 | Ecology of Atlantic Shores Erin Miller, 2008 |
| Home -------------------------- Nahant -------------------------- Narragansett Bay: Introduction Water Quality Methods Observations Results Discussion -------------------------- Bermuda: Introduction Water Quality Coral Disease Aspergillosis Hypothesis and Methods Results Discussion -------------------------- Conclusions -------------------------- References | Aspergillosis
Studies of this
specific epizootic have found that one major factor affecting incidence of
infection is sea fan health; if the sea fan is stressed by its environment it
may be more susceptible to infection (9). One such stressor is temperature, and Alker et al. concluded that high temperatures
inhibit photosynthesis in the sea fans’ symbiotic zooxanthellae, limiting the
amount of energy obtained by the sea fan. Their study supported that increased
temperatures had a negative effect on G.
ventalina growth rate up to 30°C (9). Increased nutrient levels have also been shown to
increase Aspergillosis in sea fans in experimental conditions. Bruno et al. exposed a G. ventalina colony
to nutrient levels equivalent to a mildly polluted reef, finding that
sea fans in the colony became infected twice as much as control sites (15). Left: Symptoms of Aspergillosis; lesions, galling, and purpling of the tissue (Kiho Kim, news.cornell.edu). Another factor
influencing disease incidence is colony size (19). Dube et al.
supported that larger colonies are more likely to be infected due to the high
surface area. Larger sea fans are also older, and therefore
have had longer exposure time creating an increased chance of infection. Other studies supported these conclusions, stating that 
Aspergillosis tended to infect the largest, most fecund sea fan colonies (17).
Infection resulted in decreased reproduction, causing decline in colony size.
New recruitment usually only occurred when the prevalence of disease was low,
resulting in complete eradication of the largest colonies (17). Jolles et al.
state that transmission of
Aspergillosis can occur between sea fans that are in direct contact
with one
another, or if infected sea fans shed fungal material into the water
column; another reason why larger colonies have a higher incidence of
infection (20). Right: Time series damage caused by Aspergillosis on G. ventalina (12).Aspergillosis infection of G. ventalina has also been shown to be positively correlated with decreased wave exposure and increased water depth in shallower reefs (less than 12 meters deep) (17). Nagelkerken et al. proposed that reduction in the swaying motion of the sea fans at more protected sites (greater depths) may increase the ability of A. sydowwi to attach to the sea fans and infect them.  G.
ventalina has been shown to resist Aspergillosis infection
due to chemical compounds within their tissue, a trait that is common among
many corals (21). These
chemicals typically defend against predators, but they may also serve to
protect against disease. It is possible that sea fans may adapt to an
environment with high predation or high prevalence of disease by increasing the
chemical compounds that defend against these threats. This is one of the hypotheses
for the recent decline of the Aspergillosis epizootic. Factors such as recruitment of non-resistant
individuals, increased pathogen input, and/or increased environmental stress
may promote reemergence of another epizootic (21). Left: Large G. ventalina colony at North Rock, Bermuda. Photo courtesy Todd Livdahl. |
A disease that
commonly affects G. ventalina is
Aspergillosis, caused by the fungus Aspergillus
sydowii which typically inhabits terrestrial soils (9, 17). It is hypothesized that
the fungus may have originally reached G.
ventalina colonies via offshore deposition of terrestrial sediment
(17). Infection
with Aspergillosis is characterized by lesions, galling, and purpling of the
sea fan tissue which can lead to death of a colony (9). An epizootic of this
disease in the