Time to metamorphosis of blue crab Callinectes sapidus megalopae:effects of benthic macroalgae

Abstract

There is growing evidence that postlarvae (megalopae) of the blue crab Callinectes sapidus can slow the progression through the molt cycle while in offshore nursery grounds, and delay metamorphosis until reinvasion of coastal habitat occurs. However, the cues that trigger metamorphos~s of megalopae are not well known. Thls study tested the hypothesis that the time to metamorphosis (TTM) from the postlarval megalops stage to the first crab stage is shortened in the presence of 2 potential macroalgal settlement substrates, Ulva lactuca (Chlorophyta), and Gracilana spp. (Rhodophyta). Megalopae and test water were collected from 3 locations (offshore, at a coastal ~n l e t , and inside a coastal lagoon) and tested in a completely crossed factorial experiment with algal type and location a s main effects. TTM was longest in offshore treatments (mean TTM 4.72 d ) and similar in the inshore treatments (mean inlet J T M 2.73 d , lagoon TTM 2.51 d). TTM of offshore megalopae was reduced in the presence of Ulva lactuca, but macroalgae had little effect on the inshore treatment groups. The effect of algal cues may be masked once megalopae have initiated premolt prior to invading coastal lagoons.

Effects of environmental cues on metamorphosis of the blue crab Callinectes sapidus

“…This result indicates either that water volume was not important, or that the largest test volume was still too different from the natural envlronm.ent to affect time to metamorphosis. Both Forward et al (1994) andBrunlbaugh &McConaugha (1995) found that time to metamorphosis significantly decreased when blue crab megalopae were exposed to estuarine water as compared to times in offshore water The present study found that potency varied between estuaries and cues were associated with many types of estuarine vegetation. Newport River Estuary water contained cues for accelerating metamorphosis.…”

“…Forward et al (1994) found that metamorphosis was accelerated by exposure to estuarine conditions such as low salinity water, estuarine water and the eelgrass Zostera marina. In addition, Brumbaugh & McConaugha (1995) found that the presence of the green alga Ulva lactuca, which is found in estuaries, also reduced the time to metamorphosis. Collectively, these results support the suggestion that metamorphosis is stimulated by estuarine aquatic vegetation (Orth & van Montfrans 1987, Lipcius et al 1990).…”

“…Since the previous studies indicated that chemical cues in estuarine water accelerated metamorphosis , Brumbaugh & McConaugha 1995, these expenments were designed to determine the potency and size range of the active molecules. First, molting was compared simultaneously in water from 2 estuaries with megalopae from both estuaries.…”

Postlarval settling behavior, substrate preference, and time to metamorphosis for red king crab Paralithodes camtschaticus

“…Megalopae of the blue crab Callinectes sapidus metamorphose approximately 1 d earlier in estuarine water than in offshore water, and up to 2 d earlier in estuarine water with eelgrass . TTM for blue crab can also be reduced by the addition of the macrophyte Ulva to offshore (but not inshore) water (Brumbaugh & McConaugha 1995), and by lowering the salinity of marsh (but not ocean) water (Wolcott & De Vries 1994). Acceleration of metamorphosis in C. sapidus megalopae is caused by chemical cues from several estuarine plants, but not by structure alone (Forward et al 1996).…”

Metamorphosis of the estuarine crab Rhithropanopeus harrisii:effect of water type and adult odor

“…In the case of Callinectes sapidus, metamorphosis is delayed by exposure to offshore water , 1996, Wolcott & De Vries 1994, Brumbaugh & McConaugha 1995 but accelerated by exposure to estuarine water (Forward et al , 1996, lower salinity , humic acids (Forward et al 1997), and cues from estuarine aquatic vegetation such as seagrasses (Forward et al , 1996, saltmarsh cord grass (Forward et al 1996) and macroalgae (Brumbaugh & McConaugha 1995, Forward et al 1996. For Uca sp., cues from estuarine sediment (Christy 1989, O'Connor 1991, O'Connor & Judge 1997 (Weber & Epifanio 1996).…”