Oct 224 min read

Black Tar Spot: the West Coast Tide Pooler's Worst Enemy

Tide pooling is arguably one of coastal life's most rewarding endeavors! Miraculously colorful, tenderly intricate, and thoroughly out-of-this world marine organisms can be found behind nearly every rock. A closer look, however, will win the argument that the ocean is an intense and unforgiving place. Although the sea can be a silent source of splendor for human beings, the quest for survival is a way of life for the impressive variety of oceanic lifeforms that compete for space in the intertidal zone.

For humans, the dangers of the intertidal zone are fewer--albeit, no less significant or harsh (see our blog on this topic: "Tips for Exploring Tide Pools of The Mendocino Coast" ). When out in the field, having a keen understanding of your environment is pertinent, and maintaining a general awareness of the textures presented by the organisms that live within it can help keep you (and them) safe.

Cue: seaweed.

Seaweed can be surprisingly slippery! Along West Coast shores, arguably the number one offender at the top of the slippery seaweed list is Mastocarpus papillatus; commonly known as “Black Tar Spot” in its crustose form and “Turkish Washcloth” in its plant form.

In its "crustose form," M. papillatus is called "Black Tar Spot" and it coats rocks with a dark film that will challenge any boot tread. It is unquestionably one of our top causes for falls! The worst part is that this particular algae is very similar in color to the rocks they coat, making them relatively difficult to make out to the untrained or sun-blinded eye.

In its "plant form," M. papillatus is called "Turkish Washcloth" and it grows up to 6" ruffled dark brown-to-purple leaves that typically exhibit hundreds of small nubs like a terrycloth washcloth (hence the moniker).

Below are images of (Mastocarpus papillatus) in both the crustose and plant phases.

(M. papillatus) during its crustose phase - "Black Tar Spot Algae":

(M. papillatus) during its plant phase - "Turkish Washcloth":

(M. papillatus) primarily in its plant phase ("Turkish Washcloth"), with some crustose phase ("Black Tar Spot") visible near the center of the image:

What makes this particular seaweed truly quite fascinating is the remarkable complexity of its chosen method of reproduction--which explains how a single species can appear in two entirely different morphological phases; the crustose phase ("Black Tar Spot") and the plant phase ("Turkish Washcloth"). The Puget Sound Museum of Natural History included an impressive description of this process in their blog about M. papillatus (linked at the bottom of this post), which we have quoted here:

"Algae are fascinating to look at and often beautiful in their own way, but they don’t do much. What makes them especially interesting, however, is their complex reproductive cycle, and this one is more complex than most. Male gametophytes release nonflagellated sperm into the water column, and they are carried by the current to the female plants, where they lodge on receptive hairlike structures called trichogynes.

The attached sperm undergo mitosis without cell division, forming a spermatium. A fertilization pore between the spermatium and trichogyne allows fertilization. The fertilized eggs grow into a tetrasporophyte, which often looks just like the male and female gametophytes that produced it.

Under certain conditions, however, the fertilized gametes grow into a completely different sort of tetrasporophyte, a thin crust that looks like a patch of tar, thus the other common name. This is called the Petrocelis phase, from the name originally given to this stage, thought to be a very different type of alga. The tetrasporophyte produces tetrasporangia by meiosis, and the spores are released into the water column to germinate on another rock and complete the cycle. The encrusting stage at some point actually gives rise to the familiar branched plant."

* Applauds. *

You can see why I decided to quote that!

M. papillatus grows on rock-like surfaces from the high- to mid-intertidal zones down to 750 feet deep and is native to the West Coast of North America from California to Alaska (with some rare sightings recorded as far north as Russia and as far south as Chile). M. papillatus is considered edible in its plant form, which is rich in vitamins and is known to contain properties that strengthen the immune system and suppress the growth of viruses.

Below, Turkish Washcloth makes itself at home on a limpet shell--a fancy mollusk hat, perhaps?

The presence of Black Tar Spot tends to be the most aggressive in the summer and fall months.

Here are some tips for how to best maneuver through tide pool fields that are thick with Black Tar Spot:

Familiarize yourself with what Black Tar Spot looks like before leaving home.
Consider if you may like to have a walking stick/trekking pole with you. If yes, bring one along.
In the field, while in motion, always keep your eyes on your feet and your path forward. If you need to look away, stop walking. Do not walk while looking at anything except for where your feet are going next.
Avoid directly stepping on rocks and surfaces covered in "Black Tar Spot".
If stepping on a surface covered in "Black Tar Spot" is unavoidable, take very slow steps, keep your weight centered, do not make any sudden movements, and (with the exception of a walking stick) keep your hands free and ready to catch your fall.

M. papillatus is often confused with "Turkish Towel" (Chondracanthus exasperatus). Pictured below, this seaweed also grows along the Mendocino Coast and bears a similar texture, but it tends to be larger and more red:

FRIENDLY FUNGUS PHOTOGRAPHY

Black Tar Spot: the West Coast Tide Pooler's Worst Enemy

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