Lab experiment on the effects of temperature on kelp respiration rates

Kelps act as ecosystem engineers and foundation species on many polar rocky shore coastlines. The main driver for their vertical and latitudinal distribution is the underwater light climate and temperature. Both are changing drastically in the Arctic in the course of global climate change. It was the aim of this study to analyse the effects of rising temperature and deteriorating underwater light climate on the potential habitat of kelps in the Arctic. A laboratory experiment, in which we determined temperature-related changes in the light-use characteristics of two temperate kelp species (Alaria esculenta, Saccharina latissima) at 3, 7, and 11 °C. Therefore, grown sporophytes were sampled in the field from a sampling depth of 6–9 m. Meristematic discs (Ø 2 cm) were cut and distributed between temperature treatments and replicates. The experiment ran for seven days, during which the treatment temperature was increased every two days by 4 °C until treatment temperature was reached, allowing for successive acclimation. The photosynthesis vs. irradiance curves were measured with a 4-channel optode set-up (FireStingO2 Fibre-Optic Oxygen Meter FSO2-01, PyroScience Sensor technology, Aachen, Germany) by analysing the oxygen evolution in response to different light intensities within a 25 mL Schott bottle, each containing three meristematic discs. Maximum photosynthetic quantum yield was measured using a pulse amplitude modulated fluorometer (Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany). Pigment analysis was analysed with a High-Performance Liquid Chromatograph (HPLC, LaChromElite® system, L-2200 autosampler (chilled), DA-detetctor L-2450; VWR-Hitachi International GmbH, Darmstadt, Germany)