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Increased atmospheric CO2 is driving ocean acidification (OA), and potential changes in marine ecosystems. Research shows that both planktonic and benthic communities are affected, but how these changes are linked remains unresolved. Here we show experimentally that decreasing seawater pH (from pH 8.1 to 7.8 and 7.4) leads to reduced biofilm formation and lower primary producer biomass within biofilms. These changes occurred concurrently with a re-arrangement of the biofilm microbial communities. Changes suggest a potential shift from autotrophic to heterotrophic dominated biofilms in response to reduced pH. In a complimentary experiment, biofilms reared under reduced pH resulted in altered larval settlement for a model species (Galeolaria hystrix). These findings show that there is a potential cascade of impacts arising from OA effects on biofilms that may drive important community shifts through altered settlement patterns of benthic species. [ABSTRACT FROM AUTHOR]

The midget octopus Octopus huttoni is an important link between trophic levels as a food source and a predator, but little is known about its life history or growth. This is the first study to age and quantify growth in O. huttoni from three populations in Southern New Zealand, namely Foveaux Strait, Otago Harbour, and the Otago continental shelf. Morphometries were measured for 121 individuals, ages were estimated for 109 individuals using beak and stylet increment analysis, and lipofuscin quantity was analysed for 106 individuals. Assuming that one increment equals 1 day, beaks provided the highest age estimate (up to 250 days), but are suspected to be an underestimate (40–70 days) because increments were not found on laboratory-reared paralarval beaks, suggesting that the first increment may form after settlement. Daily growth rings in stylets were validated by tetracycline marking, but low estimates of age were attributed to poor visualisation of the stylet nucleus. The relationships between lipofuscin volume ratio and age or size of the individual were not significant, lipofuscin density was low, and individual variation was high. Results indicated that this species displays indeterminate growth until death, with a maximum mantle length of 50–60 mm at an age of 200–250 days. Further, individuals from Foveaux Strait were smaller and younger than those found in the Otago Harbour, supporting an hypothesis of an ontogenetic migration onshore. [ABSTRACT FROM AUTHOR]

Transgenerational plasticity (TGP) may be an important mechanism for marine organisms to acclimate to climate change stressors including ocean warming (OW) and ocean acidification (OA). Conversely, environmental stress experienced by one generation may have detrimental latent effects on subsequent generations. We examined TGP in the embryos and larvae of the pan-tropical sea urchin, Tripneustes gratilla, in response to OA (pH 7.77), OW (+2 °C), or both OA and OW, OAW (+2 °C, pH 7.77) using a parent (F0) generation reared in treatments from the early juvenile to the mature adult, incorporating gonadogenesis and germline differentiation. Embryos and larvae of acclimated parents were reared in all four treatments to the 2-day-old pluteus stage. Larvae from OA and OAW parents were resilient to the effects of acidification, while larvae from OW and OAW parents were more tolerant to warmer temperature (29 °C). Parental acclimation, however, had predominantly negative effects on the size of offspring with reductions in larval arm lengths by as much as 21.4%, while eggs were up to 21.8% smaller in females raised at 29 °C. We highlight the complexity and trade-offs of TGP in this first transgenerational climate change study on a marine macroinvertebrate where the F0 generation was acclimated over their reproductive life. [ABSTRACT FROM AUTHOR]

Ocean acidification, or the lowering of seawater pH, is caused by sequestration of atmospheric CO into the oceans. This study investigated the effects of present-day pH 8.0, predicted ocean surface pH for the years 2100 and 2300 (pH 7.7 and pH 7.3, respectively) and an extreme pH (pH 7.0) on fertilisation and embryogenesis in the Antarctic nemertean worm Parborlasia corrugatus and sea urchin Sterechinus neumayeri. Fertilisation success was not affected by pH in P. corrugatus across a range of sperm concentrations. Fertilisation success in S. neumayeri declined significantly in pH 7.0 and 7.3 seawater, but only at a low sperm concentration. Seawater pH had no effect on the rate of egg cleavage in S. neumayeri, or the proportion of abnormal embryos 1-day post-fertilisation. P. corrugatus embryogenesis was also relatively robust to pH changes, with a significant effect detected only when the seawater pH was decreased to 7.0. While fertilisation and early cell division were relatively robust, later development through to the gastrula was sensitive to pH. In S. neumayeri, an effect of pH on development was evident by the gastrula stage, while there were significantly more abnormal P. corrugatus embryos in pH 7.0 up to the blastula stage, and in pH 7.0 and pH 7.3 at the coeloblastula stage. Our results are similar to the observations on other marine invertebrate species where fertilisation and early embryonic development are generally robust to lowered seawater pH, while the older coeloblastula and gastrula stages are more responsive. We also found no evidence to suggest that Antarctic species are more adversely affected by lower seawater pH compared with the findings for non-Antarctic counterparts. We conclude that in the two species we examined, near-future decreases in pH (decreases of ≈0.3-0.5 pH units) may not have a significant effect on fertilisation and early embryogenesis, while predicted longer term decreases (decreases of ≈0.7-0.77 pH units) could reduce fertilisation success in S. neumayeri if sperm concentrations are low and may increase abnormalities in P. corrugatus during later embryogenesis. [ABSTRACT FROM AUTHOR]

Using the ice algal community growing at the bottom of the annual sea ice in McMurdo Sound Antarctica, the response of the photoprotective diadinoxanthin (DD)-cycle to exposure to light was investigated. Changes in pigment concentration were detected using high-performance liquid chromatography. A light mixing simulator (LMS) was developed and used to simulate the pigment response to mixing in the upper water column. No DD-cycle was detected under the sea ice under natural light conditions. The DD-cycle was activated after exposure to surface natural light conditions and artificial light conditions. The first-order kinetic rates of the DD-cycle under constant artificial irradiance, natural irradiance and simulations with the LMS were found to be similar to other studies suggesting that ice algae do not vary the rate of deepoxidation depending on light history. Simulations under natural light using the LMS demonstrated that the response of the DD-cycle to static incubations and when subject to vertical mixing was not similar, and that static incubations overestimate DD-cycle activity over the long term. Algae in a simulated vertically mixed environment were able to increase the pool of xanthophyll pigments compared to static conditions where the pool remained the same or decreased. The recovery of DD in the dark or under low light was found to be significantly faster than in temperate algal communities. These results suggest that ice algae at the sea ice bottom can activate the photoprotective DD-cycle to regulate excess thermal energy. Unlike temperate species of diatoms, ice algae can rapidly reconstruct the pigment pool under low light or in the dark and is likely a particular adaptation to the unique light environment in Antarctica. [ABSTRACT FROM AUTHOR]