The ecological basis for economic value of seafood production supported by mangrove ecosystems

Study Number:

59

Author:

P. Ronnback

Abstract:

The undervaluation of natural products and ecological services generated by mangrove ecosystems is a major driving force behind the conversion of this system into alternative uses. This trend of undervaluation is partly due to the difficulty involved in placing a monetary value on all relevant factors, but lack of ecological knowledge and a holistic approach among those performing the evaluation may be even more important determinants. This article identifies and synthesizes ecological and biophysical links of mangroves that sustain capture fisheries and aquaculture production. Fish, crustacean and mollusc species associated with mangroves are presented and the ecology of their direct use of this system is reviewed. Through a coastal seascape perspective, biophysical interactions among mangroves, seagrass beds and coral reefs are illustrated. The life-support functions of mangrove ecosystems also set the framework for sustainable aquaculture in these environments. Estimates of the annual market value of capture fisheries supported by mangroves ranges from US$750 to 16 750 per hectare, which illustrates the potential support value of mangroves. The value of mangroves in seafood production would further increase by additional research on subsistence fisheries, biophysical support to other ecosystems, and the mechanisms, which sustain aquaculture production.

Main Results and Conclusions:

• Table 1 lists over 50 ecosystem goods and services provided by mangroves (236).
• Many organisms utilize mangrove habitat including: dozens of fish species (Table 2, 239), crustaceans (shrimp and crab), and edible mollusks (oysters, mussels, cockles and gastropods) (239-240).
• Mangroves offer habitat for fish and shellfish:
  • “Mangroves are characterized by high abundance of fish, crustaceans and molluscs. Fish standing stock, ranging from 4 to 25 g m-2 in intertidal mangrove habitat (reviewed by Ronnback et al., 1999), is much higher in mangrove habitat compared to adjacent coastal habitats (Robertson and Duke, 1987; Thayer et al., 1987; Blaber et al., 1989; Morton, 1990; Robertson and Duke, 1990)” (240).
  • Fish and shellfish most likely congregate in mangrove habitat due to “food abundance, shelter from predation, and hydrodynamic ability of mangroves to retain immigrating larvae and juveniles (Fig. 1)” (240). These three characteristics of mangrove habitat are discussed in more detail in pages 241-242.
• Biophysical interactions with other costal ecosystems:
  • Interactions among mangroves, seagrass beds and coral reefs are important to consider when managing and evaluating the economics of seafood production (242).
  • Interactions among these three types of habitats include: animal migrations, outwelling and physical interactions (242-243).
• Mangroves are extremely important in sustaining aquaculture production:
  • Mangroves provide insurance (storm and flood protection and erosion control), water quality maintenance (flood and erosion control, nutrient assimilation, and sediment trapping), food input (detritus and fishmeal), broodstock, and seed (Fig. 1, 238). Each of these services is discussed in more detail on pages 244-245.
• Mangroves play a significant economic role in seafood production:
  • Table 3 lists areas with their corresponding production, market price, and value (along with the sources for each study) of crustaceans, fish and mollusks associated with mangrove habitat (246).
  • “Estimates of annual economic value per hectare of mangrove ranges from US$91 (1 ha of mangrove supports a penaeid fishery production of 13 kg) to US$5292 (1 ha supports 756 kg) (Table 3). This high variability in shrimp productivity can be attributed to regional variations in the quality of the mangrove nursery, underreporting of fisheries catch, underdeveloped or overdeveloped shrimp fisheries” (245, 247).
  • “The average annual penaeid production, based on 43 data sets (summarized in Table 3), is 162 kg: ha mangrove, estimated at US$1134 (based on a market price of US$7.00: kg)” (247).
  • “The market value of commercial fish species utilising mangroves as habitat ranges from US$475 to 5330 ha: year (Table 3)” (247).
  • Economics regarding biophysical interactions between mangrove ecosystems and fisheries as well as aquaculture practices is also discussed on pages 247-248.
• Economic summary: “For crustaceans (penaeid shrimp, sergestid shrimps and mangrove mud crab), fish and molluscs that use mangroves as habitat the annual market value of fisheries per hectare mangrove ranges from US$750 to 11 280. If discarded catch in shrimp fisheries and other trawl fisheries subsidized by the penaeid fishery are included, the marketed value of fisheries dependent on mangroves ranges from US$850 to 16 750: ha per year” (248).
   

Works Cited:

Blaber, S.J.M., Brewer, D.T., Salini, J.P., 1989. Species composition and biomasses of fishes in different habitats of a tropical northern Australian estuary: their occurrence in the adjoining sea and estuarine dependence. Estuarine Coastal Shelf Sci. 29, 509–531.

Morton, R.M., 1990. Community structure, density and standing crop of fishes in a subtropical Australian mangrove area. Mar. Biol. 105, 385–394.

Robertson, A.I., Duke, N.C., 1987. Mangroves as nursery sites: comparisons of the abundance and species composition of fish and crustaceans in mangroves and other nearshore habitats in tropical Australia. Mar. Biol. 96, 193–205.

Robertson, A.I., Duke, N.C., 1990. Mangrove fish-communities in tropical Queensland, Australia: spatial and temporal patterns in densities, biomass and community structure. Mar. Biol. 104, 369–379.

Ronnback, P.,Troell, M., Kautsky, N., Primavera, J.H.P., 1999. Distribution pattern of shrimps and fish among Avicennia and Rhizophora microhabitats in the Pagbilao mangroves, Philippines. Estuarine Coastal Shelf Sci. 48, 223–234.

Thayer, G.W., Colby, D.R., Hettler, W.F., 1987. Utilization of the red mangrove prop root habitat by fishes in south Florida. Mar. Ecol. Progr. Ser. 35, 25–38.