PhD Thesis
Climate change will affect fishery resources and challenge policy makers to develop sustainable exploitation strategies. However, the information on the impacts of climate change and variability on fishery resources is still fragmentary. The present study gives an overview of literature on the impact of climate change and variability on marine environment and fish populations with a focus on the processes that govern the response of fish to marine environment and climate change. The research was conducted partly in field to assess the impacts of current climatic conditions on marine environment fish composition and recruitment patterns of mullet in mangrove ecosystem. The field work was conducted in two sites i.e. non estuarine mangroves and estuarine mangroves areas. In the laboratory the effect of projected future elevated CO2 and temperature on hatching, survival and morphology of marine fish, sillago (Sillago japonica) was examined.
The first study aimed at describing site and seasonal variations in fish species in Mbegani non-estuarine mangrove (MnEM) and Ruvu estuarine mangrove (REM) sites in Bagamoyo. Variation in fish species, selected environmental parameters (i.e. dissolved oxygen, salinity, water temperature, water pH) and meteorological parameters i.e. rainfall and atmospheric temperature) were examined between the sites. Seine nets, fyke nets and gill nets were used to collect fish samples from upper, middle and lower parts of the mangrove study sites. At each sampling station, sample collection was conducted for two consecutive days per month. Analysis of data revealed that total fish catch; species number and diversity index varied greatly among stations within site. This was caused by environmental parameters which in turn were affected by rainfall and atmospheric temperature. Species specificity to habitat could also be a factor contributing to the observed variation. Fish abundance showed no significant difference (p > 0.05) between seasons and sites regardless of the influence of Ruvu River which flows throughout the year. Multivariate analysis revealed significant (p < 0.05) separations in fish community composition among stations in two study sites. However, no clear demarcation of fish communities was observed in lower station at REM site and upper and lower stations in MnEM site. It is suggested that environmental variables such as DO, salinity and pH were the main determinant factors of community composition in Bagamoyo mangrove ecosystems.
The second study examined effect of meteorological factors on recruitment patterns i.e. annual distribution patterns and size structure of mullet of two mullet species in REM and MnEM sites in Bagamoyo mangroves ecosystem. The fish samples were collected during low tide using beach seine of 20 m long, 2 m wide with a stretched mesh size of 1.6 cm towed over an area of 100 m2. Mullet species, counts and length were collected in two consecutive days each month from January to December of 2012. The abundance of Mugil cephalus and Valamugil buchanani varied significantly (p < 0.05) between sites and seasons. The mullet collected on mangroves were all juveniles and were positively correlated (p < 0.05) with rainfall and dissolved oxygen (DO). The atmospheric temperature had significantly (p < 0.05) effect on environmental parameters i.e. DO, salinity, temperature and pH which in turn affected mullet recruitment patterns. Habitat characteristics such as muddy substrate and presence of macroalgae also contributed to the distribution pattern of mullets.
The third study examined effects of elevated carbon dioxide (CO2) and temperature on survival and morphology of Japanese whiting, Sillago japonica. The study was conducted at Ocean acidification laboratory at the Institute for East China Sea Research (ECSER), Nagasaki University, Japan. The study examined hatching success, survival and morphology of the larvae of Sillago japonica. There were four treatments namely; (i) control (C), seawater pCO2 382μatm, temperature 27 °C; (ii) high CO2 (HC), 915μatm, 27 °C; (iii) high temperature (HT), 385 μatm, 31 oC; and (iv) high CO2+high temperature (HCT), 932μatm, 31 oC. The experiment was repeated four times. Ten fertilized eggs of were incubated in each treatment for 24hrs and their hatching success determined. Fifty (50) hatched larvae were observed until the completion of yolk sac absorptions on the third day post hatching to determine effect of elevated CO2 and temperature on survival and morphology of sillago larvae. Temperature appeared to have exerted a stronger influence on hatching success and larval survival. The hatching success and larvae survival 3 days post hatching were both significantly (p > 0.05) depressed in HT (52.5 ± 1.25%, 23.8 ± 4.38%) and HCT (51.3 ± 3.13%, 20.0 ± 0.63%) treatments than in Control (C) (98.1 ± 0.94%, 74.4±2.03%) and HC (95.0±2.5%, 49.7±3.44%) treatments respectively. In contrast, CO2 was the predominant factor responsible for morphological abnormality: percentage morphological abnormality was significantly (p>0.05) higher in HC (15.8±2.72%) and HCT (41.0±10.86%) treatments than in C (0.4±0.65%) and HT (2.4±2.40%) treatments. Most individuals in HC and HCT treatments had body axis either curved or bent, with aberrant swimming behavior. These results suggest that projected future elevated CO2 and temperature will have significant negative impacts on hatching success, larval survival and morphology of S. japonica, which might have serious ramifications for recruitment of the species.
COSTECH and CCIAM