Guyana efforts to restore its degraded coastal mangrove forests are showing signs of ecological recovery, with a new study finding that restored mangroves aged between five and 11 years supported fish communities broadly similar to those found in naturally regenerated forests.
The findings, published in Restoration Ecology, follow a major restoration programme in which more than 500,000 mangrove seedlings were planted across 19 sites covering about eight kilometres of Guyana’s coastline.
Researchers compared five restored mangrove sites with five naturally regenerated sites of similar ages. The forests represented stands that were five, six, nine, 10 and 11 years old. Fish were sampled during both wet and dry seasons and during daytime and nighttime.
The survey recorded 559 fish belonging to 14 families and 18 species. Researchers found no significant differences in fish abundance between restored and natural mangroves. They also found no clear relationship between the age of a mangrove stand and the number of fish it supported.
Five species accounted for about 94% of the total catch. Sciades couma was the most abundant species, followed by Anableps anableps, Sciades herzbergii, Amphiarius rugispinis and Colomesus psittacus.
Restored forests contained about 90% of the fish species recorded in the natural mangroves. Statistical analysis also found no significant difference in fish community composition based on whether the habitat was restored or naturally regenerated, its age, season or time of sampling.
The results challenged the researchers’ expectation that older mangroves would consistently support greater fish abundance and species richness. Some younger restored forests recorded relatively high numbers of fish, suggesting that aquatic species were able to occupy the restored habitats relatively early in their development.
Guyana’s restoration programme began against a backdrop of extensive mangrove loss. The country’s coastal mangrove belt was estimated to cover about 150,000 hectares in 1983, but reported coverage declined to approximately 81,000 hectares by 1992 and 22,000 hectares by 2011. Natural erosion, harvesting, excessive siltation and coastal pollution contributed to the decline.
The government launched the Guyana Mangrove Restoration Project in 2010, planting more than 500,000 Avicennia germinans, or black mangrove, seedlings along the coast.
The restored and natural forests were not identical, however. Natural mangroves contained black, white and red mangrove species, while restored areas were largely dominated by black mangroves. The study recorded Avicennia germinans, Laguncularia racemosa and Rhizophora mangle across the sites.
Restored stands were denser overall, with 894 trees recorded compared with 446 in natural forests. Natural mangroves, however, had a 52.1% higher density of Rhizophora mangle. They were also slightly taller on average, reaching about 12.52 metres compared with 11 metres in restored areas, and had larger average trunk diameters.
Despite these structural differences, the fish communities showed no statistically significant separation between restored and natural habitats.
The researchers caution that the findings should not be interpreted as evidence that young restored forests are already ecological equivalents of mature natural mangroves. Differences in tree species, canopy development and root structure remain, and these features can change substantially as forests mature.
The study nevertheless indicates that mangrove restoration can recreate important aquatic habitat relatively quickly. The early arrival of fish communities suggests that restoring coastal vegetation may help re-establish some ecological functions even while the forest itself continues to develop.
The findings also highlight the importance of long term monitoring. Whether restored mangroves eventually develop the full structural complexity and broader ecological functions of natural forests will require observations extending well beyond the first decade of restoration.