Marine Atlas: Maximizing Benefits for Solomon Islands

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HOME, SWEET HOME: COASTAL HABITATS Solomon Islands’ famous hospitality extends to the thousands of species that call its coral reefs, mangroves and seagrasses home. These habitats house countless plants and animals that store carbon and help protect Solomon Islands’ coastal inhabitants.

Coral reefs in Solomon Islands have some of the highest diversity in the world, with almost 500 different coral species (TNC, 2004). Solomon Islands is the easternmost part of the Coral Triangle, the world’s coral biodiversity hotspot, which also includes Indonesia, Malaysia, Papua New Guinea and Timor-Leste. Seagrass beds are highly diverse and pro- ductive ecosystems that can harbour hun- dreds of associated species from all phyla, for example, juvenile and adult fish, epiphytic and free-living macroalgae and microalgae, molluscs, bristle worms, and nematodes. These beds occur in the sheltered waters of many islands of Solomon Islands. In a 2004 survey, 10 species of seagrass were found, representing 80 per cent of all seagrass spe- cies in the Indo-Pacific region (TNC, 2004). Some seagrass meadows measured up to 1,000 hectares in size, while others were 37 metres in depth (TNC, 2004). However, sea- grass maps have not been presented in the map of coastal habitats as there are currently no comprehensive publicly available data that adequately capture the distribution of sea- grass in Solomon Islands. Although coastal habitats are some of the most productive and valuable marine habitats, they are also some of the habitats most vulnerable to human activities (see also chapters “Reefs at risk”, “From ridge to reef” and “Turning sour”). These habitats therefore require special consideration in the management of human activities.

The previous set of maps in the “Support- ing values” section of the report took us on a journey from the ocean floor all the way to the surface, demonstrating the colourful biophysical features of Solomon Islands’ waters. While they are fascinating in their own right, the combination of features such as bathymetry, geomorphology, currents, nutrients and plankton are also important factors in the distribution and health of Solo- mon Islands’ coastal habitats. Coastal protection is a key ecosystem service with two components: the preven- tion of erosion and the mitigation of storm surges. Coastal ecosystems prevent coastal erosion by reducing the effects of waves and currents and also helping regulate the removal and deposition of sediment (erosion and accretion). Furthermore, they provide increased short-term protection against ep- isodic events, including coastal floods and storm surges. The benefits of this protection against extreme weather events include minimizing damage to homes, buildings and other coastal infrastructure and on important resources such as crops. Residents of Solomon Islands came to realize these benefits in May 1986, when Tropical Cyclone Namu devastated many of the nation’s islands. Cyclone Namu is consid- ered to be the worst tropical cyclone to have affected Solomon Islands on record, with over 150 fatalities reported. However, without the protection that coral reefs and mangroves provide to most of Solomon Islands, the damage could have been a lot worse. Every year, reefs and mangroves mitigate damage to houses and hotels across Solomon Islands by up to SI$58 million (Arena, 2015), demon- strating just how valuable marine and coastal ecosystem services are to Solomon Islands.

Coastal habitats such as mangrove forests, seagrass beds and coral reefs play an impor- tant role in stabilizing shorelines. As human density increases however, so too does the impact on these important coastal habitats. The role of mangroves in coastal stabilization is well known. They protect coastal areas from erosion, storm surges (especially during cyclones) and tsunamis. Their massive root systems are efficient at dissipating wave energy and slow down tidal water so that suspended sediment is deposited as the tide comes in, with only the fine particles resuspended as the tide recedes. In this way, mangroves help build their own envi- ronment. Given the uniqueness of mangrove ecosystems and the protection they provide against erosion, they are often the subject of conservation programmes and are commonly included in national biodiversity action plans.

the coastal areas they colonize. Their leaves can also slow currents, and their roots and rhizomes trap the sediments in which they grow, thereby enhancing the stability of the substrate. Seagrasses can also dissipate the energy of waves by up to 40 per cent, which can in turn increase the rate of sedimentation. As such, seagrass beds effectively help pro- tect against waves and limit coastal erosion. In addition to protecting the coast, Solomon Islands’ coastal habitats also act as nursery areas for fish and support food security, live- lihoods, tourism and other human activities. Based on village-derived economic data, it is estimated that a minimum annual subsist- ence value of US$345–1,501 per household is generated from mangroves in Solomon Islands (Warren-Rhodes et al., 2011). Sea- grass meadows and mangroves are also recognized as important carbon stores, with the preservation of healthy mangrove sys- tems contributing to climate change action. Mangroves are Solomon Islands most ex-

tensive type of wetland vegetation (Bani and Esrom, 1993), with forests covering almost 65,000 hectares and containing around 25 mangrove species (Warren-Rhodes et al., 2011). The social benefit of carbon seques- tration by mangroves in Solomon Islands’ EEZ is estimated to be worth up to SI$162 million (Arena, 2015). The map of coastal habitats presents the distribution of coral reefs and mangroves. Shallow coral reefs form some of the most diverse ecosystems on Earth. Despite occu- pying less than 0.1 per cent of the world’s ocean surface, they provide a home for at least 25 per cent of all marine species, in- cluding fish, molluscs, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs provide many bene- fits to people living in coastal areas, includ- ing food provision, supporting artisanal and commercial fisheries, tourism opportunities and coastal protection. Solomon Islands is surrounded by fringing and barrier reefs.

Seagrasses are another important coastal habitat that form extensive meadows in

MAXIMIZING BENEFITS FOR SOLOMON ISLANDS

OCEAN VALUES

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