Recognising the Importance of Our Seagrass Meadows
March 1, 2023 marks the first-ever United Nations recognised World Seagrass Day. The day is being commemorated to raise public awareness on the importance of seagrass meadows and to recognise the importance of seagrasses to the health and well-being of the planet, as well as to the people, communities, flora and fauna that rely on them.
Seagrasses are marine flowering plants that grow in the intertidal and subtidal zones along shallow tropical and temperate coasts. They are very productive, faunally rich and ecologically important marine resources that provide nursery habitats for several commercially important species such as conch, fish and lobster and a major food source for the endangered manatee and sea turtles.
Seagrasses help capture and store carbon dioxide – the most commonly produced greenhouse gas and one of the main drivers of climate change – in the ocean. Despite occupying less than 0.2% of the ocean surface, seagrass ecosystems are responsible for 10–18% of the carbon stored in marine ecosystems (Kennedy et al. 2010). On the global scale, these ecosystems provide a carbon sink of 194.2 ± 20.2 MgC ha−1 in the top meter of soil (Fourqurean et al. 2012) and therefore assist with climate change mitigation.
Seagrasses are also semi-permeable filters that stabilize bottom sediments, slow current flow, prevent erosion and filter suspended solids and nutrients from coastal waters. However, these filters are becoming overloaded as land-use changes in the coastal catchment and in the nearshore environment are impacting negatively them. The increasing population density in coastal areas has enhanced sediment and nutrient loading and nutrient over-enrichment of coastal waters has been cited as the main reason for seagrass bed decline worldwide. According to a global assessment conducted by Waycott et al. in 2009, seagrasses have been disappearing at a rate of 110 km2 yr−1 since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879.
Since 2002, the Institute of Marine Affairs has been monitoring the health and productivity of selected Thalassia (turtle grass)dominated seagrass beds around the islands. The healthiest and most productive seagrass sites in the country were once found in Southwest Tobago at Buccoo Bay and Kilgwyn Bay. However, since 2015, the seagrass beds in Kilgwyn Bay had disappeared, coinciding with a Sargassum invasion. Since then, there has been very little recovery.
Sites within the Bon Accord Lagoon recorded the lowest biomass and density in Tobago, but while the monitored sites within the Lagoon are overgrown by macroalgae, seagrasses have spread into areas adjacent to Buccoo Reef. Seagrass coverage in the Buccoo Reef/ Bon Accord Lagoon Marine Protected Area has more than doubled within the past 20 years. The grasses have colonized the Nylon Pool, a very popular shallow, sandy area in the back reef zone where visitor are allowed to swim at the end of a glass boat tour.
In Trinidad, the most productive Thalassia site was once found at William’s Bay, Chaguaramas. This area was home to a diversity of species including fishes such as seahorses, juvenile grunts, groupers and snappers, green turtles and invertebrates such as starfish, conch, bivalves, crustaceans, polychaetes worms and urchins. Since 2012, declines in Thalassia biomass and productivity were observed, and today, it is completely gone; its demise coincided with development activities taking place on the peninsula.
Thalassia communities once found on the eastern side of St Peter’s Bay, Carenage was destroyed in 2010 while the community on the western side of the bay was destroyed in 2012. These areas are now overgrown with algae (Caulerpa sp.) and sparse communities of other seagrass species (Halodule wrightii and Halophila sp.). St Peter’s Bay has been impacted by land reclamation activities over the past decades and receives sediment-laden waters from the coastal catchment which have been deforested for housing.
Poor water quality from land-based pollution and coastal development are the main factors negatively impacting the health of seagrasses in Trinidad and Tobago. The beds in Trinidad, which are found along the most intensely developed coastline, continue to be subjected to development pressures from the coastal catchment. Loss of seagrass beds would result in loss of their ecosystem services such as coastal protection, habitat and nursery for fish and other marine species. There is an urgent need to conserve, and in some areas rehabilitate our seagrass community to ensure that they can provide a haven for our rich biodiversity, protect our coastline and capture and store carbon dioxide.
In 2022, IMA initiated action to help rehabilitate degraded seagrass beds and coral reefs in Tobago. The Marine Resilience Initiative (MARIN), funded by British Petroleum Trinidad and Tobago (bpTT), started with an ecological assessment of seagrass beds in Southwest Tobago- Buccoo Reef Marine Park and Kilgwyn Bay. The seagrass beds were mapped using side scan sonar and their health and biodiversity assessed. Experimental seagrass rehabilitation work started using different replanting methods to determine suitability. This work is expected to continue over the next five years and IMA is hoping that the knowledge gained in seagrass rehabilitation techniques will be extended to other sites in Tobago, Trinidad and the Caribbean Region.
Successful restoration of any ecosystem will depend on us being able to remove the main stressor, which in this case is land-based sources of pollution and promoting ocean stewardship. Through the MARIN project, IMA is aiming to build connections between communities and their ocean backyard through baseline understanding, inclusion, education and embedding stewardship into communities. This will overlap with ongoing practical restoration in locations of active stewardship and involve knowledge transfer and capacity building. The anticipated plan and partnerships will deliver long-term marine biodiversity conservation for our seagrass ecosystem.
Join us as we celebrate ‘World Seagrass Day’ and help us restore our degraded seagrass beds. “We know that when we protect our oceans we’re protecting our future.” — President Bill Clinton