Part #6:  “Monster” Cells

Story & Photos By Dr. Eric Cole

As glaciers of the Late Pleistocene (our most recent Ice Age) melted, raising sea levels around the world, they lifted the water table within each of the Turks & Caicos Islands. A marine elevator of sorts rose up through the Islands’ porous limestone interiors, ultimately breaching the landscape and filling low-lying areas with water. These are the “anchialine ponds:” precious marine sanctuaries and natural experiments in marine-life colonization, isolation, and extraordinarily rapid evolutionary change.

As freshwater rains percolated downward meeting the rising sea table, a boundary layer formed, creating a uniquely aggressive interface that digested caverns and conduits within the “Karst” landscape. Some ponds remain isolated from their Mother Ocean, evaporating beneath the summer sun and forming salt ponds and salt flats whose cultivation supported the early colonists.

In others, rainwater dissolution of the surrounding limestone carved caverns connecting the pond to the sea through a system of submarine tunnels. Many of these ponds, though miles from the sea, exhibit tides, their waters rising and falling often hours out of synch with the ocean as water forces its way through these underground labyrinths.

This anchialine pond includes a carpet of single-celled Batophora (“Fuzzy Finger” algae) covering the floor.

These are the “black lagoons” and their unique communities of living creatures deserve special attention as they are so frequently overlooked in favor of sparkling sands, wondrous sea grass beds, mangrove forests, and coralline reefs. For some of us, an eccentric curiosity turns us from the more conspicuous and glamorous natural history landscapes to seek out the overlooked and more anonymous lifeforms to study and admire. It never disappoints.

What is more anonymous and overlooked than algae? In many of the anchialine ponds, especially those not driven by evaporation towards a salty apocalypse, a special caste of algal life has established a home. Protected from surge and storm, the inland ponds frequently boast an explosive carpet of a singular species. The photo on the previous page shows a pond in which Fuzzy Finger algae (Batophora oerstedii) cover the floor. Remarkably, each frond of Batophora represents a single cell.

Perhaps equally remarkable, these fuzzy fingers undergo sexual reproduction without flowers. A single nucleus, buried in the “rhizome” (a rootlike attachment at the base of the algae), undergoes rounds and rounds of nuclear divisions whose products migrate out into the feathery fronds creating hundreds of microscopic gametes (sex cells). This becomes visible to the alert observer as the fuzzy fronds adopt a more beaded appearance. Each bead contains dozens of motile gametes, ripe for release. For this part of their life cycle, these algae revert to a more familiar, microscopic, single-celled form, as each bead bursts—releasing gametes that swim with whip-like flagella to find and fuse with another.

This anchialine garden features Mermaid’s Wineglass (Acetabularia).

Curiously, the fuzzy finger algae are close relatives to another darling of the algal world: the “Mermaid’s Wineglass” (Acetabularia). These, too, represent single cells with nucleated root-like hold-fasts and slender stalks terminating in an adorable cup. They, too, possess a single nucleus, yet grow 3–4 inches in height.

Experiments on this species of algae with a smooth cap and a related species with a “crenulated” cap, provided the very first evidence that the nucleus of a cell determines its form. (Original experiment by J. Hammerling in the 1930s). The type of cap that regenerates is determined by the nucleus of the adjoining holdfast.

Another group of macro-algae common to the Turks & Caicos ponds (but less common in The Bahamas), belong to the genus Caulerpa. Again, our inland ponds provide a special refuge allowing these algae to grow almost without limit. Different species display a feathered or beaded appearance, or anything in between. Caulerpa send runners through the pond sediments that sprout shoots as they grow. Mounds of Caulerpa can grow into “hedges” over a meter high, or drape into the mouths of an anchialine cavern like photosynthetic waterfalls, each mound or drape representing a single organism and astonishingly, a single cell.

Another single-celled algae common in the back-reef environment is Valonia ventricosa. Its more common names are (obviously) bubble algae, sea grape, or sailor’s eyeballs.

These represent the largest single cells on Earth.  Unlike the Dasycladalys species (Mermaid’s Wineglass and Fuzzy Fingers), Caulerpa represent single, continuous cells with multiple nuclei. Honorable mention goes to another single-celled algae common in the back-reef environment, Valonia ventricosa. These go by more common names: “Bubble algae,” “sea grape,” and (your kids will love this) “sailor’s eyeballs.”

This magnificent cell also carries multiple nuclei. It achieves its enormous size by expanding an interior vacuole so that the cell’s cytoplasm occupies the thinnest possible layer just below the cell’s calcareous surface where gas exchange allows the cell to “breathe.”

If there was a theme to this bit of natural history, it would be to nudge us to celebrate the ordinary things in nature, as well as the extraordinary. “Seaweed” is so often ignored or regarded as something to avoid. Approaching and intimately observing every corner of nature reveals a world of unanticipated beauty. a

For references or more information, contact the author at co***@****af.edu.