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Global stressors, such as ocean acidification, constitute a rapidly emerging and significant problem for marine organisms, ecosystem functioning and services. The coastal ecosystems of the Humboldt Current System (HCS) off Chile harbour a broad physical-chemical latitudinal and temporal gradient with considerable patchiness in local oceanographic conditions. This heterogeneity may, in turn, modulate the specific tolerances of organisms to climate stress in species with populations distributed along this environmental gradient. Negative response ratios are observed in species models (mussels, gastropods and planktonic copepods) exposed to changes in the partial pressure of CO 2 (p CO2 ) far from the average and extreme p CO2 levels experienced in their native habitats. This variability in response between populations reveals the potential role of local adaptation and/or adaptive phenotypic plasticity in increasing resilience of species to environmental change. The growing use of standard ocean acidification scenarios and treatment levels in experimental protocols brings with it a danger that inter-population differences are confounded by the varying environmental conditions naturally experienced by different populations. Here, we propose the use of a simple index taking into account the natural p CO2 variability, for a better interpretation of the potential consequences of ocean acidification on species inhabiting variable coastal ecosystems. Using scenarios that take into account the natural variability will allow understanding of the limits to plasticity across organismal traits, populations and species.

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The particle capture mechanism in ectoprocts was described, and the pumping rates in 15 species of marine ectoprocts with divergent lophophore morphometry were quantified in order to comprehend and characterize the lophophore as a filter-pump Further, the effects of algal concentration and temperature on clearance were studied. The most characteristic feature of particle capture, apparent from video recordings, was that when the path of a particle was altered from downwards, towards the mouth, to outwards, between the tentacles, the particle was stopped by a tentacle. In most species (but never in Cr~sia eburnea which lacks frontal cilia) some of the trapped particles were seen to move along the tentacle surface towards the mouth. But more frequently, another downward transport mechanism was involved. As a result of the action of tentacle flicking restrained particles were propelled back into the central lophophore current to be carried further downwards, perhaps to be restrained by a tentacle again. These observations, supplemented with theoretical calculations, support the assumption that a mechanical laterofrontal-filter is at work which filters the water while the central current, created by the special lophophore pump-design, together with the flicking action of the tentacles, cleans the filter and transport the particles towards the mouth. Also, the measured particle retention efficiency, expressed as simultaneous clearance of particles of different sizes offered as a mixture of flagellates, supports the assumption of the presence of a mechanical laterofrontal-filter in the ectoprocts. The video recordings of particle trajectories revealed that there is a velocity profile at the lophophore entrance, the highest velocities being found in the central part of the lophophore. Thus, the mean velocity through the central area of the feeding core and the velocity through the outer area was used to estimate the pumping rates of ectoprocts. The pumping rate was found to vary between the 15 species, from 0.14 ml h ' zooid' in C eburnea to 7.5 ml h'l in Flustrellidra hispida. The pumping rates (0, ml h ' zooid"; 20°C of all examined species as a function of the total lophophore tentacle length (NL, cm) was expressed by the equation: Q = 3.390NL -0.704. A linear relationship between tentacle length specific pumping rate and total tentacle length indicates that the ciliary pump in small lophophores such as that of C. eburnea is relatively weak compared to large lophophores as found for example in F. hispida. The maximum zooidal clearance rates (F) of C. hyalina at 10, 15 and 20°C measured after an initial stimulating period, was 0.12, 0.16 and 0.17 ml m i n ' zooid", respectively. The ratio F/Q showed that about 4 0 % of the water pumped through the lophophore entrance may subsequently pass through the laterofrontal filter

Fertilization success may be severely limited in marine invertebrates that spawn both male and female gametes. In a diverse group of aquatic organisms only sperm are released, with sperm-egg fusion occurring at the mother. Here, we report fertilization kinetics data for two such 'brooding' or 'spermcast' species-representing each major clade of the animal kingdom. High levels of fertilization were achieved at sperm concentrations of two or three orders of magnitude lower than is common with broadcast spawning species. At a concentration of 100 sperm ml -1 , fertilization rates of a bryozoan and colonial ascidian were near maximum, whereas most broadcast spawners would have displayed near complete reproductive failure. A further experiment looked at the rate of uptake of sperm under natural conditions. Results suggested that sperm released at ca. 0.9 m from an acting female could be collected at a rate of 3-12 times greater than the minimum required simply to avoid sperm limitation. Thus, evolutionary pressures on gametic and other reproductive characteristics of many species that release sperm but retain eggs may be quite different from those of broadcast spawners and may confer on the former an enhanced scope for sperm competition and female choice.