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Mactromeris polynyma

In August 2013, the University of Maine at Machias received a 2-yr, $630,000 grant from the National Science Foundation to conduct applied research on Arctic surfclams, Mactromeris polynyma, and blue mussels, Mytilus edulis.  DEI is a collaborating entity in the project, along with Dr. Sandra Shumway (University of Connecticut), Dr. Christopher Davis (Maine Aquaculture Innovation Center and Pemaquid Oyster), and Dr. Kevin Athearn, University of Maine at Machias.  The project also has two commercial businesses that are participating.  For surfclams, A.C. Inc. (Beals), the largest wholesaler of seafood products in eastern Maine, is working with DEI to examine conditions in lobster impoundments for the nursery and growout phases  For blue mussels, New DHC, a company related to Cooke Aquaculture (Machiasport), the largest producer of pen-raised salmon in Maine, is working with DEI to grow mussel seed in fallowing salmon pens at sites in Eastport, Machiasport, and Beals.  Recently, NSF produced a 4-minute Science Nation video about our work with Arctic surfclams.

 The Arctic surfclam is a circumboreal species distinguished from the Atlantic surfclam, Spisula solidissima, by its purple foot, (see below), siphons, and mantle edge that all turn brilliant orange-red when cooked.  

 Currently, the Arctic surfclam is not a commercial species in the U.S., but is harvested in several placed in Atlantic Canada, including south of Nova Scotia (on Banquerau and Grand Bank), near the Magdalen Islands, and in the mouth of the St. Lawrence River.  Surfclams typically are subtidal and live in well-sorted sandy sediments at depths between 45-65 meters (150 and 225 feet).  They are commonly found with propellor clams, Cyrtodaria siliqua.  In their native habitats, Arctic surfclams are a long-lived (60+ years), slow-growing species.  Clams may attain sizes of 100 - 125 mm (4-5 inches) and be anywhere from 10 to 80 years old.  The Canadian fishery focuses on larger, older individuals with a large foot that is cut and processed for the sushi markets in North American and Asia.  The product is called "hokkigai" (Japanese translation: [hokki] -  “Back from the North”and [kai or gai]  - “Clam”).

Arctic surfclams are known to occur in coastal waters of Maine and the Gulf of Maine, as this species ranges from the Middle Atlantic Shelf as far north as the Strait of Belle Isle; however, no product is available from U.S. sources because no large wild beds have been discovered.  This presents a unique challenge and opportunity to enter the market for live and processed Arctic surfclams through farming, or aquaculture.  Successful farming techniques would create a playing field in which U.S. companies could compete for a portion of a large export market for this product.

As early as 2010, the project team received permission from the Maine Department of Marine Resources (DMR) to obtain broodstock (100-130 mm SL) from a commercial population in northern Quebec Province (Natashquan, in the Côte-Nord region, approximately 1,000 km north of Quebec City).  An initial health inspection report indicated no Dermo (Perkinsus spp.), MSX (Haplosporidium nelsoni), SSO (Haplosporidium cosale), QPX (Quahog Parasite Unknown), or neoplasia.  In addition, histological examination included general screening for ciliates, Rickettsia, and spores and cysts of organisms reported associated with these bivalves. After the successful health report, DMR personnel permitted the research team to bring several hundred animals to DEI where approximately 15 individuals remain.

  *Mactromeris polynyma* in spawning tank at DEI (4-30-2011)

Basic methods have been developed by the team to condition broodstock, spawn individuals, and rear larvae and juveniles of Mactromeris polynyma. (See video of 14-day old Mactromeris larvae)

Day 14 veliger larvae (*Mactromeris polynyma*) at 400x magnification (Photo and video credit:  Kyle Pepperman, Downeast Institute).

21-day old *Mactromeris polynyma* larvae at 400x magnification (Photomicrograph by Kyle Pepperman)

During the fall of 2010, Arctic surf clams were harvested from the Gulf of St. Lawrence, approximately 200 miles north of Quebec City, and, with the permission of the Maine Department of Marine Resources, transported to DEI's Black Duck Cove shellfish hatchery.  They were held in seawater throughout the winter in sand-filled plastic fish totes in the facility and, beginning in late March 2011, were fed copious amounts of cultured microalgae in an attempt to condition them to spawn.  Spawning was successful, and occurred in early May.  Larvae and juveniles were reared at 15oC, and as of the late summer 2011, we had produced approximately 300,000 three millimeter (3 mm) animals.  These animals were used in a variety of field studies to examine their fate and growth under a variety of stocking densities and different predator exclusion nets.

