From April- November 2022 Downeast Institute collaborated with the Friends of Taunton Bay to measure recruitment behavior of soft-shell clams and green crabs at two intertidal mudflats in Taunton Bay, Franklin, Maine. This effort also provided data on blue mussel recruitment.
Methods
Beal boxes were used to measure recruitment and survival at Karlson Point (clammers refer to it as “Tink’s”; 44o34’26.36”N, 68o15’44.29”W) and Dwelley Point (44o34’54.32”N, 68o14’36.77”W).
Three blocks of six boxes each were deployed at each of the three tidal heights. In addition to deploying boxes, six benthic (bottom) core samples (Area = 0.1963 ft2, or 0.01824 m2) were taken at each tidal height and site to establish initial density and size-frequency distribution of clams and other infaunal organisms.
Boxes remained at each site and tidal height until 6 November (204 days) when each was retrieved and the contents of each washed through a 1 mm sieve. All soft-shell clams, blue mussels, and green crabs were enumerated.
Some Results
- Densities of soft-shell clams in these boxes did not vary significantly between sites or tidal heights
- Overall mean abundance recorded in the boxes was quite low (2.1 ± 0.84 individuals/ft2, n = 24) compared with results from Raccoon Cove (Lamoine – Frenchman Bay), and other eastern Maine locations (Beal et al. unpubl.). This estimate came from boxes both with and without green crabs, which have been shown to be an important consumer of soft-shell clams (Glude 1955; Beal 2006; Tan and Beal 2015).
- Combining data from both sites, tidal heights, and box configurations, crabs occurred in 11 of 24 boxes, and in those boxes, soft-shell clam recruit density was 0.50 ± 0.66 ind./ft2 as opposed to 3.45 ± 0.95 ind./ft2 in boxes without green crabs – a nearly 7-fold difference. A similar comparison using information from core samples taken at the two Taunton Bay sites in November suggests a similar negative effect of green crabs on soft- shell clam recruits. That is, although green crab density also was low (the mean varied between 1.69 and 2.51 crabs/ft2 [n = 12] in recruitment boxes), we observed significantly more soft-shell clam recruits in boxes without crabs than in boxes with crabs.
- We discovered a weak, negative relationship between number of clams and number of green crabs per box as well as a stronger negative relationship between number of clams and the largest size green crab per box. Similar relationships between maximum crab size and number of recruits have been observed in other Maine coastal communities (Beal et al. unpublished data).
Report
Read more details in the report.
Funding and Other Acknowledgements
This work was funded by the University of Maine at Machias, Downeast Institute, Maine Economic Improvement Fund-Small Campus Initiative of the University of Maine System, and the Friends of Taunton Bay.
We thank the clammers from the Frenchman Bay Regional Shellfish Commission, J. Porada, M. Whiting, G. Zegers, H. Merriam, and A. Brown for assistance deploying the boxes and taking core samples. T. Houston and K. Nunan assisted in November 2022 with collecting boxes from both field sites and processing the contents of each. T. Houston, O. Lentchner, and E. (Chambers) King carried out counts and measurements of clam, mussel, and crab recruits. J. Robinson and J. Balicki constructed the recruitment boxes.
