Abstract:
Coral reefs are amongst the most vulnerable ecosystems to climate change. This study was conducted to evaluate
the fluxes in the adaptations of reef-building corals to climate change. In order to explore this, chlorophyll a fluorescence,
Symbiodinium abundance and types were monitored in nursery-reared corals for two years in three species
that differ in bleaching susceptibility. The species were Pocillopora verrucosa, Porites cylindrica and Acropora formosa.
Internal transcribed spacer two (ITS-2) region of nuclear ribosomal DNA genes (rDNA) was used in monitoring the
Symbiodinium types associated with the studied coral species. Pulse Amplitude Modulated (PAM) fluorometry was
used to determine seasonal changes in chlorophyll a fluorescence. In this study, it was found that A. formosa, P. verrucosa
and P. cylindrica maintained their Symbiodinium types; C3u, C1h, and C15 respectively throughout the seasons.
A. formosa and P. verrucosa responded significantly to seasonal fluctuation in both solar radiation and sea surface
temperature by regulating their Symbiodinium cell density and photochemical efficiency whereas P. cylindrica did
not. However, such seasonal fluctuations in these environmental parameters are not accompanied by acquisition
of foreign Symbiodinium types from the environmental pool. It is concluded that seasonal fluctuations in both solar
radiations and sea surface temperatures are not intense enough to effect acquisition of foreign Symbiodinium types
by reef building corals in Zanzibar waters
