Abstract
Life on Earth has evolved ingenious ways to satisfy its daily nutritional needs. Often these require macro- and micro-organisms to team up, forming intimate collaborations that are very successful and sustainable in nutrient-poor environments, like coral reefs. Photosymbiosis, a partnership between animal hosts and autotrophic microbes fuelled by sunlight, is renowned in Cnidaria (corals), but is even more diverse and complex in the ecologically important Phylum Porifera (sponges). Nevertheless, sponge photosymbiosis and its contribution to benthic productivity of marine ecosystems have been largely overlooked. Sponges are traditionally considered net heterotrophic organisms and their key role as ecosystem engineers in marine food webs has only recently been discovered. Accurate measures of marine productivity in our changing oceans are vital since the oceans provide nutrition to over half of the world’s population and mediate global carbon cycling and sequestration. My PhD research examined photosymbiosis in a keystone coral-excavating sponge, employing novel isotope visualization techniques to illustrate how symbiont and sponge cells exchange nutrients, and was recently highlighted by the New York Times. Here, I propose to leverage these methods to further elucidate the cellular and organismal physiology of photosymbiotic sponges and extrapolate their primary productivity to the ecosystem level on tropical coral reefs. First, I will investigate host-symbiont nutrient communication within various photosymbiotic sponges ranging from cryptic and excavating to open-reef species. I will also examine the physiological communication mechanisms that offer light protection to photosymbionts inside sponges, potentially increasing their productivity and their tolerance to ocean warming. Thereafter, I will scale-up my findings to include the so-far omitted contribution of photosymbiotic sponges to the total primary productivity of a coral reef. From organismal to ecosystem level, my project aims to elucidate an understudied yet important animal-microbe partnership, and to highlight its implications for ecosystem carbon fluxes, productivity and overall functioning.
Netherlands