Thermal performance curves (TPCs), which quantify how an ectotherm's body temperature (T b ) affects its performance or fitness, are often used in an attempt to predict organismal responses to climate change. Here, we examine the key -but often biologically unreasonable -assumptions underlying this approach; for example, that physiology and thermal regimes are invariant over ontogeny, space and time, and also that TPCs are independent of previously experienced T b. We show how a critical consideration of these assumptions can lead to biologically useful hypotheses and experimental designs. For example, rather than assuming that TPCs are fixed during ontogeny, one can measure TPCs for each major life stage and incorporate these into stage-specific ecological models to reveal the life stage most likely to be vulnerable to climate change. Our overall goal is to explicitly examine the assumptions underlying the integration of TPCs with T b , to develop a framework within which empiricists can place their work within these limitations, and to facilitate the application of thermal physiology to understanding the biological implications of climate change.

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Ocean acidification (OA), a consequence of anthropogenic carbon dioxide emissions, poses a serious threat to marine organisms in tropical, open-ocean, coastal, deep-sea, and high-latitude sea ecosystems. The diversity of taxonomic groups that precipitate calcium carbonate from seawater are at particularly high risk. Here we review the rapidly expanding literature concerning the biological and ecological impacts of OA on calcification, using a cross-scale, process-oriented approach. In comparison to calcification, we find that areas such as fertilization, early life-history stages, and interaction with synergistic stressors are understudied. Although understanding the long-term consequences of OA are critical, available studies are largely short-term experiments that do not allow for tests of long-term acclimatization or adaptation. Future research on the phenotypic plasticity of contemporary organisms and interpretations of performance in the context of current environmental heterogeneity of pCO2 will greatly aid in our understanding of how organisms will respond to OA in the future.

Many organisms reproduce by releasing gametes into the environment. However, very little is known about what proportion of released eggs become fertilized. We examined the influence of spawning group size, degree of aggregation, position within an aggregation, and water flow, on in situ fertilization in the sea urchin Strongylocentrotus franciscanus. This study was conducted at a depth of 9 m on the west coast of Vancouver Island, British Columbia, Canada. Males were simulated by syringes filled with sperm; females were simulated by sperm—permeable containers filled with eggs. Individuals were placed 0.5 or 2.0 m apart within a 2 x 2 or 4 x 4 (group size of 4 or 16 individuals) experimental array. The results indicate that group size, degree of aggregation, position within a spawning group, and water flow all affect fertilization success. Fertilization success. Fertilization success ranged from 0 to 82%. Increases in group size and aggregation, decreases in flow velocity, and central and downstream positions within an aggregation all lead to increase in fertilization success. Thus, individual reproductive performance is dependent on, and highly sensitive to, population parameters and environmental conditions.

Determining fertilization success of free spawning organisms in the field requires knowledge of how eggs and sperm interact under varying encounter frequencies and durations. In the laboratory, we investigated the relative influence of sperm concentration, egg concentration, sperm-egg contact time, and sperm age on fertilization in the sea urchin Strongylocentrotus franciscanus. Our results indicated that sperm concentration, sperm-egg contact time, sperm age, and individual variability were sequentially the most important factors influencing fertilization success. Egg concentration was not significant over the range tested. A theoretical model of fertilization (Vogel-Czihak-Chang-Wolf model) was used to estimate the two rate constants of fertilization kinetics: the rate constant of sperm-egg encounter and rate constant of fertilization. This model explained 91% of the variation in fertilization success, provided estimates of the rate constants involved in fertilization, and indicated the proportion (3%) of sperm-egg contacts that result in fertilization. Estimates of sperm swimming velocity and egg diameter were used to independently calculate the rate of sperm-egg encounter and confirm the predictions of the model. This model also predicts the non-significant effect of egg concentration on fertilization success found empirically.

Ocean acidification, the reduction of ocean pH due to the absorption of anthropogenic atmospheric CO 2 , is expected to influence marine ecosystems through effects on marine calcifying organisms. These effects are not well understood at the community and ecosystem levels, although the consequences are likely to involve range shifts and population declines. A current focus in ocean acidification research is to understand the resilience that organisms possess to withstand such changes, and to extend these investigations beyond calcification, addressing impacts on other vulnerable physiological processes. Using morphometric methods and gene expression profiling with a DNA microarray, we explore the effects of elevated CO 2 conditions on Lytechinus pictus echinoplutei, which form a calcium carbonate endoskeleton during pelagic development. Larvae were raised from fertilization to pluteus stage in seawater with elevated CO 2 . Morphometric analysis showed significant effects of enhanced CO 2 on both size and shape of larvae; those grown in a high CO 2 environment were smaller and had a more triangular body than those raised in normal CO 2 conditions. Gene expression profiling showed that genes central to energy metabolism and biomineralization were down-regulated in the larvae in response to elevated CO 2 , whereas only a few genes involved in ion regulation and acid-base balance pathways were up-regulated. Taken together, these results suggest that, although larvae are able to form an endoskeleton, development at elevated CO 2 levels has consequences for larval physiology as shown by changes in the larval transcriptome.

Detailed studies of lipid utilization during bivalve development have shown that lipids are important at 2 critical periods: embryogenesis and metamorphosis. Using the Iatroscan TLC/FID system I examined lipid class utilization during development of Evechinus chloroticus to determine whether lipids were also important for an echinoderm at these times. Eggs of E. chloroticus contained 34.41 ng of lipid, primarily polar lipids (52.0%) and triglyceride (29.4%). To determine whether there was a different pattern of lipid utilization between larvae reared in the presence or absence of particulate food, larvae were either fed 6000 cells ml -1 Dunaliella every 2 d or starved. While there was no change in the amount of total, structural or energy storage lipids over time, there was a significant difference in the amount of structural lipids between Fed and Starved treatments. This was related to the continuing development of Fed larvae and cessation of development of Starved larvae at the 4-arm pluteus stage. In both treatments, triglycerides were rapidly utilized from the early 4-arm echinopluteus to the late 4-arm larva with fully developed arms and gut. Another neutral lipid, free fatty acid, accumulated in the 8-arm echinopluteus stage of the Fed larvae. This suggests that lipid stored during the planktonic phase, in combination with the proximate constituents of the larval body, provides the energy for the metamorphic and perimetamorphic periods in echinoderm development. Thus sea urchins, as in bivalves, appear to have 2 critical periods for lipid use during development.

Food can act as a powerful stimulus, eliciting metabolic, behavioral and developmental responses. These phenotypic changes can alter ecological and evolutionary processes; yet, the molecular mechanisms underlying many plastic phenotypic responses remain unknown. Here we show that dopamine signaling through a type-D2 receptor mediates developmental plasticity by regulating arm length in pre-feeding sea urchin larvae in response to food availability. While prey-induced traits are often thought to improve food acquisition, the mechanism underlying this plastic response acts to reduce feeding structure size and subsequent feeding rate. Consequently, the developmental program and/or maternal provisioning predetermine the maximum possible feeding rate, and food-induced dopamine signaling reduces food acquisition potential during periods of abundant resources to preserve maternal energetic reserves. Sea urchin larvae may have co-opted the widespread use of food-induced dopamine signaling from behavioral responses to instead alter their development.