Melobesia marginata

Coarse Coralline Crust

26 June 2025

Fishboat Bay, Juan de Fuca Strait, B.C., Canada.

Tide: -0.7 foot low at 09:29 PDT (measured at Sheringham Point Tidal Station)

Weather: Overcast, wind variable 5 – 10 km/hour, sea rippled, no swell, humidity 88%, 13 ˚C.

Moon: Waxing Crescent (2.5%, 1 day); Next Phase, First Quarter, 2 July 2025 at 12:30 pm PDT; Previous Phase, New Moon, 25 June 2025 at 3:31 am PDT.

Figure 1: Cast adrift from its anchor point, this cluster of Cylindrical Forked Seaweed, Fredericqia decewii, has been the host to a profusion of Melobesia marginata crustose alga growth. The whitish looking clusters are surprisingly hard, rough, and very tough. They also are heavy (relatively speaking they are very heavy), and it looks as if their combined mass tipped the balance point for the host’s holding power. Fishboat Bay, Juan de Fuca Strait, Vancouver Island, B.C., Canada. June 26, 2025. Photo ID 27825 ©Seaweedwhisperings.com

Person 1:

Rough.

Overwhelming.

Greedy.

Thoughtless.

Very rough sandpaper.

Abrasive.

Extremely ugly.

No redeeming features.

Hard and callous.

Highly opinionated.

Not interested in understanding others or anything.

Figure 2: Whoa! This group of Ahnfeltia fastigiata looks as if it has been almost overwhelmed by the growth of the epiphyte, Melobesia marginata. The inset photo shows how the narrow wiry thalli of the host seaweed have made a fine home for Melobesia to really grow with vigor. The duo as a combined organism is much larger and messier, and to some eyes, rather ugly looking. Fishboat Bay, Juan de Fuca Strait, Vancouver Island, B.C., Canada. June 26, 2025. Photo ID 27826 ©Seaweedwhisperings.com

Person 2:

Wow! Look at this! This was my exclamation upon finding a recent cast ashore Fredericqia decewii that was coated in thick wrappings of Melobesia marginata.

I’ve seen big ‘accumulations’ of Melobesia marginata previously but this example is striking – there is so very much of this algal crust covering the stems of its host red alga that the host looks as if it is almost overwhelmed. It is a remarkable example of M. marginata doing very well, perhaps at its climax of development.

Prominent; dirty off-white colored clusters; looks like tiny casts on broken limbs.

Stiff, hard, gets too large, unbending, uncomfortable in its own skin.

Tough, hard, very hard – like concrete.

This seaweed has found its place and it intends to stay. Its simple plan is to grow, bit by bit, gradually cementing its position in the world and the personal security that comes with that.

On this host seaweed, one that has long slender cylindrical stems, the Melobeisa crust grows in such a way as to encircle it. Tiny dots of Melobesia join up and ring the host stem completely. This host seaweed combined with the crust is then far larger in diameter than the simple red stem of Fredericqia decewii on its own; it is easily double, triple or even quadruple the size. The individual bits all joined together reminded me of tapioca pudding in that there are larger parts of similar size that are connected to each other with some type of binding matrix.

They can get to a size that looks almost too large, and this is possible because some of their favorite algal hosts are wiry, cylindrical stems that are loosely spaced. The ‘forked-seaweeds’ are perfect for them to grow in thickness as well as length.

When I looked at how large the crust became I thought to myself, “What are you trying to prove, Melobesia marginata!” Maybe this seaweed can get carried away? It finds a suitable host seaweed, settles in, and then grows and grows and grows. Possibly it is fearful that if it is not large enough it will be vulnerable and too easily banished or evicted? It feels as if this kind of fear fuels the getting carried away but also their tissues are tough, they endure, so when they build upon themselves, they are definitely amassing their physical size.

