largest of Singapore’s four terminals. Together, the terminals handle about one-fifth of the world’s total container transhipment. Cyrene is at a key maritime crossroads where east-west traffic routes cross north-south traffic routes. About five hundred ships in excess of 5,000 DWT per day transit the waters around the Reefs.

Despite it’s location in the middle of this ‘Industrial Triangle’, Cyrene Reef is home to vast meadows with 7 seagrass species! Long ribbons of Enhalus acoroides are particularly spectacular when in bloom!
http://www.flickr.com/photos/wildsingapore/2291422760/
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Cymodocea serrulata covers large areas of Cyrene Reef. These seagrass meadows are home to large numbers of Knobbly sea stars (Protoreaster nodosus). A study of these sea stars found that the presence of juveniles, subadults and adults, which indicates a healthy level of recruitment at Cyrene Reef. And that Cyrene Reef may be the only sustainable population of knobbly seastars left in Singapore today.
http://www.flickr.com/photos/wildsingapore/2884908620/
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Cyrene is one of the few locations in Singapore where Syringodium isoetifolium is abundant. Other seagrass species on Cyrene include Cymodocea rotundata, Thalassia hemprichii, Halodule uninervis and Halophila ovalis.
http://www.flickr.com/photos/wildsingapore/4893420536/
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Besides massive industries, frequent dredging also takes place near Cyrene Reef. Meanwhile, further reclamation is being considered at nearby Jurong Island. Just last week, a large fire broke out at the Shell refinery on Pulau Bukom close to Cyrene Reef. The fire raged for 30 hours before it was put out. It remains to be seen whether this massive industrial accident has impacted marine life on Cyrene Reef.
http://www.flickr.com/photos/wildsingapore/5972221362/
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Cyrene Reef is one of the major sites monitored by the volunteers of TeamSeagrass, a collaboration with the National Parks Board
(NParks) and international Seagrass-Watch, the largest scientific,non-destructive, seagrass assessment and monitoring program in the world. TeamSeagrass includes about 100 volunteers from all walks of life who have been monitoring Singapore’s meadows since 2007. The data they collect is submitted to NParks for a better understanding and management of Singapore’s seagrasses and shores, and to Seagrass-Watch thus contributing to global understanding of the world’s seagrasses.
http://www.flickr.com/photos/wildsingapore/3129983657/
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TeamSeagrass also gives ordinary people the opportunity to see first hand, some of Singapore’s best shores. Volunteers also have the satisfaction of making a difference for Singapore’s marine biodiversity.

Besides monitoring, TeamSeagrass volunteers also participate in other outreach efforts such as public exhibitions and in giving talks. TeamSeagrass also has a blog and facebook page for online outreach. This is one of the posters of seagrasses on Cyrene used in TeamSeagrass public exhibitions.
http://www.flickr.com/photos/wildsingapore/2337022294/
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There is also an effort by a small team of volunteers to raise awareness of Cyrene Reef. The focus currently is to bring decision makers and selected corporations to visit the Reef and see it for themselves. Thus far, visits have been arranged for the Urban Redevelopment Authority, NParks and JTC (which manages Jurong Island).

Hopefully, these and other efforts to document and share Cyrene’s treasures will help protect this miraculous reef in the middle of an Industrial Triangle!

Find out more about Cyrene Reef and Singapore’s seagrasses at these sites
TeamSeagrass http://teamseagrass.blogspot.com/
Cyrene Reef Exposed http://cyrenereef.blogspot.com/