David J. S. Montagnes’s research while affiliated with University of Liverpool and other places

Climate change will impact coastal ecosystems, threatening subsistence fisheries including those in mangrove forests. Despite their global contributions and roles in nutrition and cultural identity, mangrove subsistence fisheries are poorly studied. Here, we offer a foundation for improving the management of mangrove subsistence fisheries to deal with the impending effects of climate change. This multidisciplinary review—drawing on organismal biology, ecology, fisheries, and social science—focuses on the climate impacts relevant to mangrove ecosystems: heat waves, low-category, and high-category typhoons. First, we provide an overview of the mangroves, their harvestable stocks (fish, crustaceans, molluscs), and the fishers, offering an understanding of how they may be affected by relevant environmental variables; i.e., shifts in temperature, salinity, oxygen, flooding, and sediments. Then, we examine the potential effects of climate change on mangrove stocks and fishers, indicating the scope of impending changes. By combining the above information, we develop a simple model that forecasts the number of “fishing-days” lost by fishers due to climate change over the next decade (between 11 and 21 days will be lost per year per fisher). This indicates which aspects of climate change will have the greatest impacts on stocks and fishers. We found that high-category typhoons had more impacts than heat waves, which in turn had a greater impact than low-category typhoons). Finally, recognising gaps in our knowledge and understanding, we offer recommendations for approaches for future work to improve our predictions. Supplementary Information The online version contains supplementary material available at 10.1007/s42995-024-00231-3.

Blooms of the cyanobacterium Microcystis threaten aquatic ecosystems. Protozoa grazing can control unicellular Microcystis populations; however, Microcystis blooms are composed of multicellular colonies that are thought to prevent grazing. We show that this is not so: the model ciliate Paramecium has an impact on Microcystis populations through grazing, even when large colonies occur, and this leads to a corresponding decrease in toxic microcystins. Notably, as the number of large colonies increased, Paramecium exerted top-down control by altering its feeding behavior: once the colony size was >12-20 μm, Paramecium no longer acted as a "filter feeder"; instead, it became a "surface browser," grazing around and between larger colonies, removing individual Microcystis and small colonies. However, as the proportion of large colonies increased, exponentially reducing the surface area to volume ratio, the impact of Paramecium decreased exponentially. This study provides new insights into how protozoa may affect Microcystis populations through top-down control of blooms.

Body size is a fundamental trait determining individual fitness and ecological processes. Reduction in body size with increasing temperature has been widely observed in most ectotherms and endotherms, known as Bergmann's rule. However, we lack data to assess if ciliates, the major consumers of marine primary production, follow Bergmann's rule and what drives the distributions of their cell size. Here, we examined a data set (287 samples) collected across the global oceans to investigate biogeographic patterns in the mean cell‐size of ciliate communities. By measuring the sizes of every ciliate cell (< 10 to > 300 per sample), we found that community cell‐size increased with increasing latitude, conforming to Bergmann's rule. We then addressed the cause. Temperature was a main driver of the trend. Ciliate community mean cell‐size decreased 34% when temperature increased from 3.5 to 31°C, implying that temperature may be a direct physiological driver. In addition, prey (phytoplankton) size also influenced the trend, with ciliate size increasing by 35% across the gradient of phytoplankton size (0.6–15.5 μm). Generally, these findings emphasized the importance of how both biotic and abiotic factors affect size distribution of marine ciliates, a key component of pelagic ecosystems. Our novel, extensive dataset and the predictive trends arising from them contribute to understanding how climate change will influence pelagic ecosystem functions.

Conventional analyses suggest that the metabolism of heterotrophs is thermally more sensitive than that of autotrophs, implying that warming leads to pronounced trophodynamic imbalances. However, these analyses inappropriately combine within- and across-taxa trends. Our new analysis separates these, revealing that 92% of the difference in the apparent thermal sensitivity between autotrophic and heterotrophic protists does indeed arise from within-taxa responses. Fitness differences among taxa adapted to different temperature regimes only partially compensate for the positive biochemical relationship between temperature and growth rate within taxa, supporting the hotter-is-partially-better hypothesis. Our work highlights the importance of separating within- and across-taxa responses when comparing temperature sensitivities between groups, which is relevant to how trophic imbalances and carbon fluxes respond to warming.

On the global average, the temperature increase in the ocean is lower than in lakes. Moreover, most freshwater organisms must cope with wider temperature fluctuations than marine organisms. Knowing if the organisms' thermal sensitivity differs in the two realms is crucial for predicting the respective climate-related changes at community and ecosystem levels. We investigated the thermal sensitivity of planktonic ciliates, which are of tremendous significance for biogeochemical cycling in all aquatic ecosystems. Marine and freshwater ciliates differ in their thermal performance; therefore, system-specific activation energies should be applied in models predicting ciliate responses to altered temperatures. This work may serve as a model study for other taxa and be of interest to many marine and freshwater ecologists. Abstract Predicting the performance of aquatic organisms in a future warmer climate depends critically on understanding how current temperature regimes affect the organisms' growth rates. Using a meta-analysis for the published experimental data, we calculated the activation energy (E a) to parameterize the thermal sensitivity of marine and freshwater ciliates, major players in marine and freshwater food webs. We hypothesized that their growth rates increase with temperature but that ciliates dwelling in the immense, thermally stable ocean are closely adapted to their ambient temperature and have lower E a than ciliates living in smaller, thermally more variable freshwater environments. The E a was in the range known from other taxa but significantly lower for marine ciliates (0.390 AE 0.105 eV) than for freshwater ciliates (0.633 AE 0.060 eV), supporting our hypothesis. Accordingly, models aiming to predict the ciliate response to increasing water temperature should apply the environment-specific activation energies provided in this study.

