Simbiosis en la arena

Una pareja de gobios de nariz amarilla (Stonogobiops xanthorhinca) rompe el molde y se desplaza regularmente fuera del alcance de las antenas de su compañero camarón. Foto de Ned and Anna DeLoach.

Interactions between different species, whether above or below water, typically revolve around “red in tooth and claw” confrontations between predators and prey. At the opposite and more harmonious end of the spectrum, a scattering of unrelated species coevolved to form lifelong alliances for their mutual security.

These relatively rare go-along-to-get-along partnerships provide a net benefit for both parties, improving each species’ reproductive success — the pinnacle of natural selection. The strategy’s apparent success makes one wonder why mutualistic relationships don’t occur more often.

Este acuerdo de convivencia cercana entre los camarones chasqueadores de ojos débiles y sus compañeros, los gobios de vista de lince, es un ejemplo clásico de simbiosis en el mar. Los camarones chasqueadores vinculados a los gobios son maestros habitantes de las arenas que cuentan con una armadura articulada y un par de corpulentos brazos con pinzas muy adecuados para excavar el sedimento blando. Mientras cavan debajo de la superficie, los camarones no tienen nada que temer de los depredadores, pero una vez que salen a la superficie se convierten en presas fáciles para los carnívoros que pasan por allí.

First described in 2019, Emily’s shrimpgoby is magnificent and rare.
First described in 2019, Emily’s shrimpgoby (Tomiyamichthys emilyae), que se describió por primera vez en 2019, es maravilloso y extraño.

La vida a la intemperie es incluso más peligrosa para los gobios. Los esbeltos peces de 5 a 8 cm (2 o 3 pulgadas) tienen pocos problemas para vigilar a los depredadores que están al acecho, pero encontrar un lugar seguro para esconderse es otra cuestión. Para mejorar sus probabilidades de supervivencia, los gobios sin techo y los camarones miopes se asocian para enfrentarse al mundo.

The gobies spend large portions of their day perched on furrows leading from burrow openings, where they uphold their primary part of the bargain by acting as sentinels, while their forever-busy partners shovel debris above ground. To sweeten the deal, the gobies supplement the shrimps’ conventional diet of substrata detritus by dutifully depositing their droppings inside the tunnels.

En el momento en que un camarón aparece en la superficie, posiciona al menos una antena sobre el gobio, generalmente cerca de la cola. Las alertas de posibles peligros varían de una leve sacudida de cola, lo que indica precaución, a una señal de alarma con un aleteo intenso. Cuando se emite un código rojo, ambos animales desaparecen en el interior de su madriguera en tan solo décimas de segundo. Pero incluso en una situación de pánico hay cánones: el camarón siempre ingresa primero.

The inch-wide subterranean passages where the partners hide out typically cuts through 2 to 4 feet of sand and rubble a foot or so beneath the surface. The descending burrows occasionally branch and often include fist-sized chambers hollowed out beneath rocks and coral rubble for support. The industrious shrimp have their work cut out for themselves maintaining their convoluted creations. The instability of the tunnels’ upper sections requires continual attention, and collapsed openings are common.

Whitecap shrimpgobies (Lotilia klausewitzi) are also commonly known as dancing gobies for the rhythmic movements of their oversized pectoral fins.
Los gobios de gorro blanco (Lotilia klausewitzi) también son conocidos comúnmente como gobios danzantes por los movimientos rítmicos de sus aletas pectorales de gran tamaño.

Por lo general una pareja de camarones y un único gobio guardián comparten una madriguera. Durante la temporada de reproducción, la cantidad aumenta cuando hembras de gobio vecinas se acercan tras ser cortejadas y dejan atrás nidadas de huevos para que los machos las mantengan a salvo. 

Acercarse a los gobios camaroneros sin que se alejen a toda velocidad para esconderse bajo el suelo es una tarea difícil. Sin embargo, la proeza puede lograrse con un poco de paciencia y práctica. Pero primero, debe encontrar sus madrigueras.

There is only a single shrimpgoby species in the Caribbean, but the group proliferates in the tropical Indo-Pacific, where more than 100 species inhabit the sandy plains and muddy inshore bottoms across. When crossing sandy patches, watch for gobies perched on the edge of furrows leading to burrow entrances. When you find one, rest assured there will be others around. Once you’ve determined a target, flatten your profile and inch forward while continually monitoring the gobies’ nervous nature to gauge every move.

The time spent is worth the effort. Watching the brawny crustaceans busily shoring up crumbling entranceways from an arm’s length away is a hoot. They go about their Herculean tasks like tightly wound robots, heaving and hoisting, jamming and cramming, poking and plowing, and at times lifting shell fragments twice their weight with their powerful claws in never-ending battles against the shifting sand.

Don’t forget the gobies. The closer you approach, the more magical they become. While the majority wears sensible camouflage wardrobes, others display bold colors and sport high, handsome fins as if taunting predators to attack. It seems these flashier shrimpgobies, including several of our favorites pictured here, are among the most difficult to approach. But, as things turned out, one of the least-elegant species proved to be the most compelling.

A small black nudibranch attaches to the fin of this Steinitz shrimpgoby.
Would it be worse to have fleas or nudibranchs? You’d have to ask a Steinitz’ shrimpgoby (Amblyeleotris steinitzi).

Its story began for us some years ago when Anna happened upon an obscure scientific paper from Japan describing the first documentation of a shell-less mollusk associating with a fish — in this case, small black nudibranchs clinging by their mouths to the shrimpgobies’ fins. Examination of hosts revealed gaping sections of fin rays and membrane missing from where the hitchhikers had once attached.

Anna naturally became obsessed with something so wondrously wacky and for years scrutinized every shrimpgoby we passed. Then one fine morning in Fiji, bingo! There it was: a jet-black, parasitic nudibranch chowing down on a goby’s dorsal fin — another example of symbiosis, but in this instance, one far less egalitarian.

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Watch the relationship between a goby and a pistol shrimp in this video.

© Alert Diver — Q2 2021

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