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

February 8, 2015

THE ENDANGERED CALICO GROUPER
A little stir arose at the fishing cooperative up the street when a fisherman brought in a fish no one had seen before. The meaty-looking, handsome, foot-long mystery is shown at http://www.backyardnature.net/n/15/150208gr.jpg.

I was invited to try to figure out the fish's identity but I was busy on another project so the above picture went off to volunteer identifier Bea in Ontario. Bea quickly determined that we had an EPINEPHELUS DRUMMONDHAYI, known by several evocative English names, including Calico Grouper, Strawberry Grouper, Speckled Hind and Kitty Mitchell.

With the name in hand, the fish's story could be learned. The species occurs throughout the Gulf of Mexico and up the US Atlantic coast to North Carolina. For a long time the Calico Grouper has been considered an important species for sports fishing and commercial fisheries. Our foot-long individual is a small, young one, adults reaching up to 3½ feet long (1.1m) and weighing up to about 65 pounds (30kg).

However, Calico Groupers have suffered greatly from overfishing, and from being caught accidentally when other species are being fished for. When brought up from the deep waters where they're normally found, they suffer "barotrauma" -- they "get the bends" from rapid decompression, and die. Off Bermuda the Calico Grouper once was an important food fish but now it has practically disappeared.

The Calico Grouper's population has suffered such a drastic decline that the IUCN Red List of Threatened Species lists it as "Critically Endangered." The IUCN page detailing the threats, and the reasons for its designation, is found at http://www.iucnredlist.org/details/7854/0.

Adult Calico Groupers inhabit offshore rocky bottoms in depths of 80-600 feet (25-183m) but are most common between 200-400 ft (60-120m). They feed on a variety of fishes and invertebrates, including shrimps, crabs, squid, and octopus. Females mature at four or five years, when they are 1½-2ft long (45-60 cm). Spawning occurs from July to September, and a large female can produce up to 2,000,000 eggs during one spawning.

Despite Calico Groupers being a mystery fish today, I suspect that at one time they were well known and much appreciated among this area's fishermen.

*****

RED STARFISH ON THE BEACH
At low tide a little red starfish only about three inches across (75mm) had been tossed ashore and either was dead on close to it. You can see the creature at http://www.backyardnature.net/n/15/150208sf.jpg.

Besides being dark red, a conspicuous field mark of this species is its covering of short, broad-based spines, shown close-up at http://www.backyardnature.net/n/15/150208sg.jpg.

Underneath, the mouth that's always present in a starfish's center, was all closed up, as seen at http://www.backyardnature.net/n/15/150208se.jpg.

An even closer look at the bottom of one of the arms, however, shows some interesting details, at http://www.backyardnature.net/n/15/150208sd.jpg.

Here on an arm's bottom surface the channel down the middle is called the "ambulacral groove." In this groove the starfish's sucker-equipped tube feet, or "podia," extend outward and coordinate into wavelike motions to pass food to the oral mouth at the body's center, plus they can attach to surfaces such as rocks. Some of the podia at the image's left corner are beginning to extend.

On both sides of the ambulacral groove are lines of toothlike "ambulacral ossicles." The word "ossicle" means "little bone," and that's what they are, just bony, smooth-topped, little nubbins. One can imagine how when the podia between the lines of ossicles pass food toward the mouth, the smooth, elevated ossicles keep the food raised above the starfish's surrounding rough skin, keeping the food from dragging or catching on it.

When a Google image search on starfish found in the Yucatan is made, many pictures of another red species turn up, the apparently abundant, similarly red and similarly spiky scaled Red Cushion Sea Star, Oreaster reticulatus. However, that starfish has thicker arms, its top scales are arranged into scale patterns, and is larger.

Our stranded starfish is ECHINASTER SENTUS, sometimes called the Spiny Sea Star. It's found in shallow waters of a variety of habitats from Florida south through the Gulf of Mexico and Caribbean to Honduras. I've seen it described as the most commonly found starfish on southern Florida's beaches.

This is my first attempt to identify a starfish and I learned a good bit doing it. During my Google-enable orientation I learned that taxonomically a starfish is a member of the echinoderm Class Asteroidea, of which about 1,500 species are known worldwide. In waters off the coast of Yucatán state about 32 starfish species have been identified.

What's the difference between a starfish and a sea star? None, except that in the old days we called them starfish but now a certain section of humanity, pointing out that they're not fish, urge everyone else to call them sea stars instead.

