Awareness and Perceived Indicators of Climate Change among Seaweed Farmers in Jambiani Village, Unguja Island

Climate change remains to be the biggest challenge threatening to undo sustainability of socio-economic activities. The study investigated seaweed farmers’ awareness and their perceived indicators of climate change in Jambiani village, Unguja Island. A cross sectional study was adopted to interview 100 seaweed farmers between September and November, 2016. A mixed approach was used, of which primary data collection tools includes Questionnaires with close and open-ended questions and Focus Group Discussion, and secondary climate data was integrated. The results indicated that, majority (93%) seaweed farmers were aware of the changes in climate, and 97.75% perceived elevation of seawater temperature, 71.76% perceived an increase in intensity of ocean waves and 93.37% south- easterly (Kusi) monsoon wind, 84.58% longer periods of north-easterly (Kaskazi) monsoon winds and 78 % perceived changes in distribution and disappearance of near shoreline fringing reefs as climate change indicators. Analysis of empirical secondary data from TMA showed elevation of terrestrial and seawater temperature by 1.22°C (y=0.03x+30.281) and 0.62°C (y=0.0219x+27.256) respectively as well as big ocean wave heights navigating between months of June and September of the year. Seaweed farmers are aware of the changes in weather and climate and capable to correctly identify and associates different environment-related uncertainties to climate changes, but lack expertise in proper use and integration of various climate instability situations into suitable and appropriate farming practices for improved production. Thus, the study recommends introduction of insurance schemes to the industry as resilience mechanisms to climate related changes in seaweed industry and extension services through extension officers meant to offer technical education and services to seaweed farmers on the best adjustment ways to on-going environmental and weather changes that meant to safeguard seaweed industry

Seagrass meadows mixed with calcareous algae have higher plant productivity and sedimentary blue carbon storage

Seagrass meadows capture and store large amounts of carbon in the sediment beneath, thereby serving as efficient sinks of atmospheric CO2. Carbon sequestration levels may however differ greatly among meadows depending on, among other factors, the plant community composition. Tropical seagrass meadows are often intermixed with macroalgae, many of which are calcareous, which may compete with seagrass for nutrients, light, and space. While the photosynthetic CO2 uptake by both seagrasses and calcareous algae may increase the overall calcification in the system (by increasing the calcium carbonate saturation state, Ω), the calcification process of calcareous algae may lead to a release of CO2, thereby affecting both productivity and calcification, and eventually also the meadows' carbon storage. This study estimated how plant productivity, CaCO3 production, and sediment carbon levels were affected by plant community composition (seagrass and calcareous algae) in a tropical seagrass-dominated embayment (Zanzibar, Tanzania). Overall, the patterns of variability in productivity differed between the plant types, with net areal biomass productivity being highest in meadows containing both seagrass and calcareous algae. Low and moderate densities of calcareous algae enhanced seagrass biomass growth, while the presence of seagrass reduced the productivity of calcareous algae but increased their CaCO3 content. Sedimentary carbon levels were highest when seagrasses were mixed with low or moderate cover of calcareous algae. The findings show that plant community composition can be an important driver for ecosystem productivity and blue carbon sequestration

An experimental assessment of algal calcification as a potential source of atmospheric CO2.

Marine vegetated ecosystems such as seagrass meadows are increasingly acknowledged as important carbon sinks based on their ability to capture and store atmospheric carbon dioxide, thereby contributing to climate change mitigation. Most studies on carbon storage in marine ecosystems have focused on organic carbon, leaving inorganic carbon processes such as calcification unaccounted for, despite of their critical role in the global carbon budget. This is probably because of uncertainties regarding the role of calcification in marine carbon budgets as either atmospheric CO2 source or sink. Here, we conducted a laboratory experiment to investigate the influence of a calcifying alga (Corallina officinalis L.) on seawater carbon content, using a non-calcifying alga (Ulva lactuca L.) as a control. In a first part, algae were incubated separately while measuring changes in seawater pH, total alkalinity (TA) and total dissolved inorganic carbon (DIC). The amount of carbon used in photosynthetic uptake and production of CaCO3 was then calculated. In a second, directly following, part the algae were removed and DIC levels were allowed to equilibrate with air until the pH stabilized and the loss of CO2 to air was calculated as the difference in total DIC from the start of part one, to the end of the second part. The results showed that C. officinalis caused a significant and persistent reduction in total dissolved inorganic carbon (DIC), TA and seawater pH, while no such permanent changes were caused by U. lactuca. These findings indicate that calcification can release a significant amount of CO2 to the atmosphere and thereby possibly counteract the carbon sequestration in marine vegetated ecosystems if this CO2 is not re-fixed in the system. Our research emphasises the importance of considering algal calcification in future assessments on carbon storage in coastal areas