Surveying for windowpane oysters

 In Fieldwork, Mangroves

I came to Marine Conservation Philippines (MCP) as a Dive Master in Training (DMT) in 2016. I knew I wanted to do my Dive master course at a marine conservation centre rather than a recreational dive shop. I was not disappointed. I found a home at MCP and blossomed into a safe, sane, responsible kickass diver under the mentorship of the incredible instructors and staff. I was not ready to leave when my time came to an end, but life happened and I had to go.

Fast forwarding six months and I was welcomed back as an intern. When I was asked if I could take on the Siit Bay Windowpane Oyster Project, I said, “Yes, of course.” without having any idea what I was getting myself into.

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In a nutshell (In an oyster shell.. ha), MCP was approached by the Local Government Unit and the Environment and Natural Resources Division of Siaton for help in locating the most beneficial area in Siit Bay to establish a marine protected area for windowpane oysters sanctuary. If you’re like me, you probably have never heard of windowpane oysters before. What the heck are they? Well, I did some research and here’s what I found. Windowpane oyster, Placuna placenta, locally known as Capiz is an edible marine bivalve mollusk with thin, translucent, shiny mica-like shells. They are usually found in the sandy-mud bottom along the coastline of mangrove forests in South East and South Asian countries (Yonge, 1977).

My job was to lead and conduct surveys to cumulate the population density of windowpane oysters. Sounds very scientific and boring doesn’t it? In reality, it was a very unique experience conducting surveys along the coasts of mangrove forests with zero visibility. I once thought bad visibility was when you could see 1 or 2 meters ahead. Last month I realized I had no idea what I was talking about while descending into the mysterious murky water along the mangrove forests in Siit Bay. I mean, I was inches away from the bottom and I couldn’t even see it! The only way to look at my compass or dive computer was to put them right in front of my mask. Now that’s, “bad viz”. It was challenging but definitely a valuable experience to work in such extreme conditions. Although, after 3 weeks of diving in the mud I was so ready to be back on the reef.

Survey team on the MCP speedboat

Survey team on the MCP speedboat

So, why should we protect the oysters? Because humans are absolute horrible creatures and are destroying everything in our paths! Ha, I joke.. but actually.. the ocean ecosystems are in great danger. Windowpane oysters were once found in such high abundant along the Philippines coastline that there is even a province named after them! (Capiz is located in the region of Western Visayas in central Philippines.) Today, they are under threat of disappearing due to exploitation. Their beautiful shells are exported worldwide to be used as raw material for handicrafts to make window pane, chandeliers, wind chimes and jewelries. They have previously had an immense economical impact in the Philippines ranking fifth among the major fishery export, generating US$36 million from 1986 to 1991 in shell crafts (Philippine Fisheries Profile, 1991).
During those years raw shells were sold in kilograms. Price raging from as little as PHP 5 to PHP 12 per kg when US$1 was equivalent to PHP 27 (Gallardo, W. G., Siar, S. V. & Encena II, V., 1994). You do the math… US$36 million worth of windowpane shells, that is an obscene amount of oysters being harvested to make chandeliers! High demands encouraged fishermen to engage in destructive methods of harvesting including dredging, trawling and dynamite fishing in order to collect as many oysters as possible. These methods not only depleted the oyster population from its habitat but also damaged and destroyed seagrass beds and coral reefs. This is why the establishment of MPAs and windowpane oysters sanctuaries is vital for the survival of existing populations.

The Siit Bay surveys were completed in 3 weeks. The data collected corresponds with Hornell’s findings in previous study that the windowpane oysters prefer sandy-muddy bottoms (1909). Madrones-Ladja’s study suggested that the windowpane oyster will reproduce more successfully in higher populated areas since fertilization of eggs and sperms occurs externally in open water. As a result, I concluded that the best location for a MPA is along the mangrove forests and seagrass beds where the oysters were found in the highest abundance. An establishment of a MPA and windowpane oyster sanctuary will provide a safe haven for juvenile oysters to grow and for sexually mature adults to reproduce during spawning seasons. As a bonus, fishermen will have a sustainable supply from the spill over outside the demarcated MPA area. (If you are interested in reading the Windowpane Oyster in Siit Bay report, click here.)
Windowpane oysters aren’t the only marine species in danger. The ocean ecosystems (mangroves, seagrass, coral reefs) all over the world are under a great deal of stress and are slowly disappearing. That is why at MCP we strive to save our home together with local communities!

The completed report can be found here

References
Gallardo, W. G., Siar, S. V. & Encena II, V. (1994). Exploitation of the Window-pane Shell Placuna placenta In the Philippines.
Hornell, J. (1909.) Report on the Anatomy of Placuna Placenta, with notes on its distribution and economic uses. Report to the Government of Baroda on the Marine Zoology of Okhamandal in Kathlawar. Williams and Norgate, London. 43-97.
Madrones-Ladia, J. A. (2002.) Salinity Effort on the Embryonic Development, Larval Growth and Survival at Metamorphosis of Placuna placenta Linnaeus (1758) Aquaculture, 214: 411-418.
Philippine Fisheries Profile (1986-1991). Bureau of Fisheries and Aquatic Resources, Manila.
Yonge, C.M. (1977.) Form and Evolution in the Anomiacae (Mollusca: Bivalvia) – Pododesmus Anomia, Patro, Enigmonia (Anomiidae); Placunanomia, placuna (Placunidae, Fam. Nov.) Philosophical Transactions of the Royal Society of London B, 276: 453-527.

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