Looking through a hand lens the structure of this crust is revealed. It seems to grow in layers, and each layer is a set of small spheres, all connected to each other but with the bumpy texture of a group of tiny rough marbles tightly collected all on one plane. Actually..., when I got a stronger lens, I could see that they are not really spherical in shape but something like a small chip of stone that has rough edges; these chips are all then joined together with a ‘glue’ that links them, one to another, forming a crust comprised of similar sized but irregular, angular pieces. This is one layer. Then Melobesia marginata seems to like to also add more layers vertically, so it progressively becomes thicker and thicker.

I shrank myself down to the size of one Melobesia ‘chip’ within its connecting matrix, and realized that they naturally prefer “high-rise” living. Crowded tightly horizontally and then also stacked vertically, they are comfortable in a crowd, or living perhaps as a colony.

I was first thinking of this term “colony” as I’ve seen them in nature as in colonies of nesting murrelets, auklets or puffins. Such colonies are composed of hundreds, even thousands of conspecific individuals living in close association. This association gives mutual benefit such as stronger defense against predators. But then I realized that the political definition fits too: a group of people of one nationality or ethnic group living in a foreign city or country. We could say that Melobesia is a foreigner that has settled in the territory of Fredericqia.

I thought about the description “like concrete” – and pondered why did I choose “concrete” as an example of hardness? There are much harder stones in nature, but concrete is a material that is created for specific purposes and it is a mix of materials bound together by the ‘glue’ of cement. Cement is primarily made from limestone, calcium carbonate, and clay which contains silica, alumina, and iron oxide. This little seaweed uses calcium carbonate in its own cells to make them strong and tough like concrete, and it is comprised of many bits all together like a conglomeration, too.

Touching the crust you can feel how it forms – the joining up of the pieces that make the crust. It is very rough, abrasive, like tiny, tiny barnacles in tight formation, or maybe like pumice stone or very coarse sandpaper. It feels like there is little that would erode or smooth this roughness – it is a trait that endures.

Figure 3: This enlarged view shows some of the Melobesia crust at its varying dimensions. The initial set of cells is laid down singly and looks quite neat, but as crowding begins the surface of Melobesia marginata becomes a bit messy or haphazard looking (as does its host). It is also more angular or cubical and much rougher and tougher in texture than you’d expect – the calcium carbonate in its cells makes hard like concrete. Fishboat Bay, Juan de Fuca Strait, Vancouver Island, B.C., Canada. June 26, 2025. Photo ID 27827 ©Seaweedwhisperings.com

Discussion:

Person 1 found some simple, harsh, and possibly uncomplimentary features for this seaweed. One of these is; “no redeeming features”. We explored that a bit further to give a bit more detail. It felt that this seaweed presents nothing obvious of value, and that there is nothing about it you would really like or want to interact with. When it really is doing well, seen from a distance this seaweed can look like some garbage or litter that has been caught in the stems of other seaweeds. It is not visually attractive and in fact is almost visually alarming – one could think, oh, what’s gone on here? Something looks amiss.

So, it can look like a collection of garbage from a distance yet it is also a compact life form that is organized in itself to grow as suits its needs. One of these needs is that it chooses to fortify itself, and it has an extremely tough exterior. Up close it looks angular and sharp and maybe like diamond chips that coat drill bits made for cutting hard materials. Why does this tiny seaweed need such a touch exterior?

We found that they desire protection and they’ve learned to build it for themselves. We found that it can feel unlikable and that they don’t want to let anyone understand that. It can feel ashamed of itself, and it can feel criticized by the ‘garbage’ type of descriptor we noted about them.

It has found that others can’t appreciate them for who they are; they have a weak connection with their inner knowing that they are a perfectly expressed life from just as they are. So, it seems, this seaweed has suffered judgments and condemnation and even ridicule when interacting with others. These opinions can overwhelm their confidence, and they consequently take the decision to go within, build a strong armor around themselves, and reveal nothing about themselves on the exterior that is in any way vulnerable.

