The aim of this work was to examine how
ultraviolet radiation (UV, 290 – 320 nm)
impacts the physiology of two temperate
phytoplankton species, as well as natural
phytoplankton assemblages, off Coastal
California. Cultures of the cyanobacteria
Synechococcus sp. (WH7803), and the
dinoflagellate Hetrocapsa pygmaea, were
each incubated in a UV-PAR growth facility at
UC Santa Barbara, consisting of 3 chambers:
Solar PAR + UV-A + UV-B (SPAB, >=290 nm),
Solar PAR + UV-A (SPA, >=325 nm), and Solar
PAR (SP, >=400 nm). There was also an Indoor
PAR (IP) control culture. Experiments on
natural assemblages were conducted in situ
inside UV drifters deployed in two distinct
water masses of the Santa Barbara Channel.
The drifters consisted of eight incubation
chambers that systematically eliminated
shorter wavelengths of UV.

In the Synechococcus sp. experiment, UV-B
caused a decrease in Chl a concentration,
affected Chl a periodicity, damaged
phycobilisome proteins, enhanced production
of the photosynthetic pigments zeaxanthin and
phycouroblin, and caused a decrease in
photosynthetic efficiency. In experiments on H.
pygmaea UV did not alter the ratio of
photosynthetic pigments within the cell, but
did decrease growth, and caused an increase
in cellular pigment concentrations.
Photoprotective pigments in H. pygmaea
increased when cells were exposed to UV-A,
and decreased or did not change when
exposed to UV-B. In natural phytoplankton
assemblages off Coastal California, UV-B
caused a change in community structure on
short time scales. Prymnesiophytes were
most heavily impacted, declining 15 – 17%
after exposure to in situ irradiances.
Depending on the integrated exposures and
dose rates, community responses varied
when released from the pressures of UV.

It is evident from results of this work that UV
affects the physiology of temperate
phytoplankton species, and can cause
changes in community structure of natural
assemblages. However, while UV-B caused
significant cellular damage, UV-A had little
effect and was beneficial in some cases. As
concentrations of stratospheric ozone
continue to decrease, leading to increases in
UV-B, it is essential that UV impacts on
phytoplankton are included in any models or
ecosystem predictions.

More information can be found at:
http://www.lifesci.ucsb.edu/eemb/labs/prezelin
/people/gorga/gorga.html