PaCES/HIMB Summer 2008 Program in Environmental Science

Project Proposal

Elevated temperature sensitivity of fertilization and early development in the mushroom coral

Fungia scutaria

Investigators

Ima G. Neous

Reel E. Ritardid

Watt A. Gyk

Luks Ugli

Project Mentor

Isa Wymp

Hawaii Institute of Marine Biology

University of Hawaii

Proposal Date

July 7, 2008

Expected Date of Completion

July 20, 2008

Introduction

Coral reef ecosystems have great aesthetic, biological and economic values (Cesar et al., 2002). They have been characterized as being extremely productive and exhibiting high biological productivity (Sargent and Austin, 1949; Odum and Odum, 1955; Gordon and Kelly, 1962; Johannes et al., 1972; Smith and Marsh, 1973; Lewis, 1977; Kinsey, 1977; Erez, 1990; Sorokin, 1990). In many respects, coral reefs may be regarded as the marine counterparts to tropical rain forests. Reefs also provide resources for human use (Craik et al., 1990, Cesar et al., 2002), such as food, objects of cultural value, and recreational playgrounds. Finally the reef protects coastlines from the erosional force of waves (Berg et al., 1998).

Thus, considerable interest has focused on the contribution of anthropogenic disturbance to the decline in the abundance and diversity of organisms in coral reef ecosystems during the last quarter century (e.g., Grigg and Dollar, 1990; Wilkinson, 1999). Increased sedimentation, resource exploitation, dredging, temperature stress, sewage effluent, toxic chemical pollution, and trampling have been cited as anthropogenic factors threatening coral reefs and their component organisms especially the corals themselves (Maragos et al., 1985; Gomez, 1988; Rogers, 1990; Craik et al., 1990; Grigg and Dollar, 1990; Buddemeier, 1993; Wilkinson, 1993; Richmond, 1993; Hunter and Evans, 1995; Gulko et al., 2000; Rodgers and Cox, 2003).

Perhaps the greatest threat to coral reefs globally is the loss of endosymbiotic zooxanthellae (bleaching) from reef corals, and their consequent mortality, in response to elevated ocean temperatures (Coles, 2001; Glynn 2001; Wilkinson, 2002). While the magnitude of the role of anthropogenic factors (e.g., production of greenhouse gases) in producing these elevated temperatures may be debated, great certainty exists regarding the cause-and-effect relationship between elevated temperature and bleaching in reef-building corals (Jokiel and Coles, 1990). The gravest concern is the fact that many corals appear to exist in environments in which the summer sea surface temperatures are only a degree or two below the temperatures known to result in bleaching (Jokiel and Brown, 2004).

While most of the interest over temperature effects on corals has focused on elevated-temperature-induced bleaching in adult corals, relatively little has been done to investigate the effects of elevated temperature on the reproduction, early development and larval survival (Table I) and only a handful of studies have dealt with the impact of elevated temperature on the earliest stages in the life cycle of coral: fertilization and early development. Addressing this lack of information, this we propose to study the effects of elevated temperature on the fertilization and early development of the mushroom coral Fungia scutaria.

Table I

Research Papers Dealing with Coral Reproduction and Elevated Temperature

Source / Aspect Studied / Response to Elevated Temperature
Edmondson, 1929; 1946 / Planula Survival and Settlement / Planulae more resistant than adults to thermal stress
Harrigan, 1972 / Planula Release and Behavior / Forced premature release of brooded planulae
Jokiel and Guinther, 1978 / Recruitment / Optimum at 27°C; substantial decrease at higher temperature
Harriott, 1983 / Planula Production / Reduced planulae production
Coles, 1984; 1985 / Settlement & Survival / Higher recruitment rates near thermal outfall discharge
Jokiel, 1985 / Planula Release / Planulae aborted
Fadlallah and Lindo, 1988 / Gametogenesis / Oogenesis correlated to temperature regime
Szmant and Gassman, 1990 / Gametogenesis After Bleaching / Inhibition of gametogenesis and reduced fecundity
Edmunds et al., 2001 / Planula Motility, Mortality, Metamorphosis & Metabolism / Increased mortality; premature metamorphosis
Omori et al., 2001 / Fertilization Rates After Bleaching / Decreased fertilization rates
Bassim et al ,2002 / Fertilization & Embryonic Development / Fertilization not affected; embryogenesis abnormal
Bassim and Sammarco, 2003 / Planula Development, Survival & Settlement / High larval mortality; decreased motility & settlement
Edmunds, 2004 / Juvenile Corals (includes recruits) / Increased density but higher mortality