The energy of this seaweed, experienced by the host algae, is something we dipped into a bit. We found that that the host seaweed could feel constricted or suffocated by the presence of Melobesia marginata but this we felt only with the individuals that were dramatically ‘covered’ with the Melobesia crust. In other examples where the algal duo was living a bit more in balance, we felt tolerance on the part of the host. Fredericqia decewii cannot really ever be said to be really enjoying having Melobesia marginata encircling its many thalli, but it could and does find a comfortable place of tolerance. From the perspective of Melobesia, they are so keen to find a suitable place to live and then to move in and set up house that they almost don’t see the host stems as much more than physical surfaces suitable for their needs. Not seeing the host as a fellow seaweed is almost a problem of scale; the host is so much larger that it could be like a mouse standing at the foot of an elephant and believing he was at the base of a large grey wall.

“Highly opinionated” is another not so flattering assessment but we felt this aspect comes from not enough interaction with others, or too much involvement with their own thoughts.

“Not interested in understanding others or anything” was a statement of how they appear on the outside. In fact this is more a reluctance to engage with much of anything that others might offer or suggest; they’ve learned this often leads to them feeling less than, foolish, or not appreciated. In reality, internally they have a keen interest in understanding many topics, but prefer to do this on their own and in private and away from scrutiny. Doing it on their own provides safety from outside ridicule or criticism. They may make mistakes in their process, but they also learn the corrections to those mistakes if they can be left to their own pace and their own way of doing things.

If they get interrupted..., this is when they can be “abrasive” and behave in an “ugly” manner; they don’t want to be sidelined from their pursuits. Interruptions are costly to them because it can take them quite a while to get back on track and settle in on their exploration once again. They don’t want anything coming in for their consideration until they are ready to seek it. Left to their own process, they reach excellent results. Interrupted in their process, nothing is excellent or works out all that well.

Layers; layers upon layers --- is that the physical mark of their explorations? Maybe it is like the growth rings of trees, the older they are the more rings there are, and this means they’ve gained more experience and can use that experience to their benefit. The hardness of these layers had us thinking of the expression “written in stone”, so some it feels like much of what they do can only come if they are settled and feel established with permanence.

Observing which seaweeds Melobesia marginata chooses to grow on, so where it makes its home, it is interesting to see that they face some pretty big difficulties. On our Whispering day we saw the Ahnfeltia fastigiata and Fredericqia decewii hosts, along with their colonies of Melobesia marginata, facing head on the force of incoming waves. They also from time to time will be completely buried in sand, and have no access to light for photosynthesis. These are tough living conditions that require tenacity, patience and endurance. These are qualities that demonstrate strengths of character and it seems that both the host seaweeds and Melobesia marginata embody these traits to successfully live in the environment of their choice.

At this point we paused the “Discussion” work on our Whispering, then returned to it after an interval of time had passed. Below are a few more points we noted.

It seems to be doing very well..., up to a point, and then it seems problems occur..., with the seaweed, the question is what broke the host away from its holdfast bringing them to their cast ashore predicament? We felt it was a matter of over doing..., over growing..., and too much weight being added to the host seaweed by Melobesia. This extra size and weight creates a larger ‘target’ so to speak for the regular forces of wave action. At a small size/weight, things are survivable; at the larger end of things, your own mass can be your downfall. So maybe their unbreakable tough and enduring physical presence ultimately makes them vulnerable, too. There is a lesson here for Melobesia around vulnerability.

When they are building personal security, we saw that with Melobesia it felt like it was also cultural security. Like the foreigners living together in a new country, if you’re just alone in a foreign place you are really alone, but if you can join a colony where your compatriots are also living you will have comfort and cultural security.

The aspect where we questioned “what are you trying to prove...?” We thought this hinted at an inherent aspect of feeling “less than”..., where there is a need to ‘prove’ themselves to others, but how they choose to do that can be misguided. As noted just above, if they get too big, they then may ‘crash and burn’. If they overwhelm their host and then together they both get overwhelmed by environmental forces (gravity and wave action)..., well, there does seem to be a fatal error involved. This suggests that there is an optimal size, an epiphyte to host ratio that must be observed otherwise mutual destruction is certain – the only question is the timing.

We paused once more, and then returned to our Whispering with a few more points.