The NSF project will continue to assess these methods and further refine them as necessary over the next two years, as several questions remain about early culture conditions as well as nursery and  field grow-out methods.

Three short-term field experiments were initiated with the overwintered animals in Spring 2012. One was a comparative trial deployed in muddy sediments on a spring tide (4-5 April to 18-19 October) near the extreme low water mark at two intertidal sites (Cutler and Beals, ME).  A generalized randomized block design (GRBD) was used to examine interactive effects of predator exclusion (flexible netting [4.2 mm aperture] vs. no netting) and intraspecific density (1, 3, 6, 12, or 24 animals [8-10 mm SL] per 0.0182 m2 experimental unit [6-inch plastic plant pot], or ca. 55, 165, 330, 660, or 1320 animals per m2) on growth and survival.  Mean percent survival was independent of stocking density at both sites, but was significantly higher in experimental units covered with flexible netting (P < 0.0001).  Differences in mean survival (± 95% CI) between sites were dramatic.  At Cutler (Duck Brook, see Beal and Kraus [2002] for a site description), survival in unnetted vs. netted units was 1.25 ± 1.15% vs. 63.8 ± 10.1% (n = 50), respectively.  At Beals, similar mean percent survival was observed in unprotected units, but clam survival in protected units averaged only 23.2 ± 8.7% (n = 50).  Most clams in netted units had been preyed on by invasive green crabs (Carcinus maenas) that can reach through the apertures of the flexible netting, pinch clam siphons and pull animals to the sediment surface, and crush them through the netting.  An extruded, non-flexible netting will be used in future to protect animals.  Growth at both sites was impressive, with mean final SL of 25.9 ± 0.79 mm (n = 62), and an absolute mean increase in SL of 16.3 ± 0.84 mm.

The second field trial was established on 9 May near the mean low water mark (not extreme low water) at Duck Brook to examine potential interspecific interactions between surfclam juveniles and cultured juveniles of another commercially important bivalve that is native to this area, soft-shell clams (Mya arenaria).  All possible intra- and interspecific combinations of the two species at three densities were used (330, 660, and 1,320 clams/m2; = 15 treatments; n = 5), and each experimental unit (as described above) was covered with a piece of flexible netting (4.2 mm aperture).  Units were collected after 162 days, on 18 October.  No significant negative effects of intra- or interspecific density on surfclam survival or growth were observed (P > 0.05).  Mean percent survival (62.6 ± 8.6%, n = 60) was remarkably similar to that observed from the field test at the same site described above.  In addition, final mean SL was 21.3 ± 0.38 mm (n = 54), with an absolute mean increase in SL of 11.9 ± 0.35 mm.

A third (one-month) experiment was established at the extreme low water mark at Cutler on 6 June 2012 to examine effects of initial surfclam size (Small = 4.9 ± 0.3 mm vs. Large = 9.6 ± 0.4 mm) on survival and growth of surfclams.  Twenty-four clams were added to experimental units (0.0325 m2; density = 740/m2) each covered with flexible netting (4.2 mm aperture).   Large clam survival was significantly higher than that of small clams (72.1 ± 10.2% vs. 28.3 ± 9.9% (n = 10), as many of the small clams apparently escaped from the units through the apertures in the netting.  Mean absolute growth was sig-nificantly greater (P = 0.018) for large (3.5 ± 0.4 mm, n = 10) vs. small (2.5 ± 0.9 mm) clams.  That study revealed that cultured juveniles of M. polynyma produce a disturbance line in the shell when placed in sediments, which is similar to cultured juveniles of Mya arenaria (Beal et al. 1999), and thus allows growth studies to proceed without having to mark animals uniquely at the beginning of the trial.

Juveniles of *Mactromeris polynyma* that were planted near the low intertidal at Duck Brook Flat in Cuter, Maine on 6 June 2012.  Photo was taken on 7 July 2013, and the "hatchery mark" is clearly apparent on each individual.

The current NSF project is examining nine research questions:

Question #1: What effect do different diets have on Arctic surfclam broodstock condition?

