The pressing challenges of mangrove rehabilitation: pond reversion and coastal protection

The 2004 Indonesia tsunami as well as the increasing storm frequency and intensity associated with climate change–sea-level rise have highlighted the coastal protection function, among the many goods and services that mangrove forests provide. This wider awareness of mangroves has increased national and international rehabilitation efforts, given only 15 million ha remaining and yearly rates of 1–3% loss. Rehabilitation programs employ two strategies: seafront planting and pond reversion. Seafront planting is necessary because coastal populations will not move to safer ground by choice, or cannot move due to poverty, and is also preferred because the sites are open access with no tenurial conflicts. However, former sites of fringing mangroves are difficult to rehabilitate as their lower intertidal–subtidal levels are not optimal for mangroves (due to frequent inundation and wave action). Planting in tidal flats and seagrass beds is also ecologically misguided. This chapter evaluates the relevant mainstream and gray literature (on site and species selection, propagule sources, nursery protocols, outplanting techniques, biophysical/anthropogenic threats, and novel interventions, e.g., integrated approaches using barriers) to improve the low survival rates of seafront planting. However, this strategy should not preclude the long-term relocation of coastal communities to safer ground and the politically difficult option of pond reversion. Given thousands of hectares of underutilized and abandoned brackish water ponds in Southeast Asia, this option holds greater potential for rehabilitation of wide areas of mangroves and greater species diversity. It is ecologically easier as it merely requires restoring hydrology (by breaking pond dikes); mangrove recruitment and succession naturally follow (if propagule sources are present) in these ponds located at mid-upper intertidal levels where mangroves naturally occur. The Philippines, with its long history of mangrove–pond conversion and problematic enforcement of laws that mandate mangrove reversion of idle ponds, is examined as a case study. The chapter assesses the Fishpond Lease Agreement (FLA) system by which vast expanses of mangroves were transferred from the public domain (government-leased ponds) to private ownership and recommends ways to improve the FLA system

Prop root production response of planted Rhizophora to abrupt subsidence-induced sea level rise

The 7.2 Mw Bohol earthquake in 2013 caused significant ground subsidence in some coastal zones northwest of the province, shifting the tidal inundation regime of intertidal habitats. These habitats included more than 500 ha of mangrove plantations particularly in island barangays which substrates are now 85% inundated annually from the 40% pre-quake conditions. Consequently, in less than three years after the quake, the effort of the subsided individual trees to produce new prop roots above the pre-quake height limits was found to be immediate, substantial, and tidally-linked. This prop root response resulted in an increase in the total length and volume by 74% and 39%, respectively, at 2.5-year post-quake relative to the 20-year pre-quake cumulative. With a mean elongation rate of ca. 1.1 m y−1, some 1.5–2.2 year period was necessary for these new prop roots to reach the substrate, and effectively establish a new equilibrium. The results highlight the role of prop roots on the aeration and stability requirements of Rhizophora, and provide quantitative evidence against the common practice of harvesting prop roots for firewood, charcoal, and other various purposes. The study presents a short-term glimpse of the prop root response of Rhizophora to the otherwise long-term gradual process of sea level rise. © 2017 Elsevier Lt

Attributes of the earthquake-uplifted intertidal habitats and their implications to the Maribojoc and Loon coastal fisheries

Other than the devastating impact on infrastructures and human lives, the 7.2Mw earthquake that shook Bohol and its vicinity in October 2013 also apparently caused massive damage on the coastal habitats: (1) collapse of many coral reefs/domes compromised by underwater cracks, mostly\u3e1m wide, traversing the numerous reef formations; (2) substantial ground subsidence (i.e., \u3e1m in Tubigon and vicinity) with sea-level-rise implications to the existing mangroves and seagrass beds, and, (3) massive loss of intertidal habitats due significant ground uplift, drying up extensive areas of mangroves, seagrass beds, sandflats, and rocky shores particularly in the municipalities of Maribojoc and Loon. This paper provides quantification of the attributes of the uplifted area, determining the pre-quake extent of the intertidal habitats, and attempting to reconstruct some intertidal community assemblages based on post-quake artefacts. We determined the total extent of the intertidal area severely affected by the ground uplift amounting to \u3e400ha, comprised of mangroves (42 ha; 10%), seagrass beds (135 ha; 32%), reef slope corals (148; 35%), and intertidal sandflats, mudflats and rocky habitats (altogether, 94 ha; 22%). This impact may be grossly translated to a US$ 4.4 million of economic loss annually. Our ground elevation- and transect truthing surveys of habitat artefacts generally validated our areal approximations. Also, across these transects, we confirmed speciose pre-quake assemblage of important invertebrates and other taxa occurring in these intertidal areas. In strong contrast to the exposed seagrass beds and coral areas, which were already all dried-up and died, most mangroves were still surviving after 8 months post uplift (i.e., practically no more tidal inundation since Oct 2013), albeit now in strong competition against the aggressive colonization of terrestrial plants. We recommend the close monitoring of the fate of the surviving mangroves and the likely transformation of such into completely terrestrial ecosystems. We likewise recommend the close monitoring of the coastal fisheries as may be linked to such post-quake loss of intertidal habitats, and carefully design management measures to mitigate such impact. © 2015 Elsevier Ltd

Impact of Haiyan on Philippine mangroves: Implications to the fate of the widespread monospecific Rhizophora plantations against strong typhoons

