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

February 1, 2015

BULL SHARK
Wednesday morning Diego came to my door saying that a fisherman down the street had just brought in a 200kg (440lbs) Bull Shark. The big fish had been netted in deep water far offshore in the Gulf of Mexico north of Río Lagartos. Within a minute I had the picture shown at http://www.backyardnature.net/n/15/150201sh.jpg.

That's my friend and student Paco astride the poor creature. Paco didn't catch the shark but he's our main crocodile wrestler on crocodile night tours and couldn't pass up posing with a shark.

A close-up of the shark's open jaws with its parallel rows of triangular teeth visible is at http://www.backyardnature.net/n/15/150201si.jpg

Diego had said that it was a Bull Shark, but I wasn't sure if that common name could be used to figure out the exact species in our photo. Fortunately, the Mexican government agency SEDUMA provides a freely available document in PDF format in which all the "elasmobranch" fishes off the Yucatan coast are listed -- an elasmobranch fish being a cartilaginous fish of the subclass Elasmobranchii, having five to seven pairs of lateral gill slits. The subclass includes the sharks, rays, and skates. The SEDUMA list can be downloaded here.

On the Internet, by comparing pictures of species of the shark genera listed in the document, simply by taking into account general shape and size, soon I felt confident that our shark was a member of the big genus Carcharhinus, of which a dozen species are listed for our coastal waters. Using pictures and data at the FishBase.Org website and noting our shark's large size, the size of its front fins (pectorals) relative to the rest of its body, its small eyes, its gray color and its short, broad snout, all the Carcharhinus names listed could be eliminated except this one: CARCHARHINUS LEUCAS. And the English name for Carcharhinus leucas was given as Bull Shark. All the other listed shark species were identified at FishBase.Org with different names, such as Silky Shark, Blacktip Shark, Whitetip Shark, Lemon Shark, etc.

FishBase.Org describes the Bull Shark as massive, with a short, broad and blunt snout, small eyes and triangular, saw-edged upper teeth. These features and the lack of an interdorsal ridge are sufficient, it says, to distinguish this species. Bull Sharks inhabit warm oceans worldwide, and have the distinction of being able to thrive in both saltwater and freshwater, sometimes traveling far up rivers. Though they are mainly a saltwater fish, they've been documented as far up the Mississippi River as Illinois.

Bull Sharks feed on bony fishes, other sharks, rays, mantis shrimps, crabs, squid, sea snails, sea urchins, mammalian carrion, sea turtles, and occasionally garbage. The FishBase.Org site describes them as probably the most dangerous species of tropical shark, repeatedly being implicated in attacks on humans. The IUCN Red List describes the species as being "near threatened."

I felt sorry for that Bull Shark, and wished that it had remained where it was, "far from shore and deep," as Diego had said.

*****

PEARL OYSTER
On the Gulf of Mexico beach of the long finger of land across the estuary from Río Lagartos, a norte with its stiff northerly breezes had heaped up great mounds of seaweed and seashells. Among the shells were the small, clam-like bivalves shown at http://www.backyardnature.net/n/15/150201oy.jpg.

These caught my eyes with their rich, amber-brown color and the unusual, irregularly formed, concentric growth-bands ornamenting the shells' surfaces. Inside the shells, which seemed thin and brittle compared to others on the beach, the surfaces were smooth and pearly white. Holding up a shell to better see the growth bands, sunlight transluced through the shell in a special way, shown at http://www.backyardnature.net/n/15/150201oz.jpg.

It's surprisingly hard to identify shells found on the Yucatan's beaches. Some small collections from the Florida and Caribbean area are online but none included this shell. Finally I remembered that one kind of shell that is somewhat irregularly shaped and pearly inside is the oyster shell, so I looked for images of shells of various oyster types, and that was the breakthrough.

