The Soft-Shell Clam Mya arenaria: Biology, Fisheries, and Mariculture

Chapter 10: Effects of Harmful and Toxic Microalgae on the Soft-Shell Clam
Mya arenaria

V. Monica Bricelj, Scott P. MacQuarrie, and Laurie Connell


This chapter focuses primarily on three harmful algal toxic groups whose geographic occurrence on the east coast of North America overlaps with the distribution of soft-shell clam Mya arenaria populations. Based on their effects, or associated human health syndrome, these phycotoxins were originally referred to as paralytic shellfish poisoning (PSP) toxins, amnesic shellfish poisoning (ASP) toxins, and diarrhetic shellfish poisoning (DSP) toxins. More recently, however, their preferred classification has been based on the structural chemistry of the toxins present, that is, the saxitoxin (STX), domoic acid (DA), and okadaic acid (OA) toxin groups (the latter including the related dinophysistoxins [DTXs] and pectenotoxins [PTXs]) (Toyofuku 2006). Here, we use these terms interchangeably. Of these three groups, however, major focus is given to the effects of paralytic shellfish toxins (PSTs), which have historically affected M. arenaria in northeastern Canada and British Columbia for over 100 years (reviewed by Bates et al. (2020]). Throughout this chapter, soft-shell clams between ca. 25 and 44 mm in shell length (SL; greatest anterior–posterior linear distance) are referred to as young adults, given that reproductive maturity occurs within this size range (Snelgrove et al. 2023, this volume). Postmetamorphic clams ca. 1–12 mm SL are referred to as “spat” (note that these size-classes were named “juveniles” and “postlarvae,” respectively, in our prior published literature on PSTs in M. arenaria).

As documented in a survey conducted between 2000 and 2017, paralytic shellfish toxin events have recurred annually on the Atlantic coast of the USA (Anderson et al. 2021) and are responsible for the majority of phycotoxin outbreaks on both coasts of Canada (McKenzie et al. 2021), where M. arenaria is a member of the intertidal benthic community. A major goal of this chapter is to provide a comprehensive account of the sequential research findings that led to the first discovery of a molecular basis for the adaptation of a bivalve mollusk to algal neurotoxins, specifically that of M. arenaria to PSTs.