Shelf and estuarine transport mechanisms affecting the supply of competent larvae in a suite of brachyuran crabs with different life histories.

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2010-01-01Department
BiologíaSource
Marine Ecology Progress Series, 410: 125-141 (2010)Abstract
Supply of competent larvae to the benthic habitat is a major determinant of population
dynamics in coastal and estuarine invertebrates with an indirect life cycle. Larval delivery may
depend not only on physical transport mechanisms, but also on larval behavior and physiological
progress to the competent stage. Yet, the combined analysis of such factors has seldom been
attempted. We used time-series analyses to examine tide- and wind-driven mechanisms responsible
for the supply of crab megalopae to an estuarine river under a major marine influence in SW Spain,
and monitored the vertical distribution of upstream moving megalopae, their net flux and competent
state. The species Panopeus africanus (estuarine), Brachynotus sexdentatus (euryhaline) and Nepinnotheres
pinnotheres (coastal) comprised 80% of the whole sample, and responded in a similar way
to tide and wind forcing. Tidal range was positively correlated to supply, with maxima 0 to 1 d after
spring tides, suggesting selective tidal stream transport. Despite being extensively subjected to
upwelling, downwind drift under the effect of westerlies, not Ekman transport, explained residual
supply variation at our sampling area. Once in the estuary, net flux and competence state matched
the expected trends. Net upstream flux increased from B. sexdentatus to P. africanus, favoring transport
to a sheltered coastal habitat (N. pinnotheres), or to the upper estuary (P. africanus). Competence
state was highest in N. pinnotheres, intermediate in B. sexdentatus and lowest in P. africanus, as
expected if larvae respond to cues from adequate benthic habitat. P. africanus megalopae were found
close to the bottom, not above, rendering slower upstream transport than anticipated.
Subjects
Upwelling; Ekman transport; Downwind drift; Selective tidal stream transport; Larval net flux; cadiz BayCollections
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