FISHERY BULLETIN: VOL. 69. NO. 4 



Figure 5. — Decline with time in surface nitrate ( A ) 

 and chlorophyll pigments concentration ( © ) in Patch 1. 

 Solid triangles ( A ) are maximum nitrate values found 

 by automatic analysis (Autoanalyzer) during under- 

 way mapping. Open triangles ( A ) are discrete nitrate 

 samples collected on station. Pigment values are max- 

 ima of fluorescence found in the mapping area. 



surface was compensated for by a deepening of 

 the euphotic zone such that chlorophyll a, stand- 

 ing crop as carbon, and photosynthesis showed 

 little variation (<twofold) when integrated 

 over the increasing euphotic zone depth. The 

 specific growth rate, ja, of the crop averaged 0.7 

 doubling/day over the euphotic zone indicating 

 it should double in 1.4 days if grazers could be 

 eliminated. Similar measurements of jx in 

 March-April 1966 off Peru (Strickland et al.. 

 1969) averaged 0.8 doubling/day for four sta- 

 tions. 



The ratio of phytoplankton carbon/chloro- 

 phyll ft (Table 8) averaged 40: 1 and was similar 

 to that reported by Lorenzen (1968), using dif- 

 ferent methods, for a phytoplankton bloom off 

 Peru. The ratio of photosynthetic rate (g C/mV 

 day) to chlorophyll a (g/m=) averaged 28 day"', 



about one-half that observed by Lorenzen 

 (1968). 



As the phytoplankton crop decreased the ratio 

 of phaeopigments to chlorophyll a also declined. 



SPECIES COMPOSITION OF THE 

 PHYTOPLANKTON CROPS 



Taxa with volumes less than that of 10 fi 

 spheres accounted for an average 73 /t (range: 

 46*:; , Station 68 to 93 ^r , Station .59) of the total 

 plant carbon. The dominant forms in both 

 patches were small (2-4 fj. and 5-7 fx) cells, often 

 flagellates, and probably cryptomonads or chry- 

 sophytes although positive identification was im- 

 possible in the Formalin-preserved material. 

 Diatoms never contributed more than 10 to 12% 

 (average pennates -)- centrics, 5.2%) of the 

 carbon content of the crop. Of the diatoms two 

 species, Coveihmn hystrix and Nitzschia delica- 

 tissima curva, were the most abundant at all 

 sites. The Corethron was one of the very few 

 large taxa that would be retained by phytoplank- 

 ton nets (35 ju mesh). The "photosynthetic" 

 ciliate, Mesodinium rnbrtim (Taylor, Black- 

 bourn, and Blackbourn, 1969) , occurred at all 

 stations but was relatively more abundant in 

 Patch 1 where numbers reached 3000 'liter at 

 Station 68. Dinoflagellates contributed 5 to 21 % 

 of the total phytoplankton carbon. Unidentified 

 naked forms of cell size <15 /x (equivalent 

 sphere) were the most common of the dinoflag- 

 ellates. Coccolithophorids (e.g., Coccolithus 

 huxleyi and Syracosphaera quadricomum) were 

 quite numerous when the patches were disap- 

 pearing, totaling u]) to 1 1 to 14 fxg C liter or 31 % 

 (Station 87, Patch 1) and 15% (Station 99, 

 Patch 2) of the plant carbon. 



MICROZOOPLANKTON POPULATIONS 



Ciliates dominated the microzooplankton pop- 

 ulations of the two patches in terms of both num- 

 bers and biomass. No marked diff"erences in the 

 ;ibundaiice of ciliates were noted between the 

 patches. Their standing stock was greatest 

 early in our samijling of each patch (i.e.. Station 

 59, Patch 1; Station 88, Patch 2) owing to rel- 

 atively large numbers of nonsheathed oligo- 



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