Beneath the Surface: The Secret Life of Seagrass and Soft Sediments

Info Graphic by Shaun Lee

Guest Blog 

By Ingrid O’Sullivan and Rebecca Gladstone-Gallagher 

Institute of Marine Science, University of Auckland 

Ingrid O’Sullivan – Research Engagement Manager 

At the University of Auckland’s Institute of Marine Science, I have the privilege of working alongside incredible researchers like Rebecca Gladstone-Gallagher. My background is in ocean law and policy, so I came into this role thinking I had an okay grasp of the ocean’s importance. But I’ve been truly humbled. 

Since joining the Institute, I’ve had my mind blown by the sheer scale and significance of marine ecosystems—not just for life in the ocean, but for life on land as well.  Life in the ocean is deeply connected to the systems that support life on land—from the food we eat and the water we drink, to the weather we experience and the air we breathe. Marine plants are responsible for producing around half of the oxygen we rely on every day!  That single fact is a powerful reminder of just how essential healthy oceans are to our survival. 

I used to imagine the seafloor as a kind of underwater desert, with life only gathering in scattered hotspots. But I’ve learned that this so-called “muddy bottom” is actually a vibrant, dynamic foundation for planetary health. It’s teeming with life and activity, much of it hidden from view but absolutely essential. 

I’ve been fortunate to collaborate with the talented Shaun Lee to help bring attention to these creatures that quietly sustain us. This visual highlights the vital roles that marine habitats—like those beneath your feet at Snells Beach—play in our ecosystem. Take a moment to explore and appreciate this incredibly busy and important hidden world!  

Rebecca Gladstone-Gallagher – Senior Lecturer, Marine Sciences 

I’ve been researching marine ecosystems for about 15 years now, and for the past six I’ve been lucky enough to get to know the beautiful and complex marine world of the Hauraki Gulf. 

Take Snells Beach, for example. Just below the high tide mark lies a striking seagrass bed, stretching across an impressive area. It might not look like much at first glance, but this seagrass produces oxygen through photosynthesis, stabilises the seabed (keeping the water clear), provides a safe nursery for juvenile fish, and fuels food webs across the Gulf. 

Step out a little further, past the low tide mark, and you’re looking across Kawau Bay. Beneath the surface is a whole other world with hundreds of marine species living on or in the seafloor. Shaun’s brilliant visualisation of the seafloor really brings this to life, showing just how rich and diverse this underwater landscape is. 

But here’s the harder truth. These ecosystems are under pressure. Seagrass, for instance, needs clear water and sunlight to thrive, yet increasing turbidity (caused by soil washing into the ocean during heavy rain) is making it harder for light to reach the seabed. And in Snells beach there has been some seagrass decline recently.

Out in Kawau Bay, the story is similar: once-abundant shellfish like mussels, horse mussels, and scallops have declined due to things like dredging and poor water quality. These losses change the way the entire ecosystem functions. 

It’s not all bad news, though. Our research is building a clearer picture of how these ecosystems work, which is crucial if we’re going to protect and restore them. And across the Gulf, there’s growing momentum. Mana whenua and local communities are leading inspiring efforts to bring these ecosystems back to life, from hands-on restoration projects to advocacy for better protections.