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Alfie the accidental ichnologist

on . Posted in General Ichnology

Alfie

This is a story about the short but productive period that Alfie the alpheid shrimp (Alpheus bellulus) spent as a member of our group.

Alfie, as he was named by Michael Garton, came to us in a plastic bag on a flight from Vancouver from an aquarium to be our startunnel building shrimp.  It was only once he arrived that we discovered that Alpheus bellulus is not a burrowing species.  Many species of Alpheus are, but this one is not.  This was to be one of the centrepieces of Chris Phillip's thesis, but it was not to be (Chris subsequently moved on to thalassinid shrimps with better success).

Alfie came with a number of buddies in the bag, but they proved to be somewhat feisty with one another when released into the lab mesocosms so  I adopted him and moved him into the tank in my office.  At about this time Michael Garton was visiting in the midst of thesis submission and he shared my office with me and Alfie.

One of the great benefits of living by the sea is that it is easy to keep marine organisms in a desktop tank, particularly tropical organisms that are happy at room temperature. Keep it oxygenated, and replace the seawater regularly and you can keep many taxa.  The good thing is, as an ichnologist, you can just add sand and watch science unfold before your very eyes.  So it transpired with Alfie.

While Alfie did not create tunnels he did spend much of his life creating sediment cones, which he liked to sit in the middle of.  His days were spent shovelling sediment from the bottom of the crater to the top of the crater. 

A number of approaches to sediment transport were used, including:

Shovelling: Creating a basket between the claws in which sediment was carried uphill

Bulldozing: Using the claws as a snowplough to scrape the sediment uphill

Current generation: Using the pleopods (swimming appendaged below the tail) to create a current to waft the sediment uphill

Once at the top of the crater the grains were either dumped down the  outer edge of the cone, or wafted off the edge by a winnowing current.  The layers (laminae) produced were thus either produced by avalanching or by settling from suspension.  Either way laminae were produced  that closely resemble the layers within a ripple (ripple cross lamination) produced by a unidirectional current.

In core, such ripple cross lamination is used to infer the environment in which the sediment was deposited.  BUT, in this case, there was no current-just a burrowing shrimp-and the rippple crest defines a crater not a ridge orthogonal to the direction of the current.

Sadly Alfie eventually popped his socks (I think I let the tank get too saline).  BUT his work is immortalized in this paper:

http://jsedres.geoscienceworld.org/current.dtl

McIlroy, D. 2010. Biogenic Cross-Lamination Produced by the Pistol-Shrimp Alpheus bellulus in Microcosm Experiments. Journal of Sedimentary Research v. 80, 151–154

 

AND

he made front page news in J. Sed res.  The handling editor says he is the cutest front page pinup they have ever had 

 

http://jsedres.geoscienceworld.org/current.dtl