Endolithic algae ( Ostreobium ) diversity in Porites corals at the
Western Atlantic and Eastern Tropical Pacific
Abstract
Ostreobium comprise endolithic algae commonly seen in conjunction
with scleractinian corals. In the past, it was solely recognized as a
coral skeleton bioeroder. Yet, their relationship with corals is
critical because they give photosynthetic byproducts and help the coral
when it loses its primary symbionts due to stress. The variety of these
algae among coral species of the genus Porites in the tropical
easter Pacific and western Atlantic was investigated here. We extracted
Ostreobium samples from seven Porites species including
two from the Tropical Easter Pacific-TEP ( P. panamensis, P.
lobata) and five from the Caribbean (P . furcata, P. porites, P.
colonensis, P. branneri, and P. astreoides). We also compared
the new rbcL sequences from algae found within various coral
species from other parts of the world. A biogeographic analysis and two
methodologies, PTP (Poisson tree process) and GMYC (General Mixed
Yule-Coalescent), were used to delineate the different species. The
findings revealed a significant degree of genetic diversity within
Ostreobium, with more than 15 groups of no more than three
individuals and 40 individual lineages. Its origins date back to the
Ordovician, 500 Ma, and it does not appear to preserve host-specificity.
The sampled locations include a wide variety of Ostreobium still,
biogeographically, varied patterns were confirmed, making it impossible
to pinpoint the precise origins of most clades. The ancestry analyses
revealed convergent events for the emergence of Ostreobium in a
few genera of local corals, but the phenomenon also occurred in genera
from far-off places.