Chromatophore tissue density and skeletal density banding as a measure of the adaptive response of healthy corals to environmental change

Chromatophores, pigment-bearing cells within the ectodermal layer of hermatypic scleractinian coral tissues, are postulated to enhance the photosynthetic activity of zooxanthellae symbionts and possibly protect the coral animal from harmful ultraviolet (UV) radiation. Yet connections have not previously been drawn between changes in the tissue density of chromatophores and the development of skeletal density bands in “apparently healthy” corals (corals with no outward visible indication of distress or disease). An integrated histological and computed tomography x-ray diffraction (MicroCT) analysis of the ecological cornerstone coral Montastrea faveolata has been completed on the reef tract of the southern Caribbean island of Curaçao across a 1-20 m bathymetric transect of increasing water depth (WD) and decreasing photosynthetically active radiation (PAR). This has established the first qualitative and quantitative baseline for the extent to which apparently healthy corals respond to changes in WD and PAR, thus creating a comparative standard for future evaluation of impacted and diseased corals. Standard SCUBA diving techniques were used to extract 2.5 cm-diameter and 2 to 3 cm-deep coral skeleton-tissue biopsies, collected in triplicate from > 1 m-diameter heads of M. faveolata within the context of coral reef carbonate depositional facies. A combination of field and laboratory photography, serial block face imaging (SBFI), two-photon laser scanning microscopy (TPLSM), and three-dimensional (3D) MicroCT image analysis was applied, making this the first study to collect and evaluate this suite of data within the 3D spatial context of an entire unprocessed coral polyp. TPLSM was used to optically thin section unprocessed tissue biopsies with quantitative image analysis to yield a nanometer-scale 3D map of the quantity and distribution of the symbionts (zooxanthellae) and a host fluorescent pigments (chromatophores), which is thought to have photo-protective properties, within the context of an entire coral polyp. Results have identified a distinct difference in the size and distribution of chromatophores in the tissues of M. faveolata at 6 m WD versus 22 m WD, as well as site-specific differences potentially driven by environmental and anthropogenic influences, which correlate with variations in skeletal density banding patterns. Taken together, this suggests that apparently healthy heads of the coral M. faveolata adapt to increasing WD and decreasing PAR by shifting toward a more heterotrophic lifestyle, which they decrease zooxanthellae tissue density, increase mucocyte tissue density, and decrease chromatophore tissue density, which combine to cause biotically-driven changes in skeletal density banding.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Ardisana, Ryanne

Contributors dc:contributor

• Fouke, Bruce W.

• coral
• coral reef
• auto- and heterotrophy
• water depth
• Montastraea faveolata
• photosynthetically active radiation
• chromatophores
• skeletal density banding

Statement dc:rights

• Copyright 2014 Ryanne Ardisana

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/49434

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/49434