December 7, 2014
WASHED-UP SEA HARES
For several days a stiff norte had blown from the north, so I was glad to visit the sandy beach on the sea side of the long, slender finger of land separating Río Lagartos and its estuary from the Gulf of Mexico. I was glad because after such northerly winds the beach always is heaped with interesting things blown ashore. For me the most interesting find was the four-inch-long (10cm) item shown at http://www.backyardnature.net/n/14/141207sh.jpg.
You wonder about that groove running down the back. A better view of it is provided at http://www.backyardnature.net/n/14/141207si.jpg.
A look at the creature's bottom, with its "foot" spread out, is seen at http://www.backyardnature.net/n/14/141207sj.jpg.
Dozens littered the beach that day, often still alive but dying from exposure. I was with a friend, biologist Wili Cruz, who said they always turn up like this at this time of year after nortes blow heaps of seaweed ashore. The creatures inhabit the seaweed so when waves uproot vegetation and blow it ashore, animals inhabiting the stems and leaves come with them. Wili called them by their local name, Agua Mala, agua mala meaning "Bad Water." The name refers to the purplish ink the animal expels into the water when disturbed, like a squid. You can see some ink that got onto Wili's fingers as he was examining one at http://www.backyardnature.net/n/14/141207sm.jpg.
You might guess that this is some kind of large, slug-like animal, thus a gastropod, which is a kind of mollusk -- Class Gastropoda, which is a subdivision of the Phylum Mollusca. Our gastropod is traumatized by being washed ashore and exposed to sunlight and wind, so he's not fully deploying his tentacles and all the features of his head, which made identification harder. Still, doing image searches on the Internet on names of marine gastropods found in the Yucatan's waters, our discovery was found to be APLYSIA FASCIATA, commonly known as a Sea Hare or Sea Slug.
Having the name, details about Sea Hare life could be looked up. It was learned that Sea Hares, like many mollusks, have protective, snail-like shells, but they're inside the body, just beneath the fleshy covering of the broad hump on top. What seems to be a groove down the top is actually just an open space formed with the animal's two broad, winglike flaps are folded over the back. When the flaps are open there's no groove, and the flaps, called "parapodia," are undulated in a way that gracefully propels the Sea Hare through the water like a Manta Ray.
Sea Hares feed on aquatic plants and algae in shallow water. They're hermaphroditic, meaning that individuals possess both male and female sexual parts, so when they mate each individual both gives and receives sperm. I read that sometimes mating sea hares form chains, one releasing sperm to the animal ahead of it, while receiving sperm from the Sea Hare behind it. Eggs are laid in gelatinous chains that can be several yards (meters) long and contain over 20 millions eggs. Normally Sea Hares occur in waters less than 65 feet (20m) but sometimes they go deeper.
That day we found Sea Hares of various sizes and stages of development, including large numbers of much smaller ones with parapodia and other features hardly developed at all, as seen at http://www.backyardnature.net/n/14/141207sg.jpg.
It's interesting that during my summer months along the Caribbean coast a few years back I never saw a Sea Hare. Probably that's because there the ocean just offshore was deeper, and it was a different time of year.
At first I threw all the stranded Sea Hares we found back into the water, but soon it became clear that there were just too many, surely hundreds of thousands all along the northern coast. It was one of those times when at some point you just have to look away, feeling bad about it.
Some consider our Caribbean Sea Hares to be separate from the Old World species, and give them the name Aplysia brasiliana. Throughout the species there's wide variation in color, many being black, and others being mottled. The broader species occurs generally in the North Atlantic and Mediterranean, and from the Caribbean to west Africa, south to northern South America.
In Ría Lagartos Estuary, flamingos aren't the only large, wading birds who become pink after eating large quantities of small crustaceans who themselves are pink because they feed on algae containing red carotenoid pigments. Another pink bird is shown at http://www.backyardnature.net/n/14/141207rt.jpg.