The mushroom coral Fungia scutaria(Anthozoa: Scleractinia) was chosen for this work because it, in contrast to many corals, spawns male and female gametes separately, minimizing problems associated with self fertilization (Krupp, 1983). This solitary coral species lives unattached on the reef surface allowing easy, damage-free collection of living animals. F. scutaria is a broadcast spawner that predictably releases gametes at dusk 1-4 days following the full moon during the months of summer and fall. Fertilization may be accomplished in vitro; and development to ciliated larva stage is rapid, normally less than 12 hours after spawning (Krupp 1983). If fertilization is inhibited,the eggs fail to undergo cleavage and usually disintegrate within several hours after spawning. Fungia scutaria is an important reef flat species in Kaneohe Bay where it seems to thrive largely because of its ability to regenerate and proliferate asexually following freshwater flooding events (Krupp et al., 1993).

Materials and Methods

Coral Collection and Maintenance

About 20-30 specimens of Fungia scutaria will be collected from shallow patch reef environments in Kaneohe Bay, Oahu, Hawaiian Islands. This number of corals is needed to ensure an adequate supply of spawning males and females during a single evening’s spawning event. These corals will be maintained in an outdoor seawater table receiving a continuous flow of unfiltered ambient seawater at the Hawaii Institute of Marine Biology located on Coconut Island, Kaneohe Bay. The corals will be shaded (ca. 10%) from full sunlight using a light mesh shade cloth because direct exposure to full sunlight often leads to partial bleaching of tank-maintained corals.

About 1-2 days prior to the anticipated spawning periods, the seawater tables were cleaned and individual corals placed into glass bowls (ca. 20 cm diameter) set up into the seawater tables now receiving continuous flows of filtered (50 µm) ambient seawater.

Since Fungia scutaria usually spawn between 1700 and 1900 (Krupp 1983), the water in the table containing the corals will be lowered to just below the height of the bowls by 1600 p.m. This procedure will isolate each individual coral into its own glass bowl before spawning preventing premature mixing of the gametes. A male will be identified during spawning because of the cloudy, milky appearance of the released sperm (the presence of active sperm was verified microscopically). A female will be identified by the release of small white eggs (approx. 100 µm in diameter) appearing as suspended particulate matter.

Gamete Collection, Fertilization and Assay Procedures

The spawned gametes from each individual will be collected with a large polyethylene cooking baster and slowly dispensed into 500 ml glass beakers containing about 100 ml filtered seawater (0.45 µm, Millipore Corp.). The collected gametes from at least three females during each spawning event will be pooled. Similarly the sperm from at least three males will be pooled. The sperm suspension will be diluted in filtered seawater (0.45 µm) to yield a density of 2-3x106 sperm ml-1. Egg densities will be adjusted to about 50 eggs ml-1. Higher egg densities often led to embryo fusion and difficulties in counting viable embryos.

Water baths containing floating borosilicate scintillation vials (20 ml capacity, Fisher Scientific) with filtered (0.45 µm) seawater (3 ml) will be pre-heated to their incubation temperatures (range = 27 - 33ºC) before addition of 1 ml egg suspension using an Eppendorf Repeater Pipette. After an additional 10 minutes for temperature equilibration, 1 ml of the sperm suspension will be added to each vial. Thus the final volume in each vial will always be 5 ml. Ten replicate vials will be prepared for each experimental treatment.

Approximately 12 h after fertilization, the vials will be examined for the presence of slow-moving, ciliated larvae. Only healthy, full-sized larvae will be counted. The results, as “percent survival”, will be calculated as the number of these larvae relative to the starting density of eggs added to the vials. Thus “percent survival” will be a consequence of both successful fertilization and early development to these motile larvae.

The results from this study will be presented at BWET/PaCES Student Project Symposium 2005 and submitted in the form of a formal scientific report to the BWET/PaCES instructors.

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Bassim, K.M., P.W. Sammarco, and T.L. Snell. 2002. Effects of temperature on success of (self and non-self) fertilization and embryogenesis in Diplora strigosa (Cnidaria, Scleractinia). Mar Biol 140:479-488.

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