Why Plants Matter: Seagrass Is the Primary Food Source for Green Sea Turtles, Dugongs, and Manatees





Seagrass Is the Primary Food Source for Green Sea Turtles, Dugongs, and Manatees

Meeting Harvard Fellow & Botanist, Barnabas Daru

October 7, 2016

I met Barnabas Daru in front of the herbarium building at Harvard. As we walked towards the cafeteria, he began telling me that the most basic of all life and food source are plants. Barnabas explained “Chloroplasts in seagrasses and all plant tissues use the sun’s energy to convert carbon dioxide and water into sugar and oxygen for growth through the process of photosynthesis. This sugar or carbohydrate in turn helps sustain the animals and people that eat them.”

We got to the cafe and sat outside on this sunny day, everything looked extra green. “No one really thinks about plants as being an important element, they are always there and really not noticed. When a Rhino gets killed the media makes a fuss, the conservationist are all up in arms. When a tree is chopped down, no one notices, it’s not as important. Yet that tree has provided nutrition, shelter and value that equals the animal life.”



Barnabas has been trying to solve this puzzle for several years now. For grad. school in South Africa, Barnabas extracted DNA from different trees to see how they were related.

“What was fascinating was that you could visually look at trees and see similarities outwardly and assume they had to be related. However, when you looked at their DNA, it could be a different story; they could be from completely different families. It was really amazing seeing how we could be fooled by appearances alone.”

Barnabas looked at the genetic diversity of all trees in seven different countries in Africa. Sequencing DNA gave him unique insight about the distribution of trees – more exciting patterns of family (phylogenetic) relationships of the species emerged. Barnabas hopes to use phylogenetic data to help magnify the need to protect endangered plant life the same way we protect endangered animal life and in turn result in global policy change.

After grad school Barnabas became more excited about plants and decided to expand his research to global scale, by moving into the sea to study seagrasses and mangroves. “Both are flowering plants that live in or near sea water. Mangroves are woody plants that border between land and sea, and seagrasses live submerged in salty shallow water”, he said excitedly. Up until that time there were only “distribution data” (geographical maps). Barnabas was interested in examining the phylogenetic (DNA) tree in addition to mapping seagrasses and mangroves. Barnabas’s goal identified BIODIVERSITY HOTSPOTS for marine plants for the first time [see map pictured]. These are areas where the seagrass and mangrove species are at high risk of extinction or have unique phylogenetic diversity. To Barnabas’s surprise, the DNA data revealed that some areas thought to be rich in species-level diversity e.g. South Africa or the Mediterranean did not emerge as hotspots for marine plants. The seagrasses they found in these areas came from an abundant family lineage. The study (http://dx.doi.org/10.1111/geb.12412) instead pointed to Chile, Hawaii, Bermuda area, Florida, Southern Australia and Central Indo-Pacific as high risk areas or places with unique species. “Sadly, these newly defined marine plants hotspots are not protected by the network of Marine Reserves.”



“Ultimately I hope the scientific data will bring about awareness about the huge need for policy change. How we need conservation funds to also go to these endemic regions to help support these high risk plants that in turn feed and shelter animals. Once these plants disappear the whole food chain will be affected: the fish that lay their eggs, the dugongs that solely eat seagrass, all the life that depend on the nutrients of these plants. The rich diversity we have now will disappear.”



  1. Seagrass is a primary food source:sea-turtle-547163_640

Dugongs, manatees, and green turtles depend on seagrass for their nutrition. If seagrass in these threatened areas disappears, these amazing animals will have huge disruptions in the food chain. Many will die. This will have a cascading impact on the food chain: sharks, fish and so on will all be affected.

  1. Seagrass is a carbon sequester

With high levels of carbon dioxide in our environment, seagrass is a huge CO2 absorber. It sequesters blue carbon and can soak up to 50% of the ocean’s CO2.

  1. Seagrass meadows are nurseries:

Various types of fish use seagrasses as substrate to lay their eggs. If there were no seagrasses, their stringy eggs would be laid directly on the ocean floor, and can easily be swept away by underwater currents. These eggs attach to the seagrass substrate and are vital for the development of the young fish when they hatch. Not to mention all the protection they provide for shelled mollusks.


I would say that the general public upon sighting any seagrass on the ocean’s shore, should at least take a photo and GPS locality of the specimen and consider sending it to any botanical institute e.g. the Harvard University Herbaria. Those could be clues toward understanding their distributions under the changing climate.


Marine reserves areas are marine protected areas where boating, dredging, fishing and other activities are prohibited in order to protect the species that live there. Conservation funds and efforts tend to focus on marine animals rather than plants. Barnabas noted in his study [linked http://dx.doi.org/10.1111/geb.12412] that marine plants are only incidentally included in the marine reserve system. His goal is to help expand marine reserves to protect the mangroves and seagrass too. By collecting both DNA (phylogenetic) and distribution data, he hopes to generate a scientific plea to the scientific community to help expand definitions of marine reserves to cover marine plants too. Policy makers need to become aware of the key role seagrasses play in the ecosystem. How in monetary terms seagrass and mangroves contribute $5.4 billion worth of ecosystem services.

“We need to have a holistic view to look at the global issues and then take action on both a global and local levels.”

What an amazing way to share my Friday morning, thank you for sharing Dr. Barnabas Daru!


More info on Barnabas Daru can be found:

Strong case for seagrass