Research ProjectLong-Term Studies of a Chesapeake Tributary

  • fish weir

    SERC fish weir, which temporarily catches fish for population surveys

Research Topics

Project Goal

The goal of this project is to gain insight into population and community dynamics of fish and macro-invertebrates in a representative subestuary of the Chesapeake Bay.

Description

weir

Spanning more than three decades, our ongoing, long-term studies describe the population dynamics and community structure of fish and invertebrates throughout the Rhode River study site, Maryland. This research tracks seasonal, annual, and decadal variation in species composition and abundance of fish and macro-invertebrates using multiple sampling methods. The long-term descriptive data, in combination with our experimental studies, provide a unique window into estuarine population dynamics and community structure. These data, along with other long-term research at SERC, enable the study of community responses to changing weather, seasons, climate, water quality, fisheries, predator-prey dynamics, land use and drivers of ecosystem change. These studies also provide data supporting the SERC Core Site of the Tennenbaum Marine Observatory Network (TMON) and MarineGEO.

The combination of long-term sampling programs gives us a larger view of how an estuarine ecosystem functions. With our long-term data, we can learn much about the life history of species, including their habitat partitioning, their reproduction and recruitment patterns and requirements, their trophic (feeding/energy) levels, and the effect of environmental changes on their behavior. Changes in environmental conditions and their subsequent effects on species may not become evident for several years, and our long-term sampling program helps to clarify often highly variable population trends. Follow the links to the right for detailed information on our five long-term studies.

Project Goal

The goal of this project is to determine species composition, habitat use, and changes over time for organisms that live in the various types of sediment in the Rhode River.

Infaunal Benthic Invertebrate Organisms

"Infaunal" refers to aquatic animals that live in the substrate of a body of water and which are especially common in soft sediments.  "Benthic" refers to anything occurring at or in the bottom of a body of water. "Infauna" are the creatures tht live in the sediments. 

In the Chesapeake Bay, benthic infauna such as clams, snails, polychaetes, flatworms, and small crustaceans, are abundant and crucial to a healthy ecosystem. 

They help to filter water, recycle organic matter, and are important forage (prey) for fish, reptiles, amphibians, and larger crustaceans (such as blue crabs and horseshoe crabs). Many of the organisms found in the benthos are suspension feeders and deposit feeders. Suspension feeders, also known as "filter feeders", process particles floating in the water column. Deposit feeders consume organic matter lying on or in the sediment.

Seasonal fluctuations of species and their abundances can be driven by recruitment (addition of individuals to a population), predation, poor habitat conditions (such as low dissolved oxygen), human impacts like shoreline hardening and meteorological events like hurricanes.

Benthic Infauna in the Rhode River

The Rhode River is a representative tributary of the Chesapeake Bay. Macroinvertebrates, such as crustaceans, worms, and mollusks comprise the Rhode River's soft bottom community. They live in or on the bottom of the river in mud, sand, clay, marsh detritus, leaf litter, or combinations of these sediment types. Infaunal species are responsible for significant interactions within the benthic environment which in turn, impact the biodiversity and functional processes within the entire estuarine ecosystem. Long-term data on these species gives us 1) information on the species composition and fluctuating abundances of these organisms over time and in differing habitats and 2) a better understanding of the processes that regulate their community and population dynamics. Such dynamics include predator-prey interactions, recruitment, habitat use and responses to environmental factors such as salinity, temperature, and dissolved oxygen. Integrating benthic infaunal data with our other long-term sampling programs provides insight into processes structuring ecosystem interactions within the Rhode River

As part of a complex food web, infaunal communities are composed of both predators and prey. Trophic level (positions in the food web) of these species may change during its life cycles as the organism grows and their size, feeding mechanism, and nutritional requirements change. 

Processes such as bioturbation (sediment disturbance) are caused by infaunal burrowing and feeding, especially by deposit feeder species such as worms or certain species of clams. Bioturbation can, among other things, affect oxygen levels in sediments, cause redistribution and decomposition of organic matter, and alter the amount of suspended particles in the water. This, in turn, may negatively or positively affect water quality, refuge patterns, and feeding behavior of organisms.

