Coastal water with coastal microbial concentrate (COAST): Microbial cell and micro-aggregate counts with parallel beta-galactosidase activity measurements

A mesocosm experiment was carried out in and October of 2015 (Mesocosm#2) using coastal water collected near Galveston Bay, Texas. Four mesocosm treatments were prepared in triplicate for this study: (1) Control (seawater only); (2) WAF (oil + seawater); (3) Chemically-enhanced WAF (CE-WAF; oil + Corexit + seawater); (4) Diluted CE-WAF (1:10 dilution). Initial mesocosm volumes were 79L. Prior to experiment initiation, phytoplankton were collected from coastal Galveston, TX waters and added to each tank to stimulate interactions between phytoplankton, oil, and Corexit. Starting at time-point zero and every 12 hours thereafter, water samples were collected from each mesocosm in clean, opaque, Nalgene bottles. For cell and aggregate counts, 10mL of water was collected from each mesocosm and fixed with 2% formalin. Fixed samples were stained with DAPI (45uM final concentration), filtered onto 25mm, 0.2um black polycarbonate filters, and counted directly via fluorescent microscopy. For beta-galactosidase measurements, parallel samples of 10um-filtered and unfiltered water were amended with 4-methylumbelliferyl beta-D-galactopyranoside. Florescence was quantified using a Tecan Spark 10M multimode microplate reader.