What Organisms Live in the Littoral Zone?

By Steve Carbol, Lake & Wetland Management Senior Biologist

  • (Introduced exotic species are denoted by an asterisk*)

littoral
/ˈli-tə-rəl; ˌli-tə-ˈral, -ˈräl/ adjective
1.1 Relating to or denoting the zone near a
lake shore with rooted vegetation.

~ The Oxford English Dictionary

A littoral zone is a narrow transitional area in a lake, pond, or ocean where land and water converge, often in a cline or shelf. Most stormwater basins constructed within the last twenty years in Florida have governmentally-mandated littoral shelves that, as required by law, must be planted with native emergent wetland plants expected to achieve at least 80% coverage of said shelves one year after installation.

For many residents moving to Florida for the first time from more northerly climes, governmentally-mandated shoreline plantings may be a novel concept, but those seemingly extraneous plants are indeed supposed to be there. In fact, littoral plantings are planned as a mandatory component from the very earliest stages of a community’s construction, even appearing on the site plans with details specifying the species, sizes, quantities, densities, and locations of the plants to be installed.

Fronds with Benefits

littoral-plantingThe benefits of littoral plants are several-fold. The so-called lakes seen in residential communities and business parks across the state may offer pleasing aesthetics, especially for those seeking a lake view and waterfront property, but those lakes are actually stormwater control and retention basins whose crucial primary function is to collect the copious amounts of rainfall Florida experiences during wet season storms and hurricanes, prevent communities from flooding, and protect the investment of residents and business owners. Other secondary functions of the basins include serving as reservoirs for irrigation water, and recreational purposes such as angling, wildlife watching, and boating.

Benefits of Littoral Shelf Planting

The littoral plants help the basins to function at peak efficiency by trapping sediment from runoff, controlling shoreline erosion, reducing nutrient loading and potential algae blooms, as well as providing crucial habitat for aquatic wildlife. As Lake & Wetland Management has grown since its inception in the 1990s, harvesting, planting, and servicing such littoral plantings through its native nursery has become an important component of the company’s business, and Lake & Wetland Management has become a leader in this industry.

You’ve Just Crossed Over into the Littoral Zone

Areas where different habitats converge typically contain and support the greatest diversity of species, and littoral zones, being sandwiched between the water and land, are no different. Planted lake littoral zones, with their abundance of nutrients and dense vegetation, serve as a refuge and nursery for many life stages of familiar and cryptic aquatic organisms. So, when I was asked to write this article in answer to the question, “What Organisms Live in the Littoral Zone?”, rather than paint a generic picture of the kinds of creatures I frequently encounter making use of the littoral zone in my duties as Senior Biologist with Lake & Wetland Management, I saw it as an opportunity to take a field trip and take a snapshot of sorts to document the species actively utilizing the shoreline plantings in one of the company’s largest and and ecologically diverse longtime accounts: Bellaggio in Lake Worth/Boynton Beach, Florida.

Livin’ On the Edge/Littoral Project Snapshot: Bellagio, Lake Worth

Bellaggio is a model community for residents who encourage coexisting with nature, and following that ethic, the management and residents have installed several wildlife projects including Purple Martin nesting colony apartments, a Wood Duck nest box trail, bat boxes, and a community butterfly garden. The site hosts multiple wetlands and preserves and 24 lakes, nearly all with native littoral shelf plantings. At 10:27A.M. on Tuesday, June 2nd, I walked down to the water’s edge on Bellaggio’s Lake #5 to see what I could see living in the site’s littoral zone.

The littoral shelf was lush with a variety of native wetland plants. The jaunty lemon yellow flowers of Golden Cannas wagged gently in the breeze atop grass green spires. Slender, cylindrical Jointed Spikerush rose like green drinking draws from the water’s surface. A cluster of Pickerelweed, flush with a profusion of periwinkle-blue blooms, was attended by flitting butterflies, skippers, and bees. Tall, gangly Lance-leaved Arrowheads stood peppered amongst the other plants with their long wands of three-petaled, waxy, white flowers shooting out at crooked angles. A few stately blue-green Southern Blue Flag Iris grew further up the shoreline, favoring the slightly drier conditions. In the deeper water away from the shoreline, the small globular golden flowers of Spatterdock peeked out from between the patchwork of broad green leaves. And here and there, tussocks of 9 – 12-foot tall Alligator-Flag stood towering like islands amidst the other plants, bicolored violet-and-lavender flowers dangling like pendants at the end of bowing zigzag stems, beads of rainwater standing like glittering gems on the broad, tropical-looking, water-repellent leaves.

