A study spanning 3,000km of East African coastline finds that seagrass meadows support disproportionately high numbers of important food fish and may play an overlooked role in coastal nutrition and food security.
Lutjanus fulviflamma or dory snapper (also known as blackspot snapper) is one of the main fishery species in coastal East Africa.
Coral reefs may contain more fish overall, but neighbouring seagrass meadows can provide considerably more of the species that matter most for feeding coastal communities, according to new research.
Scientists studying fish communities from Kenya to Mozambique found that seagrass-associated fish provided a richer combination of essential micronutrients than those associated with nearby coral reefs. For three of the region's most important food-fish species, the potential nutritional contribution was more than eight times greater in seagrass meadows.
Comparing reefs and seagrass
The researchers compared fish communities at 20 seagrass meadows and 20 coral reefs along approximately 3,000km of East African coastline.
Rather than measuring fish abundance alone, they assessed the potential supply of six nutrients important to human health: calcium, iron, zinc, selenium, vitamin A and omega-3 fatty acids.
The distinction matters. Coral reefs supported greater overall fish biomass, but the seagrass fish communities were, on average, 1.6 times more nutritionally multifunctional—meaning they potentially supplied a better combination of the six nutrients studied.
The difference became considerably greater when researchers examined three particularly important regional food fishes. Their predicted nutrient contribution was 8.4 times higher in unfished seagrass meadows than on unfished reefs, and 8.8 times higher where fishing occurred.
Two commonly eaten species illustrate the difference. The shoemaker spinefoot (Siganus sutor), a rabbitfish, had five times greater biomass in seagrass, while the marbled parrotfish (Leptoscarus vaigiensis) had 65 times greater biomass there than on neighbouring reefs.
An overlooked food system
Seagrass meadows have increasingly been recognised for storing carbon, providing nursery habitat and stabilising sediments, but their contribution to human nutrition has received considerably less attention.
This may be particularly important in coastal communities where small-scale fisheries provide essential micronutrients as well as protein. Seagrass fisheries can also be relatively accessible to people using simple fishing methods and without expensive boats or equipment.
The researchers argue that seagrass should therefore be considered not only as important marine habitat but as part of coastal food and public-health systems.
Not reefs versus seagrass
The findings do not suggest that conserving seagrass should take priority over coral reefs. Rather, they demonstrate that different habitats provide different ecological and human benefits.
Reefs support greater overall fish biomass, while seagrass appears particularly important for several food species and the nutrients they provide. Moreover, fish move between habitats, making reefs, seagrass beds and other coastal ecosystems parts of an interconnected seascape.
That makes protecting the connections between them as important as protecting individual habitats.
Yet seagrass meadows remain threatened by sewage and nutrient pollution, sediment runoff, coastal development and physical disturbance. The study suggests their loss could therefore have consequences extending beyond biodiversity and carbon storage to the nutrition of people who depend on coastal fisheries.
