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

June 7, 2015

MARSH CRABS
In deep shade beneath Black Mangroves, on limestone rocks piled at the road's edge and just above the waterline, something the color of strawberry preserves glowed as if with an inner light. You can see the source at http://www.backyardnature.net/n/15/150607cb.jpg.

It was an easy-to-spook land crab, one I'd not seen before, though later my friend Rayo told me he'd spotted them scurrying on mud among tangles of Red Mangrove stilt-roots. As soon as I inched a little closer for a better shot, the crab instantly disappeared and didn't return after a long wait. The next day I returned, though, and got a slightly different view of the skittery fellow, shown at http://www.backyardnature.net/n/15/150607cc.jpg.

This one disappeared and didn't return when I got a little closer, either. On the third day, what I assumed to be the same individual turned up on the same rocks, but the light was worse than ever. However, across the pool of mangrove water, at the water's edge and with a limestone rock at his back, another one was feeding, his pincers conducting such tiny amounts of food to his mouth that I couldn't see anything in them. This is shown at http://www.backyardnature.net/n/15/150607cd.jpg.

The black, slender spines on this one's legs appear much shorter or even absent, relative to the others, the black dots on its legs are much less distinct, and the legs themselves are more massive. Could it be a different species? I'm guessing that the differences are a matter of age, and maybe how long it's been since the last molt.

I was so eager to get pictures from different angles because on the Internet I find no pictures matching our crab or crabs. By focusing on anatomical features, however, I did figure out that surely we have a member or members of what's often called the Marsh Crab Family, the Grapsidae. Googling images of each member of the Grapsidae found in the Gulf of Mexico area, I find nothing matching ours.

I did find, however, Lawrence Abele's 1992 work "A Review of the Grapsid Crab Genus Sesarma (Crustacea: Decapoda: Grapsidae) in America, with the Description of a New Genus," in which much confusion within the group is spoken of. It's suspected that various un-named species lurk undetected among many variations sometimes assigned to a single name.

Abele's Armases angustipes is similarly structured to ours, but colored differently. A collection of that species has been made "On unpaved road from Rio Lagartos/San Felipe junction, under rock on margin of nearly dry salina," and that's just a mile or less from where ours live.

So, maybe what we have here is a variation, or variations, of Armases angustipes or, better yet, a taxon still "lurking" -- still un-named -- despite its prettiness and interesting features.

For that future expert who'll figure all this out, I'm glad to deposit our field work here under the Google-indexable keywords SESARMA, ARMASES, Marsh Crab Family, and Grapsidae.

*****

YUCATAN GAMBUSIA FISH
At a culvert beneath a road on the levee separating the estuary from mangrove swamp on the southeastern shore just south of Río Lagartos, as the tide came in, brackish water from the estuary flowed into a shallow pool on the mangrove side of the culvert. The pool's surface worked with thousands of small, brown fish about an inch long (25mm), such as the one shown at http://www.backyardnature.net/n/15/150607ga.jpg.

Another shot of a different fish, better showing some of the fish's internal organs through its semitransparent flesh, is shown at http://www.backyardnature.net/n/15/150607gb.jpg.

These fish swam with their lower jaws projected forward and upward, enabling them either to "gulp air" at the water's surface, or skim microscopic matter floating atop the water.

This behavior, the projecting lower jaws, the semitransparent bodies and the general appearance were very familiar to me, for I grew up surrounded by western Kentucky drainage ditches teeming with such fish -- mosquito fish, Gambusia affinis. We don't have Gambusia affinis here, but one Gambusia species is listed for the Reserve, and that's GAMBUSIA YUCATANA, normally called the Yucatan Gambusia, and known to be abundant in Ría Lagartos estuary. The species is endemic to the Yucatan Peninsula, Belize and part of Guatemala.

The quiet, house-size pool of water beside the road suddenly erupted at the far end with a wave of silvery, noisily splashing water that spread across the pool in a fast-moving arc. It was Yucatan Gambusias leaping from the water in unison, and I wondered what they were up to. A couple of minutes passed before the same thing happened again. Ultimately several such fast-moving waves came rushing across the otherwise quiet little pool. Then I saw the cause: A Double-crested Cormorant popped up from below the water. It'd been diving in the stream draining from the mangroves into the pool.

Suddenly another wave erupted but this time it began right beside me and rushed in the opposite direction. As soon as the water calmed enough to see below the surface, there was a needlefish with a Yucatan Bambusia crosswise in its narrow snout, about to be gulped down.

