TY - JOUR
T1 - Mechanisms of damage to corals exposed to sedimentation
AU - Weber, Miriam
AU - De Beer, Dirk
AU - Lott, Christian
AU - Polerecky, Lubos
AU - Kohls, Katharina
AU - Abed, Raeid M.M.
AU - Ferdelman, Timothy G.
AU - Fabricius, Katharina E.
PY - 2012/6/12
Y1 - 2012/6/12
N2 - We investigated the mechanisms leading to rapid death of corals when exposed to runoff and resuspended sediments, postulating that the killing was microbially mediated. Microsensor measurements were conducted in mesocosm experiments and in naturally accumulated sediment on corals. In organic-rich, but not in organicpoor sediment, pH and oxygen started to decrease as soon as the sediment accumulated on the coral. Organic-rich sediments caused tissue degradation within 1 d, whereas organic-poor sediments had no effect after 6 d. In the harmful organic-rich sediment, hydrogen sulfide concentrationswere lowinitially but increased progressively because of the degradation of coral mucus and dead tissue. Dark incubations of corals showed that separate exposures to darkness, anoxia, and lowpH did not causemortality within 4 d. However, the combination of anoxia and low pH led to colony death within 24 h. When hydrogen sulfide was added after 12 h of anoxia and lowpH, colonies died after an additional 3 h.We suggest that sedimentation kills corals through microbial processes triggered by the organic matter in the sediments, namely respiration and presumably fermentation and desulfurylation of products from tissue degradation. First, increased microbial respiration results in reduced O 2 and pH, initiating tissue degradation. Subsequently, the hydrogen sulfide formed by bacterial decomposition of coral tissue and mucus diffuses to the neighboring tissues, accelerating the spread of colony mortality. Our data suggest that the organic enrichment of coastal sediments is a key process in the degradation of coral reefs exposed to terrestrial runoff.
AB - We investigated the mechanisms leading to rapid death of corals when exposed to runoff and resuspended sediments, postulating that the killing was microbially mediated. Microsensor measurements were conducted in mesocosm experiments and in naturally accumulated sediment on corals. In organic-rich, but not in organicpoor sediment, pH and oxygen started to decrease as soon as the sediment accumulated on the coral. Organic-rich sediments caused tissue degradation within 1 d, whereas organic-poor sediments had no effect after 6 d. In the harmful organic-rich sediment, hydrogen sulfide concentrationswere lowinitially but increased progressively because of the degradation of coral mucus and dead tissue. Dark incubations of corals showed that separate exposures to darkness, anoxia, and lowpH did not causemortality within 4 d. However, the combination of anoxia and low pH led to colony death within 24 h. When hydrogen sulfide was added after 12 h of anoxia and lowpH, colonies died after an additional 3 h.We suggest that sedimentation kills corals through microbial processes triggered by the organic matter in the sediments, namely respiration and presumably fermentation and desulfurylation of products from tissue degradation. First, increased microbial respiration results in reduced O 2 and pH, initiating tissue degradation. Subsequently, the hydrogen sulfide formed by bacterial decomposition of coral tissue and mucus diffuses to the neighboring tissues, accelerating the spread of colony mortality. Our data suggest that the organic enrichment of coastal sediments is a key process in the degradation of coral reefs exposed to terrestrial runoff.
KW - Acidification
KW - Coastal management
KW - Fertilizer input
KW - Microbial activity
KW - Urbanization
UR - http://www.scopus.com/inward/record.url?scp=84862166514&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84862166514&partnerID=8YFLogxK
U2 - 10.1073/pnas.1100715109
DO - 10.1073/pnas.1100715109
M3 - Article
C2 - 22615403
AN - SCOPUS:84862166514
SN - 0027-8424
VL - 109
SP - E1558-E1567
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 24
ER -