As I walked down the grassy bank toward the water, White Peacock Butterflies cruised low over the lawn, darting flower to flower over the purple and white Frog Fruit flowers dotting the green lawn. Occupied with the butterflies, I was startled when a 2-foot-long Brown Basilisk*, the infamous “Jesus Lizard”, an exotic imported from South America, dashed forward out of the short grass at my feet. The skinny brown lizard reared onto its hind legs and sprinted down the bank, across a stretch of water, and dove headlong into the spikerush. Like many other exotics in Florida, basilisks have unfortunately become a ubiquitous sight.

Sounding like hundreds of tiny maracas, a chorus of Slender Meadow Katydids stridulated from the spikerush as I approached the littoral zone. As I walked down the bank, a crow-sized Green Heron exploded from the spikerush and, with a protesting guttural squawk like a tearing sheet, winged away across the lake. Simultaneously, a Least Bittern, a diminutive cousin of the heron, no bigger than a Blue Jay, lifted silently out of the spikerush off to my left, flew stealthily down the shoreline, and quietly dropped into a plant tussock. If not for the bittern’s larger, more vocal Green Heron cousin flushing at exactly the same time, I might not have noticed the little straw-colored bird slipping away. The Katydids, suddenly gone silent with the disruption, slowly again took up their song.

The last creature I accidentally disturbed, that I noticed anyway, was a Southern Leopard Frog. With a sharp squeak, the little amphibian leapt, and in a good five-foot arc, easily cleared the spikerush bed to land in an open pool of water beyond with a soft “plunk”; an impressive feat considering the frog’s 2-inch body length. After the frog launched itself, I noticed some potential prey it might have been waiting for to ambush before its leap.

In the bare mud between the sod line and the littoral plants, a few mantid shore flies stood nonchalantly grooming themselves. Though roughly the size of House Flies, mantid shore flies would never lower themselves to swarm open garbage cans like their more familiar cousins. Fierce little shoreline predators, mantid shore flies chase and tackle prey with forelegs modified into murderous grasping sickles, as their name implies, like those of a mantis. As I watched, a tiny Big-eyed Toadbug hopped right through the midst of three mantid shore flies. The flies snapped into action and sprung forward after the toadbug but instead of connecting with their potential bounding quarry, collided with each other and began to skirmish and grapple while the toadbug made good its escape.

In addition to being the scene of miniature insect dramas, the shoreline mud also told the story of other creatures’ passing through the littoral zone the night before and earlier that morning. The littoral shelf was littered with the empty, discarded four-inch long olive-tan shells of Paper Pondshell freshwater mussels. A few species of native mussels live in the sediment in the littoral shelf where they filter feed for plankton suspended in the water column. I looked to the mud for clues as to who might have enjoyed a recent lakeside mussel meal. The muddy tracks of Limpkins – large, enigmatic, long-billed brown birds known for their piercing cries – criss-crossed the flats. The Limpkin is known for its diet of various freshwater aquatic snails and mussels and it was obvious that a Lumpkin had neatly pried open most of the shells. There were also wandering tracks that looked like tiny human baby handprints with sharp nails – Northern Raccoons. Raccoons are consummate opportunists and regularly plunder mussels from the littoral shelf, although less adeptly than the Limpkins, as evidenced by a smaller number of chipped and smashed shells.

Looking through binoculars across the lake to the littoral plants on the opposite shore, a colorful, harlequin drake Wood Duck swam slowly in front of the green curtain backdrop of a bed of littoral plants. Beyond it, a brilliant white Great Egret stood still, belly-deep in the spikerush, before momentarily swaying to gauge distance. Then, with a lightning fast stab, its head shot serpent-like deep into the vegetation. A moment later the bird withdrew its neck from the plants with a little pair of spotted legs kicking haplessly from the end of its spear-like bill. The leopard frog I’d startled on my side of the lake was much luckier that I came armed only with binoculars, and that I’ve never much cared for frog legs anyway.

Looking to the littoral plants themselves, I saw several bubble gum-pink egg masses of the exotic baseball-sized Island Apple Snail* adhered to Alligator Flag stems. Introduced through the aquarium trade from South America, this species has supported the diet of both the Limpkin and Snail Kite, leading to population booms in both species. Along with the apple snail egg clusters, several dragonfly and damselfly exoskeletons also clung to the stems just above the water’s surface. After living for several months as aquatic crawling larvae, the insects ascend the stalks of littoral plants to shed their outer shell like an old husk and emerge as flying adults, ready to live entirely different lifestyles from those of their muddy benthic youths, to hunt and mate on the wing. And looking to the tops of the plants, there they were; the dragonfly and damselfly adults, in a dazzling array of colors and species, clutching to prominent perches, whizzing inches above the water at blinding speed, hawking bees and flies out of the sky, and periodically clashing in midair dogfights with an audible crackle of wings like rustling cellophane. As I watched, I began mentally ticking off the species I saw, recalling monikers as flamboyant as the mythical dragons and damsels for which they were named and, indeed, as the insects themselves: Common Green Darner, Roseate Skimmer, Scarlet Skimmer*, Band-winged Dragonlet, Little Blue Dragonlet, Eastern Amberwing, Blue Dasher, Eastern Pondhawk, Pin-tailed Pondhawk, Black Saddlebags, Red Saddlebags, Hyacinth Glider, Wandering Glider, Four-spotted Pennant, Halloween Pennant, Atlantic Bluet, Rambur’s Forktail. And just as the legion of dragonflies effortlessly captured bees and flies coming to sip nectar at the blossoms in the littoral zone, those dragonflies that drifted skyward in turn fell prey to Purple Martins, Swallow-tailed Kites, and Gray Kingbirds coursing overhead.

