Agriculture Science Today 010 – “Middens and Mariculture” The Science of Ancient Clam Gardens

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Butter Clam Close Up
By Cody Logan, clpo13 on the English Wikipedia (Own work) [CC-BY-SA-3.0 (], via Wikimedia Commons

This week Tim and Steph interview Amy Groesbeck about research that she took part in on ancient clam beds on the coast of British Columbia. A seasoned “coastal girl” as she calls herself she had a lot of passion speaking to us about the ancient mariculture methods she learned that she believes still hold value for us today for informing food production.

A big thanks to Cargill’s @foodsecureworld twitter account for alerting us to this paper. It certainly was an interesting read and we were so lucky to get one of the authors to come on with us and share more insights into the research.

For this week’s blog on the episode we’ll just give you some of the questions and responses Amy gave. There is much more interesting discussion in the episode so please give it a listen but these are some of the highlights:

1.     Give us an introduction of yourself (i.e. where you are now, where your previous degree(s) are from, etc).

Amy grew up in the pacific northwest and attended University of Washington earning a degree in biology. She completed a Masters in Vancouver BC at Simon Frasier University in resource management focused on humans in costal ecosystems. She currently resides in Seattle.

2.     Tell us about your research

Amy admittedly didn’t know much about clam garden before participating in this research. She now knows a great deal and shared with us what they are and how they are constructed. Clam gardens are intertidal terraces. Rocks are rolled to the bottom of the beach to build a wall and backfilled with sediment to create a more gently sloping beach. They were built by first peoples to raise littleneck and butter clams. Amy tells us what a midden heap is and why they are valuable as a living record of life to research how first peoples ate and lived.

3.     How did the subject of ancient clam gardens come about to be something of interest for you to research?

Amy had Read book by Judith Williams called ancient mariculture. We couldn’t find that book but here is a link to a similar book by her about clam gardens. Through some stroke of luck her advisor Dr. Anne Salomon was contacted by Dr. Dana Lepofsky who invited Amy to take part in this clam garden research.

 4.     Give us an introduction on the clam industry (from a food perspective)

Today’s clam farming techniques are much different than old gardens in that they remove other species than the ones being cultivated and done on a far larger scale on larger beaches than the type they studied. There are a number of cultivation methods currently employed by commercial clam farming.

5.      What were your results?

Research team wanted to know if clam beds increased number of clams raised and if so how?  They tested the hypothesis by studying walled beaches (clam gardens) and unmodified beaches. They did surveys of the beaches and transplanted some clams as tests. Clams grew twice as fast in clam gardens and higher survival rates of young clams. 4X the butter clam and 2X more littleneck clam populations in the clam gardens compared to unmodified beaches. They also found clam gardens increase the area of the beach that is at the ideal water depth for clams by flattening grade out.

6.    Tell us a bit about clams and their life cycle. How do they reproduce, migrate to new areas, etc.?

Clams reproduce through releasing gametes into the water similar to fish and other aquatic breeding species. Clams’ only opportunity to migrate to new beaches is when they are spawned and floating around as plankton in the ocean currents. They eventually settle out on a beach and grow a small shell.

7.     Do you think the results would have been different if the gardens were being actively tended to through methods noted in the paper such as adding gravel, shells, turning rocks, and thinning larger clams?

Amy predicted that if gardens had been tended in traditional ways they would have been more productive. Tending was largely a practice of thinning out competing things such as larger clams and a species of seaweed that grows on the beaches.

8.    In the paper, you mention the difficulty of these types of studies because of the lack of adequate controls. Can you discuss that and things you would do in the future to when considering studying ancient resource management in contemporary areas.

Amy said that working with first peoples to deconstruct a clam garden and reconstruct one would be a valuable experience for researchers.

9.    What are some other examples of ancient ecosystem modifications people may not know about?

Fish weirs used for the trapping or holding of fish are a common ancient modification along coasts. Stone modifications to salmon bearing rivers to make it easier to catch them are also common. Transplanting of bushes and starchy root plants was common in areas that mariculture was practiced.

10.    What are your thoughts on whether total biomass production is increased by ecosystem modification or a shifting of biomass production to one or more desired species?

At first glance it seems that clam gardens studied increase biomass but its really unclear without further study what might be missing or other things that could be there but aren’t seen. Tim brought up an interesting bit of research he heard about that seashell picking could be a problem for beaches you can follow this link to the paper he was thinking of. Amy mentioned that shells are a signal for recruitment of new clams to settle there and therefore important for beaches that house clams.

11.  If you could leave our listeners with something to remember from your research in relation to agriculture and food production, what would that be?

Amy’s message was that people have been managing and tending seascapes for millennia and they can offer techniques and strategies for cultivation that can inform how we produce food today. Traditional practices are very relevant today from a food security standpoint looking at the populations they managed to provide for in the past.


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