Here we have the Atlantic Pearl Oyster, PINCTADA IMBRICATA, an ecologically and economically important species in many parts of the world, not only the Atlantic. In many places where Atlantic Pearl Oysters aren't native, they've been introduced for the cultivation and production of natural pearls. Pearl oyster species are not closely related to either edible oysters of the Family Ostreidae, or freshwater pearl mussels of the families Unionidae and Margaritiferidae but rather constitute their own family, the Pearl Oyster Family, the Pteriidae. The "pteri" in Pteriidae" is the Latin nominative masculine plural form of "pterus," which means "winged," referring to the flattish wing extensions at the shell's rear ends, where they're hinged.

Though so far we've looked at only a handful of seashell-producing mollusks found on the beach here, this is the second species famed for its pearl producing ability. The other was the Atlantic Winged Oyster, also a member of the Pearl Oyster Family, profiled at http://www.backyardnature.net/yucatan/pteria.htm.

Finding these two pearl-producing species washed up on our beach gives the impression that our waters may be good for pearl-oyster cultivation, and maybe capable of supporting a new source of income for the region. The idea must be approached cautiously, though, for sometimes commercial aquaculture is ruinous to the local ecosystem, especially when it converts mangroves to commercial fishponds.

During his third voyage to the Americas, in 1498, Christopher Columbus found Atlantic Pearl Oysters off the coast of Venezuela, and took pearls from them back to Spain. Consequently, the first Spanish town in the New World was established in 1528 on the Venezuelan island of Cubagua to serve as a center for harvesting pearl oysters and collecting pearls. The oysters were so overharvested that eventually they nearly went extinct in those waters.

A fascinating, illustrated paper entitled "History of the Atlantic Pearl-Oyster, Pinctata imbricata, Industry in Venezuela and Colombia, with Biological and Ecological Observations" can be downloaded for free in PDF format at http://aquaticcommons.org/9736/1/mfr6511.pdf.

This whole matter of pearls is fascinating, and a good place to learn the basics of how pearls form naturally in oysters, how they are cultivated commercially, and all the things people do with pearls, is the Wikipedia Pearl Page at http://en.wikipedia.org/wiki/Pearl.

*****

GREAT EGRET
One of the most commonly seen yet always spectacular birds in our coastal wetlands is the one shown in a roadside pond just south of Río Lagartos, at http://www.backyardnature.net/n/15/150201eg.jpg.

That's the Great Egret, also known as the Common Egret, Great White Egret, and other names. It's ARDEA ALBA, and one reason for its many names is that it occurs throughout most of the world, except in the biggest deserts and the coldest regions. Another reason is that over the years experts couldn't agree on how to classify it. My dogeared 1966 field guide places them in the genus Camerodius; the 1995 guide to Mexican birds by Howell puts them in Egretta, and; most updated web pages now say they belong to Ardea. Gene sequencing has taught us that the Great Egret is actually closer related to pelicans than other birds known as egrets assigned to the genus Egretta.

In the picture, the smaller birds in the background are juvenile Northern Jacanas. The most riveting feature of the picture, however, is the big, white bird's incredibly long, slender neck. It's hard to believe that such a neck could have enough muscles to keep the head from flopping about, much less assume graceful poses and stab the head toward fish.

Flamingos fly with their necks stretched out before them, their whole bodies bobbing up and down with their wing beats. In contrast, Great Egrets fly with their necks retracted, their necks doubled back into a snug S. Maybe flamingos can get away with stretching out their necks because their necks, noted for being so long and slender, nevertheless are proportionally shorter and thicker than the Great Egret's.

Several herons and egrets in this area are white: the Snowy Egret, Cattle Egret, immature Little Blue Heron, the white phase of the Reddish Egret, and the white morph of the Great Blue Heron. Because of the Great Egret's size, it can be confused with none of these, except for the uncommonly seen white morph of the Great Blue Heron, which has yellow legs, not dark like the Great Egret. Great Blue Herons when disturbed tend to issue loud, complaining croaks, but Great Egrets are quieter, simply flying away gracefully when bothered.