Sampling Benthos in the Rhode River

Our lab has been tracking variation of benthic species composition and abundance with seasonal sampling since 1979. We have five sites in the Rhode River where we sample for benthic organisms. Two sites have sand substrate and three have mud. We take seven core samples per site. Samples are taken four to eight times a year. Sediment core samples are taken with a pipe core sampling device that is either attached to the end of a pole (mud stations) or operated by a SCUBA diver (sand stations). The pipe core collects a core sample that is 35 cm deep. All core samples are then sieved on a 500 μm mesh screen to remove smaller particles of the sand/mud. Animals >500 μm are preserved and stained to be processed later in the lab.  

In the lab, the organisms are sorted, counted, and identified to the species level under a dissecting microscope. Mollusks are measured. All data are recorded and entered into a database for analysis.

Sixty benthic species have been identified in the Rhode River's soft bottom sediment of sand and mud.

tether
Tethering gear

Project Goal

The goal of this project is to better understand the predator-prey interactions in shallow nearshore habitats of the Rhode River. 

Predation in the Nearshore Zone

Nearshore areas provide refuge, food, and nursery grounds for small fish and crustaceans. However, these areas can also have many predators such as blue crabs, fish, and wading birds. Small fish and crustaceans are important forage (prey) for the larger individuals that prey on them.

Our lab has been studying these predator-prey interactions in a representative location of nearshore habitat, Canning House Bay, in the Rhode River using the experimental technique of tethering since 1989. The data collected helps us to determine who the important predators are and how the risk of predation changes from year to year. 

Our study species are: Mummichogs (Fundulus heteroclitus) and juvenile blue crabs (Callinectes sapidus). We also collaborate on a study of grass shrimp (Palaemonetes pugio) predation with the Marine Invasion Ecology Lab.

Though there are many different kinds of juvenile and small fish that can be found in the nearshore area, we use mummichogs as a representative species. Mummichogs are a smaller fish that are abundant and hearty, making them a good species to use in our tethering study.

Juvenile blue crabs are most abundant in nursery habitats in Chesapeake Bay tributaries such as the Rhode River. These nursery areas are full of the clams, fish, worms, and small crustaceans that juveniles crabs like to eat. 

Tethering

Our tethering studies are conducted over three days/month every June, July, and August. Tethering involves securing a small fish or juvenile crab (30-70 mm carapace) to a piece of vinyl coated wire that is attached to a 6" nail spike and a float. At a water depth of 40 cm, the spike is pushed into the bottom sediment and left to sit. After specific intervals, we use each tether's marker float to pull up the crab or fish to see the status of the individual. Fish are checked after two 15-minute periods and then after 30-minutes periods until they are gone. Crabs are checked after 24 hours.

The small fish are also fashioned with a small hook dangling from a monofilament loop that is wrapped around the lower jaw, in order to attempt to catch whatever predator decides to eat the small fish -- similar to angling! This helps us learn more about what species of predator are in the area and how predation rates vary annually.

What does this data tell us?

These experiments give us some insight into the foraging behavior of predators that eat small fish and crustaceans in the nearshore area. It also gives us an idea of of what sort of predation pressure exists at these locations and what predators are there.  

What have we found?

The primary predators of juvenile blue crabs in the Rhode River are adult blue crabs. As juvenile crabs increase in size, they are less likely to be eaten. The likelihood that juveniles will be eaten increases in years when the population of adult blue crabs is large.  This very important finding is the result of our studying predation of juvenile blue crabs over the long term. We are able to compare our results with adult crab abundance data from the 25-year Bay-wide Blue Crab Winter Dredge Survey (WDS) conducted by Maryland Department of Natural Resources and the Virginia Institute of Marine Science.  

seinging
Volunteers seining

Project Goal

The goal of this project is to better understand the community structure and dynamics of the fish and crustaceans that live in shallow fringing habitats of the Rhode River. 

Nearshore Communities of Fish and Crustaceans

Shallow nearshore zones provide refuge, food, and nursery grounds for small fish and crustaceans. The nearshore area, with its shallow depths and variable habitats, can play a vital role in the survival, nurturing and growth of its juvenile fish and crustacean inhabitants and are therefore a vital part of coastal ecosystems. Our research has shown that small fish, juvenile blue crabs and grass shrimp use the shallow depths as a refuge from larger predators, as nursery grounds for larval fish and small crustaceans and as a resource for food. 

