Abstract: Coral reefs within 10 degrees of the equator generally experience <= 3 degrees C seasonal variation in water temperature. Ectotherms that have evolved in these conditions are therefore expected to exhibit narrow thermal optima and be very sensitive to the greater thermal variability (>6 degrees C) experienced at higher latitudes (>= 10 degrees N/S). The impact of increased thermal variability on the fitness and distribution of thermally sensitive reef ectotherms is currently unknown. Here, we examine site-attached planktivorous coral reef damselfishes that rely on their physiological capacity to swim and forage in the water column year round. We focus on 10 species spanning four evolutionarily distinct genera from a region of the Great Barrier Reef that experiences >= 6 degrees C difference between seasons. Four ecologically important indicators showed reduced performance during the winter low (23 degrees C) compared with the summer peak (29 degrees C), with effect sizes varying among species and genera, as follows: (i) the energy available for activity (aerobic scope) was reduced by 35-45% in five species and three genera; (ii) the energetically most efficient swimming speed was reduced by 17% across all species; and (iii) the maximal critical swimming speed and (iv) the gait transition speed (the swimming mode predominantly used for foraging) were reduced by 16-42% in six species spanning all four genera. Comparisons with field surveys within and across latitudes showed that species-specific distributions were strongly correlated with these performance indicators. Species occupy habitats where they can swim faster than prevailing habitat currents year round, and >95% of individuals were observed only in habitats where the gait transition speed can be maintained at or above habitat currents. Thermal fluctuation at higher latitudes appears to reduce performance as well as the possible distribution of species and genera within and among coral reef habitats. Ultimately, thermal variability across latitudes may progressively cause sublethal changes to species performance and lead to a contraction of biogeographical range.

Abstract: For insect herbivores, rising temperatures lead to exponentially higher metabolic rates, As a result, basic nutritional demands for protein and carbohydrates can be altered at high temperatures. It is hypothesized that temperature-driven increases in metabolic nitrogen turnover will exacerbate protein limitation by increasing metabolic nitrogen demand, To test this hypothesis, the present study examines whether metabolic nitrogen turnover at higher temperatures causes protein limitation of a generalist herbivore, the beet armyworm Spodoptera exigua Hubner (Lepidoptera Noctuidae). Third-instar S. exigua larvae were reared at 25 and 30 degrees C on three artificial diets of varying protein : carbohydrate ratios (23 : 26, 17 : 26 and 6 : 26 %P : %C, respectively) and their growth rates, metabolic nitrogen demand and consumption rates were measured. Warming was found to lead to temperature-induced protein limitation of the S. exigua larvae by increasing metabolic nitrogen demand at the same time as reducing nitrogen digestion efficiency, Because climate change is increasing atmospheric temperatures rapidly worldwide, it is suggested that a better understanding of how temperature change can influence metabolic demands will provide key information for predicting herbivore growth rates and foraging strategies in the future.

Abstract: Coral reefs are essential to millions of island inhabitants. Yet, coral reefs are threatened by thermal anomalies associated with climate change and by local disturbances that include land-use change, pollution, and the coral-eating sea star Acanthaster solaris. In combination, these disturbances cause coral mortality that reduce the capacity of reefs to produce enough carbonate to keep up with sea-level rise. This study compared the reef-building capacity of shallow-water inner, patch, and outer reefs in the two islands of Pohnpei and Kosrae, Federated States of Micronesia. We identified which reefs were likely to keep up with sea-level rise under different climate-change scenarios, and estimated whether there were differences across habitats in the threshold of percentage coral cover at which net carbonate production becomes negative. We also quantified the influence of A. solaris on carbonate production. Whereas the northwestern outer reefs of Pohnpei and Kosrae had the highest net rates of carbonate production (18.5 and 16.4 kg CaCO3 m-2 yr-1, respectively), the southeastern outer reefs had the lowest rates of carbonate production (1.2-1.3 and 0.7 kg CaCO3 m-2 yr-1, respectively). The patch reefs of Pohnpei had on average higher net carbonate production rates (9.5 kg CaCO3 m-2 yr-1) than the inner reefs of both Pohnpei and Kosrae (7.0 and 7.8 kg CaCO3 m-2 yr-1, respectively). A. solaris were common on Kosrae and caused an average reduction in carbonate production of 0.6 kg CaCO3 m-2 yr-1 on Kosraean reefs. Northern outer reefs are the most likely habitats to keep up with sea-level rise in both Pohnpei and Kosrae. Overall, the inner reefs of Pohnpei and Kosrae need ~ 5.5% more coral cover to generate the same amount of carbonate as outer reefs. Therefore, inner reefs need special protection from land-use change and local pollution to keep pace with sea-level rise under all climate-change scenarios.