Thermal Stress Affects Zooxanthellae Density and Chlorophyll-a Concentration of the Solitary Mushroom Coral, Heliofungia actiniformis
Senona A. Cesar1*,3, Homer Hermes Y. De Dios2, 3,Naomi B. Amoin3 and Danilo T. Dy3
1Visayas State University, Visca, Baybay City, Leyte
2Southern Leyte State University, Bontoc, Southern Leyte
3University of San Carlos, Cebu City
corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.
ABSTRACT
Corals lose their pigments or cell symbionts with prolonged exposure to temperatures higher by 1°C than the reef ambient temperature, leading to bleaching. Heliofungia actiniformis, a top traded coral was subjected to lower (24-26°C), ambient (27-29°C), and higher (30-32°C) thermal conditions to determine the resilience of its zooxanthellae to thermal stress. The experiment followed a complete randomized design with three different temperatures and eight replicates per treatment level. Evaluations were done in terms of density of expelled zooxanthellae, biomass of expelled chlorophyll-a, and using a coral color reference card. Thermal stress had a significant effect on the density (F2,21=3.691; p=0.042) and chlorophyll-a biomass (F2,21=10.711; p=0.001) of expelled zooxanthellae of H. actiniformis. Density and chlorophyll-a biomass of expelled zooxanthellae in the 30-32°C treatment doubled and tripled, respectively, compared to ambient conditions. However, these were still lower compared to published values for branching corals. The capability of H. actiniformis for downward migration to seek refuge, and its thick gastrodermis that harbors the zooxanthellae are possible adaptive mechanisms to survive the changing thermal conditions of tropical reefs.
INTRODUCTION
The ‘long tentacle mushroom coral’, Heliofungia actiniformis is a large-polyped discoidal coral whose tentacles are extended even during day time (Hoeksema 1989; Gittenberger et al. 2011). It is a rich host to 23 associated fauna including 14 shrimp species (Hoeksema et al. 2012). Together with other free-living fungiid corals, they act as nuclei for the formation of new patch reefs (Chadwick-Furman et al. 2000). Its high recruitment rate attributed to both sexual and asexual reproduction modes could be among the mechanisms that sustains the Heliofungia fishery albeit its high exploitation rate in the live coral aquarium trade in Indonesia. Despite its importance being among the top five traded aquarium species in Indonesia (Knittweis et al. 2009; Knittweis & Wolff 2010), information on its thermal stress response is still scanty. . . . . . . . . .
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