This was a good lesson about one use the tidewater ecosystem has for Yucatan Bambusias: They make fine eating for any number of hungry predators.

*****

UPSIDE-DOWN-SWIMMING HORSESHOE CRABS
At the front of the boat nosed into an indentation of the mangrove's green wall at the estuary's edge, Paco was showing a couple of Tasmanians what a Boat-billed Heron looked like. I've seen lots of Boat-billeds, so I was vacantly watching the estuary's high-tide waters flow in . And then into my field of vision swam the thing shown at http://www.backyardnature.net/n/15/150607hc.jpg.

I'd heard about horseshoe crabs swimming upside-down at the water's surface, but seeing it for the first time was a surprise. It was even more surprising when later I learned that horseshoe crabs NORMALLY swim upside-down, inclined at about 30° to the horizontal. A few minutes later another horseshoe crab drifted by swimming completely submerged, so you can see the crab's normal swimming position (tilted ±30° upward) at http://www.backyardnature.net/n/15/150607he.jpg.

So, I've seen about a jillion living horseshoe crabs, but these were my first upside-down ones. The deal is that normally I spot them on the estuary's muddy floor foraging right-side-up, or else disappearing into a cloud of churned-up mud as they escape from the boat's encroachment, right-side-up. These were just my first peacefully swimming ones.

The one shown above swam so close to the boat that I reached over the gunwale and brought him up, to give the Tasmanians a closer look, especially at the eyes. Guides here differ on how many eyes horseshoe crabs have, and they say that eyes are present on the creature's bottom next to the mouth in the body's center, and I wanted to look for those, too. You can see the eye situation on top at http://www.backyardnature.net/n/15/150607hd.jpg.

The spots that look like eyes with bony ridges as eyebrows are "compound lateral eyes," each composed of about a thousand lenses, or "ommatidia." These eyes are equipped with rods and cones that qualify as the largest to be found in the eyes of any known animal -- about 100 times the size of a human eyes' rods and cones.

On the one in our photograph, the spots that look like they should be nostrils are "median eyes," which can detect both visible and ultraviolet light. The HorseshoeCrab.Org website also assures us that there is one "endoparietal eye" between and a little above the median eyes, and two rudimentary lateral eyes, each close behind the compound laterals, but I can't see these on our animal.

There's also mention of a pair of "ventral eyes" on the crustaceans bottom surface, beside the mouth, as well as of a cluster of photoreceptors on the "telson," better known as the tail. These tail photoreceptors are said to keep the horseshoe crab's brain synchronized with cycles of light and dark. On our individual lifted from the water, not even scrutiny with a handlens could spot anything looking like an eye near the mouth or along the tail's length.

A variety of horseshoe-crab-vision matters are discussed at http://www.horseshoecrab.org/anat/vision.html.

Anyway, now I understood why the area's guides and the experts they get their information from so disagree on how many eyes a horseshoe crab has. It's a matter of defining what an eye is. Do these "photosensitive spots" scattered across the horseshoe crab's brittle body, especially the tail, qualify as eyes? Is each of the thousand or so lenses in each compound eye an eye?

Despite having such huge rods and cones, and so many spots and regions that gather light, horseshoe crabs are considered to enjoy relatively poor eyesight.

Some guides say that horseshoe crabs swim upside-down as a courtship behavior but I can't confirm that from any authoritative source.

*****

INNUMERABLE HORSESHOE CRAB SHELLS
A visitor clambered ashore to find the beach strewn for as far as the eye could see with horseshoe crab shells, a small part of which is shown at http://www.backyardnature.net/n/15/150607hs.jpg.

"What could have killed so many horseshoe crabs," the visitor asked.

"Nothing killed them," was the reply. "These are old exoskeletons discarded when the horseshoe crabs needed to grow larger and 'molted.' The old shell splits along its front edge and the animal crawls out, leaving the old shell behind. The new shell is relatively soft and flexible, and the animal increases in size by 25-30% during the hours before the new shell hardens."

Horseshoe crabs molt several times during their first year, during which they reach a width of about half an inch (12mm). After the first year they usually molt once a year until they reach adult size in 10-15 years.

*****

INNUMERABLE ROVE BEETLES
On Monday the rainy season began with our first good rain in many weeks. The morning after the rain, I biked into the mangroves looking for frogs or whatever the rain might have released from a long heat- and drought-imposed estivation. The first rain creatures appeared en masse while I was still in town, in the form of clouds of tiny insects that tangled in my body hairs, got into my eyes and were inhaled if I breathed through my mouth or just breathed too hard through the nose. You can see some caught in my knee hairs at http://www.backyardnature.net/n/15/150607rv.jpg.