Great Egrets are class acts wherever they are, and whatever they're doing.

*****

COZUMEL SPINY LIZARD
Between the Gulf of Mexico's waters and the low sand dunes a stone's throw inland, the sand was so glaringly white, the air so hot and salty, and the wind so blustery that the odor of decaying seaweed and the sight of a dead sea turtle with its head chopped off all seemed to fit together. What was surprising was a little lizard only about four inches long (10cm) apparently doing very well. You can see him at http://www.backyardnature.net/n/15/150201lz.jpg.

We've met this fellow before, on the Yucatan's Caribbean beach just north of Mahahual. He's the Cozumel Spiny Lizard, SCELOPORUS COZUMELAE, endemic just to the coastal Yucatan Peninsula, including Campeche state in the west and Quintana Roo state in the east, and offshore islands.

This lizard didn't seem nervous about having a human looming above him with a camera lens only a finger length away. After I'd taken the above photograph I poked at him just to be sure that he was OK, but before the finger made contact he quickly scurried away.

Though Cozumel Spiny Lizards appear to be limited to the narrow, sandy beach zone along the coast, they're common wherever they do occur, and for this reason they're not regarded as an endangered species. However, so much coastal habitat in the Yucatan is being converted to beachfront homes and tourist infrastructure that the species habitat is being rapidly reduced and its future is of concern.

*****

THE FAMOUS LOGWOOD
Something I looked forward to when coming here was finding the famous tree known as Logwood, HAEMATOXYLUM CAMPECHIANUM -- famous because from the 17th to 19th centuries the tree was logged extensively and exported to Europe for use in dyeing fabrics. I visualized having to stomp through vast swamps to reach rare remaining specimens, but now I see that it's common along the coastal road just south of Río Lagartos. Nowadays it's flowering so spectacularly that it's hard to miss. You can see its bright yellow clusters of flowers amidst dark green foliage at http://www.backyardnature.net/n/15/150201lf.jpg.

That picture shows how it usually presents itself here -- a compact tree about 15-ft tall tree (4.5m) so enmeshed in low, dense forest that its limbs entangle with, and peek from between, limbs of other trees. Up closer you see that the yellowish flowers are small and densely packed in spike-like racemes, as shown at http://www.backyardnature.net/n/15/150201lg.jpg.

Closer still, the blossom turns out to be a little peculiar, as seen at http://www.backyardnature.net/n/15/150201li.jpg.

What's unusual is the pinkish ovary in the flower's center. The ovary is lopsided and therefore asymmetrical. It arises inside a whorl of ten stamens with hairy-based anthers, and five petals that seem to be slightly asymmetric themselves, but not much. The corolla's slender tube arises from a cup-shaped calyx. Just looking at the flower, it's hard to say what plant family Logwood belongs to. However, the tree's leaves hint broadly that it's a member of the big Bean Family, as shown at http://www.backyardnature.net/n/15/150201lh.jpg.

The pinnately compound leaf is similar to several Bean Family members found here, plus notice the woody spine arising at the petiole's base, exactly like several Bean Family species in our thorn forests. Being directed to the Bean Family by the leaves, we think back to the blossom's flat ovary and can visualize such an ovary developing into a flat, legume-type fruit with only one or two beans inside, and that's exactly the case. Logwood is a quirky member of the Bean Family, and its fruits are flattened legumes usually bearing two beans.

One reason Logwood is famous is that it was largely responsible for the foundation of an English-speaking nation down in the Yucatan Peninsula's southeastern corner -- Belize. In the 1650s, the first European settlers in the territory now known as Belize were English pirates and buccaneers known as "Baymen," who settled in such an out-of-the way place trying to avoid the Spanish rulers of Mexico and Central America. The Baymen soon found that they could make good money cutting and selling Logwood to folks back in England, for dyeing fabrics. Just boil in water woodchips of Logwood's heartwood and a reddish dye comes out. Add various chemicals and the dye changes colors. Use mordants, and the dye doesn't wash out too bad. The Baymen's logwood logging camps were the beginning of English-speaking Belize.

