Nekton Ecology in Estuaries
A day in the field studying the fishes, shrimps, crabs, and squids of North Inlet Estuary, South Carolina
Welcome to North Inlet Estuary in South Carolina!
This guided tour serves as an introduction to the study of nekton, aquatic animals that move through water without relying on currents. You might know them instead as fishes, shrimps, crabs, and squid.
We will highlight some of the different habitats used by these animals within North Inlet Estuary. We will also explore a few of the ways scientists collect them to study.
Pack your sunscreen, field lunch and waders, because you'll be spending the day exploring the field while learning about nekton ecology from real scientists! Be sure to click through the videos and images in the media gallery at each location to get the full experience of the virtual field. Double-click on the images to get a fullscreen view.
North Inlet Estuary, Hobcaw Barony, and the Baruch Marine Field Laboratory
North Inlet Estuary is located on the northern South Carolina coast and sits on the edge of Hobcaw Barony , a privately owned research reserve nearly 16,000 acres large. North Inlet Estuary and Hobcaw Barony are also home to the University of South Carolina’s Baruch Marine Field Laboratory and the North-Inlet Winyah Bay National Estuarine Research Reserve .
Salt marshes and tidal creeks make up most of North Inlet estuary. A salt marsh is a productive ecosystem that is typically dominated by a single grass species, smooth cordgrass (Spartina alterniflora) in the southeastern US. Various intertidal (shallow) and subtidal (deep) creeks wind their way through the salt marshes of the North Inlet estuary. These creeks remain quite salty throughout the year, because the estuary is heavily influenced by ocean tides.
Today, we’ll join scientists from the field lab as they continue research that began nearly 40 years ago!
Why study nekton ecology?
Before we go into the field, it is important to understand what estuarine nekton are, and why we study them.
Estuarine nekton are the nekton that live in estuaries for at least part of their lives. Some of these animals are resident, spending their entire life in the estuary. Others are transient, spending only a portion of their life cycle in the estuary.
Many transient species use the estuary as a nursery during part of their first year of life, taking advantage of the food and shelter provided by the salt marshes and tidal creeks. Throughout their life cycle, both resident and transient nekton are important members of the estuarine food web. As adults, many transient return to the ocean where they are harvested by people for food, for example, shrimp.
Nekton Sampling Equipment
We'll start our field day at Baruch Marine Field Laboratory to collect our sampling equipment. The type of equipment we need depends on our sampling location and design. Today we'll use trawls and seines to sample the nekton species in different locations.
There are many types of trawls, but today we're using an otter trawl. We'll drag this large, funnel-shaped net behind our boat along the bottom of two subtidal creeks. Click here to watch a scientist from the marine lab give a detailed overview of the otter trawl we'll use in the field!
Seines (also called beach seines or haul seines) are mesh nets usually dragged through the water by hand. The bottom edge of the seine is held down by weights, and the top is buoyed by floats. Seines often have poles on either end that can be used to pull the net through the water and collect various nekton. Click here for an overview of the seine we'll use here.
Now that we have our equipment, we'll head out to the field! Check out the views as we drive to our first sampling site - pay attention to the different habitats we trailer through!
Trawl Sampling
Our first sampling location is Bread and Butter Creek. Bread and Butter Creek is a subtidal creek - that is, even at low tide, there is enough water remaining that we can take our boat in without getting stuck. The bottom of the creek (below the water’s surface) is soft and muddy.
We'll repeat this process over again at Clambank Creek - also a subtidal creek, and is about the same size as Bread and Butter. Unlike Bread and Butter, however, the bottom of the creek is firm and covered with shell and rubble.
We collected a diverse group of nekton species, including white shrimp, inshore lizardfish, and two types of anchovies. Each nekton species has a specific period of estuarine use, these are species that commonly occur in the estuary in late fall and early winter.
Scroll through the images in the gallery to see some of the nekton we collected and watch this video to see trawl sampling from all angles!
Seine Sampling
Next stop is Oyster Landing Creek. The scientists from our lab have been collecting nekton samples with seines here for nearly 40 years!
Because Oyster Landing is an intertidal creek (much shallower than the earlier creeks we sampled), we’ll use a seine to collect our samples. The bottom of the creek is a mix of soft mud and firm sand.
Check out this method from all angles by watching this video and scrolling through the media gallery. Then let's take our nekton samples from the seine back to the lab to collect some more data!
Processing Samples at the Seawater Lab
Back in the lab, we'll sort, count, and measure our samples. We'll take a closer look at the number of different species of nekton we collected (species richness), the number of individuals of each species (species abundance), and record the length of each individual. The marine lab scientists will use these data to investigate if changes in the environment, such as water temperature or salinity, are driving changes in the occurrence, abundance, and size of different nekton species found in North Inlet Estuary.
Watch this video to see researchers process our samples at the lab. Some highlight species we caught include spot , striped mullet , and white shrimp . These species are the most abundant transient nekton collected via seine in North Inlet Estuary. Spot and striped mullet are among the earliest transients to show up in our seines, and are most abundant in spring. White shrimp, on the other hand, typically don’t arrive until summer. As adults, all three species are harvested both recreationally and commercially. Spot are a favorite fish of many anglers to catch with a rod and reel, mullet are harvested for their eggs, and shrimp are one of the most valuable fisheries in South Carolina.
Check out this guide for identifying nekton species in North Inlet Estuary.
Deeper Discoveries in Nekton Ecology
We've spent the day with scientists in the field and gotten to see some lab work, too! Are you interested in seeing the data you helped collect? Do you think our results would look different if we had used a different-sized trawl or seine? How would our samples look if we used a larger or smaller mesh?
Click here for access to the data , accompanying exercise , and additional resources to dive deeper into nekton ecology!
Acknowledgments
This guided tour was developed by the Baruch Marine Field Laboratory at University of South Carolina, University of Georgia Marine Institute at Sapelo Island , and Bethune-Cookman University . This collaboration was funded by the National Science Foundation ( award #2037372 ) to develop virtual products that support marine and estuarine field science and mitigate education disruptions from COVID-19.