Seasonal changes of intertidal benthic microalgae photoacclimation during the summer to mid-winter transition period on Tromsøya

Abstract

The microphytobenthos (MPB), defined as the microscopic photosynthesizers inhabiting sediments in marine and estuarine environments, are a vital component to intertidal ecosystems. They contribute greatly to ecosystem services in many ways and are responsible for a high amount of primary productivity in their environments. Microphytobenthic abundance and community structure studies have been increasing in the Arctic, but there is still a lack of knowledge and understanding of how they function at high latitudes. Polar regions exhibit high variability in light and temperature conditions throughout the year, but microalgae have impressively adapted to be able to thrive in this variable climate.

Seasonal studies on changes in MPB abundance have been performed in polar regions, but most focus on spring and summer months and the transitions between them. This study aims to better understand temporal responses of the MPB from late August to mid-December in the intertidal zone on the island of Tromsøya, located in Northern Norway. Through this project, the topics of overall MPB abundance and community structure are examines to address whether there is visible seasonality within these communities. Surface sediment samples from September and December 2024 were examined through microscopy to obtain overall live cell counts as well as identify the various taxa that make up the intertidal microalgae here. Chlorophyll fluorescence measurements were carried out weekly using a hand-held fluorometer, allowing for the calculation of rapid response light curves and their relevant parameter estimates which inform us about algal physiology. Additionally, weekly sediment samples were analysed for chlorophyll a (Chl a) content.

Results suggest that there is indeed some seasonality aspect within the intertidal MPB on Tromsøya from late August to mid-December. There appears to be a shift to slower photosynthesis and also a lower light requirement from the algae later in the sampling season. Furthermore, taxa compositions are comparable to those of other coastal areas in the Arctic. Further studies are still needed to obtain a more complete understanding of the MPB in Northern Norway and on Tromsøya as there were many unexplored environmental factors in this study.