That's a Roseate Spoonbill, AJAIA AJAJA, one of the most striking of all North American birds, and on most of Río Lagartos's flamingo tours a few are seen, though in much smaller numbers than the flamingos. Roseate Spoonbills are big birds, standing 2¾ft tall (85cm), with a wingspan of 4¼ft (1.3m). In the picture you can see that spoonbill heads display a good bit of naked, gray skin, and that the eyes are pink. However, the big thing about a Roseate Spoonbill is its spoon-shaped bill. A picture better showing the bill's shape is at http://www.backyardnature.net/n/14/141207rs.jpg.
In both of those pictures water is dribbling from the beak's tip. That's because as our bird waded through the water he constantly swung his submerged bill back and forth in a sideways motion. When a spoonbill feels something like a shrimp in the water passing through the open bill, the beak is clapped closed, pulled from the water, and the prey is swallowed. You can see a Roseate Spoonbill feeding with his beak cracked open at http://www.backyardnature.net/n/14/141207ru.jpg.
Back in the 1930s it was fashion among women to have fans made of spoonbill feathers, so untold numbers of spoonbills were killed. At one time a previously large breeding population in Florida was reduced to 30-40 pairs. However, when spoonbills finally gained legal protection their numbers began to rebound. Nowadays their habitat -- marshes and estuaries like those here -- are gradually disappearing, so once again the species is under pressure. Some populations show high levels of pesticide residue in their eggs but so far this doesn't appear to be causing a problem.
Roseate Spoonbills inhabit marshes, swamps, ponds and rivers from Florida across the Gulf of Mexico and Caribbean south to Argentina and Chile.
In the whole world, only in the northern coastal Yucatan Peninsula can you see the bird species shown at http://www.backyardnature.net/n/14/141207wr.jpg.
Those are Yucatan Wrens, CAMPYLORHYNCHUS YUCATANICUS, and they're fairly common along backcountry roads in the ranch/savanna area around here. As you might expect of a wren, Yucatan Wrens are noisy, curious and fairly easy to see. They're closely related to Cactus Wrens of the US southwestern states and arid northern Mexico, which generally are paler top.
Howell describes the Yucatan Wren's habitat as "arid scrub with cacti, gardens, plantations," and that's exactly what we have here.
STIFF PEN SHELL
On the sandy, Gulf-side beach of the long, slender finger of land across the estuary from Río Lagartos, last week's norte -- a strong wind blowing for several days out of the north -- deposited lots of seaweed and seashells. Among the shells was the sharp-pointed one shown at http://www.backyardnature.net/n/14/141207at.jpg.
A better look at the broad-based, tube-like spines on the broad end of the shell is seen at http://www.backyardnature.net/n/14/141207au.jpg.
Such long, sharp-pointed shells are known as pen shells, and the tube-like spines mostly occurring on the big end and only on one side, indicate that this is the Stiff Pen Shell, ATRINA RIGIDA. Stiff Pen Shells turn up on beaches from North Carolina south through the Gulf of Mexico and Caribbean to Brazil.
The bivalve mollusks producing pen shells burrow their sharp ends into soft mud, leaving their broad end pointing upward into the water. The animal within the shell filters food from water circulating through the open shell's upper end. At the narrow burrowing end, a cluster of long, fine, silky threads known as "byssal threads" is introduced into the mud, to anchor the shell in place. The threads are covered with an adhesive that holds up remarkably well in water, and does a good job rooting the shell in place. The Stiff Pen Shell species is noted for its ability to heal breaks and holes in its shell. Also, black pearls may be produced by the species. These unusual features have made the Stiff Pen Shell the subject of several scientific studies.
Often a kind of small crab lives within the shell, eating food missed by the feeding clam. Barnacles and other crustaceans may attach themselves to the Stiff Pen Shell's outer shell. Starfish and certain gastropods prey on them.
And some Mexican humans prey on them, too, the large muscle holding the two shell halves together being considered worth the trouble of gouging it out.
