Giant clams, a sheltered reputation

Giant clams, Tridacna Sp., are not widely known by the every-day tourists. Three different species occur at Koh Tao; Tridacna maxima, Tridacna squamosa and Tridacna crocea. Although giant clams are not widely known, they can easily compete with the rest of the coral reef in a beauty competition due to their stunning camouflaging coloration. Moreover giant clams live up to their name and can reach impressive sizes, the largest species in this genus reaching up to 1.4 meters! At Koh Tao however the largest individuals grow up to a more conventional 40 cm.

Giant Clams get hold of food in two different ways. The first source of food for giant clams is zooplankton, which are obtained through filter-feeding, this is the main food source for giant clams in their early stages of life. Giant clams also have a symbiotic relationship with a unicellular algae (called zooxanthallae), which live in the tissues of the clams. These algae share some of the sugars and carbohydrates they produce, through photosynthesis, with the clam. Not only does the zooxanthallae provide about 90% of the clams daily energy budget, they are also responsible for the clams unique and ornate coloration.

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Throughout the past several years, the program has been conducting ever increasing amounts of research on the invertebrate organisms of the island. In 2012, our research expanded into the complex and charismatic world of the nudibranchs, and shortly after, the remaining sea slugs. In December 2015, the program published the findings of the research in the journal Marine Biodiversity.

Sea slugs are an incredibly diverse and fascinating type of organism that are found in marine environments worldwide. You can read more about sea slugs and the roles they play in our learning resources segment here. At the program, sea slugs play important roles in two of our key activities, beyond the incidental observations doing restoration work. The first of these is the inclusion of nudibranchs (and by extension the rest of the sea slugs) in our Ecological Monitoring Program (EMP) surveys which you can read about here. The second is the significance of sea slugs in our muck exploration efforts which have led to a number of interesting findings. In 2012 the research started out mapping the inventory of all known species of sea slugs found on Koh Tao, almost 3 years later the findings of the research came to a number of interesting and regionally significant conclusions.

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The Crown of Thorns Starfish, Acanthaster Sp., is a large sea star whose diet consists almost entirely of hard corals. This sea star has been known to cause devastating losses to coral reefs in areas where their populations rise, or where corals are particularly stressed by other threats such as development, over-fishing, physical damage, or bleaching. For years, we at the NHRCP have been monitoring Acanthaster populations around our island, and performing removals in areas where populations are relatively high, or coral levels are low. In 2014 we removed 138 individuals from reefs around our island, and in 2015 we removed over 277. After so many removals we started to wonder where the new sea stars are coming from, what depths are they living at, what are the population dynamics, and what corals do they prefer to eat. All of these points where investigated in detail by one of our interns, Leon Haines.

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Reef Shark Monitoring

For many years we have been visiting and monitoring the Blacktip Reef Shark Populations in Shark Bay, starting with the work of Shin Arunrugstichai during his time on our team. In February of 2015, we restarted that program, and have been monitoring the abundance and population dynamics of the sharks with improved techniques. During each survey, we record the position of the shark with a GPS, and also take data on the size, sex, and behavior. The idea was to look at the movement of the sharks pre- and post-spawning, with particular emphasis on the neonates or new born shark pups. What started as a weekly survey quickly turned into a few times a week, and then everyday once the spawning started. The high level of surveys meant that we were able to involve all of the interns and students within the program, and show them how to monitor these shark numbers. These surveys also gave the students an opportunity to learn how to survey and observe sharks in their natural environment, and how to identify the age and sex of the shark. 

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NHRCP Research papers 2015

The 2015 season continued to drive the NHRCP as an institute of research as well as conservation. During the season, eight manuscripts in particular were completed that are highlighted below. The research topics range from new discoveries in feeding of corals, to assessment of health and threats to the coral reefs of Koh Tao, and even an analysis of isotope prevalence that provided some very interesting results. Below you can see a summary of those papers, and also click on the links for more information or to download the PDF of the paper.

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Barrel Sponges – Filter Feeding Powerhouses

In normal, human, terrestrial, domestic urban or rural life, the concept of a chimney is nothing special to people. To some, the romanticised idea of a warm fireplace, to some bringing about thoughts of Christmas, and others simply curiously wondering at such ancient forms of energy acquisition. On a larger scale, like in industry, chimneys are seen as a symbol of pollution and chemical toxicity, with factories pumping clouds of black smoke into the atmosphere to produce whatever they produce. Or even larger icons of destruction, are the monstrous chimneys of Nuclear Powerplants, massive funnels billowing steam reminding us of scale of energy contained and being produced within the facility.

