title: El Niño 1997-1998 impact on the plankton dynamics in the Gulf of Nicoya, Pacific coast of Costa Rica.
abstract: The impact of the El Niño 1997-1998 phenomenom on plankton dynamics was studied during 1997 at the Punta Morales estuary, Gulf of Nicoya, Pacific coast of Costa Rica. The study covered dry season/transition and the rainy season. Phytoplankton (microphytoplankton > 30 microm and nanophytoplankton) were collected at two depths (50 and 10% light incidence) using a 5 L Niskin bottle, and samples taken to determine chlorophyll a. Temperature, salinity, oxygen, and Secchi depth were measured. Horizontal sub-surface zooplankton hauls were conducted with a conic zooplankton net of 0.49 m diameter and 280 microm mesh width, supplied with a flowmeter. Surface sea water temperature average was 29.9 +/- 0.9 degrees C, with a maximum of 31.5 degrees C in April and a minimun of 28 degrees C in March and October. Chlorophyll a concentration (phytoplankton net) averaged 3.1 +/- 1.7 mg/m3, with higher values during the rainy season and lower values during the transition. Nanophytoplankton chlorophyll a concentration averaged 2.5 +/- 1.2 mg/m3, with a maximum during the transition season. For both fractions there were significant differences between transition and rainy seasons, and for nanophytoplankton between dry and transition seasons (p < 0.05). In the last case, differences were explained by temperature. Herbivorous copepods dominated the abundance and biomass of zooplankton, with a biomass maximun of 167.3 in October and a minimun of 7.1 mg DW/m3 in December. These values are higher than those found some years ago in the same zone and those reported for some places in the Caribbean. The El Niño 1997-1998 phenomenon in the plankton dynamics appears to have produced a change in the phytoplankton structure. This is the first attempt to evaluate the possible impact of El Niño on the plankton dynamics of the Pacific coast of Central America.
authors.affiliation: Centro de Investigación en Ciencias del Mar y Limnología, Universidad de Costa Rica, 2060 San José, Costa Rica. amorales@cariari.ucr.ac.cr
authors.forename: A
authors.initials: A
authors.lastname: Morales-Ramírez
authors.forename: E
authors.initials: E
authors.lastname: Brugnoli-Olivera
mesh_terms: D000818:Animals; D018533:Biomass; D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D003364:Costa Rica; D004784:Environmental Monitoring; D010100:Oxygen / Q000032:analysis; D010933:Plankton / Q000502:physiology*; D011157:Population Dynamics; D012621:Seasons; D014887:Weather
chemical_list: D002734:Chlorophyll; D010100:Oxygen; D000077194:Chlorophyll A