Stylophora pistiUata - Science Direct

Marine Pollution Bulletin, Vol. 10, pp. 328-330 Pergamon Press Ltd. 1979. Printed in Great Britain.

0025-326X/79/1101-0328$02.00/0

Laboratory Experiments on the Effects of Crude Oil on the Red Sea Coral

Stylophora pistiUata B. RINKEVICH and Y. LOYA

Department of Zoology, The George S. Wise Centerfor Life Sciences, Tel Aviv University, Tel Aviv, Israel

Sub-lethal detrimental effects of Iranian crude oil were studied on the hermatypic coral Stylophora pistil/ata in a long term laboratory experiment. The experimental system consisted of four 1500 I. capacity tanks, two of which were periodically polluted. A significant decrease in the number of female gonads per polyp were recorded in 75070 of the colonies in the polluted tanks. It is concluded that chronicoil pollution damages the reproductive system of scleraetinian corals. The northern Gulf of Eilat, Red Sea, is one of the areas in which oil pollution has been rapidly increasing in recent years (Eisler, 1975). Loya (1975) indicated approximately three large scale oil spills per month between the years 1972 and 1973 in the vicinity of the Nature Reserve of Eilat, which borders two oil terminals. This rate of incidents continues until today, which means that this area is continuously stressed by chronic oil pollution. In previous field works, Loya (1975, 1976) noted that the Coral Nature Reserve at Eilat has been poorly recolonized by new coral colonies following a catastrophic low tide, which caused almost a total kill of the reef-flat corals. He suggested that chronic oil spills might damage the reproductive system of corals and prevent normal settlement and/or development of coral larvae (Loya, 1975). Rinkevich & Loya (1977) studied the reproduction of the branching coral Stylophora pistillata in a chronically oilpolluted area and pollution free area in the northern Gulf of Eilat. In the oil polluted area they found a decrease in viability of colonies, detrimental effects to gonads, a decrease in viability of colonies and a decrease in number of planulae produced per coral head, when compared with the unpolluted coral populations. Data concerning the effects of oil pollution on marine organisms have been obtained both from experiments in the field or laboratory and from observations of actual incidents or chronically polluted habitats (Nelson-Smith, 1972). Since field experiments are exposed to a large number of environmental variables and perturbations, we felt that controlled laboratory experiments are essential for comparison with our field results (Rinkevich & Loya, 1977). Nelson-Smith (1972) indicated that toxicity tests in the laboratory are usually designed to result in death or serious injury to the tested organisms within a few days and hence they cannot be expected to reveal long-term effects. Moreover, such studies are often made on organisms which are convenient for laboratory experiments rather than important in a threatened environment. The present paper is concerned with long-term laboratory experiments on latent and sub-lethal detrimental effects of Iranian-crude oil on S. 328

pistillata colonies. This hermatypic coral species was chosen as our experimental object, since it is the most abundant coral and one of the most important framework builders of the reefs along the Gulf of Eilat (Loya, 1972). Materials and M e t h o d s All experiments were conducted in four fiberglass tanks (15001. capacity), 2 m deep, 1 m in diameter with a 60 × 120 cm glass window. The tank system is described in detail and depicted schematically by Eisler (1975). Each tank was divided into two compartments by two perforated partitions which were placed in two height levels: 0.5 m and 2.0 m below the water surface. Filtered sea water was introduced by PVC pipes 5 cm above the bottom of each tank and removed by a PVC siphon 80 cm below the water surface. the water flow was approximately 5 1. min-~. Two control tanks and two experimental tanks were put outdoors, in front of the Marine Biology Laboratory at Eilat. Great care was taken to disturb the colonies as little as possible during collection. Thus, 100 healthy colonies of S. pistillata were carefully removed from 3 m depth, with their attached pebbles, transferred underwater into plastic buckets and then placed on the lower partitions of the tanks (25 in each). In addition, eight big colonies (more than 25 cm in diameter) were split into two halves underwater and placed on the upper partitions of the tank system. One-half from each colony was placed in a polluted tank and the other half in a control tank. All colonies were tested for healthiness, before the start of the experiments, using similar criteria described by Elgershuizen & De Kruijf (1976). All colonies were transferred into the tanks in December, which is the beginning of the reproductive period of S. pistillata (Rinkevich & Loya, 1979a). Live plankton collected from the reef by 200 tan nets and Artemia sp. larvae were added to the tanks three times per week as a food source for the corals. Every week, Iranian crude oil was slowly added at the surface of each of the experimental tanks (final concentration of 3 rnl 1_1crude oil in sea water). The corals had no direct contact with the oil film, but were exposed to the water soluble fractions of the crude oil. After 24 h exposure, the floating oil was removed by pumping. This procedure was repeated during 2 months (for the upperpartition corals) and 6 months (for the lower partition corals). In order to study possible effects of crude oil on reproduction, histological sections were made on branchsamples taken from the upper-partition colonies, using a

Volume 10/Number 11/November 1979 TABLE 1

TABLE2

Changesin the averagenumber of femalegonads per polyp in the split colonies (numberof polypsgivenin parentheses).

Theaveragereproductiveindexin S. pistillatacolonies sampledin pollutedand cleanreefs.

Averageno. of femalegonadsper polyp Before Twomonthsafttersplitting splitting Polluted Control

Colony no.

1 2 3 4 5 6 7 8

1.40±0.89(5) 0.50±0.55(6) 1.88±1.13(8) 1.43±0.54(7) 0.33 +0.52(6) 1.12+1.25(10) 1.11±0.78(9) 2.50±0.89(6)

1.07±0.92(14) 0.50+0.55(6) 0.94±1.12(16) 0.67+0.52(6) 0.12+0.35(8) 1.00±1.13(11) 1.00±0.71(9) 2.00+1.10(6)

3.17±0.75(6) 2.00+0.82(7) 2.38±1.06(8) 1.83+0.75(6) 1.25+0.84(8) 2.144-0.82(7) 1.88+1.64(8) 2.57+0.98(7)

Levelof significance (t-test) P< 0.01 P ,:0.01 P