Introduction – Background – Why This is important.

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).

Nearly every report of the shrimp and goby relationship has noted that they are symbiotically mutualistic (reviewed by Karplus 1987). The Alpheid shrimps 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 for escape 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 fish’s body' (Moehring, 1972; Karplus, 1987, 1992).

It is difficult to ask the question, “Why are the shrimp and gobies living together in this way,” because the answer is nearly impossible to test. It seems logical however that the two live together to limit predation. Thus, predation could have been a major driving force in the evolution of the system. My question remains, is this still a major selective pressure. The Hawaiian shrimp goby is endemic to the Hawaiian Islands. In many other taxa in Hawaii, the island’s isolation has led to unique relationships (predatory caterpillars, Drosophila mating, etc). Might the Hawaiian shrimp gobies have evolved elsewhere and upon arriving in Hawaii been faced with different selective pressures i.e. - different predation pressures?

Currently little work has been done how predation effects populations of shrimp gobies. The work that has been done simply compared the activity of shrimp-gobies in areas of low and high predation pressure (Y ). The other works looked at the gobies in a lab when presented a model ( Karplus 1979).

Hypothesis to be Tested:

• The density of Shrimp-Goby holes is not affected by predation.
• The density of Psilogobius mainlandi is not affected by predation.
• The density of Alpheus sp. shrimp is not affected by predation.

These questions should help answer the following questions:

• What are some of the limiting factors for shrimp-goby relationships … they could be predation, space requirements, or food requirements.
• Who are the main predators of Hawaiian Shrimp Gobies?
• What role do Hawaiian shrimp gobies play in the bay community? … are they a larger part of the prey than expected?
• Do the daily rhythm patterns of Hawaiian Shrimp Gobies seem to be the same as other shrimp goby pairs around the world?

Study Location (the field sight is located in Goby Bay, Coconut island, Kaneohe Bay, Oahu, Hawaii, USA)

1) Baseline Population study (Very little of the ecology of P. mainlandi is known. The only information available is Moehrings’s 1972 work on The Communication Systems of a Goby-shrimp Symbiosis, which dealt mostly with communication theory and used captive animals.)
a. Understand the Daily Rhythm of my species (Remote cameras).
b. Goby Bay hole densities.
c. Number of P. mainlandi per hole.
d. Size of P. mainlandi and host shrimp

2) Predator Exclusion Study.
a. Set up Predator exclusion cages.
b. Have a series of plots from (open – ¾ caged – fully caged – caged with predators)
c. Determine the hole density, number of gobies and shrimp per hole, size of gobies.

The Hawaiian Shrimp Goby (Psiligobius mainlandi) has thus far only been recorded from the Hawaiian islands. I am conducting this study on the island of Oahu, the 6th major island up the chain to the northwest. The most common habitat for shrimp-goby relationshilps is silty sandy waters. Thus, I had to find a site protected from wave action. Trade winds come from the northeast and build large windwaves on the eastern shores. Summer swells bring waves to the south and winter storm swells bring large waves to the north and west facing shores. The only suitable habitats for large numbers of shrimp gobies is thus in bays. Kaneohe Bay, on the windward side of the island, has many small reefs and islands which provide habitat for shrimp-gobies. One ideal location is on the protected side of Coconut island, where the University of Hawaii has a research station. In particular, one bay, which I've named Goby Bay, is mostly slity sand covering coral rubble - perfect for a shrimp-goby.

Goby Bay is approximately 150 meters wide by 200 meters long. On the northern side of the bay is a small, 3meter deep canal where somewhat larger fish (goatfish) congregate. The sediment in the bay tends to get slightly rockier (less silty) to the north. [I am not yet sure the effect this has on the shrimp-goby population dynamics.]

1a) Daily Rhythm of P. mainlandi and A. rapax.

Daily activity rhythms will be studied without human interference. All other studies have been conducted using snorklers or by capturing the gobies and placing them in tanks. With the use of remote video cameras, shrimp and gobies can be analyzed in a more natural condition. Activity outside the burrow will be analyzed from the beginning of activity (6am), and for every 3 hours until activity stops. ….

(first appear)-- 6am -- 9am -- 12pm -- 3pm -- 6pm --(record last emergence).

