Studies on the Factors Affecting the Macrobenthic Community Structure of the Exposed Sandy Beaches Near Karachi, Pakistan

Abstract

The principal objective of the research conducted during this study is to provide a profound knowledge of the ecological status and functioning of exposed sandy beaches of Karachi coast. This assessment was established on the basis of functionally important benthic community structure in response to environmental conditions which is the first comprehensive study at studied beaches at Karachi coast. In chapter 1, macrobenthic community structure of the exposed sandy beaches of Sandspit and Hawksbay in relation to physicochemical parameters and sediment characteristics is studied during 2013-2014. A total of 96 samples were collected in duplicate by quadrat (0.25 m-2) method from high tide (HT) and low tide (LT) mark for macrofauna abundance and sediment analysis from four stations (S1, S2, H1 and H2). Water samples were analyzed for temperature, salinity, pH, dissolved oxygen and nutrients analysis (NH4, NO3, PO4) by applying standard methods. Sediment samples were divided into three layers, each layer was analyzed for moisture and organic content and grain size analysis. A total of 1307 organisms 0.25m-2 belong to 83 macrobenthic species recorded during this study out of which 12 species are first records from Pakistan. A sum of 662 organisms 0.25m-2 were recorded from Sandspit and 645 organisms 0.25m-2 from Hawksbay. The most diversified macrobenthic groups of species were polychaeta (38%) followed by gastropoda (24%), crustacea (19%) and bivalvia (12%) respectively. Whereas, the most abundant faunal groups were polychaeta (44 %), crustacea (25 %), bivalvia (14 %) and gastropoda (11%). Euterpina acutifrons, Glycera alba, Donax hanlyanus, Prionospio sp. were the most dominant species at studied beaches. SIMPER analysis showed average similarity 37.5% between sites. The highest macrobenthic abundance was recorded in NEMS (414 0.25m-2) and PRMS (379 0.25m-2) and lowest during SWMS (211 macrobenthos 0.25m-2). ANOVA showed impact of different environmental parameters such as salinity, temperature, dissolved oxygen and moisture content on macrofaunal assemblages. The species composition and abundance showed a clear separation between studied sites during monsoon seasons indicating the significant impact of monsoon on macrofaunal diversity and abundance at studied beaches. xviii In chapter II, benthic foraminifera in relation to habitat conditions and seasonal influences was studied for the first time from Pakistani coast, based on 48 core samples collected monthly with the help of hand corer (diameter =3 cm) from stations as discussed for Chapter I. For this study the top 0-2 cm sediment slice was analyzed for both living and dead foraminiferal assemblages. A total of 6615 cm-2 specimens consisting of 3451 cm-2 dead tests and 3164 cm-2 living specimens were recorded which belong to 66 species out of which 47% species are miliolina, 42% rotaliina, 9% textulariina and 2% are spirillina. At Sandspit 3197 cm-2 specimens were recoded while a sum of 3418 cm-2 specimen were recorded from Hawksbay. The highest abundance was exhibited by rotaliina, milolina and textulariina respectively. The most dominant rotaliina species were Ammonia beccari, Pararotalia stellata, P. vensuta, Elphidium crispum and E. advenum respectively and Quinqueloculina bicarinata, Q. vulgaris, Miliolinella subrotunda, Spiroloculina antillarum and Miliamina sp. were abundant miliolina species. SIMPER showed that average dissimilarity between foraminifera abundance at Sandspit and Hawksbay is 18.51 %. The stations within sites showed similarity (82.83 % at Sandspit and 84.65 % at Hawksbay). A. beccari and P. stellata are the most similar species within stations at both Sandspit and Hawksbay. The highest foraminifera abundance was recorded in NEMS (3232 cm-2) and SWMS (1984 cm-2) and the lowest during PRMS (398 cm-2). pH, salinity, organic content and nutrients appeared to effect the foraminiferal assemblages. Benthic community structure of exposed sandy beaches of Sandspit and Hawksbay do not affected by a single physicochemical and environmental factor but multiple factors are controlling spatial and temporal distribution of macrofaunal and foaraminferal assemblages at these beaches. The most significant and governing factor for benthic abundance and diversity at these beaches is the monsoon season. Faunal assemblages on each site point out a variability in domination of species during studied seasons. Northeast monsoon was the most biologically productive season which provided a suitable environment for growth of both macrobenthic communities and foraminiferal assemblages. This is the first comprehensive study about ecological status of these highly dynamic environments which will be helpful in management of these beaches in future.