DOI: 10.5061/dryad.4qrfj6qft
title: Diversity, seasonal abundance, and environmental drivers of chaetognath populations in North Inlet Estuary, South Carolina, USA

description: Chaetognaths (Phylum: Chaetognatha) are one of the most abundant phyla of
 zooplankton worldwide and play an important role in marine trophic
 interactions. Although the role of chaetognaths in global ecosystems is
 well understood, the spatial variation and environmental drivers of
 estuarine chaetognath populations is poorly understood. To provide the
 first known record of chaetognath species composition in a coastal estuary
 in the south-eastern USA, chaetognaths were identified and quantified from
 zooplankton samples collected on a monthly basis in 2019 and 2020 from
 North Inlet Estuary in South Carolina. Parasagitta tenuis was the most
 abundant species of the five found, making up 33% of total abundance. The
 egg presence of these chaetognaths was further analyzed to gauge
 reproductive cycles. Abundance and egg presence were compared with surface
 and bottom measurements of temperature, salinity, and dissolved oxygen
 levels to determine the driving abiotic factors behind chaetognath’s
 seasonal variability and reproductive cycles. Temperature, salinity, and
 dissolved oxygen all had low (r &lt; ± 0.29), non-significant
 correlations with abundance. Chaetognath egg production was most
 significantly associated with dissolved oxygen (p &lt; 0.001) and
 seasonal changes in temperature (p &lt; 0.001). Our initial findings
 indicate the continued abundance of chaetognath in a local estuary is
 dependent on abiotic factors that are strongly influenced by a changing
 climate. 
description: Zooplankton samples were collected during one tow between 1000
 and 14000 hours each month during outgoing mid-tide from November 2019 to
 November 2020. Tows were carried out horizontally, 20 meters from the
 marsh bank, parallel to the shore, and in the direction of the ebbing
 tide. Each tow lasted roughly 5 minutes and covered 200 meters. The tows
 were conducted aboard a boat with an epibenthic sled equipped with a
 365-µm mesh net, a mouth opening of 50 cm wide by 35 cm high, and with a
 General Oceanics flowmeter attached to the net’s mouth. During the tow,
 the net mouth was just above the bottom, ~1.5m below the surface water.
 Surface (~0.5m below surface water) and bottom (~1.5m below surface water)
 salinity, temperature, and dissolved oxygen were measured from an anchored
 boat using a YSI Pro 2030 Sonde. Upon collection,
 samples were immediately preserved in 4% borax-buffered
 formaldehyde-seawater solution.  Samples were then processed in the lab
 using a dissecting microscope at 10-40X magnification. For samples with
 high volumes of animals and small detritus, a Folsom splitter was used to
 subsample. All chaetognaths found were identified to species using Johnson
 and Allen (2012), and subsequently counted and classified by egg presence.
 Egg presence was quantified by the visual presence of eggs. If egg
 presence was visible, then the chaetognath was counted as having eggs
 present, whereas if no eggs were visible, the chaetognath was classified
 as having no eggs present.
description: Microsoft Excel, Google sheet, or Notepad can be used to open the
 data in its .csv format.