Alive and dead foraminiferal assemblages at sandy beaches of Karachi coast-diversity, ecological distribution and responses to seasonal fluctuations

Abstract

Foraminifera are eukaryotic protists and play a vital role in marine community structure. However, how physicochemical environment shape meiofaunal community structure at highly dynamic exposed sandy beaches of Arabian sea is inadequately known. This is the first study about spatiotemporal distribution of alive and dead benthic foraminiferal (BF) species from coastal regions of Pakistan based on 48 core samples collected monthly with the help of hand corer (diameter = 3 cm) from four stations at two sandy beaches of Karachi coast i.e., Sandspit and Hawksbay. Sampling was done throughout the year from March 2013 to April 2014 to observe seasonal variability in southwest and northeast monsoon season. Physicochemical parameters (temperature, salinity, pH, dissolved oxygen and nutrients i.e. Ammonia, nitrate and phosphorus) and sediment characteristics (grain size, moisture content, organic content) was analysed using standard methods.The top 0–2 cm sediment slice was analysed for both living and dead foraminiferal assemblages. A sum of 6615 individuals (ind.) cm−2 of BF consisting of 3451 ind. cm−2 empty tests and 3164 ind. cm−2 living specimens belonged to 66 species were recorded, where 47% species are Miliolina, 42% Rotaliida, 9% Textulariina and 2% are Spirillinina. The similarity percentage breakdown analysis (SIMPER) showed 18.51% average dissimilarity between foraminifera abundance at Sandspit and Hawksbay but stations within sites showed similarity (82.83% at Sandspit and 84.65% at Hawksbay). The highest abundance of alive BF was recorded in northeast monsoon season (3232 ind. cm −2) associated with high levels of nutrients. Alive and dead foraminifera assemblages at Karachi coast do not seem to be measured by a single physicochemical and environmental factor but multiple factors are controlling spatiotemporal distribution of BF at these beaches. The most significant and governing factor for benthic abundance and diversity at these beaches is the monsoon season.