Preliminary investigation into the stimulation of phytoplankton photophysiology and growth by whale faeces

•The response to whale faeces was examined in three marine phytoplankton species.•Photosynthetic and growth parameters were compared during a 21 day experiment.•Faecal treatments ranged from 4375 to 220,267 μg faeces l− 1.•Two species exhibited dose-dependent faecal stimulation.•Whales are a potentially important means of marine nutrient recycling.

This study demonstrates that pygmy blue whale faeces stimulates the photosynthetic performance and growth of three marine phytoplankton species, Dunaliella tertiolecta, Chaetoceros pendulus and Phaeocystis antarctica. Photosynthetic and growth parameters were compared at four time-points over a 21 day experiment with 6 different treatments: a positive control (F/2 culture media), a negative control (iron-deplete F/2 culture media), and four faecal treatments ranging from 4375 to 220,267 μg faeces l− 1. At each time point, rapid light curves were generated using Pulse-Amplitude Modulated (PAM) fluorometry to obtain the parameters maximum quantum yield (FV/FM), maximum relative electron transport rate (rETRmax), and photosynthetic efficiency (α). Change in the relative abundance of microalgal cells and the concentration of chlorophyll a was also determined periodically for each species. The chlorophyte D. tertiolecta and the diatom C. pendulus both exhibited clear dose-dependent stimulation of photosynthetic and growth parameters within 7 days of incubation. There was also a strong interaction between incubation period and treatment in C. pendulus cultures which may be indicative of nutrient exhaustion following faecally-stimulated growth. The growth response observed for P. antarctica was less variable with respect to faecal concentration. These findings are considered preliminary, but illustrate that whales are a potentially important means of marine nutrient recycling.