Conservation of Giant Clams – Part 4

Today’s the DAY! And by the time you read this post, I should be getting ready to give my TED talk at the conference! 😀 In my 5-minute comprehensive TED talk, my idea worth sharing is that giant clams are ecologically important to coral reefs, and we need to save them! For my final part, I will describe the numerous Ecological Roles that giant clams play on the coral reefs, and why we should care about conserving them!

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For decades, giant clams have been fascinating to many for various reasons: their large body size, their colourful and highly patterned tissues, and ‘shying away’ from divers by closing up their shells! When I first started my research on the giant clams, I focused on filling the knowledge gaps on their ecology and behaviour. With time, I began to ask myself a question: Why are researchers trying to conserve giant clams? Are they ecologically important, and how so? Is there information out there to help support our cause in conserving the species?

The result of these questions was developed by our research group, and we published a comprehensive review in Biological Conservation. Trawling through hundreds of papers, reports, and books, we argued that giant clams are important sources of food for a variety of reef predators, providers of shelters for small invertebrates and reef fish, and finally, contributors to reef building and shaping (Neo et al., 2015a). Here are some interesting bite-size information on the ecological roles of giant clams on coral reefs:

  • Giant clams are ‘solar-powered’ animals, hosting a symbiotic microalgae called zooxanthellae. These tiny algae cells help provide nutrition to the giant clams, and in return, the clams provide refuge and UV protection to these algae cells.
  • Almost 75 different species of reef animals has been reported to feed on giant clams, including the pufferfish, crusher crabs, tiny pyram snails (Cumming & Alford, 1994), and even flatworms (Newman et al., 1993)! (Fig. 1)
  • Clam’s faeces are highly nutritious containing mucus and proteins, and attract fish to come eat them (Fig. 2). One species of damselfish (Neoglyphidodon melas) has been frequently observed to ‘hang out’ around the giant clams (Chan, 2007). (see below)
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A damselfish species hanging out with a giant clam.

  • Giant clams can produce large quantities of calcium carbonate in the form of their shells. Alive or dead, giant clam shells serve as additional substrata surfaces that can host a wide variety of reef animals (Figs. 3, 4; Vicentuan-Cabaitan et al., 2014).
  • Although not seen often, small shrimps (Fig. 5; Neo et al., 2015b) and pea crabs live inside the body cavities of giant clams. If you’re lucky, you may catch a quick glimpse of them moving in and out of the clam’s gills.

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So what now?

We now know that giant clams are effective ecosystem engineers that play multiple roles in coral reefs (Neo et al., 2015a). But we are only scratching the surface of understanding the impacts giant clams have on the ecosystem-level, plus populations of giant clams today are vastly different from the past due to ongoing stressors.

There are still ways to quantify their positive impacts on reefs, such as restocking programmes that present an excellent opportunity to monitor the response of the reef to enhanced clam numbers. To date, only a few studies have done so (e.g. Cabaitan et al., 2008; Frias-Torres, 2017).

We can expect any significant ecological benefits to accrue only when there are giant clams on the reefs. Protecting giant clams ensures that they continue to contribute towards the reef’s functioning, and they are already considered an indicator species in Reef Check surveys (Hodgson, 2001). But we also know that giant clams are now endangered, and we need to combine all the various efforts (discussed in Parts 1, 2, 3) to feature giant clams more prominently for conservation and incorporate them when planning for marine protected areas.

Concluding remarks

For now, a greater understanding of their contributions to the reefs provide us with ‘ammunition’ to justify their protection. In terms of applying these knowledge, I was recently involved in a collaborative effort to develop and support legal framework in protecting the true giant clam (Tridacna gigas) in the South China Sea. In this work, we utilised the argument that giant clams are ecologically important and deserve attention. We hoped that this work can be leveraged upon to eventually strengthen protection measures for giant clams in the South China Sea.

Final thoughts…

“Doom and gloom won’t save the world” – Nancy Knowlton (2017). Knowlton says “The best way to encourage conservation is to share our success stories, not to write obituaries for the planet.

This article was shared by my senior, and it caught my attention. I asked myself another question, so what should I do now? Have I been positive or negative about the situation on the giant clams? Am I on the right track? I think you still need both sides of the story, but certainly, the success will be up-lifting that is complemented by understanding the down-sides of what the planet faces today. Hence, I like to label myself a pessimistic optimist. 😉

But I do know one thing, and that is, I’m giving the giant clams a chance to fight. I stand up and give a voice to them, sharing to as many people as possible about them, and hoping that communication will help me highlight the work that needs to be done for these amazing animals. I will continue to do so for the giant clams, and other marine life – the reefs ain’t just one animal, and we need the rest too! 🙂

Reference List:

Cabaitan et al. (2008) Effects of coral transplantation and giant clam restocking on the structure of fish communities on degraded patch reefs. Journal of Experimental Marine Biology and Ecology 357: 85–98.

Chan (2007) Ontogenetic changes in feeding ecology and habitat of the damselfish Neoglyphidodon melas at Lizard Island, Great Barrier Reef. Independent Study Project (ISP) Collection, Paper 146.

Cumming & Alford (1994) Population dynamics of Turbonilla sp. (Pyramidellidae, Opisthobranchia), an ectoparasite of giant clams in mariculture. Journal of Experimental Marine Biology and Ecology 183: 91–111.

Frias-Torres (2017) Captive bred, adult giant clams survive restoration in the wild in Seychelles, Indian Ocean. Frontiers in Marine Science 4: Article 97.

Hodgson (2001) Reef check: the first step in community-based management.Bulletin of Marine Science 69: 861–868.

Knowlton (2017) Doom and gloom won’t save the world. Nature 544: 271.

Neo et al. (2015a) The ecological significance of giant clams in coral reef ecosystems. Biological Conservation 181: 111–123.

Neo et al. (2015b) Dichromatism in the commensal shrimp Anchistus miersi (De Man, 1888). Marine Biodiversity 45: 877–878.

Newman et al. (1993) Stylochus (Imogene) matatasi n. sp. (Platyhelminthes, Polycladida): pest of cultured giant clams and pearl oysters from Solomon Islands. Hydrobiologia 257: 185–189.

Vicentuan-Cabaitan et al. (2014) Giant clams host a multitude of epibionts. Bulletin of Marine Science 90: 795-796.

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