Coral Specimen in Museum Collection

The Horner Museum's natural history specimens, including rocks such as those described in the last post, come in all sizes.  One which I encountered recently was a geode the size of a basketball!  Many, however, are quite small which makes them difficult to exhibit.  For that reason, we decided against displaying this item from Samoa in the Around the World exhibit of 2017.

Stylaster sanguineus Coelenterates coral from Samoa

The Pacific nation of Samoa consists of the islands of Upolu and Savai'i plus a few neighboring small islands. The islands are nearly surrounded by coral reefs.  The reefs consist of colonies of individual coral polyps -sacs with an opening surrounded by tentacles-- living within an external skeleton of (usually) calcite. New polyps begin atop the skeletons of dead coral and secrete limestone, building up the cup that surrounds them and adding to the reef.  Zooxanthellae (a type of algae) lives within them and provide food and bi-products which increase limestone production.  Because the Zooxanthellae need sunlight for photosynthesis, most reefs are in water less than 25 meters (82 feet) deep.

             

The reefs around Samoa contain over 50 varieties of coral.  I assumed this was one. But when I started researching Stylaster elegans ver. (now known as Stylaster sanguineus) the scientific name the donor supplied for this specimen, I discovered that although commonly called “lace coral”, the stylasters are of a class of animals called  Hydrozoa, not a true coral (which belong to the class Anthrazoa). Although the outside may look like a coral, the much smaller polyps are arranged in parallel rows with specialized functions.  One group uses its hair-like tentacles which sting a threatening predator and an adjoining feeding polyp which collects and digests plankton from the ocean . They can operate in this cooperative fashion because the calcite structures in which they live are connected by tiny channels. They do not have internal Zooxanthellae and so do not need to be where light can penetrate. Nearly all are found in water at least 165 feet deep and commonly at depths of 600 to 1,000 feet.

            

Like the coral reefs on which they live, the stylasters are affected by changing water temperature and salinity and pollutants released into the oceans by human activity. The coral reefs around Samoa have also suffered from the physical effects of hurricanes and a 1978 population explosion of crown of thorns starfish, a predator which destroyed about two-thirds of Samoa's reefs. 

By Martha Fraundorf, Volunteer for Benton County Historical Society, Philomath, Oregon