Aquatic Ecosystems - Final NCS

9/27 10 a.m. Sunny & warm

Christina riverfront, Wilmington - DuPont Environmental Education Center

We started our final naturalist certification class, on aquatic ecosystems, in a new location, the DuPont Environmental Education Center, managed by Delaware Nature Society. Lesley runs the education programs at DEEC, and she was our guide for this half of the day, which would end by exploring the aquatic ecosystems at Ashland. She gave us a bit of history and an overview from DEEC’s third floor balcony, overlooking the Russell Peterson Wildlife Refuge that makes up this corner of Delaware’s biggest city.

The building has been open for five years, and the marsh refuge and education center took a decade to become reality. Lesley said former Gov. Russell Peterson, then in his 80s, attended the opening celebration and said one sentence about it being nice to get it done, then immediately turned to his current concern, saying “now we need to talk about climate change.” It seems to me that his attitude, as much as his legacy embodied in the Coastal Zone Preservation Act, make Gov. Peterson a terrific person to have named the marsh after.

The Christina River is known in northern Delaware as a very dirty river. Lesley shared that several decades ago, if workers fell in the water, they were taken ashore, hosed off, and taken to the hospital to get checked out, as a matter of course. As in many cities, the Wilmington riverfront was highly industrial, hosting first tanneries, then railroad car- and ship-building. All these industries left behind a great deal of pollution. But stretching further back, the land had been altered first for agriculture. The Christina was diked to prevent flooding, and the marshland was used to graze livestock.

Starting in the late ’90s, with the neighborhood’s industrial base disappearing, the state began a restoration project in the marsh, regrading the land to create tidal pools and allow the water to flow again. The marsh is now both freshwater and tidal, a combination that is globally rare, another distinguishing feature of Delaware’s natural world of which I was completely unaware before this class. The saltwater line in the Delaware Bay is currently just around the Delaware Memorial Bridge, so not far away, and sea level rise could make the marsh in Wilmington increasingly brackish and eventually a saltwater marsh.

The restoration has been fruitful. Although the soil is still contaminated, the marsh supports more than 200 species, and continuing efforts have reduced the area dominated by invasive phragmites (wetland grasses that grow in dense thickets and were introduced to this country as packing material in the 1800s) from 90 percent to just a third. Lesley mentioned some of the animals they have know live in or use the marsh: beaver, bald eagle, kingfishers. They once found scat from a river otter, and while the habitat should be great for muskrats, they have not yet found any sign of them.

As with the aquatic ecosystems programs with which I am familiar, though, we’re not looking to find aquatic mammals or bird watching. Instead, we grab dip nets and head to a tidal mini-pond that refills with water twice a day, at the high tide. As we sweep the shallow water looking for invertebrates, amphibians and fish, Lesley also goes over the plants nearby. There are both native and invasive plants, beneficial and damaging. We see wild rice, tick-seed sunflower, purple loosestrife, pickerelweed, creeping primrose, and hydrilla. Examples of arrowhead and arum close to each other let us see the differences (while arum leaves are very similar to those of arrowhead, they are not pointed, and the veining in arrowhead leaves are distinctly divided, while the arum’s is not).

Sorting through what we’ve caught in the mini-pond we find sideswimmers, dragonfly nymphs, tadpoles, beetles, minnows and a lunged snail. The tadpoles are green frogs, the common frog in the area, although they have seen southern leopard frogs in the marsh, which surprises me, since I don’t think of Wilmington as being part of the coastal plain. But here in the marsh, below the hills that make up most of the rest of the city, affected by the tides, it makes sense.

Finishing with the mini-pond we move around the marsh boardwalk, down to the tide gauge to check a fish trap, and from this point much of what we examine and discuss will be fish. The predominant species are mummichogs, a Lenape name meaning “goes in great numbers.” The mummichogs (Fundulus heteroclitus) grow just up to four inches long and are prey for a wide variety of animals: turtles, egrets, other birds, bigger fish. They are hardy as well, able to tolerate brackish water and low dissolved oxygen; they can even survive out of water while waiting for the tide, if they get stuck. Mummichog eggs are left out of the water after the fish spawn during new and full moons in the spring and hatch at the next high tide two weeks later. This may be helpful because mummichogs are carnivorous and will eat their own species’ eggs, in addition to horseshoe crab eggs and up to 2,000 mosquito larvae a day.

The mummichogs are a kind of killifish. We see another species n the family as well, banded killifish (Fundulus diaphanus), which are slimmer than the mummichogs and have distinct vertical bands on their sides. (Mummichogs can have faint, ill-defined bands, but those of the banded killifish are clear.)

A pumpkinseed, with the
namesake mark visible on its side

As we move from the tide gauge to the center of the pond we see a few more things alongside the boardwalk, a native praying mantis and marsh mallow, a native hibiscus. But once on the pier out in the pond, the focus is again on fish. We practice cast netting, throwing a clever weighted net into the water in a (mostly unsuccessful) attempt to catch fish. Fish traps hanging off the pier have caught many different fish for us to see up close, however, and we examine the sometimes small differences between bluegill, blueback herring, pumpkinseed, and shiners.

A bald eagle flies over the marsh, capturing everyone’s attention, and we leave the boardwalk for one last fish trap. The day before they set a trap out in the Christina, and we gather at the building to see what they’ve brought in. In a five-gallon bucket, two American eels (Anguilla rostrata) show a dramatically different side of the aquatic ecosystems in the area.