Question #2: What is the interactive effect of seawater temperature and algal diet on survival and growth of M. polynyma larvae?

Question #3: What is the effect of different mixed diets on the growth and survival of cultured juveniles from 180 – 3,000 mµ?

Question #4: What is the interactive effect of stocking density and sediment on growth and survival of cultured juveniles (3 mm) in a field-based nursery?

Question #5: How do different types and sizes of predator exclusion netting (flexible vs. extruded @ 2.2, 4.2, and 6.4 mm apertures) affect growth and survival of juveniles (10-12 mm SL) in lower intertidal/ shallow subtidal field plots?

Question #6: How well do cultured juveniles perform in lower intertidal/shallow subtidal field plots in sandy vs. muddy environments? 

Question #7: What is the interactive effect of planting date and stocking density on surfclam growth and survival?

Question #8: Can large juveniles be grown in floating, subtidal trays with or without sediments?

Question #9: What is the rate of uptake and depuration of the commonly occurring toxic dinoflagellate, Alexandrium fundyense, by juveniles of Mactromeris in both the lab and field?

 

The photos below show results from an experiment that was initiated in March 2013 at Larrabee Cove (Machiasport, Maine) and ended in late May 2014 to determine the interactive effect of Arctic surfclam size (mean shell length ± 95% confidence interval; SMALL = 6.86 ± 0.23 mm, n = 43; MEDIUM = 13.32 ± 0.43 mm, n = 48; LARGE = 20.98 ± 0.81 mm, n = 23), density (12 or 24 clams per experimental unit, 0.01824 m2; ca 660 individuals/m2 or 1320 individuals/m2), and type of protective netting on surfclam survival and growth.  Experimental units were plastic horticultural pots (see Beal, 2006) that were 15 cm diameter by 15 cm deep.  Units were dug into the flat so that the rim of each was flush with the sediment surface.  All experimental units were covered with one of two types of predator deterrent netting.  One half of the units were covered with a 45 cm x 45 cm piece of Pet Screening – aperture = 1.8 mm that was held in place with a large rubber band.  The other half received a 20 cm x 20 cm piece of extruded netting – aperture = 6.4 mm that was folded so that it fit snugly over the top of the unit and held in place by a 45 cm x 45 cm piece of flexible netting (aperture = 4.2 mm – OV 7100) that was held in place with a large rubber band.

a) 20 cm x 20 cm piece of extruded netting (6.4 mm aperture); b) 20 cm x 20 cm piece of flexible netting (4.2 mm aperture); c) Experimental unit with both pieces of netting held in place with a large rubber band.

 

A six-inch plant pot that is covered with both an extruded and flexible netting.  Netting protected 12 "Large" cultured juveniles of *Mactromeris polynyma* that were placed in the unit in March 2013.  A periwinkle (*Littorina littorea*) is on top of the netting that has been fouled by a species of kelp (Photo taken on 29 May 2014.

 

The same plant pot (experimental unit) with the flexible netting removed.

 

The same unit with the mud washed off both types of netting.

 

Ten of the 12 individuals placed in the sediments within the particular experimental unit survived the 425-day experiment.  Note the distinct mark that appears on the shells of these surfclams.  The mark coincides with the size that each was on the day the experiment was initiated.  This allows us to estimate an individual growth rate for each live clam. (Mesh screening that the animals are sitting on is 2 mm aperture.)

 

The large clams had a survival rate of 81% over the 425-day period and averaged 34 mm in shell length, adding about 12 mm of new shell over that interval.

 

Steamed Arctic surfclam (ca. 33 mm shell length).

 

One of us (Athearn, 2015) has conducted a Market Assessment for Maine-Grown Arctic Surfclams that indicates that there is good potential for selling Maine-grown Arctic surfclams as a niche product to restaurants and wholesalers in Maine. Several wholesalers and restaurants interviewed expressed strong interest in trying the product. Restaurants that promote Maine-grown products, offer seasonal menu items, and feature unique seafood dishes provide opportunities for selling small-volumes of Arctic surfclams at a relatively high price. Specialty food retailers, such as those specializing in seafood or serving Asian clientele, also appear promising as market outlets. If production constraints limit the clam size and seasonal availability, potential buyers are receptive to purchasing whole, live clams at a small shell size of about 1.5 inches during an autumn harvest season.

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