The Symbiotic Relationship Between Gobies And Pistol Shrimp
A rare marine symbiosis sees a fish and a crab lodging in burrows built porcelain crabs sharing burrows with pistol shrimp and gobies near a. In the goby and pistol shrimp symbiosis, both animals benefit. . exuviae into pieces and transported them out of the burrow as soon as their new test hardened. Details of the shrimp-goby mutualism differ a little bit depending on which the pistol shrimp Alpheus djiboutensis (Alpheidae) in artificial burrows. .. to their immediate environment before the organism is tested for survival.
If the danger approaches further, the goby will shoot into the hole through a quick C-bend of the body and enter the hole. Ecology One of the questions asked by ecologists is, "What habitat does an organism live in? There have been a few detailed studies, however, on habitat segregation and the use by goby and shrimp. These studies for the most part, show a high degree of habitat seggregation see Cummins For example, in the Seychelle Islands where Polunin and Lubbock observed 13 species of goby, 5 were only found in one habitat and an additional 4 were only found in 2 habitats.
Yanagisawa studied 20 species of shrimp-goby in southern Japan and found that they distrubuted themselves acording to distinct depth and bottom substrate preferences. Finally, Karplus showed in the northern Red Sea that while gobies may vary a little with debth and microhabitat, they show relatively little variation compared to the shrimp that are actually digging the holes. Karplus' work aboveshows how well segregated different species of gobies and shrimp can be in relation substrate.
Population Dynamics The study of population dynamics and population ecology for the shrimp-goby relationship is exceedingly difficult, is made possible by the fact that tagged individuals almost invariably will be found again in the same general region if not the same hole, on future assessments. The real key is to be able to observe a population over time and be able to recognize individuals, or at least trends in a population that would give clues as to the activity of individuals in the population over time.
One of the best examples of a well-documented population studies comes from the PhD thesis work of Cummins on One Tree Reef, Australia. The shrimp and gobies studied in this area live in a climate that tropical and thus not seasonal to any great degree.
As a result there was no seasonal variation in population dynamics as has been found in places like Japan where there is a marked seasonality Yanagisawa Cummins examined the stability of partnerships in the bay to answer the question if shrimp and goby are bound for life.
The figure above shows his results.
As it turns out, only about 70 percent of the shrimp that he was able to recognize from the first marking ended up with the same goby as before. The others had paired with either different gobies of the same species or other species altogether.
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There were also several shrimp that had not been recognized in the first treatment that were paired with gobies. Of these, about half were juvenile pairings indicating that they probably were overlooked in the first observation because of their small size.
The question then is why might these gobies move from hole to hole. Cummins offered a few explanations. First the burrows could be displaced as a bigger goby moved in. Several gobies may leave their own burrow to look for a mate, thus freeing burrows to be colonized by other individuals. Finally, death caused by predation or disease may have resulted in displacement. Another important question in population ecology deals with the life histories of the individuals. How long is it before individuals can reproduce and what is their life expectancy?
Yanagisawaattempted to deal with such a question, with his work on Alpheus bellulus and Amblyeleotris japonica in southern Japan. He found that in this species, which is highly seasonal, with new recruits of both individuals settling in September to October, the adult population consisted of 1 year olds and 2 year olds.
Both shrimp and goby reach reproductive age in a year and start breeding.
The following predators have been documented to prey on shrimp gobies: Thus, the shrimp sometimes respond to signals from the goby by working closer to the burrow opening, sometimes by working in the actual burrow opening, and sometimes by totally retreating into the burrow itself.
This quite detailed interspecific communication is very rare in nature, at least when invertebrates such as shrimp are parts of the interaction. Goby with partner shrimp The actual method of the communication between the pair is performed by contact of one of the very long antennas of the shrimp to the posterior dorsal fin of the goby.
