Symbiodinium cells under microscope (IMAGE) Penn State Caption Coral cells contain dense populations of microalgae that provide them with nutrients (pictured here under a microscope). When faced with hot water temperatures and low iron levels, these symbiotic algae grow poorly and take up trace metals in different ways. Credit Todd LaJeunesse, Penn State Usage Restrictions Credit must be provided. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.