Besides the dragonflies, damselflies, European Honeybees*, native Halictid bees, and flies, a good number of butterflies also danced between and sipped nectar at the purple Pickerelweed and white arrowhead blossoms. There were flaming orange Gulf Fritillaries, petite rusty Fiery Skippers, dark, quick Clouded Skippers, and big, familiar, orange-and-black Monarchs. I wasn’t the only one who’d noticed all this activity, however, as several Venusta Orchard Orbweaver spiders had stretched their almost invisible gossamer webs across gaps in the vegetation in the hopes of ensnaring the passing insects.

Looking like diminutive tree trunks in a tiny flooded forest, the submerged spikerush stems sheltered numerous little fish. Eastern Mosquitofish, drab, brassy, inch-long cousins of the domestic Guppy, swam between the plants, picking off midge and mosquito larvae from the water’s surface. Here and there, metallic flashes of color, brilliant against the dark silt bottom, drew my eye. It was spawning/mating season for many fish, and male Florida Flagfish and Sailfin Mollies were setting up territories, defending them from other males, and doing their best to attract the attention of females waiting just outside the circles of activity. The mollies had raised their enormous, rippling dorsal fins, nearly doubling their apparent size. Normally folded inconspicuously flat against their backs, the sail fins were now fully and boldly extended in shimmering iridescent aquamarine and gold. The pugnacious little flagfish males were in fine color as they dueled, totally living up to their name, the scales on their flanks flashing lines of red and silver-white, and a smudgy canton of indigo, a surprisingly accurate approximation of the stars-and-stripes of the United States flag. Beyond the little clearing where the flagfish and mollies postured and flashed, juvenile Bluegills delicately threaded their way between the plants, picking at the occasional insect or amphipod as they went. About the size of a bar of soap, a Striped Mud turtle slowly, methodically plodded along the silty bottom, snapping at any fish that wandered close to its hard beak, and grubbing for aquatic worms and exotic Red-rimmed Melania snails* in the mud. Even further out at the edge of the littoral shelf, nearly motionless, lurked a big Largemouth Bass, deep green in the dappled shade of the plants, quietly waiting to ambush any smaller fish straying beyond the safety of the miniature sunken forest.

Having stood quietly transfixed for a few minutes observing the fish, I was startled when two little black puffs of down tripped across my boots. Recently hatched golfball-sized Common Gallinule chicks clumsily scrambled over my boots and ran, peeping wheezily, down the shoreline. I chuckled at the ungainliness of the ugly-cute little birds, their monk-like bald spots atop their heads showing little domes of red-orange and blue skin. The chicks had ventured too far afield into the midst of a human, and their sleek, black parents were frantically trying to recall the chicks. The parents had likely nested nearby in the littoral plants, weaving a suspended nest out of stems a foot or two above the water’s surface. The littoral zone is a fertile protective nursery for numerous animals above and below the water. Scanning the lake perimeter, I also noticed normally vociferous Red-winged Blackbirds and Boat-tailed Grackles slipping quietly in and out of the plant beds, furtively coming and going to and from their own hidden nests secreted amongst the plants to tend and feed their chicks, drawing as little attention to themselves as possible.

The littoral zone really is the most biologically diverse area of any lake or pond, and to generically list all the species that could potentially occur there in any one area, even in broad strokes, would be a daunting task. In this exercise only about ten minutes had elapsed since I walked down to the shoreline to the time I made my way back up the bank, and to record and relate all that I saw in that brief time in a relatively concise account was no small undertaking. I hope that reading it, if indeed, Dear Reader, you made it this far, was not a tedious chore. I encourage everyone to get out and experience, appreciate, and become familiar with the dazzling array of wildlife that calls the littoral zone home in the nearest water body, in your very own neighborhood lakes and ponds. And, assuredly, Lake & Wetland Management will continue, as it always has, to plant, manage, and care for littoral zones to make them a hospitable and fertile home for a myriad of wildlife throughout Florida.