*****

LUGWORM CASTINGS
At low tide along the Gulf of Mexico beach, little piles looking suspiciously like freshly deposited mammal poop were scattered here and there on wet sand that's normally submerged. You can see such a pile yourself at http://www.backyardnature.net/n/15/150208lw.jpg.

Since the pile is shaped like a much smaller earthworm casting, I thought there might be a hole beneath the heap formed by a big worm who'd extruded the material from below. I nudged the pile but it had so little structural integrity that instead of being pushed to the side or lifted up, it simply smeared, exactly as if it were composed of nothing but wet sand.

By doing a Google image search on the keywords "worm beach sand castings," a page of image thumbnails was summoned from cyberspace. Some images similar to ours were labeled as lugworm castings, and that opened the door to an hour or so of learning about lugworms.

The best I can tell, here on the Yucatan's northern coast we have two lugworm species large enough to produce such heaps. One of them, Arenicola cristata, defecates sand in flat sheets, not as coiled heaps like ours. The other lugworm species, ARENICOLA BRASILIENSIS, produces coiled castings like ours. It's a clumsy way to identify a species, but from what can be found on the Internet, Arenicola brasiliensis seems to be the only creature capable of depositing such castings on wet beach sand in our area. Arenicola brasiliensis, which doesn't have a good English name, is broadly distributed worldwide, especially in warmer marine waters, occupying sand and mud in low intertidal zones.

Arenicola brasiliensis digs a J- or L-shaped burrow and orients itself so that its sand-depositing rear end is close to the surface. The head end stays well below the surface at the bottom of the J, where it ingests sand. As sand passes into the lugworm, a closed, funnel-shaped depression forms on the sand's surface above the head. Hopefully the sand contains enough organic matter to serve as food to keep the worm alive. The gut-processed sand is then defecated at the sand's surface, forming a casting like what's shown in our photo. It's hard to belive that the sand where I found this casting contains much organic matter, and in fact only a few castings were seen. Pictures on the Internet show certain beaches littered with vast numbers of lugworm castings, though the lugworms depositing them were of a different species.

Lugworm sex is about as impersonal as can be imagined. The individuals concerned stay in their borrows, never coming in physical contact with one another. Males periodically issue sperm into the water outside their burrows, the water carries the sperm to burrows of receptive females, and the fertilized females produce larvae who after a short period of development leave the mother's burrow to be transported by water currents to new areas.

As lugworms burrow in the sand they oxygenate it -- a process known as "bioturbation." They are preyed upon by a wide variety of animals such as birds. If a lugworm's rear end is nipped off by a hungry bird, it can be regrown, as with some lizard species.

Taxonomically, lugworms are segmented worms, or annelids, of the special kind known as polychaetes, or bristle worms. We've profiled several polychaete species before, all of which lived in various kinds of calcareous tubes, not burrows in sand. You can review those other polychaetes on our Worms Page at http://www.backyardnature.net/n/worms.htm.

I didn't dig into the sand to expose the lugworm to be photographed, simply because I didn't want to ruin the creature's day.

*****

MEXICAN SILVER PALM
When rare and endangered species occurring in Ría Lagartos Biosphere Reserve are listed, the Mexican Silver Palm, COCCOTHRINAX READII, always makes the list. It's endemic to the Yucatan Peninsula and in our area occurs only in small populations just behind the dunes along the shore, where salty, hot winds and sandy soil keep the vegetation low and scrubby. I've been looking for the species ever since I got here, and this week I finally found it. The small fan-palm with silvery-bottomed fronds is shown in its habitat at http://www.backyardnature.net/n/15/150208cc.jpg.

In that picture the taller, darker palms in the background are the Buccaneer Palms we profiled last week. The scrubby plants forming an almost impenetrable thicket around the silver palms are mostly Poisonwood trees (Metopium brownei), Baybean vines (Canavalia rosea), and Seaside Oxeye shrubs (Borrichia arborescens). The spear-like items pointing at the sky are old fruiting heads of Caribbean Agave, Agave angustifolia. A silver palm shown closer up is seen at http://www.backyardnature.net/n/15/150208cd.jpg.

Besides for their rarity, one reason it was hard to find them was that Mexican Silver Palms are very similar to the abundant and extremely variable-looking Thatch Palm, or Chit, Thrinax radiata. You can see the Thatch Palm at http://www.backyardnature.net/yucatan/chitpalm.htm.

For help in distinguishing the two species I went onto the very active online forum of the International Palm Society at http://www.palmtalk.org/forum/. There Aztropic in Arizona told me that petiole bases of Thatch Palm fronds split, while Mexican Silver Palm petiole bases don't. Aztropic was right, and you can see a non-splitting silver palm petiole base at http://www.backyardnature.net/n/15/150208ce.jpg.