Logwood also had a part in causing much of Belize's population today to be black, for slaves were needed to log the trees and ship them out. Eventually Logwood's value as a dye diminished, and logging Mahogany became more important, requiring more slaves and encouraging more Englishmen to come to Belize. This period of Belize's history is related in much more detail at http://countrystudies.us/belize/7.htm.

One thing that article doesn't mention is that Logwood's branches are very spiny and the trunk is extremely dense and hard. Logging these trees in the mosquito-infested swampland they inhabit must have been rough work, and I can hardly imagine what it must have been like for the slaves who did it. A shot of some stem spines is shown at http://www.backyardnature.net/n/15/150201lk.jpg.

I cut through a twig about as thick as my finger and saw no dye-producing red sapwood in the stem's center. Apparently only the trunk's red sapwood contains the dye and the tree's trunk needs to be hacked into to ge it. I just didn't want to hurt the tree to see it. The tree's distinctive trunk is shown, looking like numerous smaller trunks fused together, at http://www.backyardnature.net/n/15/150201lj.jpg.

A fine discussion of all aspects of Logwood's use as a dye is found here.  

Logwood is native to the Yucatan Peninsula, Belize and northern Guatemala, but has been planted in many tropical countries and in some places has become invasive. In it's native lands it's found in flat lowlands with clayey soils, poor drainage, and periodic flooding, but in other countries it does well in disturbed secondary forest, along roadsides, riverbanks, lowland dry forests, urban forests, and seasonal waterlogged areas. In fact, even here it may be most common along roads through the marshes.

*****

MESQUITE IN THE YUCATAN
We have mesquite trees here, and I've been eager for them to flower so I could figure out what's going on with them. For, unlike the mesquites that were so abundant back in southwestern Texas, sometimes these Yucatan ones turn up at the edges of marshes in what appears to be wet or at least moist soil. In Texas, mesquites grow on dry land. You can review the Texas mesquites, which were Prosopis glandulosa, at http://www.backyardnature.net/n/w/mesquite.htm.

This week a mesquite at the edge of a marsh just outside of Río Lagartos was flowering, and you can see its spikelike racemes at http://www.backyardnature.net/n/15/150201mq.jpg.

These flowering heads strike me as shorter and thicker than those back in Texas and northern Mexico. You can see individual flowers, the cream-colored anthers atop their slender, white filaments tipped with the tiny, white, spherical glands for which the genus is famous at http://www.backyardnature.net/n/15/150201ms.jpg.

The Y-shaped, twice-pinnately compound leaves were unmistakable mesquite leaves, though smaller than I recall the Texas ones being, as shown at http://www.backyardnature.net/n/15/150201mr.jpg.

So, this is a different mesquite species from the one we had in Texas. It's PROSOPIS JULIFLORA, native to Mexico and the Caribbean area, plus there's debate about what other regions it's native too. One reason its origin is debatable is that it's been introduced into much of the rest of the world as an adaptable, sturdy tree capable of providing good shade, firewood and livestock fodder in hot, arid, treeless zones.

In fact, Prosopis juliflora has become a major invasive species in many of the planet's hot, arid regions. For example, with great expectations the tree was introduced into Ethiopia, but now "Over 700,000 hectares of prime grazing land and cultivable land following the Awash River is currently either invaded or at risk of invasion from prosopis in the Afar Region." The IUCN document saying this and detailing the situation is freely downloadable in PDF format here

One reason Prosopis juliflora so aggressively invades treeless land is that invading treeless lands is its ecological job. In Nature, it's a "pioneer species" that stabilizes, shades and cools the soil, and holds moisture in the environment, enabling other less rugged species to take hold. In the Yucatan, mainly the tree occurs along the coast, with its numbers diminishing rapidly as one travels south and east, into areas with greater rainfall. The mystery is how this tree that shows affinities for arid land also occurs at the edges of our marshes.

