Understanding impacts of climate change stressors such as warming, acidification, and low salinity, on marine organisms are essential for predicting future community dynamics. Inter- and intra-specific variations in sensitivities are well documented and several hypotheses have been proposed to account for these variations. Broadly speaking, it is assumed that species found in fluctuating environments have larger physiological tolerance ranges and invasive species are particularly resilient. Within a species, early planktonic stage and/or calcified stages are thought to be more vulnerable to environmental stress. Focusing on the tubeworm Hydroides dirampha, an invasive species with non-calcifying larval stage and calcified sessile adults, we tested these hypotheses through a seri...[ Read more ]

Understanding impacts of climate change stressors such as warming, acidification, and low salinity, on marine organisms are essential for predicting future community dynamics. Inter- and intra-specific variations in sensitivities are well documented and several hypotheses have been proposed to account for these variations. Broadly speaking, it is assumed that species found in fluctuating environments have larger physiological tolerance ranges and invasive species are particularly resilient. Within a species, early planktonic stage and/or calcified stages are thought to be more vulnerable to environmental stress. Focusing on the tubeworm Hydroides dirampha, an invasive species with non-calcifying larval stage and calcified sessile adults, we tested these hypotheses through a series of exposure experiments. The early development (fertilization, cleavage, and larval growth) of this fouling species was robust to a 4℃ temperature increase, 10 psu salinity reduction, and -0.7 pH acidification. Warming promoted larval feeding and growth but survival decreased. Larval growth, clearance, and settlement rate of H. dirampha were elevated when salinity was reduced to 26 compared to the normal condition of 32. However, at an extremely low pH of 7.3 settled individuals were unable to secret the protective calcareous tubes during metamorphosis and those secreted at pH 7.7 had reduced hardness and stiffness. The reduced calcification suggests a potential increase in predation risk, highlighting stage-dependent susceptibility to acidification. Regardless, H. dirampha exposed to the monsoon variations of environmental conditions in Hong Kong performed well under future climate conditions. After confirming that the gametes of the conger H. elegans found at the same site is incompatible with those of H. dirampha, we concluded that the differences in salinity and pH tolerance was not due to hybrid advantage. H. dirampha had higher survivorship at low salinity (26) and was able to maintain calcification at pH 7.7 when H. elegans could not, which corroborates the succession of species observed in the field during the summer months. These observations highlighted that even sympatric congeners could have different tolerances to climate change-related stressors, and these physiological plasticities could in turn help shape their future abundance and distribution.