Nutrient fluxes through sponges: biology, budgets, and ecological implications

Marine sponges are able to process a variety of carbon (C), nitrogen (N), phosphorous (P), and silicon (Si) dissolved compounds, in addition to the particulate C, N, and P obtained through regular feeding. While Si fluxes through sponges are exclusively related to the elaboration of their skeleton of biogenic silica, C, N, and P fluxes derive from a complex combination of metabolic processes that include feeding, respiration, egestion, excretion, as well as hosting of large microbial populations within the sponge body. Because of the remarkable abundance of sponges in many benthic marine communities, they have the potential to impact the availability of the compounds they take up and release, affecting the benthic-pelagic coupling and cycling rates of chemical elements that are crucial to determine growth of bacterioplankton and primary producers at the ecosystem level. Unfortunately, our knowledge and understanding of the magnitude of the sponge-meditated nutrient fluxes and their ecological implications depends much on the compound type (i.e. C, N, P, or Si). Herein, we review the available knowledge on the subject with emphasis on recent developments.