Based on: Mourato, C. V., Padrão, N., Serrão, E. A., & Paulo, D. (2023). Less Is More: Seagrass Restoration Success Using Less Vegetation per Area. Sustainability, 15(17), 12937.

Efforts to restore seagrass meadows have been increasing, however strong currents and frequent storms often disturb newly transplanted seagrasses, making restoration efforts difficult and costly. But researchers might have figured out a new approach for planting seagrasses that could overcome some of these obstacles.

In coastal habitats around the world, seagrasses play a vital role, supporting marine biodiversity, improving water quality, and even combating climate change by storing carbon. Despite their importance, these underwater meadows are disappearing due to coastal development, pollution, and the impacts of climate change. Efforts to restore them have made progress, but the high-energy environments of open coasts present unique challenges. Researchers have been testing different approaches to overcome these obstacles, with some seemingly more effective than others. And here enters the “checkers” method.

The Checkers Method: An Efficient Twist on Traditional Restoration

Historically, the most successful seagrass restoration attempts in high-energy environments involved planting dense mats of seagrass “sods”—blocks of seagrass-covered sediment—spanning large areas. This dense planting approach, called the “mega plot” method, has been effective but requires an enormous amount of donor seagrass, which can strain the ecosystem it’s sourced from. So, researchers from the Algarve Centre of Marine Sciences (CCMAR), Portugal, decided to test a new method where that isn’t the case.

They developed the “checkers” method, arranging seagrass sods in a grid-like pattern with strategic spacing. With the plan set, it was time to test the method in the field— the question remained: Would the transplanted seagrass survive? And if yes, how much of it?

The experiment

The team set out on an ambitious experimental journey at Praia dos Coelhos within Portugal’s Professor Luiz Saldanha Marine Park. This marine sanctuary, part of the Arrábida Natural Park, is a picturesque expanse of rocky cliffs and sandy coves, precisely where seagrass once thrived. The focus was on testing the resilience and adaptability of two seagrass species, Zostera marina and Zostera noltei, across six carefully monitored plots. Each 3 x 3-meter plot was divided into 25 “checkerboard” sections, echoing the layout used in previous trials and offering open spaces intended to encourage natural seagrass expansion.

For the transplantation, researchers chose Z. marina from the nearby Sado Estuary and Z. noltei from Ria Formosa Lagoon. To protect the plants, divers carefully collected seagrass sods and transported them to the site within minutes.

In the plots, each sod was positioned into excavated holes filled with sand, with half of the plots planted with Z. marina and the other half with Z. noltei, arranged randomly. Researchers monitored the transplanted seagrass over several months, analyzing cover, density, and shoot length to gauge growth and the effectiveness of the checkerboard layout.

Seasonal Trials and Surprising Resilience

Winter was a true test for the young seagrass plots. Strong currents, stormy conditions, and sediment shifting threatened the survival of many sods, especially those on the seaward edges. By spring, some outer plots had been destroyed entirely, but a surprising number of inner plots not only survived but thrived.

Each seagrass species responded differently to the conditions:

• Zostera marina grew quickly in the first six months, showing a substantial increase in density and coverage. However, it was more vulnerable to winter conditions, and some of its plots lost significant area. Despite this, the species showed strong recovery come spring, ending the year with higher vegetated coverage.
• Zostera noltei in contrast, took a slower, steadier growth path. This species expanded less rapidly but was notably resilient to winter conditions. By the end of the trial, it showed increased coverage, density, and a remarkable resistance to the effects of storms. Its flexibility may have helped it adapt to strong currents, keeping its canopy low and reducing drag from waves.

The results highlighted an important takeaway: while each species had its strengths, both were able to increase vegetated area, suggesting that the checkers method could support a range of species under different coastal conditions.

A Promising Method with a Few Caveats

The checkers method, which used 66% less biomass than the mega plot method, appears to be a viable option for seagrass restoration in high-energy environments. Yet, the study also revealed important considerations. Location was key; inner plots shielded from direct wave impact fared much better than exposed outer plots. To improve survival, the researchers recommend either shielding the plants from storms or planting enough biomass to counter the destructive forces of winter storms.

The promising results also raise questions for future large-scale implementation:

1. Placement of Sods: The experiment suggests that positioning within the transplant site can make a significant difference, particularly for areas facing harsh coastal dynamics.
2. Donor Population: With an approach that conserves biomass, selecting donor populations with high recovery potential could minimize the impact on natural ecosystems.
3. Associated Costs: With its reduced biomass requirements, the checkers method has the potential to lower costs, though more data is needed to fully understand the financial implications.

Implications for a Greener Future

By efficiently using donor plants, the checkers method shows potential to make seagrass restoration in high-energy environments more feasible. Coastal restoration has always been a balancing act, weighing costs and ecological impacts, but this study moves the needle towards sustainability. Further research could refine this approach and determine how it performs across different coastal environments.

With seagrass restoration included in the UN Decade on Ecosystem Restoration, innovative methods like the checkers approach offer hope for healthier coastal ecosystems and a greener future. This study is a step forward, showing that strategic design, informed by the dynamics of each unique environment, might be the key to restoring these vital underwater meadows.

Written by Maria Pinto