Blooms of Myrionecta rubra in Bahia de La Paz, Gulf of California, Mexico in early summer 2005

Abstract

Blooms of the ciliate Myrionecta rubra are quite common in Bahía de La Paz. In June and July 2005, two blooms of this species were sampled to determine abundance, plankton biomass, nutrients, dissolved oxygen, and temperature. During the bloom in June, surface temperature ranged from 19.0 to 19.6 °C and dissolved oxygen from 4.2 to 4.7 mg l-1. During the second bloom, surface temperature was 24.2 °C and dissolved oxygen was 6.7 mg l-1. At 25 m depth, conditions were 20.0 °C and 3.5 mg l-1, respectively. At the surface, nutrients were low, except for ammonium (1.14–2.27 μM). High densities of M. rubra (2.14 × 106 cells l-1), chlorophyll a (55.6 µg l-1), chlorophyll c (6.0 µg l-1), and alloxanthin (8.1 µg l-1) were recorded. This last pigment is characteristic of the cryptophyte group, suggesting an association of the ciliate with this algal group. Winds from the southeast varied from 3 to 4.5 m s-1. in July . The presence of this bloom under low thermal stratification and with the highest density of the ciliates at the surface during the onset of the bloom suggest that southeastern winds mixed the shallow water column, brought up nutrients from the bottom sediments, and induced high concentrations of the cryptophytes.