These are rove beetles, of the Rove Beetle Family, the Staphylinidae, which with about 58,000 species worldwide in thousands of genera is currently recognized as the largest family of beetles, and of course beetles constitute the largest group of insects, the order Coleoptera. Therefore it's good to be able to recognize a rove beetle. Normally that's easy, because the rove beetle's hard wing-covers, the elytra, are so short that they leave more than half of the insect's abdomen exposed. When rove beetles land they fold their flexible wings beneath their elytra, which the beetle at the right in the picture is in the process of doing.

With so many species and the species being little studied in the Yucatan, I suspected that it'd be hard to identify the ones encrusting my body that morning, and that turned out to be the case. That, these looking very unusual, with their heads bearing three hornlike projections pointed forward.

So, all we can say is that on the first morning after a rain here among the mangroves, clouds of one of 58,000 possible rove beetle species crowd the streets of Río Lagartos, Yucatán, causing señoras to frantically comb fingers through their hair trying to get them out, and causing bikers to pull up to the curb and cough awhile, trying to dislodge them from noses and lungs.

*****

"HUIZACHE" FLOWERING
Among local trees that began issuing leaves and flowers well before the rainy season's first rain came is the feathery-leafed one shown at http://www.backyardnature.net/n/15/150607pe.jpg.

It's one of several spiny, feathery-leafed species we have here in the thorn forest that at first glance can be recognized as an acacia, mimosa or something close to them. The orange, spherical heads of tiny flowers look like those of Sweet Acacia, or Huisache, of which we saw so many in Texas. But, Sweet Acacia's twice-compound leaves bear much fewer tiny leaflet that this tree. In the picture, what look like the first divisions of a once-compound leaf are actually many very small leaflets (3mm, 1/10th inch), or pinnae, held close to one another. A close-up shows tiny individual pinnae of an older leaf with some pinnae having fallen off at http://www.backyardnature.net/n/15/150607ph.jpg.

So, this isn't Sweet Acacia, but something close to it, so we needed to "do the botany."

At http://www.backyardnature.net/n/15/150607pf.jpg you can see a flowering head close-up, with its densely velvety-hairy stem, or peduncle, and nearby leaf petioles. Breaking open a flowering head, we can see that each individual flower sprouts numerous -- more than ten -- stamens, just like the acacias, as shown at http://www.backyardnature.net/n/15/150607pg.jpg.

This is ACACIA PENNATULA, commonly occurring in Yucatan's arid scrub and thorn forests, and similar spots throughout most of hot, dry Mexico south through Central America into northern South America.

Acacia pennatula is a fine tree, one easy to distinguish from other similar, closely related species, even when it's not flowering or fruiting, because of its many minute leaflets and fuzzy young vegetative parts. Moreover, it's a handsome and useful tree, the wood often serving as building material and fence posts, burning well, and making good charcoal. The tree's high-protein legume-type pods commonly are eaten by livestock, and traditionally the bark has even been used in Mexico to treat diarrhea, which makes sense because the bark is full of puckery tannin.

Ecologically, the tree's spreading root system controls erosion, and the tree itself makes good shade, is frost-resistant and, as a member of the Bean Family, even fixes nitrogen for use by the rest of the biosphere.

One aggravating thing about the species is that it doesn't have a decent name. In English it's basically unknown, and Spanish speakers tend to use names already applied more widely to other similar-looking species. In many areas it's called Mesquite, but it's very different from real mesquites. It's also called Huizache, like Sweet Acacia, and there are other such names, but none just for this tree. The Maya have two names for it, Ch'i' May and K'ank' i Ilische', and even the experts have alternately assigned it to other genera, including Inga, Pithecollobium, Poponax and Vachellia.

It just shows you that you don't have to have a name to go about doing decent, benevolent things for the community at large.

*****

WHITE MANGROVE FLOWERING
At the outer edges of mangrove swamps where the ground rises just enough to be solid instead soft-muddy, White Mangroves often turn up. Our White Mangrove Page with pictures of leaves, fruits and petiole warts, or nectaries, is at http://www.backyardnature.net/yucatan/white-mv.htm.

