494 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



branched stony coral with huge, protruding polyps (pi. 10, fig. 1). 

 We soon learned to expect trouble when we collected these secluded 

 spots, for the unusually virulent nematocysts, or stinging capsules, of 

 the Gordopora polyps were easily dislodged by the currents we pro- 

 duced by swimming, and stung us so badly that we sometimes were 

 obliged to leave the water. 



Much more troublesome than Goniopora, however, was an arbor- 

 escent, colonial scyphistoma (called Stephanoscyphus) of the medusa 

 Nausithoe, which also released its nematocysts into the water upon 

 agitation by strong currents. The stings produced by this animal left 

 angry red welts that itched for days afterward, and even caused swell- 

 ing of adjacent lymphatic glands. It seemed probable to us that a 

 dense growth of Stephanoscyphus could liberate enough nematocysts 

 into the water to inflict serious stings upon unsuspecting swimmers. 

 Fortunately, this coelenterate seems to be common only locally in 

 Palau, where we found it in only two localities. 



In spite of seemingly ideal surroundings in most parts of Iwayama 

 Bay, dead corals could be found at almost any location, suggesting 

 that conditions are not always so favorable. A day or so of heavy 

 rainfall will dump tons of fresh water not only into the bay but also 

 upon the islands, from which it cascades down to the Bay, carrying 

 with it great quantities of silt and forest debris. Salinity must be 

 much reduced, especially near the surface, for many hours, if not 

 days; the normal water temperature of about 85° F. may be lowered 

 by 5° or more ; suspended matter beclouds the water and the more deli- 

 cate corals may be smothered. But, after a few clear days and several 

 tidal cycles, the water clears and the survivors continue their struggle 

 for existence. 



The northwest corner of the Bay, forming divisions M, N, and O, 

 is bathed by good tidal flow, but silt from the nearby mangrove 

 shore discourages coral growth and the reef has a sickly appearance 

 that belies the large number of species that comprise it. One of the 

 resurveyed transects crosses the reef-flat at the south end of island 15, 

 and we studied it during several low tides. Here we collected dead 

 coral heads with cylindrical black sponges growing on them, which 

 we soon found were only the external portions of a boring sponge 

 that had excavated great hollow caverns in the coral boulders. Some 

 coral heads were thus reduced to hollow shells, and we have yet to 

 learn what becomes of the sponge after it has completely "eaten itself 

 out of house and home" — whether it then assumes a massive, free- 

 living form as do some other boring sponges, or simply dies of expo- 

 sure. Whatever its fate after the destruction of the rock in which 

 it lives, it is certainly an active reef -destroying agent. At the same 

 locality we found another rock-boring sponge that attacked not only 



