What is a Shrimp Goby? (Taxonomy)
Alpheid shrimp and gobiid partnerships are widespread across the tropics. Most of the work that has been done on these shrimp-goby relationships has been done in the Red Sea (Luther, 1958; Magnus, 1967; Karplus, 1981; Karplus et al., 1981; Polunin and Lubbock, 1977) and Japan (Harada, 1969; Yanagisawa, 1978, 1982, 1984). There have also been a few smaller studies on an Atlantic association (Karplus, 1992) and only one on the Hawaiian association (Moehring, 1972). For more information visit the Shrimp-Goby Chronicles.
The study of burrows, and the dynamics of them is one of more well-known aspects of the shrimp-goby relationship. This bay be because burrows present a somewhat stationary (and often the only visible feature of the symbiosis), they are well documented. A discussion of burrows can be divided, as done by Karplus (1987), into three subjects: Structure of the burrow, Physical construction of the burrow, and Burrow dynamics.
The size and shape of a burrow, depends on the species of shrimp and the type of sediment. There are generally three types of burrow construction, seen in the following diagram:
Knowing that shrimp burrows differ depending on shrimp species, it seems logical that one should be able to determine the type of shrimp that constructed a burrow, simply by analyzing some feature or combination of features of the burrow. As it turns out, Cummins (1979), who did an extensive survey of burrows from four shrimp varieties on the Great Barrier Reef could not find any diagnostical feature between shrimp. Other researchers have proposed that the burrow structure is determined mostly by the substrate (Karplus1974; Yanagisawa 1984).
In the past, it was assumed that burrows were realtively short; around 20-10 cm (Luther 1958). But with discovery of epoxy and polyester resins, one can pour them into a hole and then dig them out later. The hole above shows the cast of one of these holes that has been overlayed into a symmulated environment where it would have been poured (Yanagisawa 1984). There are several branching sections to these holes, of which may have been old burrows openings.
Farrow (1971) found that the structure of the sediment is very important in determining the structure of the burrow. When the sediment was rocky, he found the holes were irregular but when the holes were muddy, they were regular and dichotomously branching.
As may be apparent by this point, the actual appearence of a burrow depends on many things like the shrimp and the sediment. Some burrows may be shallow and branching while others are short and deep. There are a few general standards though. First of all, if the shrimp is large, the burrow will be comparatively large (Yanagisawa 1984). Secondly, if the burrow is deep, its usually shorter than a shallow burrow (Cummins 1979). Finally, the actual morphology of a tunnel tube is relatively consistent in all shrimp. The floors will be sandy as the shrimp buldoze sand out and the the tops will be somewhat rocky or filled in with coral pieces to prevent the collapse (Yanagisawa 1984).
The construction of burrows by shrimp can be studied through aquariums where the shrimp are digging near the glass (personal obervation). In all cases (except one described by Farrow 1971), the shrimp are the sole caretakers of the burrows. Karplus (1987) has summarized the three techniques used by shrimp to maintain the burrow as follows:
The entance of a burrow is not a solid structure like you may imagine a manhole cover or even a fox hole. The burrows these shrimp dig, are built in sandy sediment that if not maintained will collapse in less than an hour (pers obser). In fact, much research has described the daily shifts of burrow entrances over extended periods of time (Magnus 1967; Karplus et al. 1974; Cummins 1979; and Yanagisawa 1982, 1984). The results have shown that for the most part the holes will change daily up to about 40 cm. As a gernal rule, the larger grain the sediment (coarser), the larger the change in goby entrance size (Karplus 1974). Yet, when analyzed over two years, as done by Cummins (1979), he found the holes in nearly exactly the same spot. Thus, while holes may change daily due to the formation of slightly new etrances, the subterrain burrows likely remain the same and change very little (see diagram below).
How might the shrimp-goby relationship have evolved? Since the invention of S.C.U.B.A., divers have been able to document a plethora of gobies that make association, whether obligate or facultative with snapping shrimp in the genus Alpheus. Currently there are over 70 species of gobies that have been found with shrimp and the number will surely grow as more in-depth studies are conducted in the marine environment (see Taxonomy). Was there one shrimp and one goby that formed a pair and subsequently all our current species evolved, or has this phenomenon arisen several times throughout the course of evolution.
Answering questions on the evolution of a species is difficult if not nearly impossible. Several generations must pass in a confined enviroment for a researcher to even attempt to see changes in behavior. In the case of the shrimp goby, it seems that the relationship has evolved from a need to escape predation, both for the shrimp and the goby. The studies by Thompson (2004) and Nelson (current study), have proven that predation does effect the behavior and population dynamics of the pair. With this information a given now, how is the need for pair formation governed?