This tendency to get too big..., we thought this seaweed can be careful (full of care) about some things, and miss entirely other areas where carefulness would be helpful. Looking at the morphology we found that its natural style is somewhat haphazard. It grows a blob here, another blob there, when crowded together they amass in clumps; it’s not orderly, haphazard is the best word for it.

We felt that Melobesia marginata will keep going, on and on, about what it believes. They can insist that others agree with them; not necessarily in a proactive way, but in a steady tortoise-wins-the-race kind of way.

Their angular shape and rough edges..., we felt that structure gives individuals some space when living close together. It will keep others away a little bit. It will give a small buffer in the crowded conditions. In this small space there is room for some individuality; as a whole, the colony is simply a crust. It’s like looking at a high-rise building in downtown Tokyo, the exterior looks pretty uniform, but every unit is not identical if you check on what’s inside. There is a kind of invisibility, a cover or protection or privacy if seen from a distance that can be desirable to Melobesia. Their individual personalities will not be casually shared. This is also how residents can view newly emigrated persons in their cities; you might see a group of people and think, “there’s a bunch of Somalis”, not knowing them well enough to say, “Oh, Jason is out with his nephew and niece. It’s good to see them enjoying time together”. The individual personalities are not learned, only the exterior shell that identifies their group.

One more layer now:

The biology of this red alga tells us that Melobesia marginata is “nearly circular in outline when developing singly; more or less angular when crowded. The “angular when crowded” character reminded us of the term “elbows up”. This term is ‘trending’ in our country since recent international trade disputes have been simmering and the term “elbows up” comes from the sport of ice hockey and one player in particular. Gordie Howe got a lot of elbowing penalties... and was nick-named “Mr Elbows” for his physically aggressive playing style. Melobesia could be called “Alga Elbows” as they really do seem to have a lot of angles and edges that are utilized to give them some room, create space, and generally keep others at a distance.

Biology also tells us that in this species “calcified cells (large) are joined by small uncalcified ones”. Then the “large cells divide to produce vertical rows of cells”. The cell structure fits in very well with our sense that this alga has a preference for “high-rise” living.

High-rise living..., no other seaweed we’ve interacted with has given us the idea that they can take part in this kind of living arrangement. Most macro marine algae are so much more flexible and fluid and reaching-their-thalli-at-length into the sea and towards the sunlight that it is difficult to imagine them ever comfortably living in residences such as we see humans do in their modern cities. But little Melobesia marginata can take up crowded living, and benefits from being tightly packed horizontally and then also expanding with levels rising vertically as well. It literally builds a solid protective structure for itself. We laughed when we thought of construction sites for modern high-rise buildings as there typically is a lot of concrete involved..., and that is what Melobesia has to work with, too. It has calcium carbonate that helps cement its parts together and make them durable like concrete. This seaweed is not fluid, it is fixed and firm and tough – and if there is any need for that particular trait, it borrows flexibility from its host seaweed. Very clever site selection, too, Melobesia! Your place and manner of living are indeed distinctive.

Figure 4: Anchored to rock that is immersed in sand, this red seaweed, Fredericqia decewii, is host to the crustose red seaweed, Melobesia marginata. The whitish colored crustose M. marginata completely encircles the thalli of the host and expands both in length and thickness as it grows. Both species endure sand abrasion, and at times, sand burial quite well. French Beach, Juan de Fuca Strait, Vancouver Island, B.C., Canada. March 8, 2021. Photo ID 27828 ©Seaweedwhisperings.com

Figure 5: Weathered and abraded as it’s been tossed around by the surf on this pebble beach, the purplish tint is strong with this cast ashore grouping of Melobesia marginata on Fredericqia decewii. Jordan River, Juan de Fuca Strait, Vancouver Island, B.C., Canada. September 24, 2023. Photo ID 27829 ©Seaweedwhisperings.com

