Apicomplexans are unicellular parasites infecting numerous animal hosts. Notable apicomplexans include the haemosporidians like Plasmodium falciparum, a causative agent of human malaria, and the coccidians, such as the opportunistic pathogens Toxoplasma gondii and Cryptosporidium parvum, which can cause severe illness and death in immuno-compromised humans. Epidemics by these parasites can affect millions of people and cost billions of dollars in damages. Although apicomplexans are an important parasitic group, little is known about those associated with invertebrates, and hermatypic (i.e., reef-building) scleractinian corals in particular. They were first described in apparently healthy Caribbean corals 25 years ago using light microscopy and it has been previously determined that 90% of Montastraea annularis - a common Caribbean scleractinian - colonies were infected utilizing DNA-based molecular markers. Additionally, apicomplexans have been found in gorgonian hosts, common constituents of Caribbean coral reefs. Therefore, it is likely that apicomplexans are widespread and common in a variety of coral hosts and infection may not be associated with visible symptoms. In order to determine their impact on coral health, it is first important to determine the extent of apicomplexan infections. Thus, this study focuses on apicomplexan parasites infecting both scleractinian (i.e., hard) and gorgonian (i.e., soft) corals and will further describe this enigmatic group.
Characterization of this group of marine apicomplexans and their associations with different host taxa has been generously funded by a PADI Foundation Grant to Nathan L. Kirk. The aims of this project are to 1) characterize the genetic diversity of apicomplexans infecting corals, 2) determine the prevalence of infection throughout the year, 3) examine potential cases of specificity with different host species, and 4) elucidate evolutionary relationships within this little-studied group of marine parasites. To this end, both molecular and histological approaches will be used to describe the diversity of apicomplexans infecting corals. This project will further our understanding of coral reef symbioses and specifically this enigmatic group of protists.