Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Sample collection
Salpa fusiformis were collected in March 2023 aboard the R/V Atlantic Explorer (AE2306) during the monthly Bermuda Atlantic Time Series (BATS) cruise (31°50'N, 64°10'W). From 2023-03-19 to 2023-03-26, nighttime tows were conducted using a 1 meter circular Reeve net with 150 µm mesh, a 20 L cod end, and a miniSTAR-ODDI pressure and depth sensor deployed to 200 m depth. Conductivity, Temperature, Density, and Dissolved Oxygen (CTD-DO) casts were conducted at the same location following BATS protocols.

Only pristine salps, actively swimming, filtering, transparent, and free of abrasions, were used. Individuals were held for 12 hours to acclimate and confirm viability before experiments.

Oxygen consumption
Measurements followed Trueblood (2019), using Firesting optodes (PyroScience GmbH, Aachen, Germany), 50 mL gas-tight syringes with 0.2 µm filtered seawater at 21°C (sea surface temperature) or 14°C (temperature at 200 m). Routine metabolic rate (RMR) was used, as spontaneous activity could not be controlled for salps in the respirometer. Background respiration, determined using blank syringes with the same filtered seawater, was subtracted from RMR.

Critical oxygen partial pressure measurement
Critical partial pressure (P_crit) was calculated using the calc_alpha and  the calc_pcrit() function in the “respirometry” package in R (Birk, 2024) based on metabolic rate (R) as a function of PO₂ (Seibel et al., 2021).

All salps were placed in cryo-vials and stored at -80ºC at sea. Samples were thawed; wet and dry weights were measured on shore. After obtaining wet mass, individuals were dried for 72 hrs at 60 ºC and then weighed.

Critical partial pressure (P_crit) was calculated using the calc_alpha and  the calc_pcrit() function in the “respirometry” package in R (Birk et al., 2021) based on metabolic rate (R) as a function of PO₂ (Seibel et al., 2021).           

Statistical analysis
Log-log power regressions of oxygen consumption vs. body mass were conducted using KaleidaGraph (Synergy Software, USA). An ANCOVA (R Foundation, Austria) tested the effect of temperature on RMR, controlling for body mass. The resulting rates were used to establish Q₁₀, the effect of a 10°C change in temperature on metabolic rate.

- Imported data from source files "2023 Bermuda Salp Masses v1.1.csv" and "Bermuda 2023 RMR data v1.1.csv" into the BCO-DMO data system.
- Joined the two data files into a single table
- combined the two columns for resting metabolic rate into a single column (RMR at 14 degrees C, RMR at 21 degrees C --> RMR), then added a new column for temperature
- Removed 'Mass Wet Weight(mg)' column from RMR data because it matched 'Net Wet Weight (mg)' column in Salp Masses data

NSF abstract:
Salps, a type of gelatinous zooplankton, play a significant role in the ocean’s ecosystems, particularly in food webs and carbon cycling. Found throughout the world’s oceans, salps can rapidly bloom, consuming vast amounts of local primary production and contributing substantially to carbon sequestration by transporting carbon to deep ocean layers. This project seeks to understand how changes in temperature and oxygen levels affect the metabolic rates and carbon export capabilities of salps. Understanding these impacts is crucial for accurate ocean carbon cycling models and can help predict future changes in marine ecosystems. This project will advance the field of marine biology by filling significant gaps in our understanding of salp physiology and their role in carbon cycling. It will also support the training and education of underrepresented groups in marine science by integrating undergraduate students, particularly from underrepresented communities, in hands-on research, thereby fostering the next generation of scientists.

Salps (subphylum Urochordata, class Thaliacea) are an often-overlooked lineage of zooplankton that play a major role in carbon sequestration exporting as much as 46% of net primary production via respiration and fecal pellet production out of the euphotic zone. Understanding salp physiology is critically important for building accurate ocean carbon cycling models. Yet, there is very limited data available on salp physiology, and almost none on the effect of temperature and oxygen concentration on rate processes such as routine aerobic metabolic rate (RMR). The proposed research will characterize changes in RMR of both blastozooids and oozooids of the three most dominant species of vertically migrating salps in the Sargasso Sea. Oxygen consumption will be measured at temperatures consistent with the surface and at 200 m depth. Individuals will be held in respirometers and allowed to breathe down oxygen to lowest detectable levels to examine the effect of oxygen partial pressure on RMR. The resulting data will be incorporated into previously published carbon flux models for Sargasso Sea salps to determine what effect temperature and oxygen have on their carbon flux. As ocean temperatures continue to change both temperature and oxygen concentration will become important constraints on aerobic capacity and will affect activity, growth, and reproduction. As these changes occur, a greater understanding of salp metabolic physiology will improve our ability to more accurately predict salp contributions to carbon flux, an area of priority research in the biological pump community. This study will benefit society by providing unprecedented insight into how salps’ metabolism and carbon flux are affected by changes in temperature and oxygen content during their daily vertical migrations as well as the impact that climate change may have on salp physiology.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.