Fouke, B.W.

Quantitative tracking of the cellular and skeletal respose of the Caribbean coral orbicella annularis to gradients i marine sewage pollution

Msc. Thesis

Abstract

Orbicella annularis is an abundant framework-building Scleractinian coral that serves as an ecological cornerstone throughout the Caribbean Sea. The O. annularis holobiont (all interacting biotic and abiotic components making up the coral) is negatively impacted by increased exposure to anthropogenic pollution, which results in altering coral physiology and increasing the risk of disease infection. Changes in O. annularis tissue cellular composition and skeletal structure have been tracked across a 75 km-long gradient from clean to polluted seawater on the fringing reef of the leeward coast of the island nation of Curaçao. A unidirectional ocean current flows to the northwest past the capital city of Willemstad, a large point source of human sewage and ship bilge. Apparently healthy coral colonies were evaluated and sampled by extracting 2.5 cm- diameter biopsies at five sites from Water Plant to Playa Kalki within the back-reef carbonate sedimentary depositional facies. As a result, environmental variables other than pollution, such as water depth, currents, water temperature, oxygenation and other factors remained constant between sites.

Two-photon confocal laser scanning microscopy (TP-LCM) was used for three- dimensional (3D) quantification of the density of zooxanthellae and chromatophore cells within the coral tissues. X-ray computed tomography (BioCT) was used to determine the density of the outermost layer of the coral skeletal being precipitated at the time of sampling in May 2014. Results indicate that zooxanthellae cell tissue densities decreased as pollution concentration increased. Conversely, chromatophore cell tissue densities exhibited no significant covariant changes along the pollution gradient and varied significantly within corals at each site. This implies zooxanthellae cell tissue density is strongly influenced by environmental stress due to pollution, while changes in chromatophore cell tissue density is controlled by other unknown factors. O. annularis skeletal density showed no significant changes across the geographic pollution gradient, as well as significant within site variations. This suggests skeletal density is not as strongly impacted by pollution as by other unknown biological, physical and chemical factors.

There was a significant positive relationship between chromatophore and zooxanthellae tissue density as well as a negative relationship between chromatophore density and skeletal density. These results have been used to create a new model for healthy coral physiology, integrating the relationship between zooxanthellae, chromatophore and skeletal density of individual O. annularis polyps to better understand their collective role in coral metabolism. 

Date
2017
Data type
Other resources
Theme
Research and monitoring
Geographic location
Curacao

Multimodal Optical Microscopy Methods Reveal Polyp Tissue Morphology and Structure in Caribbean Reef Building Corals

Abstract

An integrated suite of imaging techniques has been applied to determine the three-dimensional (3D) morphology and cellular structure of polyp tissues comprising the Caribbean reef building corals Montastraeaannularis and M. faveolata. These approaches include fluorescence microscopy (FM), serial block face imaging (SBFI), and two-photon confocal laser scanning microscopy (TPLSM). SBFI provides deep tissue imaging after physical sectioning; it details the tissue surface texture and 3D visualization to tissue depths of more than 2 mm. Complementary FM and TPLSM yield ultra-high resolution images of tissue cellular structure. Results have: (1) identified previously unreported lobate tissue morphologies on the outer wall of individual coral polyps and (2) created the first surface maps of the 3D distribution and tissue density of chromatophores and algae-like dinoflagellate zooxanthellae endosymbionts. Spectral absorption peaks of 500 nm and 675 nm, respectively, suggest that M. annularis and M. faveolata contain similar types of chlorophyll and chromatophores. However, M. annularis and M. faveolata exhibit significant differences in the tissue density and 3D distribution of these key cellular components. This study focusing on imaging methods indicates that SBFI is extremely useful for analysis of large mm-scale samples of decalcified coral tissues. Complimentary FM and TPLSM reveal subtle submillimeter scale changes in cellular distribution and density in nondecalcified coral tissue samples. The TPLSM technique affords: (1) minimally invasive sample preparation, (2) superior optical sectioning ability, and (3) minimal light absorption and scattering, while still permitting deep tissue imaging. 

 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Curacao