Award: OCE-1756465

Salps, forming episodic blooms, are gelatinous pelagic colonial organisms feeding on micron-sized prey much smaller than themselves. We used a combination of methods to determine salp impacts on Antarctic ecosystems near New Zealand. Methods included direct capture of living salps followed by grazing experiments where they were offered defined prey types, preserving captured salps and examining their gut contents, and characterizing the ambient ecosystem in terms of the organims present and their growth and mortality rates. We were able to examine ambient conditions in several nearby ecosystems, including a coastal subantarctic system where prey were dominated by diatoms, and several offshore ecosystems dominated by pico and nano-phytoplankton: we then compared these systems with and without the presence of salps. Salps form episodic blooms, with colonies of individuals, which greatly increase carbon flux to the ocean interior, resulting in significant biogeochemical impacts on the ecosystems in which they occur. Salps were viewed as trophic sinks rather than links in oceanic ecosystems, however they are consumed by higher trophic level organisms like fish and some crustaceans, so are more properly viewed as short-circuiting food webs by transferring smaller prey to much larger consumers. In this research, we established that salps are competitors with heterotrophic protists, the dominant grazers of microbial plankton, for prey, and are highly likely important consumers of these heterotrophic protists as well. The salp species examined, in particular Salpa thompsonii, consume nano-phytoplankton (2-20 micro-meter) cells, as well as larger prey such as ciliates. A new method was also developed that allows simultaneous enumeration of phytoplankton and non-pigmented bacteria on appropriate instrumentation that can be taken to sea, to obtain near-real time results on microbial population abundances. Last Modified: 12/02/2022 Submitted by: Karen E Selph