Short-term competence in larvae of queen conch Strombus gigas: shifts in behavior, morphology and metamorphic response

Abstract

Competent larvae of the prosobranch gastropod Strombus glgas Linne (queen conch) require an environmental cue to induce metamorphosis. In this laboratory investigation the planktotrophic vehgers of S. gigas were exposed to 2 cues to observe changes In metamorphic response as a function of age. The cues were extract of Laurencia poitei, an artificial cue, and detrital blades of Thalassia testudinum, a natural cue. Onset of competence began 18 d post-hatch, and veligers were competent for only 6 d at 28 to 30°C. Both cues induced the highest percentage nletamorphosis on Day 23 (88% for extract and 78% for detritus), and response dropped dramatically by Day 25 ( 3 % for extract and 15% for detritus). Shell length for successful metainorphosis ranged between 952 and 1258 pm Pigmentation change from orange to dark green on the propodium and larval operculuni indicated competence, and competent veligers exhibited a swim-crawl behavior associated with settlement. Thls study revealed that veligers of S. gigas have a unique developmental hstory. The competence period was shorter than the precompetence period. Most other planktotrophic larvae a r e competent for a time equal to or longer than the precompetence period. Short-term competence is ordinarily associated with metamorphosis to a broad spectrum of cues. This may explain why veligers of S. gigas were observed to metamorphose to a variety of benthic cues found in juvenile conch seagrass habitats.

Delayed metamorphosis of a tropical reef fish (Acanthurus triostegus):a field experiment

“…These results are consistent with the conceptual model of fish settlement that has been developed from research on invertebrate metamorphosis (e.g. Crisp 1974, Jackson & Strathmann 1981, Pecknick 1990, Davis 1994 and to date has largely been assumed I rather than demonstrated by fish ecologists. immediately upon capture…”

“…The paucity of evidence for demersal fishes contrasts with an extensive body of invertebrate literature, for which delays in settlement are well documented and experimentally examined (e.g. Richmond 1985, Lipcius et al 1990, Pechenik 1990, Pechenik et al 1993, Davis 1994, Harvey 1996, Stoner et al 1996. The present study is the first to experimentally examine in the field the capacity of a fish species to delay metamorphosis.…”

“…Thus in the laboratory, sequential preference experiments have enabled researchers to determine when larvae of a wide range of taxa are first competent to settle and how long they can subsequently postpone metamorphosis (Pechenik 1990, Davis 1994). The problem is that in culture, delays can only be demonstrated if we can ascertain when a larva becomes competent to metamorphose (Pechenik 1990).…”

Life history of Littorina scutulata and L. plena, sibling gastropod species with planktotrophic larvae

“…Variation in larval growth rates may be the result of food availability (found here), genetic variation (Hilbish et al 1993;Pechenik et al 1996), or temperature (Zimmerman & Pechenik 199 1). Geographic variation in response to settlement cues (Schubart et al 1995) may also result in variation in planktonic period, Some species, particularly those with a wide range of settlement cues and adult habitats, may have a short and relatively constant competent period (e.g., Davis 1994). However, most species seem to fit the pattern predicted by Jackson & Strathmann (198 1) that selection should favor flexibility in timing of metamorphosis and a large ratio of competent to precompetent period (Scheltema 1986b).…”

Growth, settlement and survival ofDicathais orbita(Neogastropoda, Mollusca) larvae in response to temperature, diet and settlement cues

“…The experiment was run with batches of larvae at different stages of development: the day of hatching (day 0), 10 days post hatching (dph) (day 10), 20 dph (day 20) and at 30 dph (day 30). The number of larvae responding to settlement cues in each batch was monitored for 10 min h −1 for the first 7 h and again at 18, 24, 48, 36, 60 and 72 h. Settlement observations focused on pre‐metamorphic cues, such as sinking and creeping behaviour, which have been noted in other species of gastropod larvae prior to metamorphosis (Di Salvo ; Davis ; Naegel, Rodríguez‐Astudillo, Hernández‐Ceballos & Cáceres‐Martínez ). Five settlement cues were trialled in this study: KCl, live and dead (carrion) prey ( Xenostrobus pulex Lamarck), an algal biofilm of Ulvella lens Crouan & Crouan and the mucus of adult conspecifics.…”