Ocean acidification induce changes in larval urchins behaviours: implications for transport

Chair: Gretchen Hofmann

Kit Yu Karen Chan(1), Sam Dupont(2)

1 Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
2 Department of Biological and Environmental Sciences – Kristineberg, University of Gothenburg, Kristineberg 566,SE-451 78 Fiskebackskils, Sweden

Background
Many marine organisms have multiphasic life histories, in which the benthic, sedentary adults rely on their planktonic larvae for dispersal. Larval swimming impacts transport and survival, and ultimately help shape population dynamics. However, larvae are often unprotected and are vulnerable to environmental stresses, including ocean acidification (OA). Whole-larva behaviour is an effective sub-lethal stress indicator because it is determined by energy available (physiology) and larval form (biomechanics). Thus, quantifying larval swimming behaviours provide us with a sensitive indicator of individual conditions that has a clear mechanistic link to population-level response.

Methods
Larval green urchins, Strongylocentrotus droebachiensis, were reared under different pCO2 levels, representing average present-day, present-day extreme, and predicted level for 2100. In addition to documenting larval survival, growth, and morphometerics, we applied non-invasive video motion analysis to quantify swimming of larval urchins in still and in vertical shear. We then investigated the population-level implications of the observed changes in larval development and behaviours by constructing a simple individual-based particle transport model in an idealized estuary.

Findings
Larval growth rate decreased with increasing pCO2 level. However, there was no significant difference in larval swimming between treatments on a given day of age. This conservation of swimming was accompanied by an overall change in larval shape, and likely, swimming mechanics. Model urchin larvae have higher retention rate and likelihood to reach settlement sites when they maintain their age-specific speed in spite of the increase dispersive duration, suggesting swimming maintenance may have adaptive values.

Conclusions

Larval urchins display behavioural plasticity under OA stress and maintained their swimming despite of a reduction in growth rate, and such behaviours could help reduce advective lost. However, this seemingly adaptive behaviour comes at the cost of reaching settlement site at a smaller size, which could be detrimental to the population under chronic OA stress.