It wasn't the non-splitting petiole bases, however, that enabled me to spot our tiny island of Mexican Silver Palms in an ocean of scrub and Thatch Palms. Rather it was the silver palm's silvery frond undersurfaces, shown at http://www.backyardnature.net/n/15/150208ch.jpg.

That picture was taken with the low morning sun at my back. Normally the silveriness isn't as conspicuous.

Then there was the matter of the "hastula," which is a triangular, toothlike appendage on the upper surface of some fan palms fronds, where the blade attaches to the petiole. The literature says that the Thatch Palm's hastula is triangular but the Mexican Silver Palm's can be triangular, notched at the tip, or have two distinct tips. On each of our trees hastulas can be found in different configurations, including the one shown at http://www.backyardnature.net/n/15/150208cf.jpg.

One of our trees was loaded with over-mature fruits, shown at http://www.backyardnature.net/n/15/150208cg.jpg.

Finding this rare palm has been one of the highlights of my stay at Río Lagartos, and receiving the enthusiastic help of folks at the PalmTalk.Org Forum just made the experience sweeter.

*****

THE VERY VARIABLE THATCH PALM
While hunting for our endemic Mexican Silver Palm thousands of similar-looking and locally abundant Thatch or Chit Palms, Thrinax radiata, had to be sifted through. During that process I was impressed with the Thatch Palm's many variations, some of which are shown below. First, though, you may want to see what "normal" plants look like at http://www.backyardnature.net/yucatan/chitpalm.htm.

Immediately behind the dunes running along shore, the vegetation is stunted by the salty air, the persistent hot wind, and the sandy soil, which doesn't hold rainwater and contains relatively few nutrients. You can see a cluster of Thatch Palms in an ocean of scrub behind the dunes at http://www.backyardnature.net/n/15/150208p5.jpg.

Closer up you see that these individuals have smaller fronts but thicker trunks than the same species found in the interior in friendlier environments, at http://www.backyardnature.net/n/15/150208p6.jpg.

The fronds, hardly the size of garbage-can lids, are scorched by salt and sun, and tattered by stiff ocean breezes, as shown at http://www.backyardnature.net/n/15/150208p7.jpg.

The fronds distinctive "hastulas," formed where the petiole attaches to the blade, on the blade's top surface, is normal, however, as shown at http://www.backyardnature.net/n/15/150208p8.jpg.

Frond petiole bases arising from thickets of fibers are split, also in the normal way, as seen at http://www.backyardnature.net/n/15/150208p0.jpg.

Old flowering heads extend well beyond the small fronds, as shown at http://www.backyardnature.net/n/15/150208p9.jpg.

So, as you might expect, in this severe environment the plants' gross features alter to conform to conditions, but the basic structures -- the geometries and physics of things -- stay the same.

*****

MAREÑA IN FRUIT
In December we looked at the Bean Family tree called Mareña, Caesalpinia vesicaria, when it was prettily loaded with yellow flowers. Its page is at http://www.backyardnature.net/yucatan/marena.htm.

Nowadays Mareña is as conspicuously loaded with legume-type fruits as earlier it was heaped with flowers, as shown at http://www.backyardnature.net/n/15/150208ma.jpg.

*****

GIGANTIC COMMON REED
Where the road between Río Lagartos and Las Coloradas dips into salt marshes along the estuary, some very tall grasses lean over the roadside, as shown at http://www.backyardnature.net/n/15/150208rd.jpg.

The seat on the bicycle is about one meter high, which makes the flowering head atop the tallest grass about five meters up. If you tilt the stem up so that it's vertical, then the grass is about 5.5m tall (18ft).

The grass's gracefully drooping, basketball-size, panicle-type flowering head is shown at http://www.backyardnature.net/n/15/150208re.jpg.

Inside the flowering head, stems of the first-order inflorescence divisions cluster along the rachis in irregular whorls, as shown at http://www.backyardnature.net/n/15/150208rg.jpg.

Each slender, sharp-pointed spikelet contains three or more florets, shown at http://www.backyardnature.net/n/15/150208rh.jpg.

Lugules forming where blades connect with stems consist of a low, papery collar with a few long, very slender hairs, shown at http://www.backyardnature.net/n/15/150208ri.jpg.

Probably you've noticed this grass species someplace not only because it's so conspicuous but also because it's one of the Earth's most widely distributed flowering plants. It's the Common Reed, PHRAGMITES AUSTRALIS, not to be confused with the Giant Reed, Arundo donax, we met back in Texas. The Giant Reed is most easily distinguished from the present Common Reed by leaves, which on the Giant Reed arise from the stem opposite one another, like a feather's barbs, as shown at http://www.backyardnature.net/n/h/arundo.htm.

