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Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Phenotypic plasticity has the potential to allow organisms to respond rapidly to global environmental change, but the range and effectiveness of these responses are poorly understood across taxa and growth strategies. Colonial organisms might be particularly resilient to environmental stressors, as organizational modularity and successive asexual generations can allow for distinctively flexible responses in the aggregate form. We performed laboratory experiments to examine the effects of increasing dissolved carbon dioxide (CO 2 ) (i.e. ocean acidification) on the colonial bryozoan Celleporella cornuta sampled from two source populations within a coastal upwelling region of the northern California coast. Bryozoan colonies were remarkably plastic under these CO 2 treatments. Colonies raised under high CO 2 grew more quickly, investing less in reproduction and producing lighter skeletons when compared with genetically identical clones raised under current surface atmosphere CO 2 values. Bryozoans held under high CO 2 conditions also changed the Mg/Ca ratio of skeletal calcite and increased the expression of organic coverings in new growth, which may serve as protection against acidified water. We also observed strong differences between source populations in reproductive investment and organic covering reaction norms, consistent with adaptive responses to persistent spatial variation in local oceanographic conditions. Our results demonstrate that phenotypic plasticity and energetic trade-offs can mediate biological responses to global environmental change, and highlight the broad range of strategies available to colonial organisms., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

Benthic colonial organisms exhibit a wide variation in size and shape and provide excellent model systems for testing the predictions of models that describe the scaling of metabolic rate with organism size. We tested the hypothesis that colony form will influence metabolic scaling and its derivatives by characterising metabolic and propagule production rates in three species of freshwater bryozoans that vary in morphology and module organisation and which demonstrate two- and three-dimensional growth forms. The results were evaluated with respect to predictions from two models for metabolic scaling. Isometric metabolic scaling in two-dimensional colonies supported predictions of a model based on dynamic energy budget theory (DEB) and not those of a model based on fractally branching supply networks. This metabolic isometry appears to be achieved by equivalent energy budgets of edge and central modules, in one species (Cristatella mucedo) via linear growth and in a second species (Lophopus crystallinus) by colony fission. Allometric scaling characterised colonies of a three-dimensional species (Fredericella sultana), also providing support for the DEB model. Isometric scaling of propagule production rates for C. mucedo and F. sultana suggests that the number of propagules produced in colonies increases in direct proportion with the number of modules within colonies. Feeding currents generated by bryozoans function in both food capture and respiration, thus linking metabolic scaling with dynamics of self-shading and resource capture. Metabolic rates fundamentally dictate organismal performance (e.g. growth, reproduction) and, as we show here, are linked with colony form. Metabolic profiles and associated variation in colony form should therefore influence the outcome of biotic interactions in habitats dominated by colonial animals and may drive patterns of macroevolution.

Marine larvae are often considered as drifters that collide with larval collectors as passive particles. The trajectories of Bugula neritina larvae and of polystyrene beads were recorded in the velocity field of a vertical cylinder. The experiments illustrated that the trajectories of larvae and of beads may differ markedly. By considering a larva as a self-propelled mechanical microswimmer, a mathematical model of its motion in the two-dimensional velocity field of a long cylinder was formulated. Simulated larval trajectories were compared with experimental observations. We calculated the ratio η of the probability of contact of a microswimmer with a cylinder to the probability of contact of a passive particle with the cylinder. We found that depending on the ratio S of the swimming velocity of the microswimmer to the velocity of the ambient current, the probability of contact of a microswimmer with a collector may be orders of magnitude larger than the probability of contact of a passive particle with the cylinder: for S≈0.01, η≈1; for S≈0.1, η≈10; and for S≈1, η≈100.

Maternal effects could influence the persistence of species under environmental change, but the adaptive significance of many empirically estimated maternal effects remains unclear. Inferences about the adaptive significance of maternal effects depend on the correlation between maternal and offspring environments, the relative importance of frequency- or density-dependent selection and whether absolute or relative fitness measures are used. Here, we combine the monitoring of the environment over time with a factorial experiment where we manipulated both the maternal and offspring environment in a marine bryozoan (Bugula neritina). We focused on temperature as our environmental variable as temperature commonly varies over short time scales in nature. We found that offspring from mothers kept in warmer water were smaller and more variable in size, but had increased dispersal potential and higher metamorphic success than offspring from mothers kept in cooler water. Our results suggest that, under frequency- or density-independent selection, mothers that experienced higher temperatures compared with lower temperatures were favoured. Under frequency- or density-dependent selection, there were indications that mothers that experienced higher temperatures would be favoured only if their offspring encountered similar (warmer) temperatures, though these results were not statistically significant. Analysis of time series data on temperature in the field shows that the maternal thermal environment is a good predictor of the temperatures offspring are likely to experience early in life. We suggest that future studies on maternal effects estimate environmental predictability and present both absolute and relative estimates of maternal fitness within each offspring environment.

To what extent is the development of a fluid-transport system related to flow within the system? Colonies of the bryozoan Membranipora membranacea have a simple external fluid-transport system with three components: the canopy of lophophores (crowns of ciliated tentacles), the edge of the canopy, and chimneys (raised openings in the canopy). The lophophores pump seawater into the colony and capture food particles from the seawater. The chimneys and canopy edge let the water back out of the colony. New chimneys form at the canopy edge as the colony grows. I tested whether there was a correlation between chimney formation and excurrent flow speed at the canopy edge by measuring excurrent flow speeds prior to chimney formation. Excurrent flow speeds were higher in regions that produced chimneys than in regions that did not form chimneys. Observations of changes in chimney shape after anesthetization with MgCl2 suggest that both growth and behavior determine chimney shape. Together, the results suggest that there is a strong correlation between growth and flow in this external fluid-transport system, with new chimneys forming at sites of high flow.