Nowadays our White Mangroves are prolifically producing spreading panicles of tiny flowers along branches and at their tips, as shown at http://www.backyardnature.net/n/15/150607wm.jpg.

Up close, the 5mm-tall flowers (3/16ths inches) look like short-stemmed, whitish goblets, as shown at http://www.backyardnature.net/n/15/150607wn.jpg.

A closer look inside one of the interesting flowers is provided at http://www.backyardnature.net/n/15/150607wo.jpg.

The ten stamens are inserted on the calyx -- not on the corolla -- at two different levels. The ovary is "inferior," or below the calyx and corolla. At the bottom of the cup formed the alternating five petal-like sepal lobes and five roundish petals there's a flatish, doughnut-like "disc" from the center of which arises the style topped with its shiny stigma. Most flowers don't have such discs. Up north we don't see many flowers with such a combination of features because White Mangrove is a member of the tropical and subtropical Combretum Family, the Combretaceae, a family little known by northern gardeners and wildflower lovers.

Before the rains came, lines of black ants could be seen constantly moving up and down the White Mangrove's stems, going for nectar.

*****

SALTMARSH AGALINIS
Early on the morning after our first good rain of the oncoming rainy season I was biking through the mangroves looking for rain-awakened critters. However, something that caught my eye that morning wasn't a mud-covered animal, but rather a wildflower at a salt marsh's edge. Its numerous, small, pale, diffusely arranged blossoms glowed brightly in the morning's dim light, as you can see at http://www.backyardnature.net/n/15/150607an.jpg.

Even at that distance the plant reminded me of that group of wildflowers that in the north we call gerardias, agalinises or false foxgloves. You might remember the very similar Plateau Agalinis that was so common but narrowly endemic to just a few counties in the Texas Hill Country, shown at http://www.backyardnature.net/n/h/agalinis.htm.

Up close, the salt-marsh plant's funnel-shaped, rosy flowers with speckled throats also were similar to those of Texas's Plateau Agalinises, as seen at http://www.backyardnature.net/n/15/150607ao.jpg.

A peep into the throat of the bilaterally symmetrical corolla found four stamens of two lengths inserted on the corolla tube, just as with the Plateau Agalinis, shown at http://www.backyardnature.net/n/15/150607ap.jpg.In fact, this is AGALINIS SPICIFLORA, which specializes in salt marshes, so we'll call it the Saltmarsh Agalinis. It's endemic to the Yucatan Peninsula, including Belize, and islands of the Caribbean.

I say "we'll call" because there is no good English name for the species, and other names are all a muddle. Some experts regard Agalinis spiciflora as a variety of Agalinis maritima, which sometimes is called Saltmarsh False Foxglove or Seaside Gerardia, and much of the older literature calls our plant Gerardia cereifera.

In the old days, Agalinis/Gerardia species were regarded as members of the Snapdragon or Figwort Family, the Scrophulariaceae, and to me they look like that's where they belong. However, in recent years genetic studies have indicated that Agalinis species are more closely related to members of the Broomrape Family, the Orobanchaceae, famous for its many species that are completely or partly parasitic on the roots of other plants. Agalinis species are partly parasitic and that partly explains why they were shifted to the Broomrape Family.

*****

A FORLORNNESS OF CHARA
On the morning after the first good rain of the pending rainy season I went biking looking for blossomings and awakenings the rain might have wrought. One spot along the coastal road I'd passed many times without anything there catching my attention suddenly did catch my eye. It was a low spot in the mangroves where woody plants had died, leaving a shallow pond that had dried up during the last two or three months, but in which now pooled ankle-deep, brackish water. It was brackish despite the rainwater being freshwater, because sometimes the spot is regularly flooded with saltwater. You can see why the pond attracted my attention now at http://www.backyardnature.net/n/15/150607ch.jpg.

Surrounded by the somber greenness of a wall of Buttonwood Mangrove, a confusion of black, dead tree branches was draped with white, cobwebby, soggy, lifeless "something." Up closer, the "something" began showing signs of organization, as seen at http://www.backyardnature.net/n/15/150607ci.jpg.

Much closer, features of the white stuff jogged certain memories, and I began to recognize the green alga called Chara, as seen at http://www.backyardnature.net/n/15/150607cj.jpg.

Chara alga is multicellular and at first glance resembles certain flowering land plants, because of stem-like and leaf-like structures, which nonetheless are not stems or leaves because they lack the vascular plumbing all flowering plants have. As an alga, Chara has no roots and doesn't produce flowers. It reproduces vegetatively in various ways, and sexually by producing oospores. Sometimes Chara species are called stoneworts.

