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The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.

The exponential increase of atmospheric greenhouse gas concentrations over the past 50 years has caused a rise in the global average temperature by more than 1ºC above pre-industrial levels. Ninety-three percent of this heat energy has been absorbed and stored by the oceans, increasing their temperatures, particularly in surface waters. This can produce both negative and positive impacts on the health and function of vital coastal shallow-water communities, hosting seagrasses and macroalgae, which are key primary producers and ecosystem engineers in the coastal zone. The physiological processes of these plants and the biogeochemical processes in associated sediments operate over a wide range of temperatures and their response can serve as early indicators of changes in their ecosystem function. This thesis employed a combination of laboratory, mesocosm and field based experiments to understand: 1) the responses of key physiological processes to elevated temperatures occurring frequently (and likely to occur in a future warming scenario) in seagrass meadows, and how these will affect biogeochemical processes in associated sediments, 2) the exchange of carbon dioxide between seagrass, water and atmosphere, and 3) effects of the tidal variability on biogeochemical processes of tropical seagrass sediments. The results showed that elevated water temperatures cause increased rates of photosynthesis in seagrasses up to a threshold temperature above which rates declines rapidly. The negative effects of temperatures reaching beyond threshold levels increased with repeated days of exposure. The rates of mitochondrial respiration in seagrasses increased with elevated temperatures until a collapse of their respiratory machinery occurred. Photorespiration did not increase linearly with elevated temperatures. The responses of the different components of the seagrass plant (i.e. leaves, shoots, rhizomes and roots) to temperature increase clearly differed, and varied within differe, At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript. Paper 6: Manuscript.