Cracking the Diadema Code
From Microcosm Aquarium Explorer
Special to Microcosm Aquarium Explorer: Posted to NOAA's Coral List
I am encouraged! Over the last 3 years I have been working intensively to develop a process for the mass culture of the long-spined sea urchin, Diadema antillarum, the key herbivore of the tropical western Atlantic coral reefs.
As you know, before the plague of 1983, this urchin maintained the ecological balance between coral growth and macro algae growth on our Atlantic reefs and also conditioned the limestone substrates to better accept settlement of coral and other invertebrates. Ecological restoration of western Atlantic coral reefs depends in large measure on the return of Diadema in ecologically functional numbers. This may/should eventually occur naturally as pioneer populations increase and expand, but natural restoration has been limited and spotty over the last 29 years.
If we could produce large numbers of healthy juvenile Diadema in hatcheries in a variety of sizes and ages, with appropriate genetic background and high health, and learn to stock them responsibly and effectively (see www.StockEnhancement.org), it would be an exceptional tool for research and development projects for ecological restoration on selected coral reef areas.
In fact, it may be the only effective biological tool available for ecological restoration of Atlantic coral reefs. Now the lack of herbivory is by no means the only difficulties these reefs are facing, but the return of ecologically functional herbivory will certainly help the corals of the western tropical Atlantic in their battle to survive and thrive. In Florida, the great ecological, economic, and environmental value of our coral reefs to our communities, State, and nation, estimated at 6.3 billion dollars in sales and income and more than 71,000 jobs annually, demands that we follow every real and potential pathway toward restoration of the health of our coral reefs. But Diadema are very difficult to rear, especially in mass culture. The major bottlenecks to mass culture that have been encountered in the past have been their long larval phase, which exceeds 30 days, and their delicate physical structure, which is easily damaged by conventional rearing techniques.
However, over the last three years, with the tangible and intangible support and encouragement of Mote Marine Laboratory, specifically Drs. Kevan Main, David Vaughan, and Ken Leber, through the Protect Our Reefs license plate fund grants, and the support and collaboration of Tom Capo and his staff at the University of Miami, we have made significant progress in the mass culture of larval Diadema.
The following has been accomplished:
1. Collection and maintenance of two brood stocks of adult Diadema, about 50 at Tom Capo’s lab at UM and 19 in my small lab in the Florida Keys at Islamorada. The brood stock urchins in my lab have been maintained for 3 years with repeated spawning and minimal mortality.
2. Development of a technique for non-invasive spawning of Diadema, pretty much on demand, including egg collection and incubation. 15 million good eggs have been produced in each of the last two spawnings.
3. Development in my little lab of a technique for maintenance and growth of relatively large volume cultures of micro algae for several months with simple procedures.
4. Development of 50 liter culture vessels and techniques that support and grow large numbers of Diadema larvae, 1 per ml, about 50,000 per culture vessel over 50 plus days (whatever is necessary) to the point of competency for metamorphosis. These culture vessels provide the patterns of water movement that keep the larvae in suspension while avoiding excessive turbulence that prevents normal growth and development of the larvae. The operation of the culture vessels is also very adjustable so that the variable requirements of the larvae over the span of culture can be met.
5. Discovery of the biological cues that stimulate rudiment development and competency for metamorphosis, and subsequently induce the process of metamorphosis in the larvae. This aspect of the culture process is still highly speculative, more definitive work is needed to identify and quantify the most active biochemical elements, a process beyond my capability, but in general, a workable method seems to have been established. A method that separates competent larvae with external rudiments and tube feet that are ready to settle from larvae that are still in development is being tested and apparently functions adequately.
The Cusp of Metamorphosis
Successful larvae culture is the major breakthrough of this culture project. At this point, culture day 50, thousands of larvae are on the cusp of metamorphosis with large rudiments and hundreds are apparently in the early juvenile stage. (I say apparently since once the metamorphosing larvae are in a settlement environment of rocks and algae they cannot be easily observed until they have attained a size of 3 to 5 mm test diameter. However, small representative samples of larvae transforming into early juveniles indicate that metamorphosis to a significant degree is successful in the large settlement tanks.)
The next steps in the development of this technology are to determine the best methods for settlement and early juvenile growth and survival, and to develop methods for growout of the juveniles to the sizes that might be required for restoration purposes. Successful replication of this rearing technique at other locations will also be a part of the next steps.
Although there is much to be done before large numbers of reef competent Diadema are available, the basic process has now been developed; it is not perfect, there is a lot of room for improvement and refinement in every area, but the essential workable fundamentals have been established.
The reason for my post is simply to alert you that the basics for this technology are being developed and we are encouraged by recent breakthroughs. And if one old, retired marine biologist can do this by himself in a makeshift marine laboratory in a spare room on a very limited budget, well then, it can be done wherever science meets the sea. It will take a while to figure out how to get this initial work prepared for publication and actually published, but time is of the essence and it is important to begin to think about and plan how large numbers of Diadema can be produced and utilized in coral reef research and restoration projects.
—Martin A. Moe, Jr.
Islamorada, FL June 26, 2009
UPDATE: First Diadema are now through metamorphosis. Image of 73-day juvenile here.
Editor: More details and images will be published as they become available.