The role of wind in hydrochorous mangrove propagule dispersal

Abstract

Abstract. Although wind has been recognized to be an important factor in the dispersal of hydrochorous mangrove propagules, and hence in the quantification of (meta)population dynamics, the species-specific sensitivity to wind effects has not been studied. We combined observations from a controlled experiment (flume tank) and in situ experiments to understand wind and water current contributions to dispersal potential as well as to estimate real dispersal ranges due to immediate response to tidal currents (two outgoing tides). This was done for 4 species with propagules differing in morphological and buoyancy properties (i.e. Rhizophora mucronata, Ceriops tagal, Heritiera littoralis and Xylocarpus granatum). The flume experiments revealed that the influence of wind depends on the density of a propagule (and hence its buoyancy characteristics) and that typical morphological characteristics of the dispersal unit are additionally important. H. littoralis propagules were influenced most, because on the one hand their low density (613.58 g L−1; n =10) enables them to float on top of the water surface, and on the other hand their "sailboat-like" structure provides a relatively large surface area. The X. granatum fruits appeared to be the least influenced by ambient wind conditions, explained by the smooth surface and spherical shape of which, because of the fruit's high density (890.05 g L−1; n = 1), only a small part sticks above the water surface. Although the seeds of X. granatum are of a similar size class than H. littoralis propagules, they are (like the X. granatum fruits) largely submerged due to their high density (870.66 g L−1; n = 8), hence catching less wind than H. littoralis propagules. The influence of wind on the dispersal of the horizontally floating C. tagal and R. mucronata dispersal units was strong, comparable to that of H. littoralis propagules. A differential effect of wind was found within elongated propagules, which directly follows from the floating orientation of the propagules. While the dispersal path of vertically floating propagules was influenced by the strength and direction of the water currents and to a lesser extent by ambient wind conditions, the dispersal path of horizontally floating propagules was influenced by both strength and direction of the water currents and prevailing wind forces. To validate the flume results, propagules of C. tagal and R. mucronata were released during outgoing tide in a tidal creek in Gazi Bay (Kenya), followed by observation of their dispersal distance and direction, while knowing the actual dominant wind direction. In line with the flume results, this study showed that wind plays an important role in the dispersal distance of the propagules. The present study provides important mechanistic insight into the effect of wind on hydrochorous mangrove propagule dispersal, thereby yielding an essential step towards the construction and optimization of (particle-based) hydrodynamic dispersal models.

Application of remote sensing and GIS for detection of long-term mangrove shoreline changes in Mui Ca Mau, Vietnam

“…Even at a local scale there is a poor communication between the monitoring, managing and exploiting authorities. The contact of these groups with provincial authorities is hardly present (Van Dam, 2010). We agree with Ha et al (2014) stating that forest management…”

“…Excessive erosion will prevent the propagules from establishing or stabilizing in the soil, whereas excessive accretion might cover and suffocate the seedlings. In addition, propagule buoyancy, period of obligate dispersal, anchoring time, tides, currents, wind and even dyke removal are primary factors determining dispersal and establishment of mangroves (Clarke, 1993;McGuinness, 1997;Di Nitto et al, 2013;Van der Stocken et al, 2013). After stranding and establishment, other factors become important in determining survival including predation, interspecific competition, flooding regime, and soil physico-chemical characteristics (Clarke et al, 2001;Delgado et al, 2001;Cannicci et al, 2008;Krauss et al, 2008).…”

“…In order to be able to enlarge the mangrove protection zone and to maintain the present status of the forest, more staff is needed. It could be that volunteering co-workers will step forward after awareness has risen, but still encouragement by higher authorities is necessary (Van Dam, 2010).…”

“…Remote sensing and geographical information system (GIS) techniques have been used widely to assess changes in coastal shorelines (Chen and Rau, 1998;Ghosh et al, 2001;Lin et al, 2001; Van der Wal et al, 2002;Ali, 2003; Vanderstraete et al, 2006;Genz et al, 2007;Maiti and Bhattacharya, 2009;Sesli et al, 2009;Rebelo et al, 2009;Kuleli, 2010;Kuleli et al, 2011;and Hai-Hoa et al, 2013) and the boundaries of mangrove forests and other habitats over time (Woodroffe, 1995;Solomon et al, 1997;El-Raey et al, 1999;Wilton and Saintilan, 2000;Saintilan and Wilton, 2001;Cohen and Lara, 2003;Dahdouh-Guebas et al, 2004;Fromard et al, 2004;Souza Filho et al, 2006;Gilman et al, 2007;Satyanarayana et al, 2011;Giri et al, 2011;Heumann, 2011;and Nfotabong-Atheull et al, 2013). The Digital Shoreline Analysis System (DSAS) is an extension to ArcMap and was introduced to automatically or manually generate measurements of transects and metadata based on user-specified parameters, calculating rates of shoreline (2013) changes and to provide other statistical information (Thieler et al, 2009).…”

Mangrove expansion and salt marsh decline at mangrove poleward limits

“…Mangroves are sensitive to several global environmental conditions undergoing change, including enhanced atmospheric CO 2 (McKee & Rooth, 2008), sea level (Woodroffe, 1990;McKee et al, 2007), temperature (Alongi, 2008), and rainfall (Semeniuk, 2013). All mangrove species are hydrochorous and thus often have some potential for dispersal to new localities by sea currents and drift (see Friess et al, 2012;Van der Stocken et al, 2013). Mangroves are conspicuous and can be identified from aerial photography at a scale represented in easily accessible geographic applications such as Google Earth (www.google.com/earth/index.…”