Effect of delayed
metamorphosis on larval competence, and post-larval survival and growth, in
the abalone Haliotis iris Gmelin
R.D. Roberts, C. Lapworth-2001
Journal of Experimental Marine Biology and Ecology,
258 (1): 1-13
Abstract:
Marine invertebrate species vary in their ability to
delay metamorphosis, and in the degree to which delayed metamorphosis
compromises juvenile performance. Abalone (Haliotis iris) larvae were
deprived of metamorphosis cues and the effects of delayed metamorphosis on
larval competence, and post-larval growth and survival were quantified.
Larvae were exposed to a metamorphosis inducer (the coralline alga Phymatolithon
repandum (Foslie) Wilks and Woelkerling) on Days 11, 18, 22, 26, 30 and
34 post-fertilisation (temperature 16-17°C). Post-larvae were reared on
diatoms (Nitzschia longissima Grunow) for 3-4 weeks
post-metamorphosis. Delayed metamorphosis caused progressive negative
effects on post-larval performance. Virtually all larvae initiated
metamorphosis in response to P. repandum, regardless of larval age.
The proportion of post-larvae that developed post-larval shell growth within
2 days of metamorphosis induction dropped only ~20% from Day 11 to Day 26 (P>0.05),
but was significantly lower by Day 30 and Day 34 (P<0.001). Larvae
that metamorphosed on Days 11, 18 and 22 showed high survival (>80%) and
growth rates (means of 20-22 µm shell length per day). In contrast, larvae
that metamorphosed on Day 26 and Day 30 had poor survival (30-40%) and lower
(P<0.05) growth rates (15-16 µm/day). Of the larvae that
metamorphosed on Day 34, only 7 (30%) survived their first week
post-metamorphosis, and they grew only 2 µm/day on average. Only one of
these post-larvae (4%) survived the second week. The visible yolk supply
diminished over the life of the larvae and was near zero by Day 34. Nearly
all larvae had died by Day 38. H. iris larvae remained competent to
metamorphose for at least 3 weeks after they attained competence.
Post-larval growth and survival were not reduced if metamorphosis occurred
within 3 weeks of fertilisation. This extended period of larval competence
implies that H. iris larvae can potentially disperse for up to
several weeks before successful metamorphosis.
(Cawthron Institute, Private Bag 2, Nelson, New
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