Seasonal Acclimation Modulates the Impacts of Simulated Warming and Light Reduction on Temperate Seagrass Productivity and Biochemical Composition

Abstract

Increases in seawater temperature and reduction in light quality have emerged as some of the most important threats to marine coastal communities including seagrass ecosystems. Temperate seagrasses, including Zostera marina, typically have pronounced seasonal cycles which modulate seagrass growth, physiology and reproductive effort. These marked temporal patterns can affect experimental seagrass responses to climate change effects depending on the seasons of the year in which the experiments are conducted. This study aimed at evaluating how seasonal acclimatization modulates productivity and biochemical responses of Zostera marina to experimental warming and irradiance reduction. Seagrass shoots were exposed to different temperatures (6, 12, 16, 20, and 24°C), combined with high (180 μmol photons m–2 s–1) and low (60 μmol photons m–2 s–1) light conditions across four seasons (spring: April, summer: July, and autumn: November 2015, and winter: January 2016). Plants exhibited similar temperature growth rates between 16 and 20°C; at 24°C, a drastic reduction in growth was observed; this was more accentuated in colder months and under low irradiance conditions. Higher leaf growth rates occurred in winter while the largest rhizomes were reached in experiments conducted in spring and summer. Increases in temperature induced a significant reduction in polyunsaturated fatty acids (PUFA), particularly omega-3 (n-3 PUFA). Our results highlight that temperate seagrass populations currently living under temperature limitation will be favored by future increases in sea surface temperature in terms of leaf and rhizome productivity. Together with results from this study on Z. marina from a temperate region, a wider review of the reported impacts of experimental warming indicates the likely reduction in some compounds of nutritional importance for higher trophic levels in seagrass leaves. Our results further demonstrate that data derived from laboratory-based studies investigating environmental stress on seagrass growth and acclimation, and their subsequent interpretation, are strongly influenced by seasonality and in situ conditions that precede any experimental exposure.

Effects of Current and Future Summer Marine Heat Waves on Posidonia oceanica: Plant Origin Matters?

“…Conversely, proteins are likely not a reliable warning of heat stress, because although the interactive effect between temperature and origin was found in both times of the future MHWs experiment (but not in the current ones) a unique direction of the change could not be identified. Similar observations on the protein content were recently found in other seagrasses (Beca-Carretero et al, 2021) and, likely for the intrinsic variability of protein contents, a much higher replication would be needed to define the scale of reliability of such variable. Overall, the change of the biochemical content in primary producers may have an important ecological role (Hernán et al, 2016) and needs to be further investigated also by identifying how specific groups of these biochemical contents may change in relation of heat events.…”

Sources of variability in seagrass fatty acid profiles and the need of identifying reliable warming descriptors

“…Descriptive studies that investigated the remodelling of FA composition in seagrasses have generally dealt with wider temperature ranges, often larger than 10 °C, both because of either wide temporal or latitudinal ranges (e.g. 39 , 43 ). Some manipulative experiments have instead tested the effect of a 4 °C temperature increase (treatment similar to the range considered in this study and comparable to climate change scenarios) in a relatively short time 34 , 35 , 43 to simulate a warming event.…”

“… 39 , 43 ). Some manipulative experiments have instead tested the effect of a 4 °C temperature increase (treatment similar to the range considered in this study and comparable to climate change scenarios) in a relatively short time 34 , 35 , 43 to simulate a warming event. Although different in the time of warming, the response of FA in plants subjected to the temperature treatment in mesocosms resembled the FA composition associated to SST found in this study in untouched plants.…”

“…The remodelling of leaf FA due to temperature increase has been found in a wide range of plant species living in several biomes 42 and in particular in seagrass species 40 . Results consistently indicate that heat reduces polyunsaturated fatty acids (PUFA), counterbalanced by the increase in saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA, e.g., 40 , 43 , 44 ). However, although the use of FA analysis for understanding marine ecosystem functioning is promising, the variability in FA composition, either as single or grouped fatty acids, needs to be estimated to ensure relevant and appropriate interpretations 45 .…”

“…and 49 , 50 respectively), while recently only young leaves were considered (e.g. 39 , 43 . with Zostera marina apical shoots).…”