Kingdom Protoctista

This kingdom has a fairly complicated name — at least to pronounce. It simply refers to organisms that have their hereditary information enclosed in a nucleus (like higher organisms), but reproduce by simple cell division (unlike higher organisms).

Some are food producers. Diatom cells, part of the phytoplankton, make a significant contribution the base of the food pyramid by manufacturing energy-rich oil droplets. Macroalgae, like the seaweeds familiar to anyone who has explored a shoreline, are multicellular members of Kingdom Protoctista. These store their sugar production in the form of starches or fats.

Others are consumers only: unicellular protozoa are like animals in that they do not make their own food. The wonder of protozoa is in the way they differ from animals. In animals, various cells form tissues that combine into organs, which make up whole systems (e.g. digestion or excretion). Each protozoan has all of this functionality contained within the structures of a single cell.

The slime mold responsible for nearly wiping out the estuary’s eelgrass population a couple of times in the past century, is also of Kingdom Protoctista. It, too, is a consumer.

Algae
Those of the Protoctista that manufacture their own food.

Diatoms
The shapes and designs of these cells, which can be seen only through an electron microscope, are as much fine art as they are biological wonder. Their transparent cell walls are made of silica, an element abundant in seawater and also the main component in glass. This construction allows maximum light to reach the photosynthetic pigments within. The food energy manufactured by the diatoms is stored as droplets of oil.

The walls are actually formed in two halves, a top and bottom (hence “dia”toms), which fit together like a pillbox or covered petri dish. There are two general groups: centric diatoms are radially symmetrical, and pennate diatoms are bilaterally symmetrical.

Each species of diatom has a unique geometric pattern, seemingly etched onto its surface. But what appear to be exquisitely intricate etchings are actually pits in the cell surface through which water nutrients and waste are exchanged.

The centric diatoms form the largest portion of plankton in the estuary. These are organisms carried by water flows with no locomotion of their own. Their oil helps keep them afloat near the sunlit surface. Pennate diatoms travel like amoebas, moving an extension of their cell in a wavelike motion along the surface of plants, animals and sediments. Sometimes these, too, are suspended in the water column by waves and currents.

Reproducing through simple cell division, one diatom growing in optimal conditions can produce a million daughter cells in three weeks. They are a big food source for many, mostly invertebrate animals in the estuary, from sediment feeding worms, to filter feeding oysters to grazing snails.

The thousands of varieties of marine and freshwater diatoms in water bodies around the world produce huge amounts of oxygen. Scientiests have estimated they produce more than 25 percent of the world’s oxygen supply.

Macroalgae
Some multicellular algae could be mistaken for plants, since many types of seaweed do look like they have roots, stems and leaves. But those structures belong to the plant kingdom.

Assorted macroalgae species at the base of a rock at Ordiorne Point in Rye. Many of these species can be found within Great Bay Estuary.

Since they are surrounded by water for much or all of the time, algae absorb water and nutrients directly through their cell walls. They have no need for roots to absorb water and nutrients from the ground, or supportive stems to transport water and nutrients up to the leaves.

What appear to be root structures are actually holdfasts for anchoring algae to sediments, shells, rocks, docks and other surfaces. The stem-like structures, called stipes, provides flexible connections between the holdfasts and the blades. Blades are the leaf-like structures reaching up to the sun, where nutrients are absorbed and food is produced. (Photosynthesis also occurs in the stipe and holdfast.) Together these parts are called the thallus.

The varying forms and structures of algae allow them to survive in different conditions: calcified crusts can endure crashing waves; tough, rubbery blades retain moisture in the intertidal zone; and some delicate filaments flourish off the beaten path of upper intertidal areas.

But the major distinctions of algae are based on the dominant photosynthetic pigments that give them their colors. Green algae have chlorophylls. These pigments absorb narrow portions of the light spectrum’s red and purple light waves, for use in photosynthetic food production. They reflect the color green.

Brown and red algae also have chlorophylls. In addition, they have what are called accessory pigments. These absorb waves from other parts of the light spectrum and pass them on to the chlorophylls, which begin the photosynthetic process. Carotenoids absorb blue-violet light, and reflect yellow to orange. Fucoxanthin, absorbs blue-green light, and reflects brown. Brown algae have these two kinds of pigments. In addition to chlorophyll and carotenoid pigments, red algae have reddish phycobillin pigments.

Since the colors of the spectrum are able to penetrate seawater to varying depths, it used to be taught that an alga’s color—green, brown or red—determined how far down in the water column it would be found. Green algae, for example, would stay within reach of red light waves, while only red algae flourished in deeper waters penetrated by blue light waves.

But scientists are finding that other factors influence the distribution of algae. In his book The Ecology of Atlantic Shoreline, Mark Bertness describes some of them, including concentration rather than types of pigments, competition for space, potential for grazing by herbivores, and nutrient levels in the water.

Bands of algae concentrate in certain areas in the intertidal zone, seeking optimal conditions for their kind. Brown Fucus seaweeds are commonly found draped over rocks in the middle zone of rocky shores. Red seaweeds tend to congregate in the lower zone.

Green Algae [Chlorophyta]

Sea Lettuce
Ulva lactuca
Grow in sheets only two cells thick, sometimes with gently rippled edges. Seemingly all blade and no stipe or holdfast. Found attached in intertidal to subtidal areas. This fast-growing, soft alga is popular with herbivores like snails and urchins.

