Identification of settling and early postlarval stages of mussels (Mytilusspp.) from the pacific coast of North America, using prodissoconch morphology and genomic DNA
Al. Martel et al., Identification of settling and early postlarval stages of mussels (Mytilusspp.) from the pacific coast of North America, using prodissoconch morphology and genomic DNA, MARINE BIOL, 137(5-6), 2000, pp. 811-818
Detailed inventories of the benthos and field studies of the settlement and
recruitment processes of marine benthic invertebrates require accurate ide
ntification of newly settled larvae and early juvenile stages. We provide m
orphological criteria, visible under a good quality dissecting stereomicros
cope, by which to discriminate between species of the settling larval and e
arly postlarval stages (similar to 250 to 700 mum shell length) of mussels
of the genus Mytilus on the west coast of Vancouver Island and Southern Cal
ifornia. Compared to the bay mussel (M. trossulus), the sea mussel (M. cali
fornianus) has: (i) a shallower and flatter umbo, the latter corresponding
to a significantly less pronounced prodissoconch I (PI) curvature and (ii)
a greater PI length as well as (iii) a wider separation between the provinc
ular lateral teeth (PLT). The PLT distance is a new term denoting the separ
ation between the midpoint of two reddish pigment spots of the provinculum
(larval hinge apparatus) region of settling larvae and early postlarvae of
Mytilus spp. from the East Pacific Coast. These spots mark the larger provi
ncular lateral teeth, situated at either end of the provinculum. We confirm
ed the validity of morphological criteria by comparing PCR products of geno
mic DNA of provisionally identified postlarvae. Furthermore, measurements o
f PI lengths and PLT distance from well-preserved postlarvae of sea mussels
(M. californianus) and of bay mussels (hl. galloprovincialis) from Souther
n California indicate that the PI morphology and morphometry, and PLT dista
nce criterion apply for that region as well. The criteria presented here ca
n also apply to the advanced (competent) veliger stages, as the latter may
settle (i.e. become the "settling" stage) upon encountering a suitable subs
trate. Our present and previously published work provide economical and eff
ective identification methods that can be used to discriminate among early
life history stages (similar to 250 mum to 5.0 mm shell length) of Mytilus
spp. along the west coast of North America.