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Pretty in Pink

Pretty in Pink: An abalone must choose between a bare rock and one encrusted with coralline algae

To determine if adult northern abalone prefer coralline-encrusted rocks to bare rocks, groups of four northern abalone were provided with a choice between coralline-encrusted rocks and bare rocks. Subtidal coralline-encrusted rocks were collected by snorkelers and the BMSC dive team. The adult northern abalone in the BMSC ablab are kept in large baskets, which we painstakingly subdivided into four sections using mesh and zip ties. Veronica used fishing line to sew up any holes in the mesh large enough for northern abalone to crawl through.

In total, three subdivided baskets were used in the experiment, giving a total of twelve replicates. Two baskets were placed in one sea table, and one basket was placed in a second sea table. Approximately half of the bottom of each replicate was filled with coralline-encrusted rocks and the other half was filled with bare rocks (Figure 2).

Image

Figure 1. Top down view of one of the subdivided baskets showing the coralline covered rocks and bare rocks in each of the four replicates.

Adult northern abalone were haphazardly sorted into each replicate with a little help from the rather terrifying sunflower seastar, Pycnopodia helianthoides. Moving the abalone required a combination of surprise, contact with P. helianthoides, and pipetting water from the tank housing P. helianthoides around the abalone to induce their galloping escape response. The number of abalone on each type of rock was recorded at approximately 7 pm and 8 am for three days.

The same baskets and adult northern abalone were used for the second experiment, which was designed to determine if the attraction of H. kamtshcatkana to coralline-encrusted rocks is mediated by associated bacteria.

Our preliminary results for the coralline-encrusted rock preference experiment indicate that there is a biologically significant trend towards the coralline-encrusted rocks. While setting up the second part of our experiment we were startled to find a juvenile abalone (Figure 2)! The feeling was reminiscent of the movie Children of Men. Perhaps there is hope for the struggling population of BMSC abalone, and more importantly, for the wild northern abalone population.

Juvenile abalone

Figure 2. A Juvenile abalone was found in one of the tanks. Shown with human thumb and adult abalone for scale.

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Culturing marine bacteria

Culturing marine bacteria on agar plates: The heart and brain broth or the soy?

Do adult northern abalone prefer coralline-encrusted rocks, and if so, is this attraction mediated by associated bacteria? Truly, this is the question. This post explains the sterilization procedure we will use to remove the associated bacteria from the coralline encrusted rocks, and how we will determine the effectiveness of the sterilization procedure.

A simple method for testing the effectiveness of sterilization procedures is to inoculate a sample of the sterilized media onto a culturing plate, incubate, and see what grows. Pioneers of the microbiology field sought a substance that would liquefy at a relatively low temperature, and remain solid at common incubation temperatures. Agar, a polymer harvested from the cell walls of several species of red algae, is ideal for culturing bacteria because it melts before boiling at 85 °C, solidifies before reaching room temperature at 32-40 °C and is a gel at common incubation temperatures. Ironically microbiologists rarely use agar to culture marine bacteria and shockingly little is known about marine microorganisms. The ongoing Global Ocean Sampling Expedition conducted by the J. Craig Venter Institute is rapidly filling this knowledge gap.

The plates were made in the research facilities at BMSC (Figure 1) by following a ‘How-to’ document on the internet. Trypticase Soy Agar (TSA) was mixed with deionized water, autoclaved to kill any bacteria initially present, and poured into Petri dishes to make agar plates. Balboa et al. (2012) found that a marine pathogen showed similar growth dynamics on all general media tested, but that one of the best media was Mannitol Trypticase Soy Agar. Horse blood, heart broth, and brain broth were some of the first media used, and are still in common use today. Scientists take things too far sometimes.

Figure 1. Preparing agar plates in the research facilities at the Bamfield Marine Sciences Centre.

To kill the bacteria associated with the coralline algae, but not harm the algae or the endangered northern abalone, we decided to use a sterilization procedure used by Canadian Kelp Resources. After soaking the rocks for 20 s in a diluted solution of seven percent liquid iodine, we swabbed the outside of the rock with a sterile cotton swab and transferred the inoculate to the agar plate. The plates were incubated at room temperature for 48 hours. We expected the control plates that were inoculated with seawater, and the plates inoculated with seawater swabbed from the coralline encrusted rocks before the iodine treatment to have many colonies, and the plates inoculated with seawater swabbed from the coralline encrusted rocks after the iodine treatment to have no colonies. Our results were partially consistent with our expectation, with abundant colonies on the three control plates and one of the plates from before the iodine treatment, and few colonies on the remaining plates (Figure 2). However, these preliminary findings are inconclusive and may have been affected by swabbing technique. The effectiveness of this technique requires further testing.

Figure 2. Bacterial colony growth on TSA plates inoculated with seawater (left), seawater swabbed from the coralline encrusted rocks before the iodine treatment (right), and seawater swabbed from the coralline encrusted rocks after the iodine treatment (middle), after a 48 hour incubation period at 24 °C.

The Lonely Abalone

Northern abalone (Haliotis kamtschatkana) are an economically and environmentally important species. They have long been prized by humans for their beautiful shells and, perhaps even more so, for their delicious taste. These large marine snails can be extraordinarily long-lived. Each season they lay down shell layers that can indicate what they were eating, leading some researchers in the swinging sixties to suggest using the banding patterns of Haliotis as indicators of ecological succession (Olsen, 1968).  Until recently, northern abalone was a dominant subtidal species along the west coast of North America, from Sitka Island to Baja California (Sloan and Breen, 1988).

Unfortunately northern abalone populations have been in decline for many years, resulting in a complete closing of the BC fishery in 1990. The past twenty years has not seen a recovery, and the species was listed as endangered in 2009 by COSEWIC (Seamone and Boulding 2011). There are a few factors working against the northern abalone, including illegal poaching, warming sea surface temperatures restricting their geographic range, and reduced reproductive capacity due to the Allee effect (Rogers-Bennett et al. 2011). The Allee effect results in reduced reproductive capacity at low population densities, and it is thought that the northern abalone population is below a minimum threshold required for successful fertilization.

“What can we do about it?” a classmate, Veronica, and I asked. Seeing as it is DS week here at Bamfield, we decided to investigate habitat preference in the northern abalone. The BMSC abalone hatchery (a.k.a. the ablab) has sinusoidal curved plastic sheets called waveplates that the abalone cling to in their tanks. Coralline algae encrusted rocks, collected from the natural, subtidal habitat of these animals, were recently added to the tanks as an alternative substrate to the waveplates. Do abalone prefer coralline algae encrusted rocks to bare rocks and wave plates? Stay tuned to find out.

 

References

Olsen, D. 1968. Banding patterns of Haliotis rufescens as indicators of botanical and animal succession. Biol. Bull.     134 (1): 139-147.

Rogers-Bennett, L., Allen, B.L., Rothaus, D.P. 2011. Status and habitat associations of the threatened northern abalone: importance of kelp and coralline algae. Aquatic Conserv: Mar. Freshw. Ecosyst. 21: 573-581.

Seamone, C.B, Boulding, E.G. 2011. Aggregation of the Northern abalone Haliotis kamtschatkana with respect to sex and spawning condition. Journal of Shellfish Research. 30(3): 881-888.

Sloan, N. A. and Breen, P. A., 1988. Northern abalone, Haliotis kamtschatkana in British Columbia: fisheries and synopsis of life history information. Can. Spec. Publ. Fish. Aquat. Sci. 103:1-46.