From ecological oliservations made along the coastal line of the Pearl Islands, 

 on Coita, and in the eastern part of the Gulf of Chiriqui, I conclude th-at the marine life 

 of the entire area visited dviring the expedition was in flourishing condition. There was 

 not a place where the luxuriant grov;th of littoral fauna appeared inliihited, and likev;ise 

 there was no indication of any unusual mortality among any of the sedentary organisms. The 

 area presents a most favora'ble environment for the propagation and growth of mollusks. This 

 v;as evident from the large numoer of species inhahiting the coastal waters, and ty the size 

 and ahundance of many gastropods and lamellihranchs. There was no indication in any of the 

 places visited that animal communities v/ere affected tiy red tide or lay toxic material v/hich 

 ma;,'' have heen dumped into the sea. 



Dead shells of pearl oysters. Pinctsuia mazatlaniea , and of the clams, Macrocal - 

 lista aurantiaea and Antigona multicostata , were found in several places Taelow low-water 

 mark (Stations U, 13, 18, and 21) . With the possihle exception of Station IS at the 

 northern end of Coiha Island, where large nunTjers of old pearl oyster shells were taken. Isy 

 the diver, there was no evidence of excessive mortality of these mollusks. The appearance 

 of clan and pearl-oyster shells overgro\im on both sides by Bryozoa and other fouling 

 organisms Indicated that death had occurred a long time ago. Likewise, I saw no indications 

 of a devastating effect of any predators and commensals. Many shells of various lanelli- 

 ■branchs and gastropods living v/ithin the lower level of tidal range and helow low-v;ater mark 

 had. holes drilled in them by predatory snails, boring clams ( Lithophaga ) , and boring sponge. 

 The number of dead shells was not excessive, hov;ever, and no gastropods were observed in the 

 act of drilling. It is therefore Impossible to state which of them was the most destructive. 



The predatory habits of such common forms as Cassis , Tritonalia , and Eupleura , 

 are well-knoira. It is reasonable to expect that these verj' active predators may cause a 

 great deal of destruction among other mollusks. Their prey consists mostly of other 

 gastropods ( Zonaria , Oliva , Leucozonia , small Conus , and others) , small clams (Glycemeris, 

 Sanguinolaria ) , and scallops ( Pecten circularis ) . ^A number of Tellina and Sangiiinolaria 

 shells \/ere found v;ith large holes bored, probably by sand collars ( Polinices and Nat.ica ) . 

 The family Naticidae is represented in Panama by a score of species, bu.t none of these 

 snails was found in the act of attacking clams. 



Pearl oysters, Ostrea megodon , Pteria peruviana , and Pinna lanceolata , are not 

 attacked by drills or borers, likev/ise, mollusks living within the up-oer third of the tidal 

 range ( Llttorlna , Siphonaria , Nerita, Purpura , Thais) are not molested by these carnivorous 

 snails, which apparently do not climb far above the low-v/ater level. 



One of the striking features of the ecolos^ of coastal v;ater along the coast of 

 Panama is the scarcity of calcareous algae and corals. Both groups are represented in local 

 fauna and flora, but they never attain the luxuriant growth of the typical and coral-reef 

 community. So far as temperature and salinity of water are concerned, conditions off the 

 Panama coast are comparable to those of typical coral-reef lagoons such as one encounters 

 in the Marshall Islands and other coral-reef regions of the Pacific. The q.uestion is, why, 

 ■under these apparently suitable conditions, the growth of reef-forming organisms is 

 restricted. The most conspicuous difference in the ecology of the coastal waters of Panama 

 and of the tsrpical coral-reef regions of the Pacific is the range of tide. As a rule, the 

 tidal range in typical coral-reef regions is small, averaging from 2 to 5 feet, v;hereas the 

 tidal range along the Pacific coast of Panama is almost ten times greater. I am inclined to 

 think that this is probably the main condition which inhibits the growth of reef -building 

 organisms, and at the sane time encourages the growth and propagation of mollusks. We need, 

 however, more information on the physiology and life histories of marine invertebrates of 

 Panama in order to interpret correctly our ecological observations. 



OBSERVATIONS Oil PEARl OYSTERS 



The abundance of pearl oysters in Panamanian vmters was studied by using the 

 follov;ing method. (>ro\mds to be examined were selected on the basis of information received 

 from experienced pearl divers, and by consulting with persons familiar with the pearl fish- 

 ery of the Republic. Senor Celedonio Pinzon, the diver hired by the Ministry of Agriculture 

 to work with me during the expedition, proved to be a man of high intelligence and industry. 



35 



