Cross-generational response of a tropical keystone sea urchin to global change and a selection event in a 43-month mesocosm study

Physiological and behavioural changes were measured in an experiment to test the effects of cross generational larvae of urchins from parents acclimatized to two future climate conditions.

The rock-boring Echinometra sp. A sea urchin was sourced at Trunk Reef in the central Great Barrier Reef in 2017. During a lab spawning experiment described in Uthicke et al. (2020), young recruits were transferred to treatment conditions, and kept until 25 moths of age (January 2020), when they were used for further spawning experiments. Three aquaria were used for the experiments, where temperature and pCO2 were controlled individually to ambient conditions, 2050 and 2100 predicted profiles.

Young recruits were transferred to aquaria which were set with three temperature variations; ambient temperature was based on the Davies Reef daily average 1991-2012 at 4m depth, treatment for 2050 aquaria was set to 1&deg;C above the daily average and 2100 treatment was set to 2&deg;C. pCO2 was controlled ambient treatment 400 ppm, for the 2050 treatment at 685 ppm pCO2, and the 2100 daily average treatment set to 940 ppm, all with diel variation of &plusmn;60 ppm.

Maximum diameter of the urchins was measured at 9, 14 and 25 months, and total counts for survival calculations were taken at 4 and 5 months, and at 11 months following a mortality event. Respirations and ammonia excretion rates were determined on individual urchins at their respective treatment condition in September 2018 at 9 months old and in March 2019 at 14-months old. Righting response was measured as the length of time (s) for individual urchins to right themselves to an aboral side up, after being placed oral side up in their original treatment tanks.

At the end of rearing, individuals were injected with 0.5 ml of 0.5M KCL for an artificial spawning response, to test whether they had reached full maturity. Parent generation of all urchin were kept at the three treatment levels i.e. no cross-fertilization experiments were conducted. All urchin larvae were kept at the same treatments as their parents, and were transferred to the final treatment level post settlement. 

Six treatments post settlement were used, resulting from Ambient F0 fertilization were either kept at Ambient (&ldquo;Ambient-Ambient&rdquo; treatment), or were transferred to 2050 (&ldquo;Ambient-2050&rdquo;) or 2100 (&ldquo;Ambient-2100&rdquo;) conditions. Larvae and juveniles resulting from fertilization of 2050 F0 were kept at that treatment (&ldquo;2050-2050&rdquo;) or moved to 2100 conditions (&ldquo;2050-2100&rdquo;).  Larvae from 2100 acclimatized parents were only exposed at that condition (&ldquo;2100-2100&rdquo;).

Generalized linear mixed effect models (glmer) were used to analyze size, behavior and physiology data. Survivorship was reported over 100 weeks starting at 6 weeks after initial settlement.  

For further details see the article: Uthicke, S., Patel, F., Petrik, C., Watson, S.-A., Karelitz, S.E. and Lamare, M.D. (2021), Cross-generational response of a tropical sea urchin to global change and a selection event in a 43-month mesocosm study. Glob Change Biol, 27: 3448-3462. https://doi.org/10.1111/gcb.15657

Organization: Australian Ocean Data Network