Details

Autor(en) / Beteiligte

• Liefer, Justin D

Titel

Phytoplankton community structure and the physiological ecology of the toxic, bloom-forming diatom Pseudo-nitzschia spp. In coastal Alabama

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2012

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The structure of phytoplankton communities has profound impacts on the ecological and biogeochemical roles of phytoplankton. Harmful algal blooms (HABs) involve changes in phytoplankton composition that affect aquatic ecosystem function. A global increase in HABs and their negative effects on ecosystems and human health make them an important topic in phytoplankton ecology. In this study, I examined environmental forcing of phytoplankton community structure and the dynamics of a globally-important harmful alga, the potentially-toxic diatom genus Pseudo-nitzschia, and its production of the toxin domoic acid. Pseudo-nitzschia spp. occur year-round throughout the littoral Gulf of Mexico in Alabama, USA. High densities were most common near Little Lagoon and in April-May, when annual densities were highly correlated with discharge from the local aquifer. Little Lagoon was shown to be a groundwater-fed system and both nutrients and phytoplankton there were classified into two alternating regimes, one characterized by high groundwater discharge at relatively low temperatures and the other by low discharge at higher temperatures. The phytoplankton community in Little Lagoon was dominated by chlorophytes and diatoms under the first regime (approximately Jan–Apr) and by cyanobacteria and chlorophytes during the second (approximately May–Dec). Blooms of Pseudo-nitzschia spp. only occurred during the former regime, likely triggered by groundwater discharge events during cold temperatures. Microzooplankton grazing on Pseudo-nitzschia spp. in Little Lagoon was lower than on co-occurring taxa and may also play a role in triggering blooms. Domoic acid production was observed in Pseudo-nitzschia blooms inside Little Lagoon and along the Alabama coastline. A combination of continuous monitoring, transects across environmental gradients, and mesocom experiments demonstrated that cellular toxicity of Pseudo-nitzschia spp. was associated with high salinity, low phosphorus supply, and high irradiance. Also, fish sampled during one bloom had accumulated domoic acid. This study presents strong evidence that Pseudo-nitzschia spp. occupy a niche that is defined by environmental disturbance, primarily as high groundwater discharge, during periods of favorable temperature. Toxicity of the resulting blooms is likely a response to nutrient- and light-stress. The neurotoxin domoic acid produced by the blooms can be transferred up the food chain to planktivorous fish in Alabama waters.