Karplus (1992), studied a facultative relationship off Key Biscayne Florida. In his study he concluded that this was probably the first stage in the formation of a pair. Though a process of natural selection, coevolution could then occur. While this is just a theory, it is a step forward in understanding the evolution of hte shrimp goby.
As shrimp and goby spend most of their lives inside their burrows, any observations made on the reproductive strategy of these individuals is extremely difficult. In fact, nearly nothing was known about these species until Yanagisawa (1982, 1984), studied Amblyeleotris japonica in great detail in Japan. Most of my synthisis of goby repoduction comes from that work. Below is a table of the known breeding periods of different shrimp gobies.
From this table, it is clear that there is no concrete pattern that can be observed for goby mating amoung all species. Even for one species, Amblyeleotris steinitzi, found in Australia and the Red Sea, the pattern is not consistent. It does seem however, that when gobies are not found paired all year, they are found paired predominantly in the summer months.
Pairing for Amblyeleotris japonica, occurs from May to September in Japan at which time there were maximaly only about 7 percent of associations paired (Yanagisawa 1982). Males were the individuals that would roam around within the breeding territory but rarely more than a few meters away from their burrows. Territorial displays are made between males for the right to mate and most matings occured from the largest, most socially dominant individual. There was no sign, however, of males mating with several females. Instead, they would pair with a female and remain with them for several days. When the female laid the eggs (approximately 20,000), she would leave and the male would take care of the eggs, mostly inside the burrow for the next 4-7 days until hatching.
Yanagisawa has also spent considerable time discovering the reproduction of the Alpheid shrimp in southern Japan (Yanagisawa 1984). The shrimp that pair are almost always of opposite sexes, except in a rare few documented cases (Moering 1972). When in a pair the female is slightly larger than the male. Once the two pair, which is fairly early on (50% paired in 4-6 months), they are almost always permanent. While they may pair early on, it is not until the shrimp are about a year old that they start breeding. Females will carry approximately 4,500 eggs maximally. Young, once hatched will settle alone and begin digging a hole.
A big question for shrimp-goby researchers had always been, how do the shrimp and goby find each other? In other words, who finds who and how? Finally, in 1981 Ilan Karplus published a paper entitled Goby-shrimp Partner Specificity. II. The Behavioral Mechanisms Regulating Partner Specificity whereby he experimentally figured out what attracts shrimp and goby to each other.
He discovered that the mechanism for shrimp is different for that of gobies. In an nicely designed experiment he looked at two different methods of attraction, chemical and visual.
What does this mean?
Most organisms have some sort of daily activity pattern that makes the more active in the day (diurnal) or in the night hours (nocturnal). The shrimp and goby are no different. For every species studied to this date, activity begins with sunrise (or close to it), and ends at sunset when goby and shrimp retreat into the burrow and the burrow entrance collapses (Magnus 1967; Karplus et al 1972, 1974, 1976, 1979; Polunin and Lubbock 1977; and Yanagisawa 1982, 1984).
In the case of diurnal rhythms, the activity that has been mostly studied is the activity of the shrimp, whom does all the digging and burrow maintainence. With a great deal of the studies done on shrimp gobies, have come a good understanding of the activity rhythms and some general themes amoung species.
The first aspect of the rhythm is the amount of time spent outside the burrow by the shrimp (see above figures) (Karplus 1976). Shrimp spend about one-third of their time outside the burrows in the morning, reduce the time around noon and then spend the majority of time outside the burrow at night. These rhythms can be slightly effected by the tides too. When the water level reaches 3-5cm above the burrow, activity usually stops (Karplus 1976).
The activity that the shrimp performs while outside the burrow does change however. In the morning, the shrimp usually leave with their chelae full of sediment and in the afternoon they are usually empty. Also, most of the introduction of sediment, usually in the form of organic material for food usuage later, it introduced primarily in the afteroon. Finally, the amount of burrow construction activity, in the form of reinforcing the outer walls of the burrow, are mostly performed in the afteroon (Karplus 1976).
The activity of the shrimp begins and ends around surnrise and sunset respectively, however, not all individuals will begin at the same time. The start of activity takes place when a goby emerges from the sand, followed by the shrimp (Magnus 1967, Karplus 1974; Yanagisawa 1982, 1984). Its believed that the begining of activity is synchronized by some sort of endogenous rhythm, while the end of activity is usually synchronized by the light levels, and thus the later is more sychronized amoung individuals (Karplus 1976). Finally, activity varies amoung the sex of the shrimp. Most of the activity outside the burrow is initiated by the male shrimp (Yanagisawa 1982).
