Relationship of epipelic algae populations and shrimp culture at Corpus Christi, Texas

Abstract

The unchecked growth of diatoms and cyanobacteria is a major concern in shrimp mariculture. Diatom blooms are often stimulateded, to increase productivity in ponds; at the same time, mariculturists may try to control cyanobacteria blooms because of toxic effects. Use of Solricin 235 and Simazine to control cyanobacterial growth in shrimp (Penaeus vannamei) culture ponds was evaluated. Solricin treatment significantly reduced cyanobacterial density (as measured by C-phycoerythrin concentration). Simazine treatment did not reduce cyanobacterial densities. Neither treatment significantly affected physicochemical parameters (temperature, dissolved oxygen, and pH), nutrient (nitrogen, phosphorus, and silicate) dynamics, chlorophyll concentrations or shrimp survival and growth. Natural ingestion of diatoms by P. vannamei postlarvae in relation to supplementary feed was evaluated. Diatom genera, cell condition (full and empty), and number were determined in shrimp guts and fecal pellets. For the first time it was demostrated that P. vannamei postlarvae grazed actively on epipelic diatoms, especially before feed was applied to the system. Postlarvae showed selectivity in diatom grazing and utilization, with Nitzschia and Navicula being the principal taxa utilized. The impact of shrimp postlarval culture on the temporal dynamics of planktonic and epipelic diatom assemblages in raceways was evaluated through grazing exclosure studies. Diatom communities were dominated by the epipsammic species Synedraulna, and four epipelic species Navicuia stundlii. Amphora coffeaeformis. Nitzschia socialis, and Nitzschia #1. The four epipelic species were selectively grazed by shrimp postlarvae. Epipelic diatoms may contribute significantly to postlarval shrimp production. Further research is needed on the interactions of shrimp postlarvae and A. coffeaeform is A this epipelic diatom is a domoic acid- producing form that may cause shrimp mortality.