Otherwise, Common Reed and Giant Reed are closely related and fairly similar to one another.

Current thought is that Common Reeds are native to both North America and Eurasia. Though New World and Old World plants are physically very similar, they behave differently. Old World plants introduced into much of the rest of the world have become extremely invasive, greatly expanding the species range over the last 150 years. They negatively impact native plants -- including native strains of their own species, the Common Reed -- and wildlife. The Old World invasive strain is hard to get rid of largely because during the growing season it emerges earlier than the native strains and is less susceptible to being eaten by insects.

In New England, native American strains of Common Reed appear to have already disappeared. Common Reed releases gallic acid, which is degraded by ultraviolet light into mesoxalic acid, and both of those compounds can be toxic to susceptible plants and seedlings. The introduced Common Reed strain also alters wetland hydrology, increases the potential for fire and reduces and degrades wetland wildlife habitat due in part to its very dense growth habit -- it can form large, single-species stands. Here I don't find it in extensive, single-species stands, but who knows what the wetland landscape will look like in a few years?

Whatever the case, and whatever ecological damage it may be doing as it becomes more established here, Common Reed is a handsome plant, especially when the wind blows it to one side and the sky behind it is bright, as seen at http://www.backyardnature.net/n/15/150208rf.jpg.

This is the reed Scandinavians traditionally have thatched their roofs with. In North America, indigenous people used stems of the native strain as arrow shafts, musical instruments, ceremonial objects, wove the stems the into mats, and even made cigarettes from the plant.

*****

SKYFLOWER
We've seen that folks in Río Lagartos like to paint their houses bright colors, often with pleasing effect. The colors normally are bright, primary ones, so the other day when a certain dark lilac presence caught my eye mellowing the effect of an otherwise rambunctiously yellow, orange and chartreuse house, I had to take note. It was a flowering shrub I'd not noticed before. You can see how it complemented its environment at http://www.backyardnature.net/n/15/150208du.jpg.

The flowers arose in long racemes that tapered to a point, as shown at http://www.backyardnature.net/n/15/150208dv.jpg.

The individual flowers as seen from the front were very slightly asymmetrical, with five corolla lobes that were crinkly and white along their margins, as seen at http://www.backyardnature.net/n/15/150208dw.jpg.

The blossom's asymmetry is more easily seen from the side, shown at http://www.backyardnature.net/n/15/150208dx.jpg.

When you see a shrub with two leaves arising at each stem lobe (opposite), and slightly asymmetric flowers with corollas exhibiting purplish hues, it's always a good bet to think first of the Verbena Family, the Verbenaceae. With that family in mind, it was easy to work out the genus simply by noticing this:

These details led to the genus Duranta, and the sometimes planted shrub known variously as Skyflower, Golden Dewdrop, Pigeon Berry, and whose binomial is DURANTA ERECTA.

Skyflower is native to Mexico south to South America, and the Caribbean. However, it's widely cultivated worldwide in tropical and subtropical gardens, and has gone wild in many places as an invasive species, as in Australia, China, South Africa and on several Pacific Islands.

At garden centers, Skyflower bushes are available in a wide variety of cultivar forms, including 'Cuban Gold,' 'Alba', 'Aurea', 'Aussie Gold', 'Gold Mound', 'Geisha Girl', 'Sapphire Showers', and 'Variegata.' Our Río Lagartos plant with its flowers' crinkled, white corolla lobes, is clearly a cultivar, since wild plants produce much less ornamented flowers.

*****

LUFFA GOURD PRODUCING ITS SPONGES
In November we looked at a house-size tangle of Luffa Gourd vine producing many flowers and a few gourds too immature for us to see the famous "sponges" inside them. Our Luffa Gourd Page is at http://www.backyardnature.net/yucatan/luffa.htm.

Now well into the dry season, the big heap of vines is looking bug-eaten and its leaves are drying up. Most of its gourds already are past the time when they should have been picked, if I'd wanted to harvest their sponges. However, plenty of gourds, surprisingly light and fragile, remain dangling from the vines, such as the one shown at http://www.backyardnature.net/n/15/150208gd.jpg.

If you turn around that gourd you see that the shell's back part has been shattered by an animal and the gourd's seeds removed, probably to be eaten. This has exposed the gourd's intricate network of stiff fibers, as shown at http://www.backyardnature.net/n/15/150208ge.jpg.

