Better Together than Apart, by Haley Rhae Doherty

Snapping shrimp, Alpheus (Alpheidae) re known for their ability to produce one of the loudest sounds underwater and have unbelievable strength relative to their body size due to their huge front claws. Despite their impeccable strength and inexhaustible energy used to build their burrows, these shrimp are practically blind. With such poor vision these crustaceans are constantly in threat of predation when leaving their burrows.

Figure 1. Goby fish/shrimp pair sit in alert poses.  source

Lucky for these shrimp, over 120 species in the family known as Gobiidae have formed mutualistic symbiotic relationships with these Alpheus shrimp. More specifically the studies explored in this review focus on the following genera of gobiidae: Amblyeleotris, Ctenogobiops, Vanderhorstia, Cryptocentrus, Mahidolia, Tomiamichthys, Stonogobiops, and Psilogobius (Preston 1978, Karplus 1981, and Thacker 2011). The two form an unusual pair where the shrimp builds a burrow, sheltering both species, and the goby protects the shrimp and burrow. Pictured left is an example of such a pairing. This symbiotic relationship between several species of gobiidae fish and alpheidae shrimp is a unique partnership which enhances each individual's survival and is feasible due to their unique communication.

            While the understanding of how the goby and shrimp pair up is limited, many studies have been conducted in the wild to evaluate trends between pairings. Most pairings are observed in locations relatively close to reefs. A statistical analysis conducted in the Red Sea examined 750 burrows inhabited by goby/shrimp pairs. The pairs were evaluated on a vertical and horizontal scale based on the location and composition of their burrows. This study discovered that the shallower the water and the closer the burrow was to the reef, the pairings had higher specifications for partner selection (Karplus 1981). Gobies chose shrimp based on type of sediment used (fine, coarse or intermediate) to form the burrows and the burrows’ proximity to the reef. Deeper water gobies and shrimp lacked the complexity based on burrow composition in selection, which was hypothesized due to the decrease is sediment variation (Karplus 1981). While this study did not entirely solve the mechanism behind the pairing as it excluded behavioral characteristics, it did further establish the complexity of the relationship. Other studies have mentioned gobies making selection of shrimp based on coloration or chemical discharges (Preston 1978). It can be safe to say that the selection of pairs is obviously dependent on many variables to properly combat the environment at which the pair is located. Once a pair is finally together the mutualist relationship can begin and the interspecies communication can be observed.

Figure 2. Goby and shrimp sitting at entrance of burrow.    Source. 

            Communication can be described as an exchange of information translated between a sender and a receiver. The goby and shrimp pair is one of the few examples of interspecies communication used for mutual survival (Preston 1987). It is understood that the blind shrimp uses the goby as a seeing-eye dog. While their communication to achieve this is complex, it does not start out as such. The two develop their communication as soon as the goby enters an available burrow. Once the pair begins their relationship, the goby stands at either the opening of the burrow or on top of the burrow carefully keeping alert for predators or rival gobies. The shrimp approaching the entrance of the burrow will use its longest antennae to reach for the goby’s caudal fin, where it will remain in contact while exiting the burrow. It is through this connection that the pair communicates (Preston 1987).  The goby communicates the perceived danger through dorsal fin extension, a variety of tail flicks, and sand nibbling. These actions are all interpreted by the shrimp through the antennae connection. If a signal for danger is sent, the shrimp will either “sit” or “flee”. “Sitting” in conjunction to the still goby can boost each other’s camouflage (Preston 1987). However, if the danger is too threatening, the shrimp will retreat into the burrow and the goby will follow. The goby always enters after the shrimp, never before. It is the goby who exits the burrow post-fleeing to determine if the danger is gone and will signal to the shrimp to commence excavation of their burrow. This communication is special for the pair, as gobies only alert for danger when a shrimp is present (Preston 1987). This tactile method allows the goby to focus on spotting incoming dangers. While the main form of communication between the two is tactile, there have also been suggested forms of chemical and visual communication (Preston 1987).

            The symbiotic relationship between these creatures is clearly beneficial as it remains within each other’s evolutionary lineages. There are roughly 120 species of gobies that illustrate an obligate mutualistic association with a burrow-dwelling shrimp (Thacker 2011). Through phylogenetic studies of the gobies and shrimp it has become clear that this mutualistic relationship has evolved twice. The occurrence of this association increases the fitness of both the goby and shrimp. This relationship though only occurs during the adult phase for both shrimp and goby. In studies without burrowing shrimp present gobies have higher rates of mortality without the hide. Similarly, shrimp without a goby have a noticeably slower rate of growth and excavating capabilities. However, when together the goby receives a protective burrow at night and the shrimp receives protection during the day, dually increases each other’s survivability (Thacker 2011). These boosts in protection allow both to thrive without having to expend energy on protection and redirect their energy to either excavating or guarding.

            This mutualistic symbiotic relationship can base its success due to the rare interspecies communication seen between the several species of gobies and Alpheus shrimp that live near reefs. It is obvious that both the goby and shrimp, once in its respective adult phase, have a higher survivability together as this association has occurred twice in their evolutionary lineages. Through this association individually they can spend their available energy in a way that boosts their collective productivity to ensure survival. It is for these reasons that the goby and shrimp are such a unique partnership.

                                                          

References

Karplus, I., R. Szlep, and T. M. 1981. Goby-shrimp partner specificity. I. Distribution in the northern Red Sea and partner specificity. Journal of Experimental Marine Biology and Ecology 51(1):1–19.

Preston, J. 1978. Communication systems and social interactions in a goby-shrimp symbiosis. Animal Behaviour 26:791–802.

Thacker, C. E., A. R. Thompson, and D. M. Roje. 2011. Phylogeny and evolution of Indo-Pacific shrimp-associated gobies (Gobiiformes: Gobiidae). Molecular Phylogenetics and Evolution 59(1):168-176.