When the shrimp wants to get out of the burrow the shrimp first extends one of the antennae out of the opening, contacting the fin of the goby. If the coast is clear, the goby wiggles its fin in a certain way, telling the shrimp that it can come out. As long as the shrimp is outside the burrow, its antenna will be touching the gobies fin.
Goby with partner shrimp How about nighttime, then? During the dark hours, he goby cannot see much. The burrow then turns into more of a trap than a refuge, as many of the small eels hunting on the sand can also penetrate the burrow, thus capturing both the goby and the shrimp. In the goby and pistol shrimp symbiosis, both animals benefit. This relationship is not parasitic and not commensal—it is mutual.
The shrimp builds and maintains a burrow that both animals live in, and the fish offers the shrimp protection from predators. When they are outside of the burrow, the fish keeps an eye out for predators and warns the goby with a flick of the tail if there is a predator nearby.
The nearly blind shrimp can then retreat into the burrow to be spared from predation. These animals participate with each other on a highly elaborate and evolved level—and it becomes more impressive when you think about how they are in no way related. This is an amazing partnership, but what goes on inside of the burrow that they both inhabit? Until recently, we have only been able to observe their behavior outside of their elaborate burrows.
I have been able to make some new observations with an interesting tank setup. First I will tell you the history of studying this particular symbiosis, then I will let you know how you can set up a tank specifically for viewing this symbiosis, and then I will relate my new findings.
A Scientific History Luther, when he was a junior scientist, managed to catch a goby and pistol shrimp pair and put them in a small fish aquarium after they had been discovered during a expedition of the Red Sea.
The blind shrimp and the macaroni goby
Indeed it took a lot of time until these peculiar couples were back in scientific focus. It was again in the Red Sea, and the same species of fish and shrimp that came to the awareness of biologist Ilan Karplus in the s and s. He and his associates studied how these animals communicate, their territorial behavior, the dynamics of building the burrows and the distribution of the different species.
Observing them in nature by diving was difficult at best; scientists could lay down in front of the burrow entrances until their air ran out. It took a long time to observe them because any disturbance caused them to stay inside the burrow for hours. Everyone who has tried to take pictures of them in nature is aware of this. Today we know that the symbiosis between gobies and pistol shrimp is an evolutionary model of success.
The majority of these are found in the Indo-Pacific and adjacent regions. There are goby generalists that live together with different shrimp, but there are also specialists living with just one species Karplus et al. Species differ concerning the distribution of their partners, their age and sort of substrate different gobies prefer finer or more coarse sediment.
Shrimp leave the burrows only during daylight in company with the gobies. Shrimp or gobies never lived alone in a burrow, and the minimum count was a single shrimp and a single goby. More often, a couple of gobies and a couple of shrimp were found in one burrow.
To observe the association in aquaria was another approach to find out more. The partners had to find each other in a Y-shaped testing channel, either by optical or olfactory abilities. The shrimp did not show any optical orientation at all, but the gobies did. Gobies could differentiate potential partner shrimp by sight Karplus et al.
If unsuitable partners were presented in experiments, the gobies stayed away. In reverse, the shrimp found their partners by smell.
There was interest from the beginning about what the burrow looked like, but all that was visible from outside was the entrance. The tubes were filled with sand before the experiment started. After the shrimp excavated the tubes, the partnership could be viewed. This setup, however, appeared too artificial to me. Yanagisawa even poured resin into burrow openings in the wild.
The burrows went down as far as 1. The burrow often divided, and the tunnels extended into chamberlike structures. Larger coral rubble pieces or skeleton parts of sand dollars were integrated into the burrow.
The Symbiotic Relationship Between Gobies And Pistol Shrimp
My Observations These trials to find out more about the burrow system just fueled my interest to find out what was really going on inside. Among marine aquarists, it was not even known that couples of shrimp and couples of gobies naturally live together. Most aquarists were happy to have one shrimp and one goby in their tank combined.
Where and how would they reproduce? Existing observation did not have an answer for this question. But how could I look inside the burrow?