 

Sampling in the Rhode River

Since 1980, a long-term study of the community of fish and crustaceans in the nearshore zone of the Rhode River has been one of the major sampling components of the lab. The nearshore zone within the Rhode River is generally shallow, less than one meter, with low energy tidal flow. Astronomic tidal amplitude (tides caused by the moon) is about 0.5 meters with occasional wind-driven tidal fluctuation up to 2 meters. Annual seining surveys of the nearshore zone are conducted at different sites throughout the Rhode River. Each summer, surveys of the nearshore zone are conducted at 13 different sites throughout the Rhode River. Survey sites include the river mouth, small tributaries within the river, shorelines along the mainstem, and the headwaters of the river in Muddy Creek. 

Shoreline compositions vary and include sandy beach, coarse wood debris, emergent vegetation, marsh, and forested shoreline. The sediments within each seine site are also variable and may include mud, sand, marsh detritus, clay, or a mix of each. We use a 16-meter long seine net of 7 mm mesh for sampling. Each seine samples 33 meters of shoreline with one person stationed on the shoreline and one 10 meters from shore. Two adjacent seines are pulled at each of the 13 stations. All organisms that are caught in the net are identified, counted, and released unharmed back into the water. A subset of each species of organism is measured. By sampling the same areas annually, we can determine spatial and temporal changes in species composition, population size structure, and abundance.

Results to Date     

Fifty species of fish and two crustaceans have been identified since the study originated in 1980. Nearly half of these species are rarely collected and in only one or two stations consistently. The five most abundant species are mummichog, (Fundulus heteroclitus), striped killifish  (Fundulus majalis)bay anchovy, (Anchoa mitchelli), spot (Leiostomus xanthurus), and Atlantic menhaden (Brevoortia tyrannus). 

trawling
SERC team executing a trawl survey

Project Goal

The goal of this project is to understand how fish and crustaceans use the deeper waters of the Rhode River and adjacent upper Chesapeake Bay.  

 

Epibenthic Fish and Crustaceans

One of the primary interests of the Fish and Invertebrate Ecology Lab are long-term, annual, and seasonal changes in population and community dynamics of epibenthic fish and crustaceans. Epibenthic refers to organisms that live on or just above the bottom sediments in a body of water. These organisms, many of which support commercial and recreational fisheries, tend to forage on the creatures that live in or on the sediments. We sample epibenthic species using a trawl survey that began in 1981.

The Rhode River

The Rhode River is an embayment of the Chesapeake Bay located on the western shore of Maryland. The primary source of freshwater is Muddy Creek (headwaters of the Rhode River); the Rhode shares a common mouth with the West River where both connect to the mainstem of Chesapeake Bay. The Rhode River has an area of 550 hectares (1 hectare=2.5 acres) and an average depth of 2 meters, with salinity ranging from nearly freshwater (0-1) in Muddy Creek during the spring to more than 20 (half that of full strength seawater) at the mouth of the Rhode and West rivers during the fall. (Gallegos, CL, TE Jordan, and DL correll.   1992. Limnology and Oceanography, Vol. 37:813-828).

Trawl Surveys

Our trawl surveys use a 16 ft. semi-balloon otter trawl square-mesh net, commonly referred to as an "Otter Trawl", which is much like the shrimp nets used by commercial fishermen in the South Atlantic and Gulf of Mexico. At the head of the net are two trawl doors that serve to weigh the net down, keeping it on the bottom, and to hold the net open, so it "fishes" properly. A tickle chain is next in line, and is attached to the trawl doors, stretching between them. The tickle chain serves to force animals lying on the bottom or buried just beneath the surface up off of the bottom just a little bit so the net will catch them as it is pulled by. The net, which is also attached to the trawl doors, stretches 16 feet from one side of its mouth to the other. The bottom half of the mouth is lined with lead weights that force the net to skim along the surface of the river sediment, while the top half is lined with floats, so the net mouth remains open during trawling. As animals are captured by the net they are funneled down to the "cod end", which is square-mesh netting of a smaller diameter than the rest of the net and is securely tied-off at the end. 

