Protoctista (Slime Molds and Seaweeds)


Kingdom Protoctista

The term “Protoctista” will be unfamiliar to those educated in most traditional taxonomic systems. A useful description comes from (2022):

“Kingdom Protoctista is defined by exclusion: its members are neither animals (which develop from a blastula), plants (which develop from an embryo), fungi (which lack undulipodia and develop from spores), nor prokaryotes. They comprise the eukaryotic microorganisms and their immediate descendants: all nucleated algae (including the seaweeds), undulipodiated (flagellated) water molds, the slime molds and slime nets, and the protozoa.”

So far our treatment of this kingdom on Martha’s Vineyard includes representatives of four phyla. We have only found one species of Slime Mold, but there are certainly others here since over 400 species are known in all. They all occur as a wet scum on fallen logs, bark and other surfaces and are important in facilitating the rotting of organic material. Those interested in learning more about these interesting primitive organisms should consult Stephenson and Stempen (1994).

The other three phyla are best represented by marine algae (seaweeds), though there are certainly species that occur in fresh water for which we have, regrettably, no information. About 900 species of Brown Algae, nearly all of which are marine, have been described, of which we have recorded 63 here. Like the Brown Algae, the Red Algae are also mostly saltwater species; there are about 4,100 species of which we have recorded 74. Lastly, the huge and diverse Phylum of Green Algae with at least 16,000 described species is represented here by only 18 species. Green Algae are believed by most botanists to be the evolutionary progenitors of all chlorophyll-bearing plants.

Collecting seaweeds for their beauty has been a pastime on the island for at least a century. Despite this, a thorough survey of the known species has only been undertaken recently. The paper by Treat et al. (2003) lists the 155 species for which there are credible records and provides the location of specimen material from the Vineyard. Over 300 specimens collected by Rose Treat at the island have been donated to the Polly Hill Arboretum herbarium and are available for research by serious students. Other specimens are at the Farlow Herbarium, Harvard University, and in the collection of the Marine Biological Laboratory, Woods Hole. Also listed in an appendix of that paper are 24 additional species which have been found within ten miles of the island shoreline, all of which can be expected to occur here. It is hoped that future workers will make an effort to find them and others as well. There are also some specimens in the care of the Martha’s Vineyard Historical Society, which have never been identified by a professional phycologist, another worthy project for the future.

It should be mentioned that the populations of individual species of algae are known to change over time at specific sites. Two species of red algae (Haemescharia hennedyi and Lomentaria clavellosa) arrived here for the first time within the last thirty years or so. Also, one native species (Codium fragile), which only arrived here sometime after 1957, has behaved as an invasive species, taking over an area of the ocean floor where previously it was absent and becoming much more common elsewhere (see Treat et al. 2003).

In the summer of 2004, a survey of the marine algae of Nomans Land Island was undertaken by Sears (2004). As a result of his fieldwork and literature research, a total of 61 species are now known for Nomans Land and the immediately adjacent ocean. All of these species are included in Treat et al. (2003). However, all the work done directly at Nomans Land to date has been in the summer, so the red algae which usually appear then are much better represented among the known species than the green and brown species, which are more common in the late winter and early spring.

From a phytogeographical perspective, the total marine algal flora of Martha’s Vineyard can be estimated at about 300+ species, so about half are now documented. To date those that have yet to be found include many cryptic, small, minute and rare species, some of which only live in water over 15 meters deep. Larger species, especially the green algae, are well known here in comparison to nearby areas such as the New Hampshire coast (a total of 216 species known) and New Brunswick (171 species known) where careful searches have been made by professionals over many years. It is also clear that the algal flora of Cape Cod and its adjacent islands is a combination of the floras found both to the north and the south of the Cape. It appears to be a larger flora than either that of the Gulf of Maine or the rocky coastlines of Rhode Island and Connecticut just to the south. On balance, however, the Vineyard flora’s phytogeographical affinities are slightly more northern than southern.

Additional sources for those interested in learning more about the seaweeds of the island are Taylor (1962) for taxonomy, Gosner (1979), Sears (2002) and Villard-Bohnsack (1995) for identification, Kingsbury (1969) for general distribution, and Sears (1971, 2004) and Sears and Wilce (1975) for detailed ecological studies. Copies of the Treat et al. (2003) paper are available at the Polly Hill Arboretum visitor center.

Allan Keith; edited by Matt Pelikan, July 19, 2022


Gosner, K. L. 1979. A field guide to the Atlantic seashore: invertebrates and seaweeds of the Atlantic coast from the Bay of Fundy to Cape Hatteras. Houghton Mifflin Co., Boston. 

Kingsbury, J. M. 1969. Seaweeds of Cape Cod and the Islands. The Chatham Press, Chatham,  MA.

Sears, J. R. 2004. Survey of benthic seaweeds – Noman’s Land Island National Wildlife Refuge, July-August 2004. Report to U. S. Fish & Wildlife Service and Polly Hill Arboretum. Unpublished. 16 pp. [On file at PHA Library]

__________, ed. 2002 NEAS Keys to benthic marine algae of the northeastern coast of North America from Long Island Sound to the Strait of Belle Isle, 2nd edition. Contribution 2, Northeast Algal Society, Dartmouth, MA. 161 pp.

__________. 1971. Morphology, systematics and descriptive ecology of the sublittoral benthic marine algae of southern Cape Cod and adjacent islands. Ph.D. dissertation, University of Massachusetts. Contribution No. 246, Systematics-Ecology Program. Marine Biological Laboratory, Woods Hole, MA.

__________ and R. T. Wilce. 1975. Sublittoral benthic marine algae of southern Cape Cod and adjacent islands: seasonal periodicity, associations, diversity and floristic composition. Ecological Monographs 45:337-365. (2022)., accessed 19 July 2022.

Stephenson, S. L. and H. Stempen. 1994. Myxomycetes: a handbook of slime molds. Timber Press, Portland, OR.

Taylor, W. R. 1962. Marine algae of the northeastern coast of North America. University of Michigan Press, Ann Arbor, MI. 509 pp.

Treat, R., A. R. Keith, and R. T. Wilce. 2003. Preliminary checklist of marine algae from Martha’s Vineyard, Massachusetts. Rhodora, 105(921):54-75.

Villard-Bohnsack, M. L. 1995. Illustrated key to the seaweeds of New England. Rhode Island Natural History Survey, Kingston, RI. 145 pp.