The dead, white Chara draping dead tree stems in the picture once grew in green masses suspended in water above the dead, at-that-time-submerged stems in the picture. The water level dropped, leaving the Chara stranded, dying, drying out, and turning white. At one time the water must have been remarkably dense with Chara. But, what Chara species might it be?

In 2010, Scribailo and Alix estimated that 17 Chara species occur in Mexico, but that didn't help much bringing order to the genus. You may recall that in Texas we found two Chara species fairly commonly occurring in the Dry Frio River, but were unable to identify them to species level. Mexico's Chara species are considerably less studied than those of Texas and the US.

Still, a good bit of studying pictures of identified Chara species on the Internet gave me the impression that our Chara might belong to what RD Woods in his 1965 "Monograph of the Characeae" referred to as "the species complex of Chara zeylanica." The complex consists of several highly variable “macrospecies.” My impression is based on little more than the fact that alga assigned to this complex appear to have thick, striated, stem-like structures with whorls of unusually short, leaf-like appendages, and the whorls are fairly close together.

*****

CREPUSCULAR RAYS
Tuesday a little after dusk we were returning from a trip up the estuary, approaching Río Lagartos just as lights were flickering on. Toward the west, across the estuary and far beyond the dark line of mangroves rimming the estuary, here and there distant thunderheads soared high into the sky, their silhouettes looking like far-away mountains. The sun, now below the Earth's curvature, lit up the horizon's rim, and the towering thunderheads cast their shadows across the sky. You can see the effect at http://www.backyardnature.net/n/15/150607sh.jpg.

Sometimes up North we see such shadows streaking the sky at dusk and wonder what they are, for in most of North America the air is so hazy that distant object at the horizon are hidden by haze. Here the air is so clear that you can see all the way to where sky meets Earth, and the far-away thunderheads were obviously the source of the shadow. Such streaks in the sky at dusk are known as crepuscular rays, the word "crepuscular" referring to things that appear or become active in twilight. Sometimes it's the bright areas that show up and we call them sunbeams.

Of course what's happening is that particles of dust and humidity are lighted where the sun shines, but if a big cloud blocks the sunlight, the dust and water droplets don't show up, and their part of the sky looks darker.

The marvelous thing was the dark ray could be traced across the sky above us, and then seemed to focus on the opposite side of the night sky, where a full moon at that moment was rising, barely above the horizon. That effect was too weak to photograph, but we saw it from our little boat. There in open water we just turned off the boat's engine and floated bobbing about, fully conscious that we were seeing something extraordinary, and uncommonly beautiful.

*****

DÍA DE LA MARINA
Last Monday Río Lagartos celebrated its yearly festival called the Día de la Marina. That's when the town's fishermen decorate their boats and all together sail across the estuary into the Gulf of Mexico well offshore, and throw flowers overboard. The flowers represent an offering, I'm told, to the Virgin of Guadalupe, on behalf of fishermen who have lost their lives, and in thanks for the harvest that has been taken from the sea. You can see a small part of the parade as it got underway in front of town at http://www.backyardnature.net/n/15/150607fv.jpg.

A close-up showing two boats gaily adorned and with women and children aboard is at http://www.backyardnature.net/n/15/150607fw.jpg.

The white flags are flown by supporters of PRI, one of the dominant political parties, with local elections due next week. As I took the above the picture I was standing next to a fishermen who I was surprised wasn't participating. He explained that the festival had become too politicized.

Over a week earlier a friend had told me that the dry season's first big rain would take place on the Día de la Marina, because it always rains on that date. Her prediction was accurate, and others told me the same. That got me to thinking.

For, no one can quite say when this tradition began, and it seems like something that native people might have been doing since ancient times. Also, maybe it's not coincidental that it "always rains on the Día de la Marina."

I wonder: Could the Día de la Marina have originated as an ancient time of sacrifice when the first rains of the rainy season were prayed for? Maybe in the old days they didn't just drop flowers into the water when they requested rain of the gods.

*****

FEATURED ESSAYS FROM THE PAST:

"Scouting" from the October 26, 2003 Newsletter, at http://www.backyardnature.net/n/p/031026.htm  

"Thoughts about Obsessive Thoughts" from the November 8, 2009 Newsletter, at http://www.backyardnature.net/n/p/091108.htm

*****

Best wishes to all Newsletter readers,

Jim

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