Chaetomorpha spp.
Single row of green cells. Hair-like filaments found tangled in the intertidal zone.

Enteromorpha spp.

Brown Algae [Phaeophyta]

These include the green and brown seaweeds lying in great heaps on the rocks of the intertidal zone. Their thick, rubbery parts help protect them from dehydration and grazers. They have air bladders to help them stay afloat in the sun. Larger receptacles, with bumpy surfaces, house reproductive cells. Their value as food producers is realized more after they decompose and are consumed as detritus. Their heavy canopies provide cool, moist refuge for invertebrates at low tide.

Rockweed
Fucus vesiculosus
Thallus is flat with a midrib, bladders in pairs, and receptacles at the tips.

Knotted Wrack
Ascophyllum nodosum
Thallus is more round and thin. Bladders along its length are more conspicuous, and are thought to make it less able to handle heavy wave stress.

Red Algae [Rhodophyta]

Irish Moss
Chondrus crispus
This short, dark red alga has forked stipes and rounded tips. Tufts of this algae cover the lower sides of rocks and beneath draping brown seaweeds in the lower intertidal zone to avoid exposure, where they avoid to too much air or sunlight.

Coralline Crust, Bubble Gum Algae
Lithothamnium sp.
In the lower intertidal zones on the ocean side of the estuary you sometimes see what looks to be pinkish or purplish paint or discarded gum, often coating some rocks or periwinkle shells. This encrusting alga incorporates into its cell walls calcium carbonate, the same substance used by shellfish. Though this formidable armor costs this alga additional time and energy during growth, it pays off by discouraging would-be grazers.

The limpet is the one herbivore to take on this crust. In a symbiotic relationship, the limpet is fed, and the surface of the crust is kept clear of microalgae and other debris to allow sunlight to reach its photosynthetic machinery. Sometimes you’ll see an all-white crust. This one has died.

Coral Weed
Corallina officinalis
Like the calciferous crust above, the coral weed incorporates calcium carbonate into its tissues. The delicate thallus, segmented and branching, is reminiscent of a bonsai. It can be found growing on hard surfaces like rocks or the backs of periwinkles.

Slime Molds
The slime mold mentioned in studies of Great Bay Estuary is from the phylum (major group within a kingdom) Labyrinthulata. The use of the word labyrinth in the phylum name is apt. In their book Five Kingdoms Lynn Margulis and Karlene V. Schwartz write, “With the unaided eye they look like a slimy mass on marine grass. Under the microscope, spindle-shaped cells can be seen migrating back and forth in tunnels within the slime, like little cars in tracks.” Once the colony senses a food source it secretes enzymes to break it down into molecules, which can diffuse into the slime. Transparent slime nets centimeters long can form on seagrass or benthic algae.

The catastrophic death of eelgrass in the North Atlantic in the 1930's was caused by the slime mold Labyrinthula zosterae. After rebounding in the 1960's, eelgrass in Great Bay Estuary suffered another outbreak of this slime mold in the mid 1980's. Eelgrass acreage in Little Bay and the Piscataqua River has not fully rebounded.

Protozoans
Protozoa are single-celled organisms classified by their forms and methods of locomotion. Though some are photosynthetic, thus able to produce and store their own food, all feed on organic material in the form of diatoms, bacteria, particles of organic matter and dissolved nutrients. They are described as primary consumers, since they are the initial link in the food web between simple food producing cells and larger predators.

The various species can be found floating in the water, attached to eelgrass and algae blades, moving through the sediment grains and attached as parasites to other animals.

Ciliophora
These have tiny, hair-like projections on their cell wall, which with rhythmic beating, allow some ciliates to swim in water and others to move through sediments. They also use their cilia to push food toward a mouth-like opening in the cell wall. Most do not create any hard cellular structures. However, one of group of ciliates found in Great Bay Estuary, the tintinnids, form for themselves coverings of sand or other foreign particles cemented together with organic material.

Zoomastigina
These protozoans have one or more flagella, or whip-like extensions the cells use for locomotion.

Dinoflagellates
These free-floating algal cells typically have two flagella, the rotating whip-like appendages used for locomotion. Some scientists classify them with algae because most have photosynthetic pigments for food production, though they can also consume organic material.

Their cell walls are composed of irregular arrangements of tiny plates made of cellulose, which is not transparent like the silica walls of the diatoms. Some species have structural defenses like horns, wings or spines on their cell walls.

These also multiply rapidly under optimal conditions, sometimes even transforming the water column into the color of the photosynthetic pigments in their cells. These can be red, brown or green, depending on the species.

The dinoflagellates of the genus Gonyaulax produce toxins, which are the culprits of events known as red tide. Excessive blooms of these dinoflagellates, prompted by excess nutrients in the water, can cause toxic fish and mammal kills along a coast. Filter feeders like clams and mussels can accumulate these toxins, passing them on to humans eating them. The results can be irritated lung tissue, or even paralysis.

Sarcondina
The common feature of cells in this group is the cellular extensions called pseudopods, or false feet, which they use to move across substrates. The pseudopods also help them engulf bacteria, protoctista and dissolved organic compounds into their cells.

One group found in Great Bay Estuary, called forams, secrete multiple calcium carbonate compartments in linear, spiral or overlapping structures. They extend their pseudopodia from within these compartments.

Copyright © 2006 Barbara Driscoll.