On a flamingo-viewing trip up Ría Lagartos Estuary, I was with a young guide who likes to take along dead fish to toss into the water in case there's a Common Black Hawk or crocodile who might be enticed to come closer so the tourists can snap spectacular pictures. That day he'd forgotten his fish. However, as we passed by the pier beneath the big bridge on the road between Río Lagartos and Las Coloradas, a fisherman had just dragged in his throw-net and was discarding fish he didn't want. When the young guide asked if he could have one of the throwaways, the fisherman tossed a slender, silvery, six-inch one (15cm) into the boat. You can see it dying on the boat's floor at http://www.backyardnature.net/n/14/141207wm.jpg.
Later the fish was identified by comparing the picture with those at the fine fish-ID website at http://www.snorkelstj.com/.
There, one of the first species to pop up when I looked in the "Silvery or White Fish" category looked just like what's in our picture. It was the White Mullet, MUGIL CUREMA, described at the above website as most often seen in schools racing back and forth in shallow water, searching for small organisms on sandy bottoms and on plants and algae. That's exactly what they seemed to be doing around us.
White Mullet are an abundant, widely distributed species, found generally along coasts in temperate and tropical seas of the Western Hemisphere. A reason for the fish's success is that it thrives in a wide range of water conditions, ranging from freshwater to hypersaline (saltier than ocean water) coastal waters -- everyplace from ocean beaches, bays, lagoons, salt marshes and mangrove swamps to tidal rivers. Especially young fish, which this one appears to be, are known to invade estuaries and coastal lagoons like the Ría Lagartos Estuary.
White mullet gulp up mud containing algae, plankton, and plant and animal detritus which the fish's gut can deal with thanks largely to its uncommonly muscular gizzard.
You can imagine the value of these abundant little fish to larger predators, both fish and birds.
The most common cactus in the arid savanna just south of Río Lagartos is a sprawling pricklypear, or Opuntia cactus. However, the most striking is a less abundant but somewhat common columnar, weakly branched one that often rises from among broadleaf scrub, exactly as you can see in the picture with my photographer friend Jim Legault providing scale at http://www.backyardnature.net/n/14/141207pi.jpg.
A shot better showing the cactus's typical form is at http://www.backyardnature.net/n/14/141207pj.jpg.
The cactus's pale, slender spines are arranged in clusters of about twenty pointing in all directions, sea-urchin-like. The clusters arise evenly spaced atop the stem's ridges, as shown at http://www.backyardnature.net/n/14/141207pk.jpg.
About a month ago I found one of these cacti with a flower bud about to open. You can see that, plus see how spine clusters at stem tops are woolly-white at their bases, at http://www.backyardnature.net/n/14/141207pl.jpg.
Twice I returned when I thought the flower might be open, but the cactus stood near a spot in the scrub where a fellow kept bee hives, and those bees were mean ones, apparently "Africanized" with genes from "killer bees" that a few years ago worked their way north from South America, and I was chased away. This week when I got back a month after the flower-bud picture was taken -- this time on a windy day when maybe the bees were less active -- the flower bud had developed into a green, immature fruit, with the corolla's dried-up, black remains dangling from the warty fruit's center, as seen at http://www.backyardnature.net/n/14/141207pm.jpg.
This is PILOSOCEREUS GAUMERI, endemic to just the northern Yucatan Peninsula. The species is so little known that it doesn't have a good English name, but its Spanish name is Sebucán. Some experts have regarded SebucÃ¡n as merely a variation of the more widely distributed Pilosocereus royenii, known as Royen's Tree Cactus and occurring throughout the Caribbean. However, now the general consensus appears to be that our Yucatan plants are indeed a separate species.
I missed the flower, but I hope to see the fruit at maturity, and maybe sample its contents, for the fruit is edible, filled with sweet, juicy, red pulp in which many seeds are embedded.
Over the years cassia species, often referred to as sennas, have been encountered everyplace we've gone, sometimes as herbs, sometimes as bushes or trees. Cassias are members of the huge Bean Family, with most of their maybe 350 or so species occurring in the tropics, but with several common temperate ones. With yellow flowers and pinnately compound leaves, cassias belong to that relatively small sub-group of the Bean Family whose flowers are NOT "papilionaceous" -- not with the top petal much expanded, with narrower side petals, and two lower petals united along their margins to form a scoop-shaped "keel." Instead, cassia flowers are only weakly bilaterally symmetrical, their petals are on short stems and, most strikingly, their five or ten stamens are normally of conspicuously different sizes, with some being much smaller than the others and sterile.
