May 8, 2011
A SEA URCHIN'S WAVING SPINES
In about a foot of water I was working my hand through a dense stand of Turtlegrass, Thalassia testudinum, just to see what was there. It wasn't long until my fingers wrapped around something like a heavy, spiny egg, and that spiny egg seemed to be sticking to my fingers...
Lifting the thing from the water I realized that during my earlier stay here I'd found cast-up remains of such a creature on the beach. You can see such a golf-ball-size skeleton with its spines broken off at http://www.backyardnature.net/yucatan/urchin.jpg.
The living, spiny specimen found this week is shown at http://www.backyardnature.net/n/11/110508ur.jpg.
That's the Variegated Sea Urchin, sometimes also called the Green Sea Urchin, LYTECHINUS VARIEGATUS. The species commonly occurs in calm, clear waters from North Carolina and Bermuda southward through the Caribbean to Brazil. Beds of Turtlegrass constitute one of its preferred habitats.
I wanted to take a good look at this strange little being that somehow stuck to my fingers so I picked up a trash plastic cup that had floated onto the beach, filled it with seawater, put the urchin in it, got on my hands and knees, and began watching.
It was amazing. The spines weren't fixed in place as I'd imagined, but rather slowly waved back and forth. Also, there were slender projections among the spines wiggling even more energetically than the spines. With my digital camera I made a video, which I hope you can view at http://www.youtube.com/watch?v=jtVa3EJWrrk.
In the video you can see the urchin not only shifting from place to place, but also slowly working a leaf of Turtlegrass across its spine tips. How can a spiny sphere be so mobile and manipulative? And where does its stickiness come from? I could hardly wait to Google my questions about sea urchin anatomy.
It turns out that not only spines radiate in every direction from the spherical urchin body, but also there are hundreds of "feet," which are thin, muscular tubes with suction cups at the ends. So, those feet with their suction cups accounted for the animal's "stickiness," and the waving feet and spines together enabled the creature to shift about and move its Turtlegrass leaf. In the video, best I can determine, the lines of dark, shorter, fast-waving items between the white, longer spines are the feet.
One last surprise about my sea urchin: That hole at the top isn't the mouth as I'd assumed, but rather the tail hole. The mouth is at the bottom.
Stanford University offers a nice page on Sea Urchin anatomy and physiology, with some diagrams, at http://www.stanford.edu/group/Urchin/anaphys.html.
SNAIL-LIKE ON A ROCK
Well aware of my profound ignorance about the sea's living things, I waded among half-emerged rocks at a rocky point just up the beach, not knowing at all what to expect. The first living creature spotted was a thimble-size, snail-like critter stuck to an algae-encrusted limestone rock that most of the time was submerged as waves rolled over it, but sometimes, between waves, emerged above the water, as shown at http://www.backyardnature.net/n/11/110508mk.jpg.
The shell was easy to pry from the rock. You can see his shell ornamented with purple-banded ridges at http://www.backyardnature.net/n/11/110508ml.jpg.
Tilting the shell, I found the animal protectively retracted into his shell, as shown at http://www.backyardnature.net/n/11/110508mm.jpg.
Obviously this is a mollusk -- an animal mantled with a single shell carried above a muscular foot, the animal's internal organs protected by the shell. Snails are the best known mollusks.
Happily, Bea in Canada, who in the past has volunteered to identify our insects, now has offered to ID our "seashells." She hadn't had my above pictures for long before she wrote back that our rock- living creature was a Four-tooth Nerite, NERITA VERSICOLOR, and she even said that IDing it had been easy. Here's how she said she did it:
"I entered some search words in Google, most likely something like 'seashells Gulf of Mexico' which brought up lots of websites. I started checking out a few until I came across this one called Holman Shell Collection: http://research.fit.edu/shells/ I started clicking on the different groups of shells starting at the beginning of the list, skipping the ones I was familiar with and knew that it wasn't, for example a conch. I would check out just one in each group. Once I clicked on a Limpet for example, I knew it wasn't any of the other Limpets, so I would try the next group. I kept going until I came across the Nerites and said AHA!!"
Having the name, now I could search for information on the Internet. There I learned that Four-tooth Nerites move up and down the shore in step with the tide's high water level, and that they're particularly resistant to periods of heat and desiccation. Nerites seem to occur in nearly all the world's tropical and subtropical seas, except the eastern Pacific.
We ran into another nerite species, Neritina virginea, back in 2006 at Río Lagartos on the Yucatán's northern coast. You can some of the many variations of that one at http://www.backyardnature.net/yucatan/nerites.htm.
