Using microscopy, the gastrovascular systems of four hydroids (Eirene viridula, Cordylophora lacustris, Hydractinia symbiolongicarpus, and Podocoryna carnea) and two distantly related alcyonacean octocorals (Acrossota amboinensis and Sarcothelia sp.) were examined and compared within a phylogenetic framework. Despite a range of stolon widths (means 53–160 μm), the hydroid species exhibited similar patterns of gastrovascular flow: sequentially bidirectional flow in the stolons, driven by myoepithelial contractions emanating from the center of the colony. Unlike the hydroids, the gastrovascular system of A. amboinensis (mean stolon widths for 5 colonies, 0.57–1.21 mm) exhibited simultaneously bidirectional flow with incomplete, medial baffles (width 4–20 μm) separating the flow. Baffles visualized with transmission electron microscopy consisted of endoderm, mesoglea, and occasionally another layer of tissue. Mean flow rates of the gastrovascular fluid for seven stolons ranged from 125 to 275 μm s−1, with maximum rates of 225–700 μm s−1. In Sarcothelia sp., stolons were of comparable width (means for 13 colonies 0.55–1.4 mm) to those of A. amboinensis. These stolons, however, were divided by several partitions (width 8–25 μm), both complete and incomplete, which were spaced every 100.5±5.1 μm (mean±SE; range 27.1–283.7 μm) and appeared structurally similar to baffles. In lanes defined by these partitions, ciliary motion was visible in image sequences, and flow was unidirectional. Within a single stolon, flow moved in different directions in different lanes and changed direction by moving from lane to lane via occasional spaces between the partitions. Mean flow rates for 30 stolons ranged from 75 to 475 μm s−1, with maximum rates of 85–775 μm s−1. For both octocorals, flow rates of the gastrovascular fluid were not correlated with the width of the stolon lumen. While octocoral gastrovascular systems probably exhibit differences based on phylogenetic affinities, in all species studied thus far, gastrovascular flow is entirely driven by cilia, in contrast to the hydroid taxa.

Perturbed colonies of Phenganax parrini and Sarcothelia sp. exhibit migration of symbionts of Symbiodinium spp. into the stolons. Densitometry and visual inspection indicated that polyps bleached while stolons did not. When migration was triggered by temperature, light and confinement, colonies of Sarcothelia sp. decreased rates of oxygen formation in the light (due to the effects of perturbation on photosynthesis and respiration) and increased rates of oxygen uptake in the dark (due to the effects of perturbation on respiration alone). Colonies of P. parrini, by contrast, showed no significant changes in either aspect of oxygen metabolism. When migration was triggered by light and confinement, colonies of Sarcothelia sp. showed decreased rates of oxygen formation in the light and increased rates of oxygen uptake in the dark, while colonies of P. parrini maintained the former and increased the latter. During symbiont migration into their stolons, colonies of both species showed dramatic increases in reactive oxygen species (ROS), as visualized with a fluorescent probe, with stolons of Sarcothelia sp. exhibiting a nearly immediate increase of ROS. Differences in symbiont type may explain the greater sensitivity of colonies of Sarcothelia sp. Using fluorescent probes, direct measurements of migrating symbionts in the stolons of Sarcothelia sp. showed higher levels of reactive nitrogen species and lower levels of ROS than the surrounding host tissue. As measured by native fluorescence, levels of NAD(P)H in the stolons were unaffected by perturbation. Symbiont migration thus correlates with dramatic physiological changes and may serve as a marker for coral condition.

Chapter 1 Introduction………………………………………………………………………………………………1 1.1 Sulfur Isotope geochemistry as a tracer of ancient environments and metabolisms …...….…..2 1.2 Antiquity of Acetyl-CoA and its relationship to alkaline hydrothermal vents ………………..……4 1.3 Enzymes involved in dissimilatory Sulfur reduction …………………………………………….….8