In the aftermath of super typhoon Haiyan, which devastated central Philippines on 08 November 2013, mangroves gained renewed national interest. Other than claiming thousands of lives and displacing millions of people, Haiyan wrought massive damage to infrastructure, crops, and coastal systems including mangroves. In this paper, the impact of Haiyan on mangroves across the entire impact corridor (i.e., Samar-Palawan stretch; broad-scale survey) was assessed, with particular focus on the planted Rhizophora cohorts (various forest age; detailed assessment) in Bantayan Island, typical of the massive planting programs in the country. Of the 21 mangrove species recorded within the impact corridor encompassing some 28,000 ha of heavily defoliated forests, the large-sized (older) Rhizophora spp. individuals were generally unable to produce epicormic sprouts resulting in mass mortality, in contrast to the other dominant mangrove taxa with high epicormic resprouting potential (e.g., Sonneratia, Avicennia, and Aegiceras). Focusing on the Bantayan cohorts, this paper found that, overall, 45% of the existing 20-ha, multi-aged Rhizophora plantations was severely damaged by typhoon Haiyan, but with mortality gradient being clearly directly related with stand age, i.e., for those \u3e32 yr old, mortality was massive (\u3e95%), while those \u3c 8 yr old, although similarly totally defoliated, full recovery was attained \u3c 2 years after Haiyan. Within old plantations, this paper also found significant differences in the mortality of trees in the core and in the periphery. These findings (1) offer a number of insights on the general age-frequency distribution and the growth architecture of Rhizophora spp. vis-a-vis other mangrove species within typhoon belts in the Philippines and in other countries with similar circumstances, and (2) demonstrate the high vulnerability of Rhizophora plantations against super typhoons, eventually suffering mass mortality upon attaining certain age threshold (\u3e32 yr). Thus, the post-Haiyan mangrove enhancement practices which still insist to prefer Rhizophora as the main taxa for planting, must be seriously reconsidered to avoid similar fate, taking into account the wind exposure - growth and forest architecture dynamics, as Haiyan uniquely demonstrated in this paper. © 2016 Elsevier Lt

Priority reef areas in the Pacific Coast of the Philippines for marine protected area deployment

The present paper seeks to provide a scientific basis for the establishment of marine protected areas (MPA) through an integrated and objective analysis of biodiversity survey data, which permits ranking of various sites in order of their importance as potential MPA. The approach proposed here involves the determination of biodiversity values for each of the four taxonomic groups (corals, reef fishes, seagrasses and seaweeds) and an assessment of the levels of risk for each of the survey sites to human degradation and natural disturbance. The biodiversity and risk scores were then combined into one MPA priority score using a conversion table. Five of the 17 geographic units (mostly small islands) stand out as high priority sites for conservation: Biri in Northern Samar; Ticao and Palaguigue Islands in Masbate; Pujada Bay, Davao Oriental; Homonhon and Suluan Islands, Eastern Samar; and Laoang, Northern Samar. The approach described here provides a framework by which an objective, repeatable prioritization of conservation value of various areas could be undertaken. Although the final measures are not absolute, it allows one to make explicit the assumptions made about the characters and measures used in prioritization and assign relative weights to various species, taxonomic groups and data sets, thereby reducing the impact of an observer\u27s subjectivity

Estimating biomass from the cover of Gelidiella acerosa along the coasts of Eastern Philippines

In three Gelidiella acerosa beds on the poorly-studied eastern coasts of the Philippines, cover and biomass of this commercially important agar-producing red alga were measured. The three selected G. acerosa beds represented low (mean cover \u3c 5%), medium (approximately 10%) and high cover (\u3e 20%) vegetation. In each of the sites, we estimated the cover of G. acerosa fronds within 10 x 10 cm grids (n ranged from 33-36) in various strata. All G. acerosa fronds within each grid were harvested, cleaned of attached epiphytes and sediments, and subsequently, oven-dried at 60°C to constant weight. We applied regression analysis to establish empirical relationships between cover and biomass. All linear regression lines were highly significant (p \u3c 0.001, R2 \u3e 0.6) indicating that biomass could be confidently estimated from cover estimates: low cover (y = 0.017 + 0.310; R 2 = 0.67, p \u3c 0.0001), medium cover (y = 0.0363x + 0.118, R 2 = 0.83, p \u3c 0.0001) and high cover (y = 0.0304x + 0.481, R 2 = 0.80, p \u3c 0.0001). Evidently though, sites with higher overall mean cover (also longer thalli) had significantly steeper regression slopes, which was most pronounced when comparing sites with the lowest (\u3c 5%) and highest (\u3e 20%) mean cover. Nevertheless, we subsequently projected a minimum annual yield from the known 51 ha along the eastern coasts amounting to, at a minimum, 23 t dw y-1. Such yield may translate to approximately 68.8 million pesos (US$ 1.38 million) in gross sales of agar

I-C-SEA change: A participatory tool for rapid assessment of vulnerability of tropical coastal communities to climate change impacts

We present a synoptic, participatory vulnerability assessment tool to help identify the likely impacts of climate change and human activity in coastal areas and begin discussions among stakeholders on the coping and adaptation measures necessary to minimize these impacts. Vulnerability assessment tools are most needed in the tropical Indo-Pacific, where burgeoning populations and inequitable economic growth place even greater burdens on natural resources and support ecosystems. The Integrated Coastal Sensitivity, Exposure, and Adaptive Capacity for Climate Change (I-C-SEA Change) tool is built around a series of scoring rubrics to guide non-specialists in assigning scores to the sensitivity and adaptive capacity components of vulnerability, particularly for coral reef, seagrass, and mangrove habitats, along with fisheries and coastal integrity. These scores are then weighed against threat or exposure to climate-related impacts such as marine flooding and erosion. The tool provides opportunities for learning by engaging more stakeholders in participatory planning and group decision-making. It also allows for information to be collated and processed during a “town-hall” meeting, facilitating further discussion, data validation, and even interactive scenario building. © 2015, Royal Swedish Academy of Sciences