Our present Nerita versicolor, as its species name versicolor implies, also is very variable. So I'm getting the impression that nerites are unusually colorful, commonly occurring, aquatic, snail-like creatures to be identified not by color and pattern but rather by structure.
Right up the road a dead tree holds the nest of a Common Black Hawk. You can see the male near the nest at http://www.backyardnature.net/n/11/110508bi.jpg.
The incubating female peering over the nest's edge is at http://www.backyardnature.net/n/11/110508bh.jpg.
This is a classic stick nest. Common Black Hawks are often seen here next to the mangroves.
LINGERING ROYAL TERNS
Royal Terns are known as winter residents in this area, migrating northward for the summer. Still, here in May we still have a few -- in winter plumage -- as shown at http://www.backyardnature.net/n/11/110508tn.jpg.
Howell in A Guide to The Birds of Mexico and Northern Central America reports a couple of isolated breeding colonies of Royal erns in the Bay of Campeche across the Yucatán Peninsula, and "possibly also off Belize," so maybe it's impossible to know whether the birds I'm seeing now are late migrating northward, or intend to stay here all summer.
Since migration patterns are changing as global warming takes place, I figure it's a good idea to note document unusual occurrences, for researchers trying to make sense of the matter. The above picture was taken here on May 3rd.
Brown Pelicans, Semipalmated Plovers, Ruddy Turnstones and Blue-winged Teal also are mostly winter visitors here, except for a few isolated breeding colonies, but I'm still seeing them here, too.
The low sand ridge I'm living on now is bordered by the Caribbean to the east and a vast mangrove swamp to the west. In this part of the world four different woody species are known as mangroves. The species forming a wall on our eastern side is Buttonwood, CONOCARPUS ERECTUS, a member of the mostly tropical Combretum Family. You can see its 10-ft-high face at http://www.backyardnature.net/n/11/110508bw.jpg.
Usually Buttonwoods bear flowers and/or fruits in distinctive, cone-like clusters, as shown at http://www.backyardnature.net/n/11/110508bx.jpg.
In that picture the brownish clusters at the left are more mature. At the peak of maturity the clusters crumble into separate fruits.
If you can't find a tree with flowers or fruits, Buttonwood's leathery, evergreen, alternate, simple leaves with entire margins are similar to several other woody trees in this area. However, the trees' petioles, or leaf stems, bear a distinctive pair of bulging glands, as shown at the left in the picture at http://www.backyardnature.net/n/11/110508bz.jpg.
As you'd expect of a mangrove, Buttonwood lives in brackish or saline environments, the term brackish referring to water that's saltier than fresh water but not as salty as seawater. My impression is that of the four mangrove species Buttonwood occupies soil spending less time underwater than the other three species. In fact, Buttonwoods can be grown on dry land well away from the ocean.
Ecologically, Buttonwood is noted for withstanding high winds better than the other mangrove species. Often it occurs at the edge of mangrove swamps, serving as a buffer for the ecosystem. Buttonwood thickets provide habitat for many species, including crabs and Bald Eagles. Unfortunately, its wood, which is exceptionally heavy, makes excellent firewood and is cut for charcoal production.
Buttonwood is distributed from central Florida through the Caribbean, and northern Mexico south to Ecuador and Brazil, as well as western tropical Africa.
Along our sandy roadsides a knee-high plant is conspicuously flowering now, looking a little like the North's goldenrods, but it's something else entirely. You can see the silvery leaves and yellow flowers of one at http://www.backyardnature.net/n/11/110508yt.jpg.
A close-up of a flower-head cluster is shown at http://www.backyardnature.net/n/11/110508yu.jpg.
That inflorescence really looks like a goldenrod's, but goldenrods, genus Solidago, simply don't occur in this part of the world. A close-up of some Yellowtop achene-fruits proves that our plant isn't a goldenrod, at http://www.backyardnature.net/n/11/110508yv.jpg.
You may remember that goldenrod achenes are topped by fuzzy, white parachutes that help the achenes travel on the wind. You can see that Yellowtop's achenes bear no parachutes -- have no "pappi," as a botanist would say.
Since this wildflower lives on Florida's beaches, hammocks and in pinelands, as well as in similar places here in the Yucatán, the Bahamas and Cuba, it's treated in the online Flora of North America. There it's given the name Narrowleaf Yellowtop. It's FLAVERIA LINEARIS, a member of the Composite or Sunflower Family. Species in the genus Flaveria frequently occupy alkaline, saline, or gypsum-rich soils, and often occur in disturbed, moist areas.
The genus name Flaveria is based on the Latin word "flavus," meaning yellow.