Here in Mexico Prosopis juliflora is honored for the nectar it provides bees, and traditionally its resin has been used to treat dysentery and certain eye ailments. Also a tea from its cooked leaves has been used for inflamed eyes. A tea from its cooked flowers and root bark has served as a purgative, against intestinal worms, and for stomach aches.

*****

SEABLITE
The broad, pleasant-to-walk avenue next to the seawall encircling most of Río Lagartos is called the Malecón. On the southeastern side of town, the Malecón continues south of town, separating the estuary from adjacent mangrove swamps. In roadside rubble barely above the mangrove's salty water, a certain much branched, woody-based, sprawling, succulent-leafed, two-ft-high plant caught my eye with its reddish leaves -- this in a landscape where in general leaves don't turn bright colors as they do in autumn up north. You can see the scraggly, untidy-looking plant at http://www.backyardnature.net/n/15/150201st.jpg.

Up closer, the plant exhibits more composure and comeliness, as evidenced at http://www.backyardnature.net/n/15/150201su.jpg.

The slender, round-in-cross-section, succulent leaves are similar to other leaves of local halophytic plants in salty soils, such as Sea Purslane, Saltwort and Wolfberry. However, notice the strange feature that some of the reddish leaves elongate and swell to several times the size of others. At first I thought they must be capsular fruits but they weren't, just juicy, salty leaves that tasted pretty good when nibbled upon.

Branch tips appeared to be occupied with a kind of soft crumbliness, so out came the hand lens, and the tiny crumbs revealed specific shapes, as seen at http://www.backyardnature.net/n/15/150201sv.jpg.

Objects at the base of fingerlike leaves looked like deeply lobed ovaries of mint flowers, in which the individual lobes eventually mature into separate "nutlets" from which can sprout new plants. But I've never seen succulent nutlets. An even closer look of the items is at http://www.backyardnature.net/n/15/150201sw.jpg.

The thing in the picture's center, wedged between two succulent leaves, appears to be 4-lobed, exactly like a mint-flower ovary, plus in the depression where the four lobes meet there's a dark, bushy cluster that could hardly be anything but the remains of a flower's stigmas and styles. Therefore, the 4-lobed item is definitely a fruit. But notice that at the right in the picture there's another fruit, which is 5-lobed, something I've not seen in a mint flower.

After searching the tips of many branches, finally a just-opened blossom turned up, one with five stamens radiating from the flower's center, each stamen's slender filament inserted beneath a cream-colored disc, which was the expanded base of the style, known as a stylopodium. This is shown at http://www.backyardnature.net/n/15/150201sx.jpg.

Only a few plant families produce stylopodia, particularly the Parsley Family, the Apiaceae. However, this plant's flowers aren't arranged like those of the Parsley Family, in umbels, so this is getting interesting. Examining more maturing fruits, it became clear that the fruits often developed irregularly, with one to five lobes, and the lobes could be of various sizes, as seen at http://www.backyardnature.net/n/15/150201sy.jpg.

A common weed up north with branch-tip clusters of flowers that develop into spike-like heads of soft, crumbly fruits is the tasty potherb known as Lamb's Quarters, which is a member of the old Goosefoot or Spinach Family, the Chenopodiaceae, lately merged into the Amaranth Family, the Amaranthaceae. However, members of that family normally produce hard, black, egg-shaped little seeds very unlike anything these succulent, deeply lobed maturing ovaries seemed capable of producing. Still, this halophyte along the Malacón was so convincingly a member of that group that I removed some fruits and squished them between my fingers. Instantly something like grains of sand could be felt amidst the juicy pulp. You can see what was felt at http://www.backyardnature.net/n/15/150201sz.jpg.

