Behavioral Study: Introduction

ABSTRACT
A symbiotic relationship between the Hawaiian Shrimp goby Psilogobius mainlandi and a snapping shrimp Alpheus rapax was studied in Goby bay, Coconut Island, Oahu, HI. The fish and the shrimp are one of several shrimp-goby relationships worldwide that have been reported to be a mutualistic symbiotic relationship. It has however, never been shown that the shrimp or the goby depends on the other. Thus, I examined the possibility that the relationship may be parasitic in nature whereby the goby is manipulating the shrimp. Observations of the shrimp with and without a goby at the entrance (physically removed) showed a distinct shift in behavior. Without a goby the shrimp spent 53.6 +/- 21.8 percent of its time outside the hole compared to 6.5 +/- 2.5 percent when a goby was present. The time a shrimp actually spent out on one individual ‘bout’ was also decreased with an average 14.0 +/- 6.4 second bout time with a goby but only a 2.9 +/- 0.25 second ‘bout’ time without. Finally, shrimps varied in the ratio of times they came out of the hole with sand and without sand. Without gobies they came out with sand 100 +/- 0.0 percent of time and with gobies only 52.7 +/- 25.1 percent of the time. This data seems to suggest shrimp activity is negatively impacted by removal of a goby. Conclusions, however, are difficult to make without determining the absolute costs and benefits of certain activities to the shrimp.

Keywords: goby-shrimp associations, symbiosis, mutualism, parasitism, cost-benefit

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 one Hawaiian association (Moehring, 1972).

Nearly every report of the shrimp and goby relationship has noted that they are a symbiotically mutualistic relationship (reviewed by Karplus 1987). The Alpheid shrimp dig holes in the predominantly sandy habitats where they live providing protection for the gobies. The gobies stay at the entrance of the hole during the day, in close enough proximity to dart in and at night for a resting hole. The gobies, which have much keener eyesight, provide a kind of ‘advanced warning system’ by being able to see potential predators earlier. The goby relays this information back to the shrimp through 1) its head-first entries and 2) a series of tail flicks which the shrimp detects through its antenna that are ‘continuously positioned on the fishes body’ (Karplus, 1987, 1992).

The described observations of the relationship of the shrimp and goby seem to make it clear that they are mutualistic – protection for the goby, protection for the shrimp. Yet these arguments are based solely on observational studies of the predicted benefit that each will obtain. In fact, observations of Hawaiian shrimp-goby relationships show that the shrimp often do not maintain contact with the goby, thus, not being able to be ‘warned’ when predators are near. It seems clear that the goby is benefited by the shrimp, simply because of its use of the hole for escape from predators. However, the benefit to the shrimp seems theoretical and there have been no manipulation studies looking at the importance of the goby to the shrimp. Thus, it seems logical to question the assumptions of the previous research. Is the relationship really mutual or could the gobies actually be parasitizing the shrimp. Thus, the aim of this study is to manipulate the presence of the goby in the relationship then to determine through behavior observations of the shrimp, the relative importance of the goby to the snapping shrimp.