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UBC Theses and Dissertations

The fate of salp blooms : decomposition and sinking of salp carcasses Orlov, Polina


Gelatinous zooplankton (GZ) biomass is an important, yet often overlooked, vector of particulate organic matter (POM) export in the ocean and a nutritional prey source for the mesopelagic and benthic environments. To better quantify the potential impact of their blooms on surrounding biogeochemistry and food webs, we performed decomposition and sinking experiments under two different temperature regimes, 6 and 12 °C using 260 Salpa aspera, sampled in the Northeast Pacific during May 2021. Salps were suspended in large seawater tanks with continuous water filtration systems and kept in the dark for a maximum of 30 days. Decay was exponential and occurred ~1.5 times faster in the warmer conditions. Comparison of GZ across literature studies supported the strong influence of temperature on their decomposition (Q₁₀ = 3.46) and revealed S. aspera to decay at a lower rate compared to most other GZ taxa. Carcass sinking rates were higher than previously reported for this species but slowed with prolonged decay. Biochemical (proteins, carbohydrates, lipids) and elemental (C: carbon, N: nitrogen) composition was determined for samples at various stages of degradation. Energetic content, estimated from total organics using published conversions, was typical of GZ but notably lower than common crustacean zooplankton. The high water (~97%) and low organic content of 27.8 ± 7.1 percent of dry weight (% DW) was typical of other thaliaceans. S. aspera carcasses were relatively rich in C (15.6 ± 1.66% DW) and somewhat low in N (2.42 ± 0.53% DW). Carbohydrates accounted for the majority of total organics (45.3%), followed by lipids (42.1%) and protein (13.3%). However, possible under-detection of protein could have served to overestimate lipid content and skew macromolecular ratios. The high C:N ratio (6.61 ± 1.14) of S. aspera, in comparison with a typical ratio of <5 for many thaliaceans, suggests their carcasses to be valuable sources of C flux beyond the euphotic zone. Changes in carcass biochemical and elemental composition during decay are described with potential implications for nutrient availability for deep ocean communities.

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