Kelp growing on tubeworms

 

Steve Rubin of the USGS collecting data while buried in kelp fronds. 29 August 2021 photo by Ian Miller

I had the opportunity to once more join the Elwha Interagency Dive Team this summer, suiting up, as I have for the last 13 years, to survey sub-tidal sites scattered along the central Strait of Juan de Fuca.  I've posted frequently in the past about these surveys, and what we see each summer.  I wanted to focus this year on an interesting phenomenon that I haven't really seen described well elsewhere - kelp growing on tubeworms.  

Bull kelp fluttering in the current near the Elwha River mouth. 28 August 2021 photo by Ian Miller

First off, kelps were heavily impacted during removal of the Elwha dams, primarily due to reduced light as sediment laden water shaded the seafloor.  One of our motivations for continuing our surveys is associated with tracking and trying to understand the pace of kelp recovery after that die-back event...and in fact our survey work this year was funded as part of a larger, region-wide, kelp restoration and recovery effort.  Largely that recovery seems to have happened around the Elwha River mouth, with the notable exception of the handful of sites where formerly coarse substrates were buried by finer sediments. 

Steve Rubin of the USGS emerging out of a plume of fine sediment, kicked up at a site that used to host a higher density of kelps...but where the substrate is now fine enough that kelps have a hard time finding a place to grow.  2 August 2021 photo by Ian Miller

Kelps typically like to attach to and grown on coarse substrates - either bedrock, boulders or large cobbles on the seafloor that allow kelps stay in place in the fierce currents that characterize many of the places they like to live.  

Kelp stipes attached to cobbles.  As the kelp grew larger they eventually became buoyant enough that these cobbles have been picked up off the seafloor.  14 September 2021 photo by Ian Miller

But in places where there isn't suitable substrate we've found that kelps can still grow by attaching to other organisms, notably tubeworms, which build strong and stable tubes that anchor them in soft substrates.  

A tubeworm tube, in this case Eudistylia vancouverii, emerging out of soft sediment at a site near the Elwha River mouth.  28 August 2021 photo by Ian Miller

We've seen this at sites around the Elwha in the past, but this year the phenomenon was very notable at a site right about here, to the west of the Elwha River mouth.  This site has always been a good one for tubeworms, perhaps because its a generally pretty silty site.   This year kelps, especially Bull kelp (Nereocystis leutkeana), found those tubeworms to be an attractive substrate to grow on.  As I cruised around here after we finished our survey I was struck that MOST of the Bull kelp I observed at this site was growing on a tubeworm.  

A Bull kelp holdfast and stipe.  The holdfast here is growing on and around a tubeworm tube.  28 August 2021 photo by Ian Miller

Close up of a Bull kelp holdfast growing on and over a tubeworm.  The tubeworm tube provides an extraordinarily stable and strong substrate for growth, that can support fully grown Bull kelp.  28 August 2021 photo by Ian Miller