Activity will be measured by using a 10-minute period of measurement with the aid of remote video. Activities will be measured for both the shrimp and the goby. The following activities will be measured

• Shrimp -- number of exits -durations of exits – Total time outside the burrow – time spent digging – time spent probing sediment
• Goby – time spent outside burrow.

Measurements will be taken using the program BEAST.

See predicted Tables [ exits vs. time / duration vs. time / digging vs. time]

Each hole will be measured for 1 entire day. At least 10 holes will be measured by this method and compared between times and between holes.

As an extra piece to this study I would like to determine if there is in fact a snorkler effect. To do this I will have equal amounts of data collected using a portable digital video camera held by a snorkler.

1-b,c,d) Goby Bay hole Densities (Top)

To determine the density of gobies in the bay, random line transects will be used. Each line transect will be 20 meters long by 1 meter wide. Densities will be measured by snorklers traveling along a 20m line and using a 1 meter wide bar to make sure holes are within the transect.. Transects will be conducted at low tide (so that snorklers can crawl slowly across the bottom as motionless as possible, thus keeping gobies above ground before shrimp and goby leave the area). Each hole will have the following data included.

· Substrate / Location in the Bay / Distance along line / nearest neighbor / number of shrimp / number of gobies / goby size / shrimp size / Predatros (spp, number, size)

[See sample Graphs] – size vs nearest neighbor / goby size vs. shrimp size / goby size vs. number of shrimp / goby size vs. number of gobies.

2a) Predator Exclusion Cages

To determine the effect of predators in the bay, fences must be constructed to keep predators from affecting the shrimp-goby pair.

I have decided that one of the easiest cages to build is a 12’ by 12’ cage (using only 10’ by 10’ in the middle.) I then use a 50’ section of chicken wire (with a few extra feet left over) and wrap it around 4 T-posts that I pound in with a post-driver. Then the stakes will be driven in around the 10’X10’ plot and fishing wire strung in-between so that there is a grid of 100 squares.

Material needed for 1 cage

T-Posts 4 (est $15)
50’ Chicken wire 1 ($50)
Wire ties 16 (miniscule)
Fishing wire 260’ 1 ($5)
Small stakes 40 ($5)
TOTAL ($75)

2b) Cage placement in the bay. (TOP)

I plan on building a series of 6 cages, which will be distributed in goby bay. Each cage will be a full cage and a partial cage several times. This way I will be able to determine the change between cages and between one cage. Cages will be placed in 3 areas of the bay – right – middle – left. This is because the bay changes in substrate type (although only slightly) as one travels across the bay. This should accommodate these changes. Each section of the bay will thus have paired cages that can be analyzed against each other, if there are any differences in density with substrate type. All cages will be placed in roughly the same depth water and placed 10 feet from its partner cage. To make sure there is little cage effect one cage will be ¾ open while the other will be fully closed. Every month they will be switched.

2c) Data Collection and Time Tables (TOP)

All six cages will be built and allowed to equalize for 3 weeks. At the end of three weeks data will be collected, the cages will be altered and then let set for another 3 weeks. This will continue for 4 months.

Week 0 – build cages
Week 1-3 – equalization
Week 4 – Data collection – altering cages
Week 5-7 – Equalization
Week 8 – Data collection – altering cages.
Week 9-11 – equalization
Week 12 – Data collection – altering cages
Week 13-15 – equalization
Week 16 – Data collection – altering cages

During the collection weeks a snorkeler will enter one of the cages and take data for each individual hole. Data will consist of the following:

· Hole grid location / closest neighbor / Substrate / number of shrimp / number of gobies / goby size / shrimp size.

2d) Data Analyses

Once data is collected from the 16-week period, it must be analyzed. I will use a simple Paired t-test against the null hypothesis that caging excluding predators) does not have an effect on the density (+ size, paired ratio, …) of shrimp-gobies. I can examine each set (right, left, middle) individually, separate by time of measurement, and lump all results together.

Hole Density % paired gobies % paired shrimp Avg goby size Avg shrimp size
Full ¾ Full ¾ Full ¾ Full ¾ Full ¾
Cage 1 R
Cage 2 R
Cage 3 L
Cage 4 L
Cage 5 M
Cage 6 M

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