Identification of settling
and early postlarval stages of mussels (Mytilus spp.) from the
Pacific coast of North America, using prodissoconch morphology and genomic
DNA
A. L. Martel, L. M.
Auffrey, C. D. Robles, B. M. Honda-2000
Marine Biology, 137 (5/6): 811-818
Abstract:
Detailed inventories of the benthos and field studies
of the settlement and recruitment processes of marine benthic invertebrates
require accurate identification of newly settled larvae and early juvenile
stages. We provide morphological criteria, visible under a good quality
dissecting stereomicroscope, by which to discriminate between species of the
settling larval and early postlarval stages (~250 to 700 µm shell length)
of mussels of the genus Mytilus on the west coast of Vancouver Island
and Southern California. Compared to the bay mussel (M. trossulus),
the sea mussel (M. californianus) 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 provincular lateral teeth (PLT). The
PLT distance is a new term denoting the separation 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 provincular lateral teeth,
situated at either end of the provinculum. We confirmed the validity of
morphological criteria by comparing PCR products of genomic DNA of
provisionally identified postlarvae. Furthermore, measurements of PI lengths
and PLT distance from well-preserved postlarvae of sea mussels (M.
californianus) and of bay mussels (M. galloprovincialis) from
Southern California indicate that the PI morphology and morphometry, and PLT
distance criterion apply for that region as well. The criteria presented
here can also apply to the advanced (competent) veliger stages, as the
latter may settle (i.e. become the "settling" stage) upon
encountering a suitable substrate. Our present and previously published work
provide economical and effective identification methods that can be used to
discriminate among early life history stages (~250 µm to 5.0 mm shell
length) of Mytilus spp. along the west coast of North America.
(Bamfield Marine Station, Bamfield, British Columbia
V0R 1B0, Canada; and Research and Collections Division, Canadian Museum of
Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada Tel.:
+1-250-7283301; Fax: +1-250-7283452, e-mail: amartel@mus-nature.ca)