Salt Marshes, Mangroves and Wetlands

1. Salt Marshes, Mangroves and Wetlands Chapter 5

2. Salt marshes • Intertidal zone, emergent vegetation • Plants have adapted to saline soils, inundation • Salt glands – salt on leaves of Spartina alterniflora • High productivity in marsh due to sunlight • Peat and sediment accumulation in soil • Detritus production high - exported to estuary • Habitat complexity is high (shoot density) - refuge from predation • Halophytes – salt-tolerant plants, 600 species in marsh worldwide • Species in NC:Spartina alterniflora, Spartina patens, Salicornia sp., Juncus roemeranus, Distichilis spicata, Pluchea camphorata (Table 5.1)

3. Mangroves • Mangrove – taxonomically, one of eight families of trees, salt-tolerant, 12 major genera worldwide. In Florida (USA): • Avicennia – black mangrove • Rhizophora – red mangrove • Laguncularia – white mangrove • All species grow in loose saline soils in intertidal environments. • "Mangrove" has also been used to describe the whole community of plants and animals where these trees are found (mangrove swamp or forest) • Viviparity – the "propagules" – not seeds, because inside the seeds have germinated already and are ready to sprout • Respiratory roots – pheumatophores stick up out of soil (Avicennia) or are on stilts (prop-roots) in Rhizophora

4. Latitudinal Zonation • Mangroves: • 29 ºN -- 29 ºS – tropics and subtropics • Mostly 25 ºN -- 25 ºS, but exceptions include: • Black mangroves scrub at 29 ºN (Dog Island, Florida) • 10-15 ºfurther south in Africa, Australia • 7 º further north in Japan • Salt Marshes • From 25 º N -- 65 º N, and 35 º S -- 60 º S • 38 º N -- 65 º N – no above ground winter biomass due to ice scour • In southern hemisphere, only salt marshes in South America

5. Regional Zonation • Rainfall, ground water seepage may influence the type of marsh or mangrove found in a region. • Lots of rainfall = wide band of marsh or mangrove. As salinity decreases, the plant communities change, individual species vary in salinity tolerance • Mangroves – • Rhizophora, Avicennia, Laguncularia (in polyhaline areas) • Typha in oligohaline areas • Salt marshes • Species diversity declines with increased salinity • saline marsh: 6 species plants (Juncus, Spartina, Distichlis) • brackish marsh: 7 • fresh water marsh: 14

6. Elevation Effects • Different plants can tolerate different amounts of inundation (and salt content). • Salt Marsh • Spartina alterniflora – near edge, low elevation. • Juncus roemerianus – higher elevation • Panicum - highest elevation • Mangroves • Trees in mangroves. Rhizophora – Avicennia – Laguncumra

7. Succession in Marshes • Primary succession – S. alterniflora in SE marshes • In marshes in N.E., after disturbance, succession: • Salicornia europea first to colonize (0-2 yrs) • Distichlis spicata next to invade, vegetatively (2-3 years) • Juncas or Spartina will out-compete Distichlis (3-4 years) • Juncas or Spartina will dominate, but outcome depends on elevation. • climax – upland forest

8. Biological Interactions • Predation and competition may determine local patterns of abundance in both salt marshes and mangroves: • Juncus gerardi competitively excludes Spartina patens at high marsh/terrestrial zonation boundary. • Distichlis spicata is out-competed by both and is a disturbance fugitive species) (Bertness 1991) Ecology 72:125-137 • Smith (1987) transplanted propagules of 4 species of mangroves in Australia (high intertidal – high salt, low inundation; low intertidal – low salt, high inundation). • Transplanted to zone that was not its "normal" zone – it was zone-dominated by Rhizophora racemosa. • Although growth and survivorship was greatest in high intertidal, number of individuals was greatest in low intertidal.

9. Marsh Zonation - caused by physiology? • Physiological tolerance model not supported by field studies. • Lab studies suggest that there are opportunities for growth • Multi-factorial experiments on mangroves in which salinity, pH, redox, soil characteristics, etc. are varied have not been completed • Some support indicated – more data needed

10. Mangrove Zonation • Tidal Sorting hypothesis • large propagules not able to be transported to high intertidal, but take root in low intertidal, high inundation. • Small propagules are not transported to all intertidal areas. • Rhizophora propagules are large and this tree is found in low intertidal; • Avicenna propagules are smaller and found in high intertidal as well as low. • Unfortunately, there are other examples which suggest the opposite is true • This hypothesisnot supported by data in literature

11. Mangrove Seed Predation • Crabs eat many propagules, graspid crabs in particular. • Smith (1987, 1988) tethered propagules across intertidal in Australia. • Found inverse relationship between predation rate on propagules and adults in canopy • When protected by cages from crabs, Avicennia propagules grew and survived in areas where adults not normally found • Seed predation probably important!

12. Competition in Marshes and Mangroves • Mangroves: Smith (1988) tested competition for Ceriops. • C. tagal and C. australis were grown in mono and polycultures in salinities 0-60%. • C. tagal grew better than C. australis at low salinities. • C. australis grew better than C. tagal at high salinities. • Marshes: Bertness & Shumway (1993) – experimentally created bare patches followed succession over four years in a Juncus dominated and Spartina dominated zone • When Spartina removed, Distichlis % cover increases • Spartina % cover is the same, whether Distichlis is removed or not • In high marsh, salt stress inhibits recolonization by Juncus. Juncus grows back more slowly with other species removed in the unwatered plots. • Removal of other species improves growth of Juncus with the watering and lowering of salt stress. • Alleviating salt stress shifted the nature of interspecific interactions from facilitative to competitive.