The ability of organisms to combine autotrophy and heterotrophy gives rise to one of the most successful nutritional strategies on Earth: mixotrophy. Sponges are integral members of shallow-water ecosystems and many host photosynthetic symbionts, but studies on mixotrophic sponges have focused primarily on species residing in high-light environments. Here, we quantify the contribution of photoautotrophy to the respiratory demand and total carbon diet of the sponge Chondrilla caribensis, which hosts symbiotic cyanobacteria and lives in low-light environments. Although the sponge is net heterotrophic at 20 m water depth, photosynthetically fixed carbon potentially provides up to 52% of the holobiont’s respiratory demand. When considering the total mixotrophic diet, photoautotrophy contributed an estimated 7% to total daily carbon uptake. Visualization of inorganic ¹³C- and ¹⁵N-incorporation using nanoscale secondary ion mass spectrometry (NanoSIMS) at the single-cell level confirmed that a portion of nutrients assimilated by the prokaryotic community was translocated to host cells. Photoautotrophy can thus provide an important supplemental source of carbon for sponges, even in low-light habitats. This trophic plasticity may represent a widespread strategy for net heterotrophic sponges hosting photosymbionts, enabling the host to buffer against periods of nutritional stress.

生物体结合自养和异养的能力产生了地球上最成功的营养策略之一：混合营养。海绵是浅水生态系统和许多宿主光合共生体的组成部分，但对混合营养海绵的研究主要集中在高光环境中的物种。在这里，我们量化了光合自养对海绵Chondrilla caribensis的呼吸需求和总碳饮食的贡献，它拥有共生蓝藻，生活在弱光环境中。虽然海绵在 20 m 水深处是净异养的，但光合作用固定的碳可能提供高达 52% 的全息生物呼吸需求。在考虑总的混合营养饮食时，光合自养占每日总碳吸收量的 7%。无机¹³ C- 和^{15的可视化}在单细胞水平上使用纳米级二次离子质谱 (NanoSIMS) 进行 N-掺入，证实原核生物群落吸收的一部分营养物质被转移到宿主细胞中。因此，即使在光线不足的栖息地，光合自养也可以为海绵提供重要的补充碳源。这种营养可塑性可能代表了承载光共生体的净异养海绵的广泛策略，使宿主能够缓冲营养压力时期。