Fish Nurseries in the Susquehanna

Resilient to the pressures of flooding, ice scour, drought, and oft times really poor water quality, Water Willow (Dianthera americana, formerly Justicia americana) is the most common herbaceous plant on the Susquehanna’s non-forested alluvial islands.  Yet, few know this native wildflower by name or reputation.

Water Willow on Alluvial Island
Pure stands of emergent Water Willow endure at times brutal conditions on non-forested islands in the Susquenanna.
Water Willow (foreground) and Black Willow.
Alluvial deposits of sand, clay, gravel, and silt create ideal substrate for mats of Water Willow along shorelines of the Susquehanna and its larger tributaries.  Provided the loose substrate remains moist, this emergent thrives even when water levels retreat during periods of dry weather.  The woody plant in the background, the native Black Willow, shares similar soil preferences but is found growing on slightly higher ground as a non-emergent tree or shrub.  It is a member of the willow family (Salicaceae).
Water Willow in bloom.
In bloom now, the orchid-like flower of the Water Willow is a quick giveaway that it is not a close relative of the willow trees but is instead a member of the acanthus family (Acanthaceae) and is allied with the genus Ruellia, the wild petunias.

The spring of 2024 has been very kind to our beds of Water Willow.  Rainfall in the Susquehanna watershed has been frequent enough to maintain river levels just high enough to keep the roots of the plants wet.  During the interludes in storm activity, dry spells have rolled back any threat of flooding on the river’s main stem, thus eliminating chances of submerging the plants in muddy water and preventing the sun from keeping them warm, happy, and flowering early.  Thundershowers throughout the basin earlier this week have now raised the river a few inches to inundate the base of the plants and make mats of Water Willow favorable places for newly hatched fry and other young fish to take refuge while they grow.  Here’s a look…

Spottail Shiner
The Spottail Shiner (Notropis hudsonius) is a common native minnow of the Susquehanna.  This juvenile was found among several dozen small fish taking refuge in the cover of Water Willow below Conewago Falls.
Mimic Shiner
The Mimic Shiner (Notropis volucellus) is generally regarded to be a native transplant from the Mississippi drainage that has become established in the Susquehanna and many of its tributaries, possibly after introduction by way of bait buckets.  However, the fish tends to be very fragile and dies quickly upon handling, so its use and transport as a bait species may be impractical.  The Mimic Shiner is very common in around Conewago Falls.
Juvenile Mimic Shiner
A juvenile Mimic Shiner less than one inch in length found among flooded Water Willow below Conewago Falls earlier this week.
Juvenile Quillback
One of about a dozen juvenile Quillbacks (Carpiodes cyprinus) found in Water Willow just below Conewago Falls.  For spawning, local populations of this compact native species of carpsucker favor the gravel-bottomed pools among the Jurassic-Triassic boulders of the falls’ pothole rocks.  Probably hatched within the last eight weeks, this specimen was just one inch long.
Spotfin/Satinfin Shiner among Water Willow Rhizomes
As summer progresses, stands of emergent Water Willow begin to expand their size by sending out rhizomes.  Increasing numbers of small fish like this Spotfin/Satinfin Shiner (Cyprinella species) concentrate in the cover of the thickening vegetation.
Spotfin/Satinfin Shiners
The importance of these patches of emergent wildflowers (sounds weird, doesn’t it?) is demonstrated by the numbers of fish gathered within their underwater forest of stems and leaves by summertime.
Spotfin/Satinfin Shiners (Cyprinella species)
To protect them from burial by silt and to prevent them from being swept away by current, spawning Spotfin/Satinfin Shiners deposit their eggs in crevices of submerged rocks and wood, often in or near mats of Water Willow.  Males guard the eggs until hatching.  The fry must then take shelter among boulders, cobble, and plant cover.  Note the breeding-condition male in the upper right.
Green Sunfish
Panfish like this non-native Green Sunfish (Lepomis cyanellus) will often choose nesting sites in deeper water adjacent to beds of Water Willow, particularly if submerged growth like this Water Stargrass adds to the availability of cover for their young after hatching.
Smallmouth Bass
Smallmouth Bass gather in a pool adjacent to a Water Willow-covered island.  These non-native predators rely on beds of these indigenous plants to provide habitat for their young, then, after spawning, lurk in the waters surrounding them to ambush less-than-vigilant minnows and other victims.

By now you’ve come to appreciate the importance of Water Willow to the sustainability of our populations of fish and other aquatic life.  Like similar habitat features that reduce sediment runoff and nutrient pollution, undisturbed stands of terrestrial, emergent, and submerged native plant species are essential to the viability of our freshwater food webs.