The complexities of communication between the shrimp and the goby were first revealed by Lynn Moehring in 1972 when she produced her Master's Thesis at the University of Hawaii. These findings were later published under her new last name, Preston, in 1979. The symbionts she used are shown artistically in the image to the right. The goby was Psilogobius mainlandi and the shrimp, Alpheus rapax and A. rapicida. They are the same species I'm studying as part of a Predation study on Shrimp-Gobies.
She found that there is a complex warning communication between the two. The goby is essentially the 'guardian of the hole' as the shrimp has very limited visual abilities. Because of this, the shrimp, while outside the burrow, holds one antennae on the goby. If the goby sees a potential threat, it will give a slight tail flick. This vibration is picked up by the shrimp who consequently darts into the hole. If the danger approaches further, the goby will shoot into the hole through a quick C-bend of the body and enter the hole.
One of the questions asked by ecologists is, "What habitat does an organism live in?" A lot of the studies that have been done on shrimp gobies, that describe their habitat and how they use it seem to be only side notes or casual observations in the scheme of a larger taxonomic study (Karplus 1987).
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 1979). For example, in the Seychelle Islands where Polunin and Lubbock (1979) observed 13 species of goby, 5 were only found in one habitat and an additional 4 were only found in 2 habitats. Yanagisawa (1978) 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 (1984) 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 (above), shows how well segregated different species of gobies and shrimp can be in relation substrate.
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 (1979) 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 1984). Cummins (1979) 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. 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? Yanagisawa (1982, 1984) attempted 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. Mortality is high for new recruits, with 60% mortality in 3 months and 80% mortality in a year.
The following predators have been documented to prey on shrimp gobies:
Click here to see a study done on Predators of Gobies in Hawai'i.
Probably the most interesting predatory aspects is that of the Lizardfish / Goby interaction. The lizardfish that prey on gobies are not much larger than the food they eat. In fact, I have seen a 5 cm lizardfish eating a 3 cm Hawaiian Shrimp Goby! Thats pretty impressive.
There are surprisingly very few good resources on information for the lover of Shrimp Gobies. Most of the available web information comes from a few Marine Fish retailers. These sites primary purpose is to sell fish, not give information.
If you've found this sight while doing your own shrimp-goby research, I'd liked to hear about it. And, if you don't have a site of your own, I'll put your article on the Shrimp Goby Chronicles, where it's sure to be seen!
Scientific Works Cited:
Harada, I. 1969. On the interspecific association of a snapping shrimp and gobioid fishes. Publ. Seto Mar. Biol. Lab. 16: 315-334.
Karplus, I. 1981. Goby-Shrimp partner specificity. II. The behavioural mechanisms regulating partner specificity. J. Exp. Mar. Biol Ecol. 51: 21-35.
Karplus, I. 1987. The association between gobiid fishes and burrowing alpheid shrimps. Oceanogr. Mar. Biol. Ann. Rev. 25: 507-562.
Karplus, I., Szlep, R. and Tsurnamal, M. 1981. Goby-Shrimp partner specificity I. Distribution in the northern Red-Sea and partner specificity. J. Exp. Mar. Biol. Ecol. 51: 1-19.
Luther, W. 1958. Symbiose von Fischen (Gobiidae) mit einem Krebs (Alpheus djiboutensis) in Roten Meer. Z. Tierpsychol. 15: 175-177.
Magnus, D.B.E. 1967. Zur Okologie sedimentbewohnender Alpheus Garnelen (Decapoda, Natantia) des Roten Meers. Helgolaender. Wiss. Meeresunters. 15: 506-522.
Moehring, L.J. 1972. Communication systems of a goby shrimp symbiosis. Ph.D. thesis, University of Hawaii, 373 pp.
Polunin, N.V.C. and Lubbock, R. 1977. Prawn-associated gobies (Teleostei: Gobiidae) from the Seychelles, western Indian Ocean: Systematics and ecology. J. Zool., Lond. 183: 63-101.
Yanagisawa, Y. 1984. Studies on the interspecific relationship between gobiid fish and snapping shrimp. 2. Life history and pair formation of snapping shrimp Alpheus bellulus. Pbul. Seto. Mar. Biol. Lab. 29: 93-116.
Yanagisawa, Y. 1978. Studies on the interspecific relationship between gobiid fish and snapping shrimp. 1. Gobiid fishes associated with snapping shrimps in Japan. Publ. Seto mar. Biol. Lab. 24: 269-325
Yanagisawa, Y. 1982. Social behavior and mating system of the gobiid fish Amblyeleotris japonica. Jap. J. Ichthyol. 28: 401-422.
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