Mangrove expansion and salt marsh decline at mangrove poleward limits

Abstract

Mangroves are species of halophytic intertidal trees and shrubs derived from tropical genera and are likely delimited in latitudinal range by varying sensitivity to cold. There is now sufficient evidence that mangrove species have proliferated at or near their poleward limits on at least five continents over the past half century, at the expense of salt marsh. Avicennia is the most cold-tolerant genus worldwide, and is the subject of most of the observed changes. Avicennia germinans has extended in range along the USA Atlantic coast and expanded into salt marsh as a consequence of lower frost frequency and intensity in the southern USA. The genus has also expanded into salt marsh at its southern limit in Peru, and on the Pacific coast of Mexico. Mangroves of several species have expanded in extent and replaced salt marsh where protected within mangrove reserves in Guangdong Province, China. In south-eastern Australia, the expansion of Avicennia marina into salt marshes is now well documented, and Rhizophora stylosa has extended its range southward, while showing strong population growth within estuaries along its southern limits in northern New South Wales. Avicennia marina has extended its range southwards in South Africa. The changes are consistent with the poleward extension of temperature thresholds coincident with sea-level rise, although the specific mechanism of range extension might be complicated by limitations on dispersal or other factors. The shift from salt marsh to mangrove dominance on subtropical and temperate shorelines has important implications for ecological structure, function, and global change adaptation.

Mangroves Response to Climate Change: A Review of Recent Findings on Mangrove Extension and Distribution

“…Mangroves in this estuary have expanded to 38 ha in the north arm and 9 ha in the south arm of the estuary, lining 9.5 km of shoreline and is the southernmost confirmed mangroves on the west coast of South America (Saintilan et al 2014), however, similar to other areas, such as the South Atlantic latitudinal limit, evidence is still scarce to support poleward expansion due to global climate change.…”

“…In a review on mangrove expansion beyond their poleward limits, Saintilan et al (2014) reported that historical data in Japan, for example, are insufficient to confirm mangrove expansion. Saintilan et al (2014) also noted that the delimitation of mangrove limits in China and Taiwan are complicated due to extensive clearing.…”

“…In a review on mangrove expansion beyond their poleward limits, Saintilan et al (2014) reported that historical data in Japan, for example, are insufficient to confirm mangrove expansion. Saintilan et al (2014) also noted that the delimitation of mangrove limits in China and Taiwan are complicated due to extensive clearing. However, in the Zhanjiang Mangrove National Nature Reserve on the Leizhou Peninsula of Guangdong Province, China, one of the few locations where mangrove and salt marshes co-exist in near natural state, mangroves within this reserve have expanded fourfold, including encroachment on salt marsh area.…”

“…Saintilan et al (2014), showed that mangrove area in the country has increased in 40%, within the past three decades with the largest expansion occurring in the Umhlatuze estuary with an increase from 197 ha to 489 ha over new sedimentary deltaic areas in that estuary (Bedin 2001, Ward andSteinke 1982).…”

The cost and feasibility of marine coastal restoration

“…Mangrove forests have been removed across the tropics for conversion to aquaculture ponds (Valiela et al 2001, Alongi 2002, Giri et al 2011, although clearing for forestry, agriculture and urban/industrial developments are important causes of loss in some locations. Saltmarshes have been highly modified by drainage for agriculture for centuries (Bromberg-Gedan et al 2009), are severely affected by coastal eutrophication (Deegan et al 2012), and are presently being replaced by mangroves due to climate change (Rogers et al 2005, Saintilan et al 2014. A recent investigation reported that more than 80% of native oyster stocks worldwide have been overharvested in the last century and most of the remaining stocks are close to functional extinction (Beck et al 2011).…”