Those are classic amaranth-type seeds next to a squished ovary. One seed was produced per lobed ovary, the seed seeming to be formed below the collection of lobes. Maybe the succulent lobes are merely to attract animals who might find such a salty, juicy fruiting head tasty, eat them, and then later deposit the seeds in poop at a new location.

Now convinced that the plants were members of the Amaranth Family, it was easy enough to scan the list of members of that family listed for Ría Lagartos Biosphere Reserve, and with help of pictures summoned from the Internet identify our plant as one known by several names, among them Annual Sea-blite, Narrow-leaf Seablite, Southern Sea Blite, and Annual Seepweed. It's SUAEDA LINEARIS, found in salt marshes and on sandy beaches and other coastal wetlands all along the US Atlantic coast south to our area, and eastward through the Caribbean. In areas with freezing temperatures the plant is strictly an annual, but down here it's a woody-based perennial.

At first I thought the name seablite disparaged the plant as a "blight of the sea." However, the Online Etymology Dictionary reports that the word "blite" derives from the Latin blitum, based on the Greek bliton, used to describe spinach, or plants like it. So the term seablite loosely translates to "spinach of the sea," which is appropriate because the succulent, salty leaves taste pretty good.

Green Deane at his "Eat The Weeds" website refers to the edibility of our local Seablite as "absolutely excellent boiled," and he also praises it in its raw state. He offers a recipe for "Sea Blite and Sour Cream Salad" at http://www.eattheweeds.com/suaeda-linearis-maritima-edible-blite-2/.

*****

GIANT SWORD FERN
About a kilometer into the mangroves east of Río Lagartos, at Petén Tucha where we've seen Spider Monkeys swinging among branches of strangler fig trees, some years ago a tree fell, opening the canopy so that sunlight, at least at mid-day, floods onto the forest floor. The forest floor there is ankle-deep in brackish water. Nature's reaction to this penetration of sunlight into an otherwise shadowy and somber understory has been to engender the massive tangle of eight-ft-tall (2.5m) ferns shown at http://www.backyardnature.net/n/15/150201fn.jpg.

Those giant ferns glowing in sunlight during their brief mid-day photosynthetic rush put one in mind of the Carboniferous Period 300 million years ago, when giant dragonflies glided among treelike lycopods, seed ferns, horsetails and cordaites, whose dead bodies when sunk into swamp mire eventually lithified into the stuff we call coal. But the sunlight does something else, too: They backlight certain fronds so that their clusters of fruiting bodies, or sori, easily can be seen on pinna undersides, as shown at http://www.backyardnature.net/n/15/150201fo.jpg.

Seeing the sori is important because every fern has its own way of grouping its spore producing sporangia, so if you can see the sori, you've seen important field marks. In the last photo this big fern's sori look like round warts in single file just inside the pinnae's margins. Another good field mark is the fern's stiff main stem, or rachis, that almost looks woody, and is round in cross section.

This is the Giant Sword Fern, NEPHROLEPIS BISERRATA, occurring throughout the Earth's tropical and semitropical regions in a variety of habitats, not only in mangroves and woody swamps but also sometimes in clearings and roadsides, and even epiphytically on trees. In the US they occur in southern Florida.

At Petén Tucha the Giant Sword Fern is so rank and robust that you can't imagine taming it in a pot on your patio, but that's exactly what many gardeners do. Then the fern at best gets only half the size we see here, but it makes a handsome landscaping plant, and even looks good in baskets hung so that the fronds cascade over the size.

*****

FEATURED ESSAYS FROM THE PAST:

"Social Conservatism" from the November 10, 2008 Newsletter, at http://www.backyardnature.net/n/p/081110.htm

"Sociobiology" from the July 21, 2008 Newsletter, at http://www.backyardnature.net/n/p/080721.htm

*****

Best wishes to all Newsletter readers,

Jim

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