lixanlnatlon of plankton 



Plankton samples v;ith a small plankton net lov/ered to the iDottom and slowly 

 hauled up to the surface v/ere taken at each station, primarily for the purpose of oljtaining 

 information regarding the presence of pearl-oyster larvae and of red-tide microorganisms. 

 The material collected in the field \iras imi.-iediately examined under the microscope, and then 

 preserved in 2 per cent formalin in sea v;ater. 



In general, the iDlankton was not abundant. At most of the stations, it consisted 

 primarily of such pelagic diatoms as Rhizosolenia , Biddvaphia, Ditylum hrightwellli (West) , 

 Chaetoce ras, Coscinodiscus , Eueampia , Thallasiothryx, and others. Dinoflagellates were 

 less ahundant. They v;ere represented hy Dinophysis , Ceratiua , and various Peridiniaceae. 

 None of these forms vja« predominant. Tintinnoidea were freauently present, and at certain 

 stations IToctiluca was ahuudant. Fairly large nma'oers of Appendicalariae were found in 

 many samples. 



Large numhers of nauplii, lamellihraach and annelid larvae, present in the 

 majority of the samples, indicated norraal propagation of planktic and sedentary forms. 

 Presence of copepods, Sagittae, and other forms usually found in coastal waters completed 

 a picture which suggested a normal eq.ullihrium hetvfeen the various components of plankton. 

 There was no indication of the hlooning of the sea which may have Tjeen associated with the 

 red tide (Galtsoff, igUg and 19^9)- 



Jiucous-secreting algae played a conspicuous role in the plankton. At some of the 

 stations (Station 2, Sahoga Islandi Station 11, Tahogai Station 13, Pedro Gonzalez), they 

 outnumbered other organisms. In some places (Pedro Gonzalez) , the patches of mucous drift- 

 ing nesir the surface were so large that they were noticeahle to the unaided eye. Micro- 

 scopic examination shov/ed two types of gelatinous massesJ in one type the amorphous and 

 trans-oarent suhstance contained large numhers of a diatom resemhling Thalassiosira suhtilia 

 (Osteij) (see Cupp, I9U3, p. 51)5 iii ^^^ other type, no recognizahle cells of diatoms or 

 any other algae v/ere found, hut the gelatinous mass contained minute, light-refringent, 

 oval granules. The identity of these granules, measuring ahout 2 mu. in length has not 

 yet heen estahlished. The large patches of mucous acted as a plankton collector, entrap- 

 ping many organisms floating in the sea v/ater. 



At several stations, the samples of plankton contained straight-hinge larvae of 

 the genus Ostrea. It was, however, impossible to identify the species. No pearl-oyster 

 larvae were found in any sample. This is not surprising, because of the very small number 

 of adult pearl oysters remaining at present in the Gulf of Panama and Gulf of Chiriqui. 



In general, the total amount of plankton in the water was small. The slightly 

 greenish water was very clearj its transparency, measured by Secchi disc, varied between 

 '^ and 5 meters. Diatoms prevailed at virtually all of the stations, v;ith the exception of 

 Station ik (Isla San JosI, Unsenada Plaza Grande) where rather suddently we encountered 

 water of dark blue color and greater transparency (6 meters) . It contained large numbers 

 of small Salpae about I5 mm. long, slowly drifting with the tide. Quantitative sampling 

 near the surface disclosed that there were 220 individuals per liter of water. Salpae were 

 not found at any other station. 



The general picture obtained from the examination of the samples was that of a 

 tyDical marine plankton of warm coastal waters. There was no evidence of any abnormal 

 conditions in the sea which could have affected the pearl-oyster grounds of that area. 



OBSERVATIONS ON EDrBM OYSTERS OF THE GEITOS OSTREA 



The genus Ostrea is represented along the Pacific coast of Panama by the follow- 

 ing species: Ostrea cumingiana mexicana Sov;erby, 0. iridescens Gra;/-, 0. megodon Hanley, 

 0. chilensis Philip-ii" and 0. colunbiensis Hanley. Smith (194^, p. 51) lists also 0. 

 conchaphila Carpenter , 0. multistriata Hanley, and 0. tubulifera Dall; and Zetec C19I8, 

 p. 52) mentions 0. aequatoriales d'Orbigny. These species were not encountered in ny 



m 



