The competition between coral and algae in marine reefs is pervasive through geologic time;that competition determines the structure and composition of reef communities, which we see in the fossil record. However, the...The competition between coral and algae in marine reefs is pervasive through geologic time;that competition determines the structure and composition of reef communities, which we see in the fossil record. However, the relationships between coral and calcareous algae in reefs are poorly understood. To study this relationship, several hand samples and thin sections were examined from nine different foralgal reef localities around the world. Foralgal reefs typically extend from about 20 m depth or shallower on the seaward side of the reef. The first section is Salt Mountain, Alabama, which preserves a Paleocene reef. It contains a high percentage of red coralline algae with benthic foraminifera. The second section is IDOP-U1376, IIA Limestone, it is Middle Eocene, in the form of an isolated reef sandwiched between two igneous beds. The third section is the Utoe’ Limestone, New Caledonia, it is Middle Eocene in age and is composed mainly of grain-boundstone units with some igneous interlayered. The fourth section is the Darnah Formation in the West-Darnah roadcut section, Northeast Libya, it is Middle Eocene in age, it is composed of highly fossiliferous limestone (corals, red coralline algae, echinoids, mollusks, foraminifers, and bryozoans). The fifth section, the Al Bayda Formation (Algal Limestone Member) in Northeast Libya, is in the Drayanah—Al Abyar roadcut, Northeast Libya, it has several species of algae but also includes a high percentage of buildups of coral species. The sixth section is the Oligo-Miocene Al Faidiyah Formation (Al Fatayah Cement Quarry) limestone unit in Northeast Libya. The seventh section is (Core-core 20) late-early to middle Miocene Limestone Unit-Cicuco Field, NW Colombia. The eighth section is the Benghazi Formation at Benghazi Cement Quarry, in Northeast Libya, it is fossiliferous limestone, consisting of coral, algae, mollusks, and echinoids. The ninth and tenth sections are Quaternary reefs in the Bahamas and the Florida Keys, respectively. These reefs contain a high percentage of coral, red coralline algae, echinoids, mollusks, foraminifers, and ostracods. Based on the data and static analysis results on the thin sections and hand specimens, this study determines the occurrence and outcomes of coral-algal interactions among different coral growth forms (branching, upright, massive, encrusting, plating, and solitary). The Early Paleogene (Paleocene to Eocene) has the highest percentage of algae in two forms (crustose and frondose), which is a good indicator of a warm climate. In the Middle Eocene to Late Eocene, coral replaced algae in different localities in sections of that age. This change is an indicator of climatic cooling, especially in the western Lutetian Darnah section. In the Oligocene time, high-branching corals became abundant and escaped competition with the algae due to Icehouse conditions, as shown in the Al Bayda Formation. In the Miocene, coral species started to decline because of the return to Greenhouse conditions. Coral can lose its competitive edge when chemical and physical defense systems reduce growth and production due to warming. On the other hand, crustose-form algae attract the larvae of the coral. Algae induce them to get a more highly competitive frondose form, which is useful for corals as they decrease growth and production. Algae can quickly colonize the dead reef by using the firm substrate to rebuild themselves. This research may prove valuable when predicting the response of modern coral reef systems to future climatic warming conditions and provides a model for what future reefs may look like.展开更多
Roles of tillage erosion and water erosion in the development of within-field spatial variation of surface soil properties and soil degradation and their contributions to the reduction of crop yields were studied on t...Roles of tillage erosion and water erosion in the development of within-field spatial variation of surface soil properties and soil degradation and their contributions to the reduction of crop yields were studied on three linear slopes in the Sichuan Basin,southwestern China.Tillage erosion was found to be the dominant erosion process at upper slope positions of each linear slope and on the whole short slope (20 m).On the long slope (110 m) and medium slope (40 m),water erosion was the dominant erosion process.Soil organic matter and soil nutrients in the tillage layer were significantly related to slope length and 137 Cs inventories on the long slope; however,there was no significant correlation among them on the short slope,suggesting that water erosion lowered soil quality by transporting SOM and surface soil nutrients selectively from the upper to lower slope positions,while tillage erosion transported soil materials unselectively.On the medium slope,SOM,total N,and available N in the tillage layer were correlated with slope length and the other properties were distributed evenly on the slope,indicating that water erosion on this slope was still the dominant soil redistribution process.Similar patterns were found for the responses of grain yield,aboveground biomass,and harvest index for slopes.These results indicated that tillage erosion was a major cause for soil degradation and grain yield reduction on the linear slopes because it resulted in displacement of the tillage layer soil required for maintaining soil quality and plant growth.展开更多