There's a whole subculture of genteel beachcombers known as "sea-beaners," and many of them make pilgrimages to Mayan Beach Garden for their sea-beaning. Sea beans are beans and other beanlike seeds that float on ocean currents and end up washed onto beaches, often having floated from distant lands. Sea-beaners think that sea-beans are pretty, and they're fascinated by finding things that have drifted from distant lands. There's an extensive website just on sea-beans and -beaning at http://www.seabean.com/.
Gray Nickernut plants, which are woody, scrambling shrubs climbing up to 16 feet high (5m) produce one of the most sought-after sea-beans, and those beans wash onto the beach here. A few years back Marcia planted some Gray Nickernut beans next to the hotel and now the plants robustly clamber over all other vegetation, clear into the mangrove swamp. You can see a small section of one such shrub, bearing twice-compound, 15-inch-long (40cm), prickly leaves, upright racemes of tiny flowers, and some green, soft-spiny fruits, each fruit containing one or two nickernuts, at http://www.backyardnature.net/n/11/110508nc.jpg.
A close-up of three nickernut legumes is shown at http://www.backyardnature.net/n/11/110508nb.jpg.
A necklace owned by Marcia in which gray, lustrous, spherical Gray Nickernut beans are strung appears at http://www.backyardnature.net/n/11/110508nd.jpg.
We don't know what the dark, spotted items in the necklace are, but you can see that the nickernuts shine like pearls.
Gray Nickernuts are known to science as CAESALPINIA BONDUC.
Gray Nickernut plants, thanks to their beans' ability to float long distances on ocean currents, occur in tropical and subtropical coastal environments nearly worldwide, including the US's coastal Florida, Louisiana and Texas. They are abundant near the beach in nearby Sian Ka'an Biosphere Reserve.
WHITE SCROLL ALGA
Friday afternoon the tide was so low that up at "The Point" rocks that usually are submerged stuck from the water, and there were tide pools to snoop into. Tide pools are seawater-filled rock holes that come into existence at low tide, look like sunken bathtubs, and usually are filled with interesting organisms. You can see one such tide pool about two feet across at http://www.backyardnature.net/n/11/110508al.jpg.
A close-up of the pale flat organisms in the pool is at http://www.backyardnature.net/n/11/110508am.jpg.
I had no idea whether this was a plant, animal, fungus or something else. However, back at Mayan Beach Garden's little library I didn't need much time thumbing through identification guides to organisms of Caribbean coral reefs to figure out that this was the White Scroll Alga, PADINA JAMAICENSIS, apparently a common alga in the Caribbean, including along the shores of southern Florida.
White Scroll Alga is a brown alga, along with Kelp and Sargasso. The genus Padina is a common one with many of its species bearing leafy, fan-like blades like ours. They attach to rocks and other hard substrates in shallow water. A study of White Scroll Alga found that when fish fed heavily on it, instead of forming fan-like blades they produced slender strands. Remove the fish and then the same plants begin producing fan- like blades.
PICKING UP TRASH
Enormous amounts of trash, little of it originating locally, wash onto the beach here. Especially after a weather system blows in, the next day the beach with all its plastic bottles and caps, half-buried sheets of plastic, rubbery flip-flop soles, Styrofoam cups, Bic lighters, torn fish-netting, frayed rope, all entangled in washed-up seaweed... looks pretty bad.
You think of all the turtles out there with plastic bags twisting in their stomachs because the bags floating in water look like jellyfish. You think of all the fish that died because butane-filled Bic lighters floating at the water's surface look like small, surface-feeding fish. And if you keep thinking about it, eventually you realize that if someone doesn't pick up this garbage it'll just wash back into the sea the next storm that comes along.
So, eventually you get out there with garbage bags and start picking things up. The wind does this thing with flimsy garbage bags causing the bags' leeward side to suck in and cling to the front so that the bag stays closed. Opening the bag, which also twists in the wind, is hard. After you bend over a few hundred times picking stuff up, every time having to fight the bag to open it, you start wondering what kind of perverted psychology or decadent sociology is responsible for all that garbage in the first place.
But, you can't go there. If you start assigning blame, finding fault, before long you don't like anyone, including yourself.
So, why get out there and pick up trash, struggling with those stupid wind-sealed bags, when there's no end to the situation in sight and, in fact, each year there's just more and more garbage dumped into the oceans?
Maybe that's like asking why members of the orchestra kept playing as the Titanic sank. To some people it's perfectly clear that those musicians were crazy, but to others they were heroes.
I suspect that the Titanic's musicians saw themselves as neither crazy nor heroic, but rather each musician asked himself, "At this critical moment in my life, what other worthy, dignified thing, right now and given my options, can I really do... ?"
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