The network of fibers, which are the fruit's dried-up vascular system consisting of xylem and phloem bundles, is still intact enough to be used as a kind of scratchy rubbing pad, though it's hard to see that it would have much value as a sponge. You can see the fibers removed from the gourd at http://www.backyardnature.net/n/15/150208gf.jpg.

Here it doesn't appear that anyone is using this important plant. It's just a weedy vine ignored by everyone.

*****

MERMAID'S FAN
Full moons such as we're having these days produce exceptionally high and low tides. During a flamingo-viewing trip when the tide was very low I got to see some estuary-bottom vegetation that normally lies too deep to see. Simply leaning over the boat, I temporarily uprooted what's shown at http://www.backyardnature.net/n/15/150208mm.jpg.

Those leathery, fan-shaped items are well enough known to bear the English name of Mermaid's Fan. Mermaid's Fans are green algae of the genus Udotea, possibly Udotea flabellum.

However, it seems still to be true what I read in a 2009 study by Ligia Collado-Vides et al in the journal Revista de Investigaciones Marinas, entitled "Una Revisión Taxonómica del Género Udotea en El Caribe Mexicano y Cubano." There the author writes, "We conclude that the taxonomy of the genus Udotea in the Western Tropical Atlantic is still unclear."

Of the various species our plants could be, I mention Udotea flabellum because it's a common species often described as occurring in our area, it lives in calcium-rich waters like ours, and ours looks similar to pictures of that species found on the Internet. Most other Udotea species appear to have thinner blades and lack slender stems. Well formed Udotea flabellum individuals display very broadly spreading, turkey-tail-like blades, not narrower, lobed blades like ours. However, the species is known to be very variable in its appearance. Our specimens appear to have suffered from animal nibblings and competition from surrounding Shoalgrass.

*****

CAULERPA ALGA
Another green alga plucked from the estuary bottom during a very low, full-moon tide was the tongue-shaped one shown at http://www.backyardnature.net/n/15/150208ca.jpg.

A shot showing a submerged population with the blades heavily covered with the marly silt that collects on everything in the estuary's waters is at http://www.backyardnature.net/n/15/150208cb.jpg.

This looks like CAULERPA PROLIFERA, listed in a study by Morales and Ortegón, that was presented at a symposium in 2013 sponsored by the Universidad Autónoma de Yucatánas. That study found Caulerpa prolifera to be the second-most commonly detected alga off the Yucatan's shores. Ocurring in warm, shallow, marine waters, it's spottily distributed pretty much worldwide. Often it's grown in home aquaria because it's handsome and easy to grow. Still, there's no good English name for it, so people just call it Caulerpa prolifera.

Caulerpa prolifera is a much more complex plant than what it looks like. Like other members of the green alga order Bryopsidales, each Caulerpa prolifera plant consists of a single giant cell with multiple nuclei. Some species of the genus Caulerpa are several yards (meters) across, so here we're talking about potentially mind-bogglingly large cells. Having no cell walls to impede movement of organelles within the plants, photosynthesizing chloroplasts migrate from one part of the organism to another, responding to light levels. One thing this means is that the fast growing plant's new parts that develop during the night are white, without green chloroplasts, but with sunlight the parts turn green. If sediment covers part of the blade, chloroplasts migrate to parts receiving more sunlight.

Normally, Caulerpa prolifera reproduces by fragmentation. Pieces of it no larger than a fly can grow into new plants. However, under special conditions, as when waters cool drastically, individuals can reproduce by a process known as "holocarpy." Holocarpy is when the entire contents of the giant cell forming the plant are used up to create sexual cells, or gametes, converting the entire plant to nothing more than an empty husk filled with untold numbers of sexual cells. These gametes, which bear little tails enabling them to swim, escape into the water where they fuse and form zygotes, a zygote being the first cell of a new organism. Caulerpa plants are "monoecious," so each plant produces gametes of both sexual types.

Caulerpa prolifera plays a big part in the estuary's ecology, for it helps keep in place and consolidate the estuary floor, enabling more complex flowering plants -- especially seagrasses -- to get established, and we've seen that seagrasses, like prairie grasses, engender complex and beautiful ecosystems.

*****

FEATURED ESSAYS FROM THE PAST:

"White Morning-Glory" from the February 13, 2011 Newsletter, at http://www.backyardnature.net/n/p/110213.htm

"Why Does Experiencing Beauty Feel Good" from the May 16, 2010 Newsletter, at http://www.backyardnature.net/n/p/100516.htm

*****

Best wishes to all Newsletter readers,

Jim

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