文摘The competition between coral and algae in marine reefs is pervasive through geologic time;that competition determines the structure and composition of reef communities, which we see in the fossil record. However, the relationships between coral and calcareous algae in reefs are poorly understood. To study this relationship, several hand samples and thin sections were examined from nine different foralgal reef localities around the world. Foralgal reefs typically extend from about 20 m depth or shallower on the seaward side of the reef. The first section is Salt Mountain, Alabama, which preserves a Paleocene reef. It contains a high percentage of red coralline algae with benthic foraminifera. The second section is IDOP-U1376, IIA Limestone, it is Middle Eocene, in the form of an isolated reef sandwiched between two igneous beds. The third section is the Utoe’ Limestone, New Caledonia, it is Middle Eocene in age and is composed mainly of grain-boundstone units with some igneous interlayered. The fourth section is the Darnah Formation in the West-Darnah roadcut section, Northeast Libya, it is Middle Eocene in age, it is composed of highly fossiliferous limestone (corals, red coralline algae, echinoids, mollusks, foraminifers, and bryozoans). The fifth section, the Al Bayda Formation (Algal Limestone Member) in Northeast Libya, is in the Drayanah—Al Abyar roadcut, Northeast Libya, it has several species of algae but also includes a high percentage of buildups of coral species. The sixth section is the Oligo-Miocene Al Faidiyah Formation (Al Fatayah Cement Quarry) limestone unit in Northeast Libya. The seventh section is (Core-core 20) late-early to middle Miocene Limestone Unit-Cicuco Field, NW Colombia. The eighth section is the Benghazi Formation at Benghazi Cement Quarry, in Northeast Libya, it is fossiliferous limestone, consisting of coral, algae, mollusks, and echinoids. The ninth and tenth sections are Quaternary reefs in the Bahamas and the Florida Keys, respectively. These reefs contain a high percentage of coral, red coralline algae, echinoids, mollusks, foraminifers, and ostracods. Based on the data and static analysis results on the thin sections and hand specimens, this study determines the occurrence and outcomes of coral-algal interactions among different coral growth forms (branching, upright, massive, encrusting, plating, and solitary). The Early Paleogene (Paleocene to Eocene) has the highest percentage of algae in two forms (crustose and frondose), which is a good indicator of a warm climate. In the Middle Eocene to Late Eocene, coral replaced algae in different localities in sections of that age. This change is an indicator of climatic cooling, especially in the western Lutetian Darnah section. In the Oligocene time, high-branching corals became abundant and escaped competition with the algae due to Icehouse conditions, as shown in the Al Bayda Formation. In the Miocene, coral species started to decline because of the return to Greenhouse conditions. Coral can lose its competitive edge when chemical and physical defense systems reduce growth and production due to warming. On the other hand, crustose-form algae attract the larvae of the coral. Algae induce them to get a more highly competitive frondose form, which is useful for corals as they decrease growth and production. Algae can quickly colonize the dead reef by using the firm substrate to rebuild themselves. This research may prove valuable when predicting the response of modern coral reef systems to future climatic warming conditions and provides a model for what future reefs may look like.
基金Supported by the National Natural Science Foundation of China (No. 40771027)the National Key Technology R&D Program of China (No. 2008BAD98B04)the National Basic Research Program (973 Program) of China(No. 2007CB407206)
文摘Roles of tillage erosion and water erosion in the development of within-field spatial variation of surface soil properties and soil degradation and their contributions to the reduction of crop yields were studied on three linear slopes in the Sichuan Basin,southwestern China.Tillage erosion was found to be the dominant erosion process at upper slope positions of each linear slope and on the whole short slope (20 m).On the long slope (110 m) and medium slope (40 m),water erosion was the dominant erosion process.Soil organic matter and soil nutrients in the tillage layer were significantly related to slope length and 137 Cs inventories on the long slope; however,there was no significant correlation among them on the short slope,suggesting that water erosion lowered soil quality by transporting SOM and surface soil nutrients selectively from the upper to lower slope positions,while tillage erosion transported soil materials unselectively.On the medium slope,SOM,total N,and available N in the tillage layer were correlated with slope length and the other properties were distributed evenly on the slope,indicating that water erosion on this slope was still the dominant soil redistribution process.Similar patterns were found for the responses of grain yield,aboveground biomass,and harvest index for slopes.These results indicated that tillage erosion was a major cause for soil degradation and grain yield reduction on the linear slopes because it resulted in displacement of the tillage layer soil required for maintaining soil quality and plant growth.
