Anthropogenic Disturbance of Caribbean Mangrove Ecosystems: Past Impacts, Present Trends, and Future Predictions

Study Number:

58

Author:

A. M. Ellison & E. J. Farnsworth

Abstract:

We review historical, current, and projected future impacts of four classes of anthropogenic disturbance-extraction, pollution, reclamation (coastal development), and changing climate on Caribbean mangrove ecosystems (mangal). These disturbances occur, respectively, at increasing spatial and temporal scales, and require increasing recovery time. Small-scale selective extraction has little system-wide effect, but regeneration is slow even on single hectare clear-cuts (deforestation) due to rapid soil acidification. Petroleum is the primary pollutant of Caribbean mangal, and results in tree defoliation, stand death, and loss of associated sessile and mobile animal species. Hydrocarbons persist in mangrove sediments for decades, and are correlated with increasing seedling mutation rates (extinction). Chemical, industrial, and urban wastes are associated with increased heavy metal content of seedlings, stand die-back, reduced system-wide species richness (extinction), and higher incidence of Vibrio spp. (shellfish poisoning). Mangal has been reclaimed for urbanization, industrialization, and increasingly, for tourism (coastal development). Overall, the region is losing mangrove forests at 1 percent per yr, although the rate is much faster on the Caribbean mainland (- 1.7% yr-1) than it is on the islands (=0.2% yr-1). The region’s fisheries are declining at a similar rate, as most commercial shellfish and finfish use mangal for nurseries and/or refugia. Few Caribbean states have legislation or enforcement capabilities to protect or manage mangal, although at least 11 international treaties and conventions could be applied to conserve or sustainably use these forests. These treaties may protect riverine and basin mangal, but are likely to be moot with respect to fringing mangal, which may vanish as a consequence of global climate change. Growth enhancements of mangroves resulting from increasing atmospheric CO2 probably will not compensate for negative effects of concomitant rises in regional sea level. 

Main Results and Conclusions:

• Thirty-two countries were surveyed for mangrove habitat coverage (see Table 1).
• Natural history and mangrove coverage in the Caribbean:
  • In 1990, 13,501 km2 of mangrove habitat remained; “Coastline length and mangrove area data for Colombia, Costa Rica, Guatemala, Honduras, Nicaragua, and Panama’ are lengths and areal extent only for Caribbean coastlines…Data from Groombridge (1992), Lugo & Bayle (1992), Alvarez-Leon (1993), Bacon (1993c), D’Croz (1993), Polanfa (1993), Garrity et al. (1994), and Giglioli (1994). NA: data unavailable” (Table 1, 551).
  • “Based on the data presented in Table 1, overall mangal area in the Caribbean declined by -10 percent during the 1980’s. Mangal area declined by -17 percent on the mainland, but by only -2 percent on the islands”(552). 
• Anthropogenic Disturbances:
  • Extraction – any form of moderate/sustainable extraction of mangrove resources does not yield devastating consequences. Large-scale extraction of mangrove forest (deforestation), however, results in “rapid soil sulfide accumulation and subsequent soil acidification (Hamilton & Snedaker 1984).” Additionally, fishery yields may become damaged by mangrove forest extraction because it causes a loss of juvenile fish habitat (553).
  • Pollution—
    • “[Petroleum] oil pollution resulting from off- shore oil exploration and production, pipelines, tanker accidents, and intentional clearing of ship’s ballast tanks affects mangal throughout the Caribbean (reviews in Rodriguez 1981, Burns et al. 1993, IUCN 1993a)”(553). Dozens of oil spills have occurred in the Caribbean since the 1980s, and, in some cases such as an oil spill at Galteta, Panama, causing mangrove forests to experience “massive tree defoliation, followed by seedling, sapling, and tree death…(Garrity et al 1994)”(553). Mangrove rehabilitation after oil spills is virtually non-existent due to the difficulty in growing mangroves in oil-polluted areas.
    • Thermal pollution from power-plant cooling systems also affects mangroves negatively (554).
    • Other pollutants identified in the paper (cited from other studies) include: mercury, mine tailings and compounds, sewage, urban runoff, pesticide contamination, N2O, and sedimentation from urban (coastal) development (554-555). 
  • Reclamation – this involves transforming mangrove habitat into urban development spaces (coastal development). Massive reclamation projects have been enacted in many countries throughout the Caribbean including Columbia and Venezuela (555). Tourism has also played a role in massive reclamation projects (mangrove forest conversion into resorts, golf courses, etc.) (555).
  • Climate Change – while rising sea level may negatively affect certain mangrove habitats where recession is impossible due to anthropogenic obstacles or improper soil composition, rising CO2 levels may help compound these negative effects, but only slightly (557-558). Higher atmospheric temperatures may also negatively affect mangrove forests (557).
• Mangrove conservation varies among the countries in the Caribbean (558). Up to 11 international treaties could be used to protect mangroves in the Caribbean and up to six could be used to for indigenous use and/or (sensitive) ecotourism (560). Table 3 lists multiple treaties that either have or have not been ratified by countries both within and outside the Caribbean (559).
   

Works Cited:

Alvarez-LEON, R. 1993. Mangrove ecosystems of Colombia. In L. D. Lacerda (Ed.). Conservation and sustainable utilization of mangrove forests in Latin America and Africa regions. Part I-Latin America, pp. 75-114. International Society for Mangrove Ecosystems, Okinawa.

Bacon, P. R. 1975. Recovery of a Trinidadian mangrove swamp from attempted reclamation. In G. E. Walsh, S. C. Snedaker, and H. J. Teas (Eds.). Proceedings of the international symposium on biology and management of mangroves, pp. 805-815. Institute of Food and Agricultural Sciences, Univ. of Florida, Gainesville.

Burns, K. A., S. D. Garrity, and S. C. Levings. 1993. How many years until mangrove ecosystems recover from cata- strophic oil spills? Mar. Poll. Bull. 26(5): 239-248.

D’Croz, L. 1993. Status and uses of mangroves in the Republic of Panama. In L. D. Lacerda (Ed.). Conservation and sustainable utilization of mangrove forests in Latin America and Africa regions. Part I-Latin America, pp. 115-128. International Society for Mangrove Ecosystems, Okinawa.

Garrity, S. D., S. C. Levings, and K. A. Burns. 1994. The Galeta oil spill. I. Long-term effects on the physical structure of the mangrove fringe. Est., Coast. Shelf Sci. 38: 327-348.

Giglioli, M. E. C. 1994. The boom years in Grand Cayman: environmental deterioration and conservation. In M. A. Brunt and J. E. Davies (Eds.). The Cayman Islands: natural history and biogeography, pp. 509-526. Kluwer Academic Publishers, Dordrecht.