This study deals with the distribution pattern and diversity of hard corals and associated and non-associated communities (fish, invertebrates and seaweeds) in the coastal waters of Sindh as well as paleodiversity of hard coral settings in the uplifted strata along Balochistan coast of Pakistan. Chapter 2 reports on live corals collected through SCUBA surveys, coral-associated fauna (fish, invertebrates), and environmental impacts on the calcareous animals (corals). A total of 21 hard coral are first report from Pakistan. All together 50 live coral species recorded from Pakistan. In addition, 13 molluscs, 3 sponges, 3 sea anemones, 3 echinoderms, 2 crustaceans and 54 fish species were also identified and recorded. Fishes were not documented scientifically but relayed on photographs taken in situ for identification. Semi-quantitative measure of relative abundance (DACFOR scale) of corals and other invertebrate fauna indicated that northern sheltered sites of Churna Island followed by Mubarak Village support high diversity of corals, and other associated fauna. HCO3-, CO32- and OH- were determined. No significant acidification impacts were noted as pH values remained in the normal range particularly in offshore waters (Churna Island) but pH levels are decreasing. Fish and invertebrates distribution patterns appeared to be associated with habitat complexity. Further studies on large scale with special focus on chemical and environmental parameters are recommended. Chapter 3 deals with characterization of macroalgal communities in the subtidal coastal waters of Sindh. Rich algal flora is reported from the coast of Pakistan supported by nutrient loadings through convective mixing and upsloping of nutrient rich upwelled waters. Previous studies on seaweeds in Pakistan are mainly confined to intertidal areas or on the basis of drift samples with much emphasis on taxonomy and phycochemistry without an in-depth study of the ecology. The present study reports for the first time the outcome of underwater surveys at 5 dive sites. Quadrat techniques were used to determine the relative diversity and abundance of benthic macroalgal communities. A total of 36 species (16 Phaeophyceae, 12 Rhodophyta, and 8 Chlorophyta) were recorded. An increase in diversity and distribution patterns was noted from west to east along the coast. High diversity occurred at Hawks Bay followed by French Beach. The coral sites (northern sheltered site of Churna Island and Mubarak Village) had less diversity. Very few recorded species had a restricted distribution (Yemen, Oman and India). One species (Stypopodium shameelii) was found endemic to Pakistan whereas the rest are widely distributed in the entire Indian Ocean, Atlantic and Pacific. Distribution and diversity patterns appeared to be linked with habitat type, topography, wave exposure and prevailing climatic conditions. Growth of seaweed appears to be impacted through oceanic processes. For example, stunted growth of Sargassum species and changes in community structure were observed after the Cyclone ‘NILOFAR’. Anthropogenic threats currently are not evident on seaweed communities. Huge beds of Sargassum were observed in submerged habitats along the Karachi coast. Their sustainable use can provide alternative source of livelihood for coastal communities and can reduce pressure on fisheries sector that is already under stress. The fossil coral communities in the uplifted strata along Balochistan coast of Pakistan and their comparison with the modern distribution of hard corals in Pakistan waters is reported in Chapter 4. Being important palaeoclimate archives and a rich source of information on past, uplifted Quaternary terrain along Balochistan coast is the perfect place to study the palaeoclimatic and geological changes that have shaped the Balochistan coast. The present study fills the gap exists in the knowledge pool on the palaeodiversity of corals in this region. The samples collected using line intercept method from four uplifted sites (Balochistan coast: one at Gwadar, and three at Jiwani) were analysed for relative distribution and diversity of Scleractinian fossil corals. A total of 48 fossil coral species were recorded in nine families and 22 genera. High diversity of corals was recorded in the uplifted landward sites of Jiwani and Gwadar headland. Terraces close to the shore at Jiwani had lower diversity. The corals seem to be Quaternary; most likely Pleistocene to Holocene. Comparing fossil fauna with modern distribution indicated that modern fauna lacks many species recorded in the fossil community, thus suggesting a faunal turnover in diversity and redistribution of coral fauna, which may be linked with past geological events and increasing anthropogenic pressure. Finely, for the development of effective conservation strategy detailed studies are desiredable in uplifted strata and submerged habitats with respect to climatological, environmental, anthropogenic and geological variations. As coastal environment does not seem to favour coral growth, conservation of already existing coral sites is necessary. The local community and wider public may be involved in restoration work so that they can appreciate the importance of these natural resources. Development of artificial reef at suitable low energy submerged habitats would provide a chance for many species to grow. These reefs and natural coral sites (Churna and Astola Islans) may be used as sites for pleasure diving and for the promotion of ecotourism.