University of Alberta, Edmonton, AB, Canada.
Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada.
Sci Rep. 2018 Jan 15;8(1):756. doi: 10.1038/s41598-017-19107-x.
Sponges link the microbial loop with benthic communities by feeding on bacteria. Glass sponge reefs on the continental shelf of western Canada have extremely high grazing rates, consuming seven times more particulate carbon than can be supplied by vertical flux alone. Unlike many sponges, the reef building species Aphrocallistes vastus has no microbial symbionts and removes little dissolved organic carbon. To determine how reef sponges therefore get enough food to sustain such substantial grazing we measured stable carbon and nitrogen isotope signatures of water, sediment and sponge tissues. To ensure samples were temporally associated, we also studied the duration particles were retained in tissues in controlled feeding studies using microscopic beads and C-labeled bacteria. Although fecal pellets were expelled from sponges within 24 hours of feeding, intact bacteria were still found in tissues and sponge tissues retained elevated C levels for at least 14 days. These independent lines of evidence suggest that carbon in reef sponge tissues may reflect food consumed from days to weeks earlier. Stable isotope analysis suggests that heterotrophic bacteria ingested by the sponges comes from a confluence of trophic subsidies: from terrestrial and oceanic sources, and also potentially on sediment-borne bacteria resuspended by tidal currents.
海绵通过摄食细菌将微生物环与底栖群落联系起来。加拿大西部大陆架上的玻璃海绵礁具有极高的摄食率，消耗的颗粒态碳是垂直通量单独供应的七倍以上。与许多海绵不同，造礁种维纳斯盔形海绵(Aphrocallistes vastus)没有微生物共生体，也很少去除溶解有机碳。为了确定造礁海绵如何获得足够的食物来维持如此大量的摄食，我们测量了水、沉积物和海绵组织的稳定碳和氮同位素特征。为了确保样品在时间上是相关的，我们还在使用显微镜珠和 C 标记细菌进行的受控摄食研究中，研究了颗粒在组织中保留的时间。尽管海绵在摄食后 24 小时内就会排出粪便颗粒，但在组织中仍能发现完整的细菌，而且海绵组织中的 C 含量至少在 14 天内保持升高。这些独立的证据表明，海绵组织中的碳可能反映了数天到数周前摄入的食物。稳定同位素分析表明，海绵摄取的异养细菌来自多种营养物质的汇集：来自陆地和海洋的来源，也可能来自被潮流悬浮的沉积物携带的细菌。
