Effect of altered sediment pH and algal addition on infaunal invertebrate communities in the Bay of Fundy

Background/Question/Methods

In coastal environments, eutrophication and ocean acidification both decrease pH and impact the abiotic conditions experienced by marine life. Open ocean pH has already declined due to anthropogenic CO2 emissions, and it is projected to decrease 0.15 pH units more by 2050. Algal blooms due to eutrophication and their subsequent decomposition can also increase CO2 and decrease pH. Infaunal invertebrates are exposed to more extreme pH conditions that epifauna as porewater pH is typically lower than the overlying water. Here, we investigated the impacts of altering sediment carbonate chemistry, through the addition of transplanted green algae and/or crushed shell hash, on the infaunal community. In particular, we wanted to see if infaunal invertebrate communities would respond to changes in sediment carbonate chemistry. This factorial field experiment was conducted on an intertidal mudflat in New Brunswick, Canada from July to September of 2020. There were eight blocks set up on the mudflat with ten treatment plots per block. Sediment samples were taken monthly to quantify the invertebrate community and measure pH profiles. Statistical analysis examined the effect of the algae and shell hash treatments on multivariate community composition, individual species responses, and univariate biodiversity indices.

Results/Conclusions

Sediment pH was impacted one month after the addition of shell hash, but this effect disappeared by month two. There was no effect of algal addition on sediment pH. There was a significant multivariate difference in the invertebrate community composition between months 1 and 2 of the experiment. After month one, there was a significant effect of shell hash and significant interaction between block and algae treatment on multivariate similarity in the invertebrate community. The community composition was more similar between samples when a high amount of shell hash was added to the treatment plots, no matter the algae treatment. After month two, there was only an effect of block. Only two of the most abundant invertebrate species were significantly affected by either the algae treatment or an interaction of the treatments. In our study, the effect of shell hash disappeared after one month suggesting the necessity for repeated application if it is used as a possible remediation technique for sediment acidification. Due to the complexity of the processes driving carbonate chemistry in the coastal ocean, further experiments focusing on the drivers and effects of sediment acidification are required to deepen our understanding of their impacts on infaunal marine species.