Scleractinian Pocillopora Damicornis Research Articles

Stages of the symbiotic zooxanthellae–host cell division and the dynamic role of coral nucleus in the partitioning process: a novel observation elucidated by electron microscopy

The relationship of the symbiotic algae or commonly referred as zooxanthellae (zo) and its host invertebrate species is uniquely observed among cnidarians where these tiny single-celled endosymbionts are used to reside densely within the gastrodermal tissue. However, at the ultrastructural level, little has been known on how zo are maintained through proliferation within its host cells. In the present study, the stages of division of the zo that occurred in the coral cells were investigated by electron microscopy. Scleractinian Pocillopora damicornis was fixed by freeze-substitution methods using a high-pressure freezer and embedded in resin. Ultrathin sections were observed using transmission electron microscope. Symbiotic cell at interphase showed the cortical fine structures of the non-dividing zo enclosed by the outermost plasma membrane (zpm). Overlying them, two distinct layers of intermediate membranes (inm) and a symbiosome membrane (sm) were found. When cytokinesis occurred, the zpm at the opposite division regions formed ‘U-shaped’ furrows which led amphiesmal vesicle (av) to protrude inwardly. As they invaginates, new avs and series of cortical microtubules (mi) are used to develop concomitant with the symbiont’ nuclear division. After the cytokinesis, the overlying membranes successively invaginate; thus, the daughter zooxanthellae were transformed into coccoid cells. These cells, however, remain contiguous to each other until when the coral nucleus (cnu) migrated toward one of the cleavage sites to intervene and dissociate them. Upon occupying the interzooxanthellar space, host nuclear division occurred prior to cytokinesis. These events involving the role of cnu in the partitioning process are first reported in this study, in which its dynamic intervening behavior had been elucidated as a novel finding from the cnidarian species.

Effect of nutrient enrichment on the complementary (secondary) metabolite composition of the soft coral Sarcophyton ehrenbergi (Cnidaria: Octocorallia: Alcyonaceae) of the Great Barrier Reef

A long-term study of the effects of nutrient enrichment on coral reefs (ENCORE Experiment) was carried out at One Tree Island (23°30′S; 152°96′E), Great Barrier Reef, between 1992 and 1996. The experiment involved the addition of water-soluble nutrients to 12 microatolls which contained a range of organisms and were situated within the larger lagoon. Three replicates of each of three nutrient treatments (nitrogen, phosphorus, nitrogen plus phosphorus) and an untreated set of three control atolls were prepared using the 12 selected microatolls. As part of the larger ENCORE experiment, changes in the chemical composition of the alcyonacean soft coral Sarcophyton ehrenbergi Marenzeller (Octocorallia: Alcyonacea), placed in the treatment microatolls, were monitored for a 1 yr period in an attempt to detect any responses attributable to nutrient enrichment. Multivariate analyses were performed to determine whether there were any patterns of response in the different nutrient treatments. At the level of individual metabolites, there were no clear treatment effects. However, the ratio of bioactive or stress metabolites (terpenes) to energy storage metabolites (lipids), referred to as the “physiological-change indicator”, revealed effects of nutrient enrichment. Nitrogen enrichment resulted in a trend towards higher physiological-change indicators than control or phosphorus treatments in the majority of cases, while phosphorus enrichment significantly decreased the ratio relative to controls. In most cases, the physiological-change indicator increased in soft soft corals relocated into contact with the scleractinian Pocillopora damicornis. The potential of soft corals to serve as indicators of a changed nutrient regime is discussed.