Nowadays along roadsides here there's a dense, much branched, ten-ft-tall cassia (3m) that very prettily is loaded with 1½-inch broad flowers (4cm) and slender, flat, stiff legumes. Since so many similar-looking cassia species exist -- nine are listed for the Yucatan -- for identification purposes it's important to pay attention to details.
First, you can see a single flowering and fruiting branch of this week's cassia at http://www.backyardnature.net/n/14/141207sn.jpg.
A field mark worth noting in that photo is that most flowers occur in pairs atop short, slender stems, or peduncles. Sometimes there are more or less than two, but the predominant twin-flowered condition turns out to be important when separating this species from all the rest. Another good field mark is seen in the flower close-up shown at http://www.backyardnature.net/n/14/141207so.jpg.
There notice that the larger anthers (like two stuck-together bananas) are topped by slender, fingerlike appendages. A closer look at those big, curved anthers with their appendages is at http://www.backyardnature.net/n/14/141207su.jpg.
A view of a flower from behind showing the species' sepals, which are distinctively different from one another in size and shape, is at http://www.backyardnature.net/n/14/141207sq.jpg.
A shot of a section of hairy, flat legume is at http://www.backyardnature.net/n/14/141207sp.jpg.
The bush's leaves are classic pinnately compound ones, which alternate on the stem, and whose leaflets arise opposite one another on the leaf midrib, or rachis, as shown at http://www.backyardnature.net/n/14/141207ss.jpg.
On the rachis of each compound leaf, between the bottom-most leaflets (those next to the woody stem), there's a conspicuous, conical gland, possibly producing a substance that attracts ants who might attack a herbivore starting to eat the leaves, as shown at http://www.backyardnature.net/n/14/141207st.jpg.
Though this pretty cassia species doesn't occur in English speaking lands (except Belize) it has an English name because sometimes it's planted in gardens. It's the Twin-flowered Cassia, SENNA PALLIDA, of which about twenty varieties are recognized. Ours is Senna pallida var. gaumeri.
In the 2003 book Nomenclatura, Forma de Vida, Uso, Manejo Y Distribución de Las Especies Vegetales de la Peninsula de Yucatan. Etnaflora Yucatanense Fasiculo 20 by Alberto Arellano and others, it's reported that the Twin-flowered Cassia is a good pollen producer for foraging bees, and that the leaves when crushed and boiled in water produce a water good for washing stinky feet.
SESBANIA ALONG ROADS
Nowadays a common and eye-catching weed along the road paralleling the coast and passing through the marshes south of Río Lagartos is the ten-ft-tall one (3m) shown at http://www.backyardnature.net/n/14/141207sb.jpg.
Here at the beginning of the dry season the plants are mostly leafless, their stems dead, but bearing long, slender bean pods, or legumes. A closer look at the eight-inch long (20cm), curved pods, their sides bulging over each tiny bean inside, is at http://www.backyardnature.net/n/14/141207sc.jpg.
Though along the stretch of road where the above picture was taken, all the dozens of plants were leafless, elsewhere in a slightly different location the plants' branch tips bore freshly sprouting, pinnately compound leaves, and yellow, typically bean-flower-shaped (papilionaceous) flowers, as seen at http://www.backyardnature.net/n/14/141207sd.jpg.
By "papilionaceous" is meant a Bean Family flower with five petals, the top one, called the standard or banner, usually expanded, then there are two side petals called wings, and finally the two lower petals are fused along their common margins, forming a scoop-shaped structure called the keel. A close-up of a flower showing the much expanded, speckled standard with its sides drooped over the rest of the flower is seen at http://www.backyardnature.net/n/14/141207se.jpg.
When the standard and the nearest wing are removed, the scoop-shaped keel is discovered to be reddish-tipped, as seen at http://www.backyardnature.net/n/14/141207sf.jpg.
