Spawning/Bleaching -NW Gulf of Mex.
sgittings at ocean.nos.noaa.gov
Fri Sep 5 20:13:59 EDT 1997
Mass spawning by reef corals and other organisms at the Flower Garden Banks
National Marine Sanctuary (northwest Gulf of Mexico) was observed on four
consecutive nights in August.
Sunday, 24 August 1997
Spawning began around 21:10 hrs CDT and continued until 22:30. Montastraea
franksi and to a lesser extent Diploria strigosa, were the dominant spawners
with one sighting of spawning by a female Stephanocoenia intersepta (formerly
S. michelini) and M. cavernosa. Several Ophioderma rubicundum (ruby brittle
stars) and Spirobranchus giganteus (christmas tree worms) were also spawning.
Spawning activity by a congregation of approximately 40-50 black durgon
(Melichthys niger) was observed during the early morning hours over a sand
flat. Creole wrasse (Clepticus parrae) exhibited spawning behavior as usual
Monday, 25 August 1997
Spawning began around 20:20 CDT. D. strigosa was the dominant spawner
(hundreds of colonies) of the early evening with peak activity around 21:00
hrs. Other spawners included M. franksi (abundant), both male and female M.
cavernosa, one male Stephanocoenia intersepta numerous christmas tree worms,
and brittle stars, and a banded coral shrimp with brood pouch was observed.
All of this occurred primarily between 20:40-22:30 hrs CDT, with possible
peaks around 21:00 for most corals, and 22:00 for other invertebrates.
Between 22:30-23:30 CDT there was a different group of spawning corals that
included M. faveolata and M. annularis. Both of these species were observed
spawning during this time, although mostly it was M. faveolata. We also
noticed other unusual levels of activity including several large grouping of
Diadema antillarum (each with more than 6 large [test diameter ~ 16 cm]
individuals within two square meters of each other).
Tuesday, 26 August 1997
Spawning by D. strigosa and M. franksi was again observed on this evening
between 21:30-22:40, with a surface slick forming around 21:00 hrs. Spawning
activity was light however when compared with previous evenings. Most of the
spawning on this evening was contributed by D. strigosa (more than 3 dozen
colonies were observed spawning by a single dive team), with roughly 14
colonies of M. franksi observed either at the setting stage or spawning. Two
male S. intersepta colonies were observed spawning around 22:30.
Additional observations of M. faveolata spawning were made shortly after
Wednesday, 27 August 1997
First observations of gametes at the surface began around 20:05 CDT. Our
divers witnessed spawning of Colpophyllia natans spawning between 20:40-21:00
hrs. Colonies down to roughly 12 inches (36cm) in diameter were spawning. In
addition, a few individuals of several other coral species including D.
strigosa (22:00 hrs), M. franski (22:10 hrs) and M. faveolata (22:30 hrs) were
observed spawning. We also saw S. intersepta were spawning late in the
evening. The ratio of males to females was estimated by one diver to be about
5:1. Both males (22:15 hrs) and females (22:30 hrs) of this species were
observed spawning in numbers that were far greater than on previous evenings.
Bleaching - as of 8/28, the Flower Gardens appeared to be experiencing more
coral bleaching than normal, though it cannot be considered extensive. Most
fire coral colonies (Millepora alcicornis) were either partly or completely
white, as were portions of a number of colonies of Siderastrea siderea and
Colpophyllia spp. The event seemed to increase in severity substantially
between August 11th and the 28th. Temperature records will be made available
after thermographs are collected and dumped in the next couple of weeks.
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