Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This dataset includes CTD data from 23 casts in water depth of 25 to 40 meters from three cruises in May, August and December 2015 on the RV/Savannah to the South Atlantic Bight. In addition to salinity, conductivity, temperature and depth, also reported are light, fluorescence, oxygen saturation and nitrogen saturation.

CTD sampling methodology is standardized by the marine technician and crew of the UNOLS vessel R/V Savannah. Down-cast and up-cast winch speed is maintained at 25 m/min unless sea conditions require alteration. The CTD is deployed to 2 to 1.5m above the surface of the bottom to minimize benthic influences on the water samples and the possibility of damaging the instruments.  All water samples are collected in Niskin bottles are retrieved on the upcast after allowing the CTD to equilibrate at the desired depth for at least 30 seconds. Data from the CTD carousel is archived to an onboard Server running Windows Server 2012 at 4 hz as hex files with header and bottle files.  The software used to control the CTD is Seaterm and Seasave. 

Data quality control is monitored in real time during each cast by comparing surface salinity and temperature to the thermosalinograph data. Sensors are maintained to manufacture specifications and calibrated as specified by the manufacturer or as needed if anomaly’s or drift is observed. The precision and accuracy of the data is dependent on the limitation of each individual sensor and the rate of change in depth of the CTD through the water column vs. the frequency of data collection. For a list of the sensors used: deployed sensors. Data is provided to the chief scientist from the ship as raw data at the end of each research deployment.

Raw CTD data was accessed using the SBE Data Processing software (ver 7.23.2, Sea-Bird Electronics, Inc.). The data conversion feature of the software was used to convert the raw hex data to an ascii format. For each CTD cast, data was converted only from the scans that were made during the down casts of the CTD deployments.  Scans were stored as converted data files (.cnv). A total of 22 variables were converted from the CTD scans and included location, time, depth, temperature, salinity, and conductivity parameters. Microsoft Excel was used to archive the converted data. No further data processing was performed on the converted files.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- added columns for cruise id, cast, lat_start, lon_start. date, time obtained from CTD cast headers

Project description from NSF award abstract:
Gelatinous (soft-bodied) zooplankton can play a crucial role in food webs and in cycling of materials in the world's oceans, and it has been suggested that they may become even more important in the future. However, because they are so difficult to study, gelatinous species remain poorly understood. This is especially true for smaller filter feeding gelatinous animals such as pelagic tunicates (salps, larvaceans, and doliolids). For example, it remains unclear what and how much these abundant filter feeders eat in nature and who eats them. This project will address this large and significant knowledge gap by using a combination of new and traditional methods to investigate the diet of the gelatinous pelagic tunicate Dolioletti gegenbauri, a species common on productive continental shelves such as the South Atlantic Bight. This project will also help train the next generation of ocean scientists to be competent in classical biology, modern molecular biology, and ecosystem modeling. Training will also focus on increasing representation of African Americans in the future science, technology, engineering, and math (STEM) workforce.

This study will provide the first quantitative estimates of the in situ diet of a key continental shelf gelatinous zooplankton species, the doliolid Dolioletta gegenbauri. Large blooms of doliolids have the potential to control the trophic structure of shelf pelagic ecosystems by shunting primary production to the microbial food web and by limiting copepod production via the consumption of their eggs. The long-term objective is to understand the ecological role and significance of doliolids in continental shelf pelagic ecosystems, specifically the underlying processes that lead to their high level of spatial and temporal patchiness. The basic questions to be addressed here include: What do doliolids eat, in situ, at different life stages? Are early life stages of larger metazoans important components of their diets? Do doliolids act as trophic cascade agents promoting primary production and phytoplankton diversity? Because of methodological challenges, there have not yet been definitive studies addressing these fundamental questions. In this project, the investigators will conduct field-based studies that will combine state-of-the art molecular techniques with more traditional methods in zooplankton ecology to answer questions about trophic interactions. Monthly oceanographic expeditions in the South Atlantic Bight will allow the research team to study wild doliolids at different time points in their life cycle and under different plankton bloom conditions. Application of recently developed molecular diagnostic assays will enable the quantitative description of the diversity and quantity of prey consumed, unbiased by experimental manipulation. Additional experimental and theoretical modeling will allow the investigators to link these data with larger ecological significance and scale.