Responses to climate change of the sea urchin (Pseudechinus sp.) and sea star (Odontaster validus) through hybridisation, local adaptations and transgenerational plasticity

Abstract

Climate change, through ocean warming and ocean acidification, can affect the life cycles and population dynamics of marine species, which react by developing acclimation mechanisms. Sea urchins (Pseudechinus sp.) may hybridise with sympatric species or induce local adaptations geographically and sea stars (Odontaster validus) may develop transgenerational plasticity (TGP) in response to climate change. I studied their stress responses and if they developed potential acclimation capacity against climate change.

1) Ocean warming favours native or hybrid progeny, I exposed progenies of sympatric sea urchins P. huttoni and P. novazealandiae to thermal gradients (5.9 to 21.1°C) with near-future increased temperatures. Both hybrid progenies (P. huttoni ♀ x P. novazealandiae ♂ and P. novazealandiae ♀ x P. huttoni ♂) showed normal developmental rates like their native maternal counterparts. At 4-days post-fertilisation, P. huttoni ♀ x P. novazealandiae ♂ showed similar developmental rates to their native maternal progeny, while P. novazealandiae ♀ x P. huttoni ♂ progeny showed slowest and irregular development, indicating hybrid depression. P. huttoni ♀ x P. novazealandiae ♂ larvae developed significantly enlarged stomachs and larger postoral arms. Due to the small sample sizes, this experiment was rendered as preliminary.

2) P. huttoni populations from Fiordland and Otago Shelf respond better to climate change as native or hybrid progeny. I tested crossed offspring of the two populations against a combination of thermal gradients (5.9°C to 21.1°C) and pH levels (pH 8.1 and pH 7.7). Both intra-site progenies developed better than inter-population groups (Fiordland ♀ x Otago ♂ and Otago ♀ x Fiordland ♂), and both inter-population groups responded similar as their maternal intra-site populations. Both intra-site groups held withstand up to +3°C above the regional thermal limit, but the developmental rates decreased with acidic pH. Morphological changes were observed in total length, total width and postoral arms. Pluteus larvae of the hybrid Fiordland ♀ x Otago ♂ were wider with enlarged stomachs area at decreased pH level, while other pluteus larvae developed smaller.

3) Offspring of sea star O. validus develop TGP against ocean warming. Adults were preconditioned at either ambient 0.5°C or experimentally 3.5°C in the laboratory a year prior to experiment. Embryos and larvae were tested for TGP against an environmentally-thermal gradient between 2.0 to 11.3°C. TGP was not clearly evidenced, with progenies responding poorly to warmer temperatures above 6°C. Progeny of warm-acclimated adults had broad thermal windows, but their normal developmental rate was poorer than those of cold-acclimated offspring. Warm-acclimated adults developed bigger eggs, but of lower quality than those of cold-acclimated adults. The short experimental acclimation period led to immature gonads prior spawning, a longer acclimation period is essential for further investigation.

These experiments demonstrate that sea urchin and sea star offspring experience stressful development against ocean warming and ocean acidification. Increased warming can affect physiological performance, development and thermal tolerance during fertilisation and early developmental stages, while decreased pH can disrupt calcifiying functions and metabolism in larvae. Extensive research is needed to understand the impacts of these responses to climate change.