P.F. Hensel
J.W. Day
P. Delgado
2001
<p>Establishment of<span> </span><i>Laguncularia</i><span> </span><i>racemosa</i>,<span> </span><i>Avicennia</i><span> </span><i>germinans</i>, and<span> </span><i>A</i>.<span> </span><i>bicolor</i><span> </span>was measured along intertidal gradients (mud bank (MB), lower intertidal (LI), and upper intertidal (UI)) on point bars and islands in a Costa Rican tropical estuary. Successful establishment showed the following order —<span> </span><i>Laguncularia</i>: LI (73%)>MB (52%)>UI (18%), with UI significantly lower than LI and MB;<span> </span><i>Avicennia</i><span> </span>spp.: LI (66%)>UI (51%)>MB (29%), with LI significantly higher than MB. Establishment of<span> </span><i>Laguncularia</i><span> </span>in UI was significantly lower than<span> </span><i>Avicennia</i><span> </span>spp. due to selective crab herbivory. After 25 days, 52% of<span> </span><i>Laguncularia</i><span> </span>propagules were eaten compared to 5% for<span> </span><i>Avicennia</i><span> </span>spp. Total mortality of<span> </span><i>Laguncularia</i><span> </span>propagules and seedlings was significantly higher than that of<span> </span><i>Avicennia</i><span> </span>spp. in all three zones.</p><p>The hydrological regime affected propagule establishment under controlled mesocosm conditions. Four hydrological treatments included flooded according to tidal cycle (FT), no flooding (NF), continuous flooding (F), and flooded according to tidal cycle with propagules additionally buried (FTB).<span> </span><i>Laguncularia</i><span> </span>establishment under NF (93%) and F (84%) was significantly greater than under FT (63%).<span> </span><i>A.</i><span> </span><i>germinans</i><span> </span>establishment under NF (97%) was greater than under FT (69%).<span> </span><i>Laguncularia</i><span> </span>showed significantly higher establishment than<span> </span><i>A.</i><span> </span><i>germinans</i><span> </span>under F conditions.<span> </span><i>Laguncularia</i><span> </span>propagules sank soon after their radicles protruded (5–8 days), and subsequently established under water.<span> </span><i>A.</i><span> </span><i>germinans</i><span> </span>propagules floated during the 25-day experiment and never established. Propagule establishment under FTB was greater for<span> </span><i>Laguncularia</i><span> </span>than for<span> </span><i>Avicennia</i><span> </span>(11 and 1%, respectively). Height increase of established<span> </span><i>Laguncularia</i><span> </span>seedlings was significantly different among treatments: FT (5.2 mm per day)>NF (3.4 mm per day)>F (2.4 mm per day). Growth of established<span> </span><i>A.</i><span> </span><i>germinans</i><span> </span>seedlings did not differ between FT (4.8 mm per day) and NF (5.0 mm per day), but it was significantly higher than<span> </span><i>Laguncularia</i><span> </span>under NF.</p><p>These results show that both genera can successfully establish on the lower intertidal zone when artificially retained. However, propagule buoyancy, availability, dispersal, and the effect of water movement on propagule anchoring limit<span> </span><i>Avicennia</i><span> </span>spp. establishment in this regularly flooded environment. In the upper intertidal zone, however, differential predation on<span> </span><i>Laguncularia</i><span> </span>propagules favors<span> </span><i>Avicennia</i><span> </span>spp. establishment and dominance.</p>
application/pdf
10.1016/S0304-3770(01)00188-7
en
Elsevier
The importance of propagule establishment and physical factors in mangrove distributional patterns in a Costa Rican estuary
article