Figure 6: This grouping of ‘forked seaweeds’ - the larger and brighter red Fredericqia decewii and the much finer and wiry Ahnfeltia fastigiata, are both hosting our species of note Melobesia marginata. All the seaweeds involved are just exposed at a very low spring tide (minus 0.7 feet) and, as seen in this photo, are being washed by the incoming surf. Fishboat Bay, Juan de Fuca Strait, Vancouver Island, B.C., Canada. June 26, 2025. Photo ID 27830 ©Seaweedwhisperings.com

Biology & Natural History Information:

Description:

First some understanding can be gained from the description of the genus, Melobesia that was published by Lamouroux in 1812. He tells us that the thalli are small, crustose and circular in outline unless densely crowded. This seaweed at first grows with a thickness of one cell and it is composed of laterally adjoined radiating filaments. As the seaweed matures, all cells except the marginal ones divide horizontally into a small uncalcified cell and a large more-or-less calcified cell; this larger cell, the calcified one, then may divide transversely to produce a vertical row of 2 to 15 cells. The portion of the thallus that is more than one cell thick is not sharply differentiated into hypothallium (base part of the thallus) and perithallium (surrounding part of thallus).

Foslie, in 1902, described Melobesia marginata, the species we interacted with in this Whispering. He says that that thallus forms orbicular crusts, at length extended patches on other algae, 50-100 µ thick. The conceptacles of sporangia are crowded, convex or subconical, 150-200 µ in diameter. He tells how it grows. The alga at first forms small orbicular, or sometimes rather irregular, purplish crusts on other algae. These crusts “by and by” anastomose (connection formed between previously separate parts forming a network) and at some length form extended patches almost covering certain parts of the frond of the host algae (in our waters that includes the Ahnfeltias and Osmundea). The crust is 50-100 µ thick and composed of at least up to 9 layers of cells. The basal cells are almost square, or more frequently, vertically elongated, up to 12 µ long and 5-8 µ broad. The upper cells on a section are square or somewhat rounded, occasionally forming short rows. Cortical cells are smaller. The cell walls are frequently rather thick.

The Marine Algae of the Monterey Peninsula gives a bit more of the picture. The thalli are described to be 5-8 mm in diameter and whitish purple in color. They are nearly circular in outline and with slightly lobed margins when developing singly but they become more or less angular when crowded. Thallus is two cells thick at the margin; up to 15 cells thick adjacent to conceptacles. Cells in the vegetative portion are cubical. The tetrasporangial conceptacles are numbers and slightly elevated above the thallus surface.

Habitat:

Epiphytic on their algal hosts, fleshy (non-calcareous) red algae including Ahnfeltia fastigiata, Fredericqia decewii and Osmundea spectabilis, in the low intertidal zone.

North Pacific Distribution:

From Haida Gwaii, British Columbia south along the Pacific coast to Mexico.

Classification:

Empire: Eukaryota

Kingdom: Plantae

Subkingdom: Biliphyta

Infrakingdom: Rhodaria

Phylum: Rhodophyta

Subphylum: Eurhodophytina

Class: Florideophyceae

Subclass: Corallinophycidae

Order: Hapalidiales

Family: Hapalidiaceae

Subfamily: Melobesioideae

Genus: Melobesia

Species: Melobesia marginata Setchell & Foslie 1902

Former name(s):

Homotypic synonyms: Epilithon marginatum (Setchell & Foslie) Setchell & Foslie null; Lithophyllum marginatum (Setchell & Foslie) Setchell & Foslie 1905; Lithothamnion marginatum (Setchell & Foslie) Setchell & Foslie 1908.

Figure 7: This is a typical view of how one might encounter Melobesia marginata in situ. A sandy beach with buried or partially immersed rock and cobble is needed. Then you simply need to look for light colored clusters of ‘something or other’ – they stand out even from a distance and they look a bit like flotsam or trash. Only when you look closely can you recognize the pattern of this coralline alga crust, and even then you might mistake it for a marine animal such as a bryozoan rather than a seaweed. Fishboat Bay, Juan de Fuca Strait, Vancouver Island, B.C., Canada. July 24, 2021. Photo ID 27831 ©Seaweedwhisperings.com