The otter trawl is deployed for 10-minute intervals, and pulled for a distance of 900 meters, usually behind the R/V SERC 41. When the net is pulled into the boat, the cod end is untied, and the catch is poured into waiting bins of water. The catch is then separated into fish and crabs. The first twenty fish of each species is measured. After being measured, each fish is released alive back into the river. Once twenty fish within a species have been measured the remainder of that species is counted and released. Data are collected for all captured blue crabs, including: carapace width (distance from one carapace point to the other), sex (either male, mature female, pre-pubescent female, or immature female), autonomy (leg loss), and molt stage. All blue crabs are released once these data have been collected. Trawl samples are collected three times a month, from March through December, from one station in the Chesapeake Bay, two stations at the mouth of the Rhode River and one station at the head of the river.

What have we found?

The accumulation of thirty plus years of otter trawl data has resulted in the collection of 61 different species of fish and crabs. In particular, bay anchovy, spot, white perch, Atlantic croaker, hogchoker, and blue crabs account for nearly 87% of the catch. The other 55 species are encountered less frequently.

These data are providing a unique overview of the population dynamics and community structure of the Rhode River subestuary. Trawl data can be used to examine long-term as well as annual and seasonal variation in community structure of the Rhode River. In addition, trawl data and short-term experiments provide insight regarding predator/prey interactions within the system, reproductive strategies and molting behavior of blue crabs, and habitat partitioning of fish and crabs.

weir
Fish weir in Rhode River

Project Goal

The goal of this project is to understand the value of small tidal marsh creeks for fish, crustaceans and other species. 

Muddy Creek: a Small Tributary of the Rhode River

The Rhode River System is a small tributary of the Rhode River located approximately 200 km (120 miles) north of the mouth of the Chesapeake Bay in Edgewater, Maryland. Salinity in the creek ranges from 0.5 (nearly freshwater) to 18 (half the salinity of the ocean), a range characteristic of the oligohaline/mesohaline zones of the estuary. Salinity fluctuations are primarily dependent upon local precipitation and major flood events of the Susquehanna River. The creek is fringed by Spartina-and Phragmites-dominted marsh, hardwood forest, adjacent agriculture, private development, and the sediments are primarily fine sand and mud. The Rhode River experiences semi-diurnal tides with an amplitude of approximately 1 meter. Water temperatures cycle seasonally between 0°Celsius in January when the creek sometimes freezes over, and 30-33°Celsiuc in July.

Small tidal marsh creeks such as Muddy Creek provide habitat for many species of fish and invertebrates. These habitats are used for spawning by white perch, as refuge from predators for male blue crabs molting to maturity, and nursery grounds for a number of fish, reptiles, and amphibians. Our lab has been examining the population dynamics and community structure of such organisms in Muddy Creek since 1983. We use a weir in order to see what is using the creek.  

The Fish Weir

The weir is a series of v-shaped fences that span the mouth of Muddy Creek as it enters the Rhode River. The fences help direct organisms moving along the creek into nets. Fish, invertebrates, and other organisms are funneled into two openings, one facing upstream, and the other facing downstream. Once each week, nets are deployed at the two openings for a period of 24 hours. Organisms traveling both upstream and downstream are thus collected during a full tidal cycle and day-night cycle. All captured individuals are identified to the species level and enumerated while a subset of 20/species is measured. When the nets are not deployed, a gate located in the center of the weir is opened to allow fish and crabs (and kayakers) to pass freely.

weir diagram
Fish weir structure

 

What's Using Muddy Creek?

Since 1983, 133 species of fish, invertebrates, amphibians, reptiles, birds (ducks) and mammals have been collected by the weir. Most species occur at relatively low abundance. However, five species of fish account for over 92% of the total catch: mummichog (Fundulus heteroclitus), Atlantic menhaden (Brevoortial tyrannus), Atlantic silverside (Menidia menidia), sheepshead minnow, and spot (Leiostomus xanthurus).

Other frequently encountered species include white perch (Morone americana), blue crab (Callinectes sapidus), striped killifish (Fundulus majalis), bay anchovy (Anchoa mitchilli), striped bass (Morone saxatilis), pumpkinseed (Lepomis gibbosus), green sunfish (Lepomis cyanellus), common carp (Cyprinus carpio), brown bullhead (Ameiurus nebulosus) and gizzard shad (Dorosoma cepedianum).