We've seen this plant before -- back in Mississippi where it grew in wet sand along creek margins. You can see those tall plants still bearing green leaves at http://www.backyardnature.net/n/h/sesbania.htm.
This is SESBANIA HERBACEA, known by such names as Hemp Sesbania, Coffee-weed, Indigo-weed, Peaweed and a host of others. Back in Mississippi I'd developed the notion that Hemp Sesbania needed to be near streams, so I was surprised to find these growing in very dry, sandy, roadside soil, even though the road passed through marshes. Apparently what the plant likes is the soil's sandiness, not necessarily its wetness.
Hemp Sesbania occurs throughout the US's warmer states and sometimes farther north, plus all through Latin America into central South America. Despite its size, it's an annual plant, which explains why ours are dying here at the end of the rainy season. Despite its being an annual, its stem fibers are so strong that early indigenous Americans used them for weaving nets and for other uses.
Sometimes during flamingo trips up Río Lagartos Estuary, the boat passes through patches of water where it looks like someone has dumped a lot of lawn grass pulled up with their rhizomes attached. It's easy enough to reach over the boat's edge and snatch up samples, which is what I did to get the picture at http://www.backyardnature.net/n/14/141207ha.jpg.
The grass-like blades issue from short vertical stems at the base of which brown, shaggy scales occur where the stems attach to the white, succulent, rootlike rhizome, as seen at http://www.backyardnature.net/n/14/141207hc.jpg.
Pluck as many of these blades-attached-to-rhizomes as you want from the water and you'll not find any with flowers attached. Therefore, it took a bit of study of tropical American estuary aquatic vegetation before it occurred to me that our grasslike plants weren't grasses at all, but rather members of the small, seldom-heard-of but profoundly important Manatee-Grass Family, the Cymodoceaceae, whose members are all aquatic plants.
The only member of the Manatee-Grass Family listed on the list of plants occurring in Ría Lagartos Biosphere Reserve is Halodule beaudettei, which most botanists now call Halodule wrightii. Happily, pictures on the Internet labeled Halodule wrightii look just like ours. Another closely related and similar aquatic, grasslike species occurs in the area, but that species produces rounded leaves. Our plant's leaves are decidedly flat, like blades of grass, as you can see at http://www.backyardnature.net/n/14/141207hd.jpg.
Therefore: That grass appearing uprooted and floating at the estuary's surface during flamingo-seeing tours is HALODULE WRIGHTII, usually called Shoalgrass, the term "shoal" referring to an area of shallow water.
Shoalgrass occupies the Gulf of Mexico's shallowest waters, normally less than seven feet deep (2m). In fact, the plants are often exposed during low tides. The plant occurs in intertidal zones with sandy or muddy floors from North Carolina south along Mexico's Gulf Coast and the Caribbean islands to northern South America. Also, there's a disjunct population in the eastern tropical Pacific and the Indian Ocean, and it's a dominant seagrass species in Brazil and West Africa.
Manatees used to occur in Ría Lagartos Estuary where so much of the aquatic biomass belongs to the Manatee-Grass Family, but they've been exterminated.
The University of Florida provides a fine page describing the importance of seagrass, of which Shoalgrass is an important one, despite its not being a grass -- a member of the Grass Family. That page is at http://fmel.ifas.ufl.edu/habitat/seagrass_beds.shtml.
Ecologically, among the various seagrasses, Shoalgrass is thought of as functioning as a pioneer species that revegetates lagoon floors that have been disrupted or cleared of vegetation, plus it is more tolerant of low salinity than other seagrasses. Salinity varies a great deal throughout the Ría Lagartos Estuary.
FEATURED ESSAYS FROM THE PAST:
"Lively Little Towns" from the May 2, 2010 Newsletter, at http://www.backyardnature.net/n/p/100502.htm
"Lino's Metalwork" from the January 9, 2005 Newsletter, at http://www.backyardnature.net/n/p/050109.htm
Best wishes to all Newsletter readers,
All previous Newsletters are archived at http://www.backyardnature.net/n/.