In addition to the very different shape, of course, the eels are also a good deal larger than any of the fish we saw in the pond in the marsh. They are also nocturnal, feeding at night and hanging out towards the bottom of the river during the day. By now many people know that eels spawn in the Sargasso Sea, traveling to the section of the Atlantic Ocean east of Florida and south of Bermuda from the freshwater in which they spend their entire adult lives, but this was only discovered in the early 20th century. The young eels were originally thought to be a different species, they are so different in appearance, described as a “small, flat, transparent organism shaped like willow leaf” by Maynard Raasch in “Delaware’s Freshwater and Brackish-Water Fishes.”

The young eels reach the East Coast after about a year in the Gulf Stream traveling from the Sargasso Sea, and the males then settle in tidal waters while females tend to move further upstream. They can cross wet ditches and meadows to reach ponds and can get past dams as they move upstream. They live in freshwater up to 10 years and growing usually to about five pounds before heading back to the Sargasso to spawn at the end of their lives.

September 27 1:06 p.m. sunny and warm

Ashland Hockessin, Delaware

After the morning at DEEC, we regrouped at Ashland for an afternoon exploring two habitats in which I have taught aquatic ecosystems before: the Piedmont creek and a millpond. I had not previously had the benefit of our instructor, whose name I neglected to note but who was passionate and knowledgeable. Before we walked to the first habitat we would explore, she showed us a map of northern New Castle County watersheds, talked about the connection from Ashland to DEEC, and pointed out that the animals we would be concentrating on at Ashland - various invertebrates, are easy to overlook but amazing in their own way. Invertebrates make up 79 percent of all species on the planet, and 96 percent of the animals.

Damselfly larva

We started at Indian Rill, sweeping for animals between the parking lot and Brackenville Road. I feel like groups I’m with tend to do better at Wildflower rather than Indian Rill, but there was no shortage of interesting life found with the NCS class. We caught damselfly and dragonfly nymphs, the latter of which can unhinge its lower jaw to capture prey much larger, one of the reasons they are known as ferocious predators in the miniaturized world of the stream.

Someone came up with a fish, and while that is about as far as the identification goes when I’m out with groups of kids, having some teacher-naturalists with us who work more at DEEC, I learned it was a blacknose dace (Rhinichthys atratulus). Dace are members of the Cyprinidae family along with carp, minnows and shiners. There are 23 members of the family in Delaware, the best represented of any fish family in the state. Blacknose dace are found in the “faster flowing streams in northern New Castle County,” according to Raasch. They grow up to four inches long, although they are often shorter.

In addition to the fish we found some things we can usually count on seeing - caddisflies, mayflies - and a couple that are a bit less likely and fun to see: a very young crayfish, a couple of dusky salamanders that still had their feathery gills floating out from their necks like grasses in the current. Many adult salamanders, including the dusky, two-lined and red-backed, the most commonly found in our area, are both lung-less and gill-less, breathing through their skin. But Dusky salamanders (Desmognathus fuscus) have very distinctive gills in their larval stage.

A dusky salamander with gills

We learned a bit about the common insect larva we found as well. Caddisflies undergo complete metamorphosis, that is, they have a pupal stage after which they emerge as wholly different adults, while the other common larva we saw (stoneflies, mayflies, dragonflies and damselflies) are all examples of incomplete metamorphosis, moving from the egg and larval stages to adulthood. You can see the wings or at least wing pads on the larvae.

I am used to talking about what we find in the stream in terms of what they tell us about the water quality (pretty good at Ashland), but our instructor explained another approach emphasizing the ecosystem by pointing out the various ways in which the stream life eats. Invertebrates may filter feed from the water flowing by, scrape algae and detritus from the rocks, and prey on other invertebrates or sometimes even larger animals. Depending on how they feed, the invertebrates exhibit different adaptations, from mouth parts optimized to the food they eat to spinning webs of sorts to catch organic debris as it flows downstream. In identifying invertebrates, we usually stop at the family, but there is an incredible diversity even within the families. Mayflies, for instance, have species in every feeding category; there are more than 1,000 species of mayflies worldwide.

2:18 p.m. Millpond

From the Indian Rill we headed to the millpond across the road to see what we might catch that would differ from the stream. For a quick orientation, our instructor shared that a pond is distinguished from a lake largely by its depth. In a lake, the water is deep enough for there to be different water temperatures, affecting the species that live there. A pond, however, tends to be shallow enough that light reaches most or all of the water, meaning more vegetation.

A hellgramite, or dobsonfly larva

Using long-handled nets and a seine net, we set to catching what we could out of the pond. There were many invertebrates here as well, though different kinds: backswimmers, water boatmen, diving beetles and dobsonfly larvae, also called hellgramites. These last are predators intimidating in appearance and capable of giving humans a nasty bite if mishandled, but they are neat-looking. The backswimmers and water boatmen can be hard to tell apart - both are true bugs that use their wings to take air bubbles underwater with them for breathing. Both insects give the impression of being rowboats with long central legs as the oars, the principal difference being the water boatmen swim right side up while the backswimmers are upside down.

We found more than just the insects in the pond, however. Several red-spotted newts were caught, along with a couple different small fish - shiners, bluegills. The largest animal, brought up in the seine, was a brown bullhead catfish (Ameiurus nebulosus). Brown bullheads are the most common catfish in Delaware, usually growing up to three pounds, although the record in the state is just over six pounds. Bullhead catfish have tails that are only slightly indented rather than forked, and the brown bullhead can be distinguished from the yellow bullhead by its barbels, the appendages under the fish’s jaw that evoke cat whiskers. On the brown bullhead, these barbels range from grey to black; those of the yellow bullhead are white.

Catfish lay thousands of eggs in nests they excavate in the soil and the parents guard both the eggs and the fry. They will sometimes clean the eggs by taking them into their mouths and gently blowing them back into the nest. Brown bullheads are particularly hardy fish, able to tolerate low oxygen and even evaporating waterways by lying dormant in the mud for weeks.