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James M. Cervino cnidaria at
Thu Jan 15 07:35:09 EST 1998

Response to Hector Reyes' Posting:

Reefs in the past probably bounced back after bleaching events that were
due to increased sea-surface temperatures. This stress induced the
expulsion of symbiotic macroalgae (zooxanthellae). Observations of photos
and field studies from Papua New Guinea (Pacific) show signs of
recolonization one year after a 1994-95 bleaching event. This could be due
to low incidence of stressors outside the increased temperature realm.
Kimbe Bay, in New Britain (Papua New Guinea),  has a low population of
divers, and development. Macroalgae overgrowth was minimal after the '95
bleaching event.

Degrees of bleaching, within and among coral colonies and across reef
communities, are highly variable and difficult to quantify (Glynn P. Global
Change Biology, 1996).  Some species are more susceptible to temperature
stress (bleaching) than others, I have seen bleached colonies of M.
cavernosa & franksi directly next to unbleached Diploria and Siderastrea

Questions: 1) are these observations localized or are they observations of
the whole region? 2) Supporting Ann Cohen's question, "Are you sure these
corals were killed by bleaching?," were they stressed/bleached for a few
months and then killed by macroalgal overgrowth"? Localized bleaching might
be due to anthropogenic stressors such as pollution, sewage runoff,
agricultural runoff, storm damage, and sedimentation.

Global Bleaching Events: Present evidence suggests that global scale
bleaching events are due to elevated sea temperatures and high solar
irradiance (UV wavelengths) (Glynn, '93,  Coral Reefs 12:1-17; Goreau &
Hayes, '94, Ambio).
NOAA satellite-derived sea-surface temperature records at seven Atlantic
reef locations show that mass bleaching events took place following the
warmest periods recorded. Hot spot data can provide scientists with
information to predict future global bleaching events (Goreau, Hayes, '94,

After the expulsion of zooxanthellae (corals photosynthesizes), the corals'
metabolic activity is weakened, and the coral is basically starving. That
leads to: a decline in its calcium laying ability, which has stopped
(growth and calcification); impairment of reproduction; and, tissue
necrosis. A decrease in growth rate could reduce the capacity of corals to
compete favorably for space with algal turf, coralline algae, unfavorable
macrophytic algae, sponges and tunicates. After temperature stress, we now
have a stressed coral with no ability to compete with unfavorable
microphytic algae, that will soon colonize the coral. In the Journal of
Coral Reefs (1997 16:168) "Reef SitesTitled Epizoic red alga alleopathic(?)
to a Caribbean coral," shows Dasyopsis colonizing and killing M. decactis
off Caicos Island. The microphyte had recruited and colonized on the tops
of the coral in an outward direction growing directly on the living coral
tissue, which later died. According to Mark Littler and Diane Littler; the
cause of coral death, hypothetically, appeared to be an allelochemical
interaction. According to the published literature, the only other source
of epizootic alga deadly to reef building corals is black band disease
(BBD, also known as Phormidium corallyctium) (Ruetzler & Santavy 83;
Richardson, L. AMLC Symposium 97). Coral reefs subject to adverse
environmental conditions, BBD may play an important role in restructuring
the community and may be contributing to the demise of reefs observed in
Jamaica (Bruckner A. & Bruckner R. 1997). Coastal waters around Jamaica are
highly eutrophic and under siege from a wide variety of anthropogenic
stresses that recruitment/recolonization is minimal. Cyanobacterial
invasion will disrupt the symbiosis between host and zooxanthellae,
increase mucus-secretory production causing a wider surface area on the
surface of the coral, and cell erosion. Bacterial populations will lead to
the development of anoxic conditions on the surface of the coral, inviting
a community of heterotrophic sulfide oxidizing bacteria, and sulfate
reducers. This will lead to the corals demise (Peters, E. 84).

According to personal observations since 1980, and photos from the '70s, I
have seen higher indices of coral reef diseases at reefs suffering from
eutrophication, compared to reefs with less stresses due to excess

Nutrients and Corals: Are Reefs Oligotrophic?
The role of nutrient enrichment as a concomitant factor enhancing the
growth rate and carrying capacity of the macroalgal overgrowth on corals
needs to be investigated following bleaching events. Coral reefs are
susceptible to nutrient enrichment due to the low thresholds for dissolved
inorganic nitrogen (DIN;1.0µM) and soluble reactive phosphorus (SRP; 0.1µM)
Bell, 1992.) Corals compete for space with macroalgae and turf algae and
the competitive results are influenced by growth rates and nutrient
availability. Eutrophication increases the biomass of macroalgae, however,
also reduces the reproductive rates of hermatypic reef corals (Tomascik,
1991), and inhabits coral larval settlement and survival (LaPointe et al.

In Conclusion: And in aggreeance with Dr. LaPointe; "coastal eutropication
needs to be vigorously confronted by scientists and resource managers"
Bleaching events have been more frequent in the past 20 years, monitoring
the effects of eutropication, and coral reef diseases after such events is
the key factor in understanding the dynamics of coral reefs of the next
century. This being the International Year of The Ocean should be the year
to also support the goals established from the Year of The Reef!

Comments are welcome! James M. Cervino

James M. Cervino
Marine Biologist
Global Coral Reef Alliance
124-19 9th ave. College Point
New York, N.Y. 11356
Phone/Fax-(718) 539-8155

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