Zooplankton samples from Banco Chinchorro were taken in the surface layer, in September 1999 and March 2000. Eleven species of Appendicularia, belonging to three genera, were identified from 16 samples collected in both reef lagoon and oceanic areas off Banco Chinchorro. Oikopleura
longicauda was the most abundant in the surveyed area (69.81%), followed by O. fusiformis f. typica and Fritillaria formica with 8.30% of the overall numbers for each one. Maximum abundance was recorded at stations 7 (5943 org/1000 m3) and 3 (5792 org/1000
m3) both taken in September in the oceanic area. In March, mainly from collection within the reef lagoon, a density of 3582 org/1000 m3 was recorded at station 3. The species richness of the appendicularians and its numerical abundance was remarkably higher (92.24%) at
the reef lagoon in March (stations 14, 17, 18, 19); whereas, in stations 15 and 16 they showed similar abundance and richness as in September. The richness of appendicularians and average abundance was 5.9 times higher in the oceanic area (3222 org/1000 m3) than in the reef lagoon
(539 org/1000 m3).
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