Friday, September 26, 2014

Long distance kelp rafting

Bull kelp (credit
Today's post is about a new paper by a good friend of mine, Gary Saunders from the University of New Brunswick in Fredericton, Canada. Gary is happily barcoding seaweeds pretty much since the first days of DNA Barcoding and he assembled some 12 000 specimens barcodes to date. Every time we have a chance to meet at conferences, symposia, or even in the field, sure enough he will have a very interesting story to tell and most of the time they have to do with findings that stem from his barcoding work on algae. 

Last year at the international DNA Barcoding conference in Kunming he gave a talk about something that had puzzled him for a while and we had a few discussions over beer in the evenings. I think it is best to quote Gary at this point and let him describe the observations:

Routine DNA barcoding of the Haida Gwaii seaweed flora revealed ‘endemic species’ attributed initially to this region's past as a glacial refugium. However, subsequent barcode records from central California rapidly eroded this list leaving species characterized by disjunct distributions between California and Haida Gwaii. This observation prompted a more detailed look at species for California and British Columbia and revealed that 33 of 180 DNA-barcoded genetic groups in common between these regions (~18%) predominantly displayed disjunct distributions between California and northern British Columbia.

Such a distribution pattern points to long distance dispersal and in marine environments there are several mechanisms that could have been at work. Passive dispersal through currents or rafting on debris or other organisms are possible explanations. A few years earlier a red abalone shell found in Haida Gwaii (far north of its range) had a float-bearing kelp (Nereocystis luetkeana) holdfast attached to it, which shows one possible reason for the pattern Gary observed. The kelp simply hitch-hiked on a mussel that was carried northward through a current.

Consequently, Gary now postulates the The kelp conveyor hypothesis which describes the migration of Californian species growing on substrata that are carried along with kelp rafts to Northern British Columbia on the winter Davidson Current which is a coastal countercurrent of the Pacific Ocean running north along the western coast of the United States from Baja California, Mexico all the way up to Alaska.

A lot of this would have never been discovered without extensive DNA Barcoding work and several recent seaweed invasions demonstrated how important it is for us to understand distribution mechanisms of algae. It seems that these new findings brought us a little forward:

The work here and that cited by colleagues all point to seaweed dispersal by buoyant seaweed as a significant contributor to global macroalgal biogeography. This conclusion is not overly surprising as in this author’s experience there are few floras that lack at least some buoyant seaweed species.

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