Interactive effects of near-future temperature increase and ocean acidification on physiology and gonad development in adult Pacific sea urchin, Echinometra sp. A

Abstract

Increased atmospheric CO 2 will have a twofold impact on future marine ecosystems, increasing global sea surface temperatures and uptake of CO 2 (Ocean Acidification). Many experiments focus on the investigation of one of these stressors, but under realistic future climate predictions, these stressors may have interactive effects on individuals. Here, we investigate the effect of warming and acidification in combination. We test for interactive effects of potential near-future (2100) temperature (?2 to 3°C) and pCO 2 (*860-940 lAtm) levels on the physiology of the tropical echinoid Echinometra sp. A. The greatest reduction in growth was under simultaneous temperature and pH/pCO 2 stress (marginally significant temperature 9 pH/pCO 2 interaction). This was mirrored by the physiological data, with highest metabolic activity (measured as respiration and ammonium excretion) occurring at the increased temperature and pCO 2 treatment, although this was not significant for excretion. The perivisceral coelomic fluid pH was *7.5-7.6, as typical for echinoids, and showed no significant changes between treatments. Indicative of active calcification, internal magnesium and calcium concentrations were reduced compared to the external medium, but were not different between treatments. Gonad weight was lower at the higher temperature, and this difference was more distinct and statistically significant for males. The condition of the gonads assessed by histology declined in increased temperature and low pH treatments. The Echinometra grew in all treatments indicating active calcification of their magnesium calcite tests even as carbonate mineral saturation decreased. Our results indicate that the interactive temperature and pH effects are more important for adult echinoids than individual stressors. Although adult specimens grow and survive in nearfuture conditions, higher energy demands may influence gonad development and thus population maintenance.

Urchins in a high CO2 world: partitioned effects of body-size, ocean warming and acidification on metabolic rate

“…This highlights the highly partitioned nature of these factors, and suggests that the mechanisms by which each influences metabolism are relatively separated within the physiological pathway. By contrast, other studies of marine invertebrates, albeit often with brief acclimation and narrow size ranges, suggest that the combined metabolic effects of temperature and pH are highly interactive Matoo et al, 2013;Melatunan et al, 2011;Paganini et al, 2014;Uthicke et al, 2014). The increased energetic costs that are associated with a R, metabolic rate (oxygen uptake, mg O 2 h −1 ); M, ash-free dry mass (see also Fig.…”

“…After 69 days exposure, the tropical sea urchin Echinometra sp. A (Uthicke et al, 2014) was found to exhibit no metabolic response to warming or OA in isolation, but there was a slight increase (5.9%) when these were combined. However, the treatments used were moderate (+2-3°C and −0.2 pH units).…”

“…The effect of combined warming and acidification on R in sea urchins has been investigated in two studies (Catarino et al, 2012;Uthicke et al, 2014), but metabolic scaling across body size was not incorporated. Both of these studies found the effects of temperature and OA to be interactive.…”

In situ developmental responses of tropical sea urchin larvae to ocean acidification conditions at naturally elevated p CO 2 vent sites

“…As with a number of taxa, the larval stages of the sea urchin's life cycle are especially vulnerable to reduced OA [31,32]. There have been numerous studies that show a detrimental effect of elevated pCO 2 on the growth, survival, respiration, calcification and gene expression patterns of sea urchin larvae in controlled laboratory experiments [33], including those on Echinometra developmental stages [18,23]. The latter studies showed that under low pH/ high pCO 2 larval development is stunted, and that larvae undergo altered development patterns expressed in arm asymmetry and abnormality.…”

“…For example, laboratory studies on the tropical sea urchin genus Echinometra have suggested that a lower seawater pH can induce a range of deleterious responses, including reduced calcification [21], slower somatic growth [22] and impaired reproduction [23]. By contrast, Hazan et al [24] found no change in growth or reproduction in Echinometra viridis over an 11-month exposure to pH (nbs) 7.7, while Moulin et al [25] found no effect on growth, respiration and test properties of Echinometra mathaei exposure to pH (T) 7.6 in large mesocosms over a 13-month exposure.…”