Relative importance of bacteria, microalgae and yeast for growth of the sponge Halichondria melanadocia (De Laubenfels, 1936): A laboratory study

Bacteria, microalgae and yeast less than 10 μm in size are the primary food source of sponges but their relative contribution to somatic growth is poorly understood. In a laboratory study, the sponge Halichondria melanadocia was fed for 6 weeks a diet consisting solely of four bacterial strains, or a mixed diet consisting of bacteria, microalgae and yeast. Both diets were fed at three concentrations, based on the natural concentration (NC) of particles available to sponges: 1/5, 1 and 5NC. Mean final size of H. melanadocia was 40% greater on a mixed diet than on the bacteria diet, probably because of the greater supply of carbon and other essential nutrients in microalgae and yeast. Cell concentration also significantly affected the growth of H. melanadocia, with greatest growth for sponges fed at the highest cell concentration. The estimated carbon requirement for H. melanadocia to meet metabolic costs was 0.356 mg C l^− 1 or 103 μg C h^− 1 gDW^− 1. Many H. melanadocia appeared to be optimizing their surface area for food uptake.