Join the soft-shell clam recruitment network

published January 29, 2020 in The York Weekly, Portsmouth Herald and Foster’s Daily and online at titled ‘Nature News’

Clam recruitment boxes will be placed on clam flats in Wells Maine this spring Brian Beal photo

Dr. Brian Beal, Director of Research for the University of Maine at Machais Downeast Institute (DEI)-the easternmost marine research laboratory in the entire United States – gave a talk a week or so ago up in Wells about a research project that will start this spring all along the coast of Maine. The main focuses of the DEI all have to do with shellfish, primarily clams.

Brian was down in Wells explaining why large wooden boxes would be appearing on some clam flats in Maine, from Wells north to Sipayik, this spring and summer. The boxes are part of a study aimed at understanding how best to protect young soft-shell clams at a critical time in their development-when they are transiting from a water-born planktonic life to settling into the mud and sand flats and growing into delicious steamers. 

The clam recruitment boxes appear to provide a safe place for juvenile planktonic clams to settle Brian Beal Photo

Protecting soft shell clams from what? Primarily the invasive European green crab (Carcinus maenas).  Green crabs were introduced to New England back in the early 1800s by travelling in the ballast of ships carrying cargo from Europe to the United States.  Since then they have travelled up the East Coast, decimating the soft shell clam industry and have more recently (the late 1980s) reached the West Coast where they are wreaking similar havoc from San Francisco up to Seattle.  One reason green crabs are such a problem is that, unlike our native crabs, green crabs can swim out onto the mudflats to hunt. Our native rock and Jonah crabs don’t do this-they can’t swim and can’t get out and back to the mud flats as the tides ebb and flow..  Adult green crabs swim out to the mud flats at high tide, grab the soft-shell clam siphons (the fleshy clam ‘necks’), pull them out and eat them. Our soft-shell clams have adapted to this by digging deeper into the mud so that they can escape. However, a probably bigger problem is that young green crabs  (-perhaps a couple millimeters in size) also settle on the mudflats and prey upon anything smaller than themselves-juicy morsels like young soft-shell clams. 

To understand how the recruitment boxes work you have to know a little bit about a clam’s life cycle.  Before I joined the Wells Clam Conservation Commission almost a decade ago, I hadn’t understood how complex that life cycle is and how threatened it is by the invasive green crab. 

The life of a soft-shell clam (Mya arenaria) begins on a warm spring day when both male and female clams release their sperm and eggs into the water, if the two should meet-fertilization occurs.  This is called broadcast spawning and time is everything. The young that develop from this union are planktonic, they don’t look much like adult clams, instead they look like tiny blobs with tufts of fine cilia that they use to swim through the water.  These larval forms are called trocophore larvae that then mature into veliger larvae. The veligers look like a shell-less swimming clam. These baby clams come to intertidal flats via the water column. They swim for 2-3 weeks depending on seawater temperature and location along the coast, and then settle to the flats.  They are about the size of a grain of sand. This is when they are most vulnerable to predation. Here is where the recruitment boxes come in.  

Recently settled clams are at most danger from juvenile green crabs Brian Beal photos

Recruitment boxes are large wooden boxes with mesh on both the top and bottom.  Planktonic clams that settle into these boxes appear able to have much higher survival rates than those settling on the unprotected mud or sand flat.  

Mesh on both top and bottom of the boxes protects young clams from many predators Brian Beal photo

Why put out recruitment boxes? Soft-shell clam landings across Maine have declined by 45% since 2001, and few seem to be aware of this. An interesting tie-in with climate change appears to be that warmer sea surface temperatures (as we have been seeing in the Gulf of Maine) encourage explosive growth of green crabs.  Brian’s project aims to increase public awareness of what is occurring within this iconic fishery and create a statewide data set for fisheries managers in the Department of Marine Resources, and for other fisheries scientists, to better understand factors that affect the health and well-being of the soft-shell clam fishery.  

Whether you live in Maine or New Hampshire, if you want to get involved in this ‘recruitment network’ contact Brian at the Downeast Institute.  Dr Beal is looking forward to working with clammers, clam conservation committees, elected officials, schools and students in each community to learn about the early life-history of clams and what may be regulating or controlling their numbers.  Ultimately, he would like to create a network where the coastal communities that are part of this first trial are a subset of a larger group of communities all doing similar work that may play an important role in how soft-shell clams are managed.