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Student blog: 'Gone with the Goby'

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Goby

Question: Does frequency of divers on dive site locations alter the response and recovery time of gobies to perceived threats?

Throughout the Indian, Pacific, and Atlantic Oceans, species of Goby fish (Gobiidae) form a mutualistic symbiotic relationship with species of alpheid shrimps, commonly known as pistol or snapping shrimp (belonging to the family Alpheidae). Interactions between species lead to different advantages and benefices for all the concerned individuals, for instance protection against predators, food supplies or a safe place for breeding (Karplus and Thompson, 2011; Karplus, 1974).

I was curious and fascinated by this buddy team since my first time in the ocean, practising my skills over the sand. Witnessing these sentinel gobies guarding their little shared kingdom with their powerhouse shrimp, rearranging the furniture. With Koh Tao being one of most popular places to dive, I wanted to find out if higher diver traffic on dive sites affected these species, and in what way. So, I embarked on a 2-week research project to find this out.

Here on Koh Tao, there are several species, but I decided to conduct my research on three species of Goby. The Yellow Prawn Goby (Cryptocentrus Cinctus) in both yellow and black variants, the Red Margin Goby (Amblyeleotris Rubrimarginata) and the Masked Shrimp Goby (Amblyeleotris gymnocephala). I selected these species due to them being the most common of the genera on Koh Tao. 

We conducted a total of 84 separate studies across six dive sites in the space of two weeks, illustrated in the graph below. My initial hypothesis was that goby fish on dive sites with higher diver traffic such as White Rock and Twins, would be desensitised to human activity and would respond slower and recover quicker.SportDiver 20230829 113720

I started our studies with a few variables that after my first survey I had to remove/change. Threat reaction time (time of subject diving into their burrow) was difficult to measure due to the time it took me to locate a subject, place the camera and conduct the experiment. All of this set-up time gave the subject time to react, which I believed would affect the results. Distance to the threat was also difficult to control, as placing a tape measure from the burrow resulted in the subject reacting and diving into their burrow before the ‘start’ of the experiment. I was however able to record recovery time after hiding in their burrow and found that my initial hypothesis was not correct.

The data I collected suggests that goby living at dive sites such as White Rock and Twins with higher diver activity would stay longer in the burrow compared to those living in the less disturbed locations of other dive sites. I believe this may be due to them being aware that from the first sign of activity, the area around their burrow will be disturbed multiple times, as more of the dive group passes by. We can see from the second graph that on average, the Red Margin goby remained in their burrow longer than the other species. Further studies/research would need to be done to understand this more.

There are several changes that I could make to this project to improve the results. All my surveys were conducted in the afternoon and once per dive site. Repeated surveys of dive sites, including possible repetition at different times of the day, would give me more representative data across dive sites and goby species. In this project, waving my hand over the burrow was my method of recreating disturbance. I could improve upon this by having a second diver act naturally, swimming over the burrow. This would allow me to also record behaviour and reaction in a more realistic environment. I found that a few gobies didn’t immediately dive into their burrow as I approached, and only dived into their burrow after the hand wave. The business of dive sites was determined based on my own experience as a Koh Tao diving instructor, rather than recording the number of divers throughout the project. Alongside this study I could record the number of divers across locations where gobies are present and record diver numbers empirically. Weather and dive conditions could also be a variable that could have affected reaction/recovery time.

As with all research, more time and data are always needed to get more accurate/representative results. I have really enjoyed these past four weeks, learning significantly more than I expected, therefore allowing me to enrich my own students when introducing them to the underwater world.

 

Written by Liam Summerville; Roctopus SCUBA Instructor and Marine Ecology and Conservation Internship student with the Roctopus ecoTrust.

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