Marine Invertebrate Diseases

Science Center Objects

Coral reefs worldwide are under tremendous stress primarily due to human activities along the coasts. While climate change, over fishing, and coastal development have been implicated as a major cause of coral reef decline, diseases seem to play an increasing role.

Coral reefs are a constant struggle between slow growing corals and fast growing algae, and urchins play a critical role in maintaining that balance given their roles as important grazers.  Unfortunately, we have little idea of what drives declines of urchins on reefs, and even fewer clues as to the causes of coral diseases.

 

Surveillance

We are applying methods used in investigation of animal diseases to corals and urchins.  This begins with systematic descriptions of lesions at the gross and microscopic level.  For instance, corals respond to insults in one of three basic ways:

1)     Discoloration where there is a change in color from normal in the coral tissue. While this often applies to what is known as bleaching (loss of pigmentation and symbiotic algae in the tissues revealing the white skeleton underneath), it can apply to any coral manifesting areas of tissue discoloration (pallor, complete loss of pigment, or change in pigmentation). 

2)     Another response is tissue loss where there is absence of tissue revealing bare or algae covered skeleton.                                 

The USGS National Wildlife Health Center in collaboration with NOAA and other partners is currently responding to the Florida Reef Tract coral disease outbreak, a disease event affecting the continental United States' only living barrier reef. Learn more about the Florida Reef Track Coral Disease Outbreak.

3)     Finally, there are growth anomalies manifesting as abnormal growth of skeleton or tissue.  Gross observations are complemented by microscopic examination of tissues. 

As for urchins, we are trying to get a better idea of how to monitor their health from a biomedical perspective.

 

Research 

Applying these tools to corals reveals that they, like other animals, are prone to a variety of infectious and non-infectious causes of mortality such as fungi, algae, cyanobacteria, parasitic corals, and ciliates.  A significant challenge now is better characterization of host response at the light and electron microscope level along with development of cell markers to better understand pathogenesis of disease.  For urchins, we are getting a handle on basic information such as gross and microscopic anatomy and how cells respond to insults.

 

Resources

Collecting corals for histopathology. A practical guide (English language edition) (Spanish language edition)

Sea Star Necropsy Protocol

Histology Manual for Tripneustes gratilla (Collector Urchin)

Coral Disease Cards: In collaboration with various partners, we have made underwater cards that will help divers describe lesions in corals from Hawaii, American Samoa, and New Caledonia.  The cards can be printed on underwater paper or laminated to help divers describe lesions in corals (cards designed to print front to back).