Return to Pulau Semakau (South) mangroves

A full team surveys here at predawn for the first time! The original mangroves, seagrass meadows, and reefs of Pulau Semakau lie next to the Semakau Landfill. They are very much alive.

We land next to the Landfill wall, on living seagrass meadow at first light of a glorious sunrise! I will update later with finds by the rest of the team. The ongoing Sudong reclamation looms in the distance.

For the first time in more than 15 years, I had company to check up the back of the original mangroves here! The Pink-eyed pong-pong trees (Cerberus manghas) were still there! Blooming profusely, scenting the morning air with their perfume. Small mangrove saplings are still growing well in the back. As well ans some common back mangrove plants, as well as some small signs of mudlobters. But we couldn't find the Seashore bat lily (Tacca leontopetaloides) that I last saw here in 2011. The younger folk made the trek to the inner lagoon but couldn't find the Api-api jambu (Avicennia marina) that I also last saw in 2011.

More about mangroves at Pulau Semakau
It is NOT true that the construction of the Landfill created the marine life found on Pulau Semakau. The marine life was there long before the Landfill was built. Just as Changi Airport and Changi Beach are not the same even though they are near one another and share a name, Pulau Semakau is NOT the same as the Semakau Landfill. The Landfill was created by destroying all of Pulau Saking, and about half of the original Pulau Semakau by building a very long seawall. Fortunately, the landfill was constructed and is managed in such a way that the original mangroves, seagrass meadows and reefs on Pulau Semakau were allowed to remain. 

A look at the seawall (left) with planted mangroves, and the Landfill wall (right).

As on our last survey in Apr 2025 and Nov 2024, the seagrass coverage remains dense near the Landfill seawall and in the mouth of the stream from the mangroves. Mostly fresh green Needle seagrass uniformly covered the area. In the stream bed and pools lots other seagrasses including Spoon seagrass and Sickle seagrass - most generally free of epiphytes. Nearer the seawall, I saw a few clumps of Tape seagrass with longish leaves (about 30cm), most were still cropped short (10cm or less). Alas, I looked and couldn't find any dugong feeding trails today. In Nov 2024, Kok Sheng saw some in seagrasses near the Landfill wall! The last time this was observed was in 2011. 

Every time we survey this shore, we check out the Barramundi Group's fish farm that is located very close to natural mangroves, reefs and seagrass meadows there. On our Nov 2024 survey, the farm seems totally abandoned. The situation seems unchanged today 1.5 years. Similar to what we saw on our Apr 2025 survey, the big barge with equipment and supplies, and floating dorm for workers were gone. And cages were falling apart with derelict small boats nearby. During our survey in Oct 2023, the farm was not yet in this state of decay. In Jul 2023, it was reported that Barramundi Group will stop stocking its sites off Pulau Semakau, Pulau Senang and St John’s Island until “an efficacious vaccine is available” against the scale drop disease virus (SDDV). SDDV was first formally described in Singapore farmed fish in 2011 and can kill more than half of the barramundi raised in a cage. The virus has caused “significant mortalities and financial losses” for Barramundi Group's Singapore operations, which recorded a loss of $31.9 million for FY2022.

It was good NOT to see a few key things. It was a relief to see zero live Horse mussel clams. The shore where they used to be today is smooth and covered with small seagrasses. In Oct 2023, the mussels covered a large area from the landfill seawall to the stream opening between the old mangrove and replanted mangroves. This suggests some sort of imbalance in the ecosystem. The area is opposite Barramundi Asia fish farm and most of the mussels were very much alive. I already noticed during our last survey in Dec 2022 that they seem to be spreading out. I first noticed small groups of them in Mar 2019, by Oct 2020, there were a lot more and closer together. Covering an area of about 20m2. By Nov 2024, they disappeared from the shore, the same time that the Barramundi Asia fish farm shutdown. 

We also did not see any long fish nets laid on the shore. In May 2023, we came across a 300m long net which had trapped 14 sharks and many other fishes. The lack of these destructive activities seem to coincide with the closure of the fish farm. The other thing we didn't see was a bloom of Sargassum. Seems that at least here, the seasonal bloom is over.

The ongoing reclamation at Pulau Sudong seems to be in full swing today! With huge piles of sand and heavy equipment on the worksite. 

We plan to survey Terumbu Bemban and Terumbu Menalung this week to have a closer look at possible impacts.

What is the fate of Pulau Semakau South?

These shores slated for massive reclamation outlined recently in the Long-Term Plan Review.

The Singapore Blue Plan 2018

Pulau Semakau and nearby islands and submerged reefs have been recommended by the Singapore Blue Plan 2018 for Immediate Conservation Priority. The Blue Plan recommends the intertidal and subtidal marine areas of Pulau Semakau and adjacent Pulau Hantu, and Pulau Jong to be designated Marine Reserve. 

Some common animals I saw today.
The rest of the team make all the special sightings.

The Blue Plan highlights that Pulau Semakau and its associated patch reefs comprise many ecosystems: coral reefs, mangrove areas, intertidal sandflats, seagrass meadows, and coral reefs. The subtidal area of Pulau Jong is larger than the terrestrial area. Pulau Hantu is a popular dive site has seen increasing interest in the past decade due to biodiversity awareness. If protection is accorded to these three islands, zonation plans for use can be implemented to manage tourism and human impacts.

DOWNLOAD the Plan, SUPPORT the Plan! More on the Singapore Blue Plan 2018 site.

Photos by others on this survey

Chay Hoon


Jianlin Liu


Che Cheng Neo


Others on this survey: Lester Tan, Rui Quan Oh, Samuel Lau, Richard Kuah, Muhd Nasry, Marcus Ng, Jayden Kang, Foo Meijuan, Jun Ze, Tammy Lim, Isaac Ong, Che Cheng Neo, Dylan Seng