Urban Coast Algae: Changes in Type, Amount, and Nitrogen Levels

Jim Crocker
23rd April, 2024

Urban Coast Algae: Changes in Type, Amount, and Nitrogen Levels

The red macroalga Botryocladia sonderi was the most common species observed in the study area, forming persistent, semi-perennial mats at deeper sites where it acts as a significant accumulator of anthropogenic nutrients.

Photographer: Darcy Nugent / CC0. Photograph of species not from study.

Key Findings

  • In Port Phillip Bay, Australia, the amount of drift macroalgae dropped by 92% over 22 years
  • The types of algae present changed significantly, with a high turnover of red algae species
  • Human-derived nitrogen, from sources like sewage, was found to be a major nutrient in the algae
Coastal ecosystems are dynamic environments where the interplay between natural processes and human activities can have profound impacts. A recent study by researchers at the University of Bergen[1] sheds light on the changes in drift macroalgal communities in Port Phillip Bay, Victoria, Australia, over a 22-year period. The study aimed to understand the relationship between local anthropogenic nutrient sources and the production of drift macroalgae, which are free-floating seaweeds that can accumulate in large masses. The findings of this study are critical for several reasons. Drift macroalgae are not just seaweed adrift; they play a pivotal role in coastal ecosystems. They can serve as habitat for marine life, contribute to food webs, and affect nutrient cycling. However, when their growth is fueled by excess nutrients from human activities, such as sewage discharge or agricultural runoff, macroalgal blooms can occur, leading to negative ecological and economic consequences. The researchers conducted surveys comparing data from 1995/1996 with that from 2017/2018. They discovered that the overall biomass of drift macroalgae in Port Phillip Bay had plummeted from 631 to 49 grams per square meter. Moreover, there was less than 13% similarity in species composition between the two survey periods, with a significant turnover at the genus level, particularly among red algae. This indicates a substantial shift in the bay's macroalgal community over time. Interestingly, the study also found that drift macroalgae are significant accumulators of nitrogen, a key nutrient that can be detrimental in high concentrations. Isotopic analysis, which helps to trace the origins of nitrogen found in organisms, revealed that a high proportion of the nitrogen in the macroalgae was derived from human sources, especially close to points of nutrient discharge and during times of heavy wastewater output. This finding echoes previous research that has highlighted the global impact of human activities on marine ecosystems[2], as well as the specific effects of nutrient enrichment on macroalgal blooms in estuaries like Narragansett Bay[3]. The University of Bergen study expands on this knowledge by quantifying the changes in macroalgal communities and directly linking them to anthropogenic nitrogen sources. Additionally, the study builds upon earlier work that has identified various sources of nitrogen pollution in coastal waters, including sewage and agricultural runoff[4]. The isotopic signatures of nitrogen in Port Phillip Bay's macroalgae suggest that, similar to previous findings, there are multiple sources of nitrogen contributing to the bay's nutrient load. The implications of this research are twofold. Firstly, it provides a clearer picture of how local human activities have influenced the bay's ecology over time, which is crucial for managing and mitigating the impacts of nutrient pollution. Secondly, it suggests that harvesting drift macroalgae could be a cost-effective method for removing excess nutrients from the water, potentially offsetting the impacts of anthropogenic nitrogen inputs. However, the researchers caution that before implementing macroalgae harvesting as a management strategy, it is essential to assess the potential consequences for marine fauna and nutrient cycling. Removing large quantities of macroalgae could disrupt the ecosystem in unforeseen ways, so a careful evaluation is needed. In conclusion, the study from the University of Bergen provides valuable insights into the long-term changes in macroalgal communities and the role of human-derived nitrogen in shaping these changes. It highlights the need for continued monitoring and the development of sustainable management practices to preserve the health and productivity of coastal ecosystems like Port Phillip Bay.

EnvironmentEcologyMarine Biology

References

Main Study

1) Spatio-temporal patterns in the biomass, species composition and nitrogen content of drift macroalgae in an urbanised coastal embayment

Published 22nd April, 2024

https://doi.org/10.1007/s10811-024-03249-3

Related Studies

2) A global map of human impact on marine ecosystems.

https://doi.org/10.1126/science.1149345

3) Spatial and temporal variability in macroalgal blooms in a eutrophied coastal estuary.

https://doi.org/10.1016/j.hal.2017.07.011

4) Sources and cycling of nitrogen revealed by stable isotopes in a highly populated large temperate coastal embayment.

https://doi.org/10.1016/j.scitotenv.2021.150408


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