Histological observations in the Hawaiian reef coral, Porites compressa, affected by Porites bleaching with tissue loss M. Sudek a , T.M. Work b , G.S. Aeby c , S.K. Davy a,⇑ a School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand b US Geological Survey, National Wildlife Health Center, Honolulu Field Station, 300 Ala Moana Boulevard, Room 5-231, Honolulu, HI 96850, USA c Hawaii Institute of Marine Biology, University of Hawaii, P.O. Box 1346, Kaneohe, HI 96744, USA article info Article history: Received 27 December 2011 Accepted 12 July 2012 Available online 20 July 2012 Keywords: Coral disease Coral bleaching Porites compressa Porites bleaching with tissue loss (PBTL) Discoloration Hawaii abstract The scleractinian finger coral Porites compressa is affected by the coral disease Porites bleaching with tis- sue loss (PBTL). This disease initially manifests as bleaching of the coenenchyme (tissue between polyps) while the polyps remain brown with eventual tissue loss and subsequent algal overgrowth of the bare skeleton. Histopathological investigation showed a loss of symbiont and melanin-containing granular cells which was more pronounced in the coenenchyme than the polyps. Cell counts confirmed a 65% reduction in symbiont density. Tissue loss was due to tissue fragmentation and necrosis in affected areas. In addition, a reduction in putative bacterial aggregate densities was found in diseased samples but no potential pathogens were observed. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction In recent decades, coral diseases have increased in prevalence and geographical extent worldwide, threatening the health and survival of coral reefs (Harvell et al., 2004; Sokolow, 2009). How- ever, descriptions of most coral diseases have been based on field surveys, and many diseases lack systematic morphological descriptions at both the gross and cellular levels (Work et al., 2008). Confounding the presence of lesions with causation of disease without appropriate laboratory confirmation has led to considerable confusion in the literature (Richardson, 1998; Work and Aeby, 2011). The use of a standardized nomenclature that provides a systematic morphological description of coral disease lesions at the gross and cellular levels allows uncoupling of the description of the lesion from the inference of causation and comparisons across geographical areas (Work and Aeby, 2006, 2011; Work and Rameyer, 2005). Systematic descriptions of le- sions at the gross and cellular levels provide the initial step in the development of case definitions and may assist in identifying possible pathogens (Work and Rameyer, 2005; Work et al., 2008). Porites compressa is one of the main framework building corals in Hawaii. In Kaneohe Bay, Oahu, this species is affected by Porites bleaching with tissue loss (PBTL) that manifests as diffuse areas of white discoloration (secondary to translucence and visibility of skeleton through tissue) of the coenenchyme with pigmented pol- yps that are often retracted (Fig. 1). The lesion may be located in the center or on the periphery of a colony or may be colony-wide (on smaller colonies). In most cases, PBTL results in partial tissue loss with subsequent algal colonization of the dead skeleton (Su- dek et al., 2012). Coral bleaching is defined as a de-pigmentation of the coral’s tissues due to a disruption of the symbiosis between the endosym- biotic dinoflagellates (Symbiodinium spp.) and the coral host; it is typically characterized by the loss of the symbiotic dinoflagellates (Glynn, 1996; Glynn and D’Croz, 1990; Hoegh-Guldberg and Smith, 1989). Environmental stimuli such as high or low seawater tem- peratures (Glynn, 1996; Hoegh-Guldberg and Fine, 2004), high light or UV radiation (Drollet et al., 1995; Glynn, 1996), or bacterial infections (Kushmaro et al., 2001) can trigger this process. PBTL does not appear to be a response to elevated sea surface tempera- tures as it occurs only in isolated colonies at times when water temperatures are well within the thermal threshold of this species. Given the uncertain causes of this disease, we set out to character- ize PBTL at the cellular level. Specifically, we measured tissue thickness and Symbiodinium cell densities and described changes at the cellular level. This study presents the first histological infor- mation on PBTL, so providing a foundation for a case definition of this disease. 0022-2011/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jip.2012.07.004 ⇑ Corresponding author. Fax: +64 4 4635331. E-mail address: simon.davy@vuw.ac.nz (S.K. Davy). Journal of Invertebrate Pathology 111 (2012) 121–125 Contents lists available at SciVerse ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip