JIM CONRAD'S
NATURALIST NEWSLETTER
Issued in Río Lagartos, on the northern coast of
Yucatán, MÉXICO
in Ría Lagartos Biosphere Reserve

March 8, 2015

TREE OYSTERS
At low tide we were on the mudflats across the estuary from Río Lagartos developing a new tour concept, "Low Tide Tours." We were looking around to see what there was to show tourists later. At the edge of the mudflat Jorge waded into a dense, shadowy tangle of Red Mangrove stilt-roots and soon called me over. He pointed into a dark, dank part of the tangle where I could see nothing special, even when my eyes adjusted to the darkness. The thing Jorge was showing was so well camouflaged that he had to tap it with a stick. You can see where he pointed at http://www.backyardnature.net/n/15/150308ow.jpg.

That picture shows alga-covered Red Mangrove roots barely above the water, with what Jorge was trying to show me occupying the lower, left third of the image. It's a collection of vertically positioned, flattish, brownish oysters clinging to roots. Once you knew what to look for, there must have been thousands of them, hundreds of thousands in that general area, a major presence I'd never realized was there.

These are Flat Tree Oysters, ISOGNOMON ALATUS, found throughout the Caribbean and Gulf of Mexico from southern Florida to Brazil. Its main habitat is the roots of Red Mangroves but also it occurs in shallow, rocky areas down to depths of 50 feet (15m).

Flat Tree Oysters are filter feeders who draw water into their shell and pass it through gills, extracting plankton and small organic particles for food. The mollusks reach about 3½ inches (9cm) in length and attach themselves to roots and rocks by a "byssus thread." A byssus is a group of strong filaments secreted by some families of bivalve molluscs, for attaching themselves to hard surfaces. In the past, a fine fabric called "byssus cloth" was made from the byssuses of pen shells.

Jorge, wanting to add some to the aquarium back at the restaurant/tour office, pulled some oysters from their roots. You can see one, its shell covered with tiny Spirorbis Worm Tubes (polychaetes in curled, snail-like tubes) and a barnacle, with pieces of mangrove bark sticking to its byssus threads, at http://www.backyardnature.net/n/15/150308oy.jpg.

A side view showing its flatness, with a small bivalve incongruously wedged among its byssus threads, is shown at http://www.backyardnature.net/n/15/150308oz.jpg.

Flat Tree Oyster shells are pearly and lustrous inside but the species isn't known for producing pearls. Locally folks sometimes eat them, though you don't see the oyster being collected for food the way you do with conchs on the mudflats.

*****

SCORPIONFISH
At low tide Rayo and I were wading ankle-deep in a Shoalgrass bed that normally lay too deep for such exploration. Spotting a funny looking fish nicely camouflaged atop the mud among Shoalgrass leaves, Rayo scooped the critter into the cut-off bottom of an old Purex jug. You can see what the three-inch-long (8cm) fish looked like then at http://www.backyardnature.net/n/15/150308sf.jpg.

It almost looks like a catfish, but note the long fin atop the body, the dorsal fin, which catfish don't have. Rayo said he'd met this species before, because one day his barefooted brother Jorge stepped on one, causing his foot and lower leg to swell and hurt for three or four days. Therefore, instead of taking the fish into his hand for a better view, unceremoniously he dumped it onto an alga-encrusted rock barely poking from the water. To our surprise, the fish quickly stood itself right-side-up, supporting its body with its side, or pelvic, fins, as if it had a mind to walk off with them. You can see this at http://www.backyardnature.net/n/15/150308sd.jpg.

In that picture you can see that something funny is going on with the eye. Before flipping the fish back into the water I got the close-up eye shot shown at http://www.backyardnature.net/n/15/150308se.jpg.

It was hard to identify this fish, but it appears to be the rather common Spotted Scorpionfish, SCORPAENA PLUMIERI. My difficulty arises from the fact that the species' appearance changes as it ages. The vast majority of pictures of this species on the Internet show adults, and we have a young one. Spotted Scorpionfish reach almost 18 inches in length (45cm), and can weight nearly 3½ pounds (1.6kg). As Spotted Scorpionfish age and grow, their body surface acquires an impressive collection of warts, bumps and fleshy appendages that contribute to the fish's camouflage, making it look like an alga-encrusted rock. Also, I read that normally the fish is rusty hued, but in shallow water, where we found ours, it becomes grayish, like ours. Some big Spotted Scorpionfish are surprisingly brightly colored and outlandishly shaped. You might enjoy seeing an older one photographed in Honduras at http://www.flmnh.ufl.edu/fish/gallery/photoout.asp?id=6822.

TheDivingBlog.Com website said that scorpionfish are members of "the infamous scorpionfish family." "Infamous," probably because The Scorpionfish Family, the Scorpaenidae, includes many of the world's most venomous species. As Jorge can testify, scorpionfish have venomous spines on their backs. The family also may be "infamous" because among its members are the Lionfish, an invasive species native to the Indo-Pacific, currently threatening coral reefs in our area. One study suggests that they may ultimately decrease Atlantic reef diversity by up to 80%.

But that's invasive Lionfish, and here we have the native Spotted Scorpionfish, which does nothing more aggressive than envenom any creature that mistreats it. Normally Spotted Scorpionfish feed on crustaceans and other smaller fish, using the lie-in-wait strategy. They suck in small prey who wander too close to their mouths by simply snapping open their big mouths incredibly fast, causing water containing critters to rush into the vacuum created by the sudden opening. Predators of Spotted Scorpionfish include large snappers, sharks, rays and moray eels.

And what of those eyes? Lots of people take close-up pictures of the eyes, but so far I can't find any explanation for their strange appearance. I do read that among scorpionfish species eyes often are set atop the head, enabling them to see what's going on when they bury themselves in sand, with their eyes poking out.

*****

FIREWORMS
At low tide, some particularly slimy looking gunk was pooled inside an old, abandoned, mostly rusted-away dredging pipe, and one part the slime was working with worms. You can see the mess at http://www.backyardnature.net/n/15/150308fw.jpg.

The worms were pinkish and wrapped around one another like mating earthworms, but this habitat was too wet for earthworms. In other words, probably these were yet another form of polychaete, polychaetes being a huge, very diverse group of bristle-equipped, segmented worms, of which we've been seeing many kinds in our local estuarine and marine environments. I separated a worm from its mud, nudged into the palm of my hand, washed it off, and you can see it curled up there at http://www.backyardnature.net/n/15/150308fy.jpg.

The worm's segmentation is easy to see, as well as the disposition of its spines -- two lines of them, one above the other, on both sides. In that picture the spines look as if they're very thick-based, or "bulbous," narrowing to extremely sharp tips, as we've seen in stinging plant hairs where toxins are stored in the bulbous bases. However, what seem to be single, thick-based spines are really tufts of very fine spines held together by adhesive forces. The slender, pliable spine tufts are behaving like soft bristles of a watercolor brush. When submerged, the bristles spread away from one another, but when removed from water they adhere to one another forming a single, sharp-pointed brush. In the picture, the bottom-most spines sopping water from my hand better display their tufted nature. This matter is important because the vast majority of pictures of this creature on the Internet show submerged worms with obvious tufts of bristles, not the broad-based, sharply pointed ones ours seem to have.

Soon the curled-up worm began uncoiling itself, surprising me with its length, expanding like an accordion opening up, but much more so, as shown at http://www.backyardnature.net/n/15/150308fx.jpg.

This is the Fireworm, sometimes called Orange Fireworm, EURYTHOE COMPLANATA. The fire in its name possibly relates to its pinkish hue, but most probably it refers to the fact that the worm can deliver a painful sting with those tiny, white bristles along it body edges. I read that its bristles, or setae, are hollow and contain venom, and that they can break and stay in one's skin, causing long-lasting pain. I wasn't stung, and it's hard to imagine such a small worm with such fine hairs delivering much of a sting, but ours is a small one. They reach about six inches long (15cm).

Fireworms often are abundant in shallow, tropical, marine waters. In earlier years they were regarded as worldwide in distribution, but lately studies have indicated that several look-alike species probably are involved, so now some experts say that our Eurythoe complanata is limited to the tropical Western Atlantic -- the Caribbean to southern Brazil.

The Fireworm's favorite food is carrion. It moves around at night, and during the day can be found under rocks, inside calcareous algae and corals, or buried in soft sediments, like ours. They have a complex sexual reproductive cycle involving a freely floating "trochophore larva" stage, but also it can reproduce by fragmentation. When broken into pieces, each part grows a head and tail, and becomes a complete worm.

And Fireworms are indeed polychaetes, members of the family Amphinomidae, of which Fireworms are the best-known members. In general, polychaetes are considered to be the most "primitive" of living annelids -- to most closely resemble the common ancestor of all segmented worms, and maybe even all segmented animals. Our view of them enmeshed in gray goo evokes the notion of primitive life in primordial slime, and that may be close to the way it really was early in the history of Life on Earth.

*****

THE COMMON ATLANTIC MARGINELLA
During low tide on the polychaete-rich mudflats, the remains of a large crab -- eaten by a Raccoon, judging from the tracks -- caught our attention. Up closer we saw numerous small, shiny-white, snail-like mollusks a little less than half an inch long (12mm) scavenging the crab's remains. A small part of the assembly is shown at http://www.backyardnature.net/n/15/150308pr.jpg.

Despite the many individuals before us, this little mollusk species had escaped my attention until now. It was surprising how so many could congregate in one place, seemingly out of nowhere. Down on hands and knees, the little white snails displayed other surprising features, too. For example, look at the long, slender "snout" projecting from below and between a snail's golden eyes, and look at the curious, white-on-white splotching or vertical banding on the shell's sides of a well camouflaged individual shown at http://www.backyardnature.net/n/15/150308ps.jpg.

Not all individuals displayed such white-on-white patterning, and some showed in-between states, as you can see at http://www.backyardnature.net/n/15/150308pt.jpg.

In that picture, on the nearest snail, the banding covers nearly the entire shell, but on the shell in the picture's left, side banding is restricted to the shell's bottom. Moreover, if you look closely at the shell in the picture's top, right corner, it seems that sunlight highlights what appears to be the rim of a membrane-like structure expanding from the shell's bottom. All this was very confusing; I'd not run into such a thing before. Hoping for more evidence about what was going on, a snail's bottom was photographed, shown at http://www.backyardnature.net/n/15/150308pu.jpg.

Somehow volunteer identifier Bea in icy Ontario figured out that our snails belong to the Margin Shell Family, the Marginellidae, broadly described as a family of small, often colorful sea snails, the taxonomy of which has long been in a state of confusion, and still is. There's no agreement on how many species the family embraces, but there's a lot of them and often they're very similar to one another. The Margin Shell Family takes its name from the thickened margin on the shell's outer lip. You might enjoy exploring the family as seen by a commercial shell collector, who describes shells of the family as predominantly small, shiny and jewel-like, at a website here. .

After poring over many possibilities, Bea finally gave her official but UNprofessional opinion that our little, white, carrion-eating snails were PRUNUM APICINUM, sometimes known as the Common Atlantic Marginella. Moreover, she thinks that the white-on-white splotches are exhibited by "mantle flaps," which are fleshy extensions of the body that in some snail species can be wrapped up around the shell, exactly as our snails seem to be doing. Common Atlantic Marginellas occur in shallow saltwater from North Carolina in the US south through the Caribbean and Gulf of Mexico, to here. Their habitat is described as submerged tidal flats and shallow seagrass beds, which is exactly where we found them here.

Little information is known about its general abundance, but off the coast of the US Southeast it's regarded as the most common of the marginellas. Also little is known about its life history. The Smithsonian Institution page for the Common Atlantic Marginella says that "... the species likely scavenges organic material from the sand," so here we can confirm this. The same page says that the species probably is preyed upon by a variety of fishes, crustaceans and larger predatory snails.

So, here's a little-known, tiny, modest-looking creature that, if you get on your hands and knees and pay close attention, turns out to be uncommonly interesting and pretty. In other words, it's like nearly everything else in Nature.

*****

MEXICAN PALMETTO
On a birding tour into the ranchland south of town, which was palm- and grass-rich savanna before livestock was introduced, two fan palms stood next to one another, as shown at http://www.backyardnature.net/n/15/150308sb.jpg.

What caught my eye wasn't their different trunk lengths and widths, for this can be explained by age and individual palm tendencies to retain petiole bases of old fronds. What I noticed was that on the palm at the right old flowering clusters, or inflorescences, projected far beyond the fronds, which is the behavior of our abundant Huano Palms, or Thatch Palms, Sabal yapa. However, the palm on the left also has an old inflorescence, but it's much shorter than the fronds, barely visible drooping in the shade on the trunk's right side. A closer look at another such palm's old inflorescence is at http://www.backyardnature.net/n/15/150308sc.jpg.

Something else to notice in that picture is that the old petiole bases covering the stem are split at their own bases. Our abundant Huano petiole bases don't split like this. Here we have a different species of the genus Sabal.

CICY, the Centro de Investigación Científica de Yucatán, lists four Sabal species for the Yucatan. Our abundant one is Sabal yapa. Another species, Sabal mauritiiformis, occurs from southern Mexico south to northern South America, but in the Yucatan it appears to be restricted to the rainier southeastern section, plus its inflorescences extend beyond its fronds, so our palm with its short, drooping inflorescence isn't that one.

Sabal gretheriae, endemic to just the Yucatan and possibly found in our area, was recognized only in 1991, and is so similar to the fourth species, the Mexican Palmetto, Sabal mexicana, that some experts regard Sabal gretheriae as just a local variation of Sabal mexicana. Our tree on the left is one of these two taxa, if Sabal gretheriae exists, but which one? Working just with our photos and lacking flowers and seeds, I can't say which species it is. However, Sabal mexicana would be more likely here, plus the inflorescence of Sabal gretheriae is described as strongly ascending, while that of Sabal mexicana is "arcuate," meaning that it arches outward. Our old, drooping inflorescence doesn't seem to have ever strongly ascended. I'm calling our tree SABAL MEXICANA, found in dry lowlands from the Lower Rio Grande Valley of Texas south to Nicaragua. It's one of the most widespread and common of Mexico's palm trees.

Something interesting about Sabal Mexicana's presence in our area is what Scott Zona writes in his 1990 "A Monograph of Sabal (Arecaeae: Coryphoideae)." He says of the species that "Its presence in Yucatán may be attributed to the activities of pre-Columbian peoples." He doesn't regard it as naturally occurring here.

Zona's monograph on Sabal can be downloaded for free at http://www.virtualherbarium.org/PDF%20Files/Zona_Sabal_monogr.PDF

*****

GOOSEBERRY-TREE
On a backstreet a couple of blocks from where I stay a certain small tree that has lost all of last season's leaves, this week has been loaded with yellow, cherry-sized fruits, as shown at http://www.backyardnature.net/n/15/150308pj.jpg.

Some branches already are issuing the upcoming season's leaves, which are pinnately compound. The tree's bright, yellow fruits and fresh, green leaves are pretty to see against our normally blue sky, as seen at http://www.backyardnature.net/n/15/150308ph.jpg.

The fruits dangle in attractive clusters, shown at http://www.backyardnature.net/n/15/150308pi.jpg.

Up closer you see that the fruits are curiously angled, or ribbed, as shown at http://www.backyardnature.net/n/15/150308pk.jpg.

Biting into the fruit you find a large, hard, woody, shallowly grooved item in the center to which the fruit's fibers strongly attach, as shown at http://www.backyardnature.net/n/15/150308pl.jpg.

In Spanish our tree is called Grosello. Maybe the best English name is Gooseberry-Tree, even though our tree is not closely related to the Gooseberry plants Northerners know. Our Gooseberry-Tree is PHYLLANTHUS ACIDUS, a member of the Spurge or Euphorbia Family, the Euphorbiaceae, while the North's gooseberry trees belong to the Currant Family, the Grossulariaceae. Gooseberry-Trees are planted in warmer zones worldwide, and go by many names. Another English name frequently encountered for it is Otaheite Gooseberry, the word "Otaheite" being an early name for the Pacific island Tahiti.

Gooseberry-Tree has been so widely planted for so long that its native land isn't known, though some suppose it might have come from Madagascar. The species spread through much of southern Asia in prehistoric times and gradually made its way among Pacific Islands. It's said to have been first brought into the Caribbean in 1793 when Captain William Bligh carried the plant from Timor to Jamaica.

In the Yucatan's little Maya villages you don't see this tree as commonly as other fruit-bearing trees, but probably most towns have at least one, for the fruits are very acidy and can be made into a drink similar to lemonade, or candied with lots of sugar. Some people who can stand the tartness nibble the fruits raw. In certain cultures the fruits are soaked in salt or vinegar-salt solution and sold along roads, though I've not seen that here.

Different cultures use it medicinally in different ways. The online Atlas de las Plantas de la Medicina Tradicional Mexicana reports that in the Yucatan it's used against diarrhea and as a disinfectant. In Quintana Roo, where Cancún is located, a tea is made from the flowers to cure coughs.

Botanically, the fruit is unusual. With such a hard center it seems similar to a one-seeded cherry, which is a drupe. However, the hard thing in the fruit's center isn't a typical seed such as a drupe would have. The object's hard cover normally surrounds six to eight smooth seeds, instead of just one. Such fruit sometimes are said to be "drupaceous," meaning "drupe-like." Technically the Gooseberry-Tree's fruit is a berry, meaning that, like the tomato, it's a pulpy fruit derived from a flower's single pistil, and contains more than one seed.

*****

A HANDSOME WILD BEAN VINE
Out in the ranchland south of town where palm- and grass-rich savanna has been fenced in for cattle grazing, grown-over spots along the road where the cows can't reach often support interesting plants. One such plant this week has been a twining vine of the Bean Family, its long, slender, straight legumes and large, purplish flowers shown at http://www.backyardnature.net/n/15/150308vg.jpg.

Not unlike the compound leaves of a garden bean-vine, this vine's leaves are divided into three leaflets, shown at http://www.backyardnature.net/n/15/150308vi.jpg.

The pretty flowers are papilionaceous -- having a large top petal, two flaring side petals and two lower petals fused along their common margins to form a scoop-shaped "keel" -- typical of the Bean Family, but the blossoms are surprisingly boldly colored, as seen at http://www.backyardnature.net/n/15/150308vh.jpg.

This flower's bottom "keel" has elongated into a slender tube that curves upward counterclockwise. This remarkable keel helps us peg our vine as VIGNA CANDIDA. Despite its prettiness, Vigna candida just doesn't have a good English name. The genus Vigna is famous for providing several important food species, including the Adzuki Bean (Vigna angularis), the Cowpea (Vigna unguiculata), and the Mung Bean (Vigna radiata).

Our vine's flowers are more intensely colored than those of other Vigna candida pictures found on the Internet. My impression just looking at this one plant is that as the flowers age they turn lighter, and the big top petal enlarges.

Vigna candida is a widely distributed species, found from southern Mexico south through Central America into the northern half of South America. With such a nice bean pod developing, you'd think the beans might be edible. However, I find no traditional uses for the vine other than as a forage plant for livestock.

*****

GAUMER'S MAMMILLARIA FLOWERING
During my 2006 visit to Río Lagartos I was introduced to the very narrowly endemic Yucatan cactus known as Guamer's Mimmillaria, MAMILLARIA GAUMERI. Our page showing and describing it is at http://www.backyardnature.net/yucatan/mam-gaum.htm.

Nowadays the low, barrel-type cactus is producing small, creamy-white flowers, as shown at http://www.backyardnature.net/n/15/150308mm.jpg.

A close-up of a flower as well as the interesting spine clusters, each atop a "tubercle" shaped like a green chili pepper, is at http://www.backyardnature.net/n/15/150308mn.jpg.

*****

FINE-TUNING THE YUCATAN'S BEACH TRASH
In 2011 during our stay on the Caribbean beach north of Mahahual and the Belize border, I made an informal analysis of the abundant trash that every day washed up on the sandy beach there. The study is described at http://www.backyardnature.net/yucatan/trash.htm.

Much of the trash was labeled with its presumed country of origin. Of 33 items whose origin could be identified, garbage from 15 countries was found. The nation providing most garbage was Colombia, with 9 pieces, or 27%. The next most represented country was Mexico itself, with 5 pieces, or 15%, and then Venezuela with four pieces, or 12%. Countries contributing 2 pieces, or 6%, were Jamaica, Trinidad and Tobago, Suriname and Honduras. The remaining countries sending only one piece of trash each were St. Lucia, Haiti, Guatemala, Netherlands, Singapore, China, USA and Russia. I'm guessing that items from the last four countries were dumped from passing ships.

That study was done on the Yucatan's eastern shore, on the Caribbean side. Now we're on the northern coast, facing the Gulf of Mexico. Is the abundant trash that washes ashore here on the northern coast facing the Gulf of Mexico similar to that found on the eastern shore facing the Caribbean?

When I began conducting the same study here, I cut it off after identifying the origin of only ten items, because they were all from Mexico. Ocean currents off the northern coast obviously are different from those on the eastern coast. On the eastern, Caribbean side, the Gulf Stream carries trash up from northern South America and Central America. Here on the northern coast, there's an offshore current generally flowing from east to west, but apparently that current doesn't branch off the big one carrying international trash northward off the Yucatan's eastern coast. A map at the University of Miami sums up the situation at http://oceancurrents.rsmas.miami.edu/caribbean/yucatan.html.

To me that map doesn't really explain why all the trash I find on our northern beaches is Mexican. However, while I was at the University of Miami website I took advantage of an invitation to write in the guest book, asking about the lack of international trash on our northern coast. Later that same day Dr. Arthur Mariano at the University of Miami's Rosenstiel School of Marine & Atmospheric Science wrote this to me:

"I think it is because there is a wide shelf and the Yucatan Current has a large northerly flow component between the Yucatan and Cuba. It would take strong winds from the North to get the garbage onto the northern shores and those winds events, I think, are rare in that area."

So, normally we don't have strong winds from the northeast here, and they're needed to blow international garbage floating northward atop the Yucatan Current carrying things past the Yucatan's eastern coast toward Florida. What garbage that turns up here, then -- and there's plenty -- is all Mexican stuff, unless a strong wind from the northeast kicks up.

*****

FEATURED ESSAYS FROM THE PAST:

"Garlicky Stews" from the February 2, 2009 Newsletter, at http://www.backyardnature.net/n/p/090202.htm

"Frost & Green Tomatoes" from the November 30, 2003 Newsletter, at http://www.backyardnature.net/n/p/031130.htm

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.