This design, to eject masses of by-products into surrounding environment, long pre-dates human thinking. Coral reefs around the world are filled with its own chimneys, often well over the height of the tallest ape and sometimes several meters in circumference, Barrel Sponges are the towering columns of the marine world. These structures are some of the simplest, and are descendants of some of the oldest forms of life on our planet, and they serve an often overlooked role in saving coral reefs. Above the waves, chimneys direct waste gasses into the air above to dissipate over a wider area and the same mechanism is utilised by the barrel sponge on coral reefs. The reefs of Koh Tao have a diverse range of sponges but none are more impressive and dominating the reefscape than the Barrel Sponge (in this case, Xestospongia testudinaria).

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Drowning in “Despair”

It was a momentous week for us here at the NHRCP, as we sunk 3 of our newest sculptures in Chalok Baan Kao on the subject of ‘Despair’. This was, in no small part, due to the efforts of our incredible team of volunteers, interns and staff. Without them, none of these concepts would ever come to fruition and I can’t thank them enough for their continued support.

Restoration work has already begun on the sculptures, as fragments were transplanted to their surfaces using epoxy. Acropora corals were chosen for the bases of the structures while slower growing sub-massive species (Porites, Favites, Goniastrea, etc.) were planted onto the topmost surfaces. The faster growing branching species of Acropora will create a wealth of structurally complex habitat around the bases of the structures, while allowing the sub-massive corals time to mature without the risk of being shaded. 

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The Good Samaritans

Each year, we are blessed to receive many people coming to Koh Tao to assist on our marine conservation program from all ages, countries, and demographics. Yet, we are always surprised at how little those involved in the rest of the diving industry actually do to protect the environment, and the same goes for society as a whole. Is there something unique about these people who come to dedicate weeks or months of their lives to helping the sea? What could it be about their personalities, life history, or character that makes them put the wellbeing of others, or the environment, over their pursuit of other things. Or, more importantly in terms of changing the future; why do so many people not get involved in humanitarian or environmental projects. How is it that they can overlook the suffering of other humans, animals, or entire ecosystems and do nothing?

For the most part, it is not because they lack empathy or don’t care. Indeed most people can see problems, and often complain about them. But why does that not lead to action?

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Gelatinous Salps and Hungry Corals

Heteropsammia are a unique group of stony corals which do not attach to the substrate. These free living corals have a flat base, and live in calm sandy areas, usually in the depths outside of the coral reefs. With many of the species of Heteropsammia, the larvae settle down onto the shell of very small snails, which are then engulfed as the coral grows. They also have an obligate commensal relationship with a small worm, known as a sipunculid, which protrudes from a small hole in the bottom of the coral and helps the coral right itself, move around, and prevents it from being buried in the sand. Because this worm can also move the coral around, the corals are known in the aquarium trade as “Walking Dendros.”

Almost the entire upper portion of the 2.5 cm wide coral is a mouth, meaning that it is able to consume much larger prey than most other hard coral species. Being a coral which lives deep, this is an advantage as there is less light available at depth to power photosynthesis for the coral’s symbiotic algae. These corals thus rely more on predation than the functionally autotrophic corals of the shallow oceans. But what exactly do they eat is a question that is still being answered. Recently, on the island of Koh Tao in the Gulf of Thailand, the corals have been observed eating salps, an observation that was recently published in the Journal of Marine Biodiversity.

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A New Future in Electric Coral Reefs

Coral reefs around the world are being lost at an alarming rate due to the localized effects of human activities, natural causes, and the global effects of climate change. One of the more unique methods used to restore and preserve corals in the face of oceans that are becoming warmer and more acidic is the use of electric artificial reefs, or Biorocks™. Biorocks™, or mineral accretion devices, were invented by Dr. Wolf Hilbertz, and use a process of sea electrolysis to improve the growing conditions for hard corals and other marine life. On these electrified structures, corals and other animals grow faster, and can better survive problems such as temperature changes, disease, predation, or ocean acidification. Corals growing on the devices not only are healthier than their natural counterparts, but also have a higher reproductive output – meaning more larvae to seed and restore damaged coral reefs nearby.
Although the technique was patented in 1996, the vital technology is not yet widely used around the world. Although the technology is not very complicated, it is more expensive than many other artificial reefs and requires regular maintenance, but that is not the main reason why you may have never seen or even heard of them. One of the major problems with the technology is that up until recently is has remained patented, trademarked, and proprietary information of the Biorock Company. Because of these ownership and patent restrictions, the technology has not been freely available to the reef managers and local communities who could have benefited most from its use. 19 years has essentially been lost, over which time tools that could have helped save reef areas and preserved coral diversity in places around the globe has been forestalled.

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