Temperature drives performance and therefore adaptation; to interpret and understand these, thermal performance curves (TPC) are used, often through meta‐analyses, revealing trends across divergent taxa. Four discrete hypotheses—thermodynamic‐constraint; biochemical‐adaptation (hotter is not better); specialist‐generalist; thermal‐trade‐off—have arisen to explain cross‐phyletic trends. In contrast, detailed comparisons of closely related taxa are rare, yet trends arising from these should reveal mechanisms of adaptation, as taxa diverge. Here, we combine experimental work with TPC theory to assess if the current hypotheses apply equally to closely related taxa. We established TPC for six species (and two strains of one species) of the animal model Tetrahymena (Ciliophora)—characterized by SSU rDNA/COX1 sequences—by examining specific growth rate (r), size (V), production (P = rV), and metabolic rate (rV−0.25) across 15–20 temperatures. Using parameters derived from the mechanistic “Sharpe and DeMichele” function, we established a framework to test which hypothesis best represented the data. We conclude that superficially the “hotter is not better” hypothesis is best but argue that the mechanistic theory underlying it cannot apply at the genus level: trends are likely to arise from little rather than substantial adaptation. Our further analysis suggests: (1) upward shift in the maximum‐functioning temperature (Tmax) is more constrained than the optimal temperature (Topt), leading to a decreased safety margin (Topt−Tmax) and suggesting that species initially succeed in warmer environments through an increase in Topt, followed by increasing Tmax; and (2) thermal performance traits are correlated with phylogeny for closely related species, suggesting that species gradually adapt to new thermal environments.

Plankton ecologists ultimately focus on forecasting, both applied and environmental outcomes. We review how appreciating planktonic ciliates has become central to these predictions. We explore the 350-year old canon on planktonic ciliates and examine its steady progression, which has been punctuated by conceptual insights and technological breakthroughs. By reflecting on this process, we offer suggestions as to where future leaps are needed, with an emphasis on predicting outcomes of global warming. We conclude that in terms of climate change research: i. climatic hotspots (e.g., polar oceans) require attention; ii. simply adding ciliate measurements to zooplankton/phytoplankton-based sampling programs is inappropriate; iii. elucidating the rare biosphere’s functional ecology requires culture-independent genetic methods; iv. evaluating genetic adaptation (microevolution) and population composition shifts is required; v. contrasting marine and freshwaters needs attention; vi. mixotrophy needs attention; vii. laboratory and field studies must couple automated measurements and molecular assessment of functional gene expression; viii. ciliate trophic diversity requires appreciation; and, ix. marrying gene expression and function, coupled with climate change scenarios is needed. In short, continued academic efforts and financial support are essential to achieve the above; these will lead to understanding how ciliates will respond to climate change, providing tools for forecasting.

To succeed, a scientist must write well. Substantial guidance exists on writing papers that follow the classic Introduction, Methods, Results, and Discussion (IMRaD) structure. Here, we fill a critical gap in this pedagogical canon. We offer guidance on developing a good scientific story . This valuable—yet often poorly achieved—skill can increase the impact of a study and its likelihood of acceptance. A scientific story goes beyond presenting information. It is a cohesive narrative that engages the reader by presenting and solving a problem, with a beginning, middle, and end. To create this narrative structure, we urge writers to consider starting at the end of their study, starting with writing their main conclusions, which provide the basis of the Discussion, and then work backwards: Results → Methods → refine the Discussion → Introduction → Abstract → Title. In this brief and informal editorial, we offer guidance to a wide audience, ranging from upper-level undergraduates (who have just conducted their first research project) to senior scientists (who may benefit from re-thinking their approach to writing). To do so, we provide specific instruction, examples, and a guide to the literature on how to “write backwards”, linking scientific storytelling to the IMRaD structure.

Free-living eukaryotic microbes may reduce animal diseases. We evaluated the dynamics by which micrograzers (primarily protozoa) apply top-down control on the chytrid Batrachochytrium dendrobatidis (Bd) a devastating, panzootic pathogen of amphibians. Although micrograzers consumed zoospores (∼3 μm), the dispersal stage of chytrids, not all species grew monoxenically on zoospores. However, the ubiquitous ciliate Tetrahymena pyriformis, which likely co-occurs with Bd, grew at near its maximum rate (r = 1.7 d–1). A functional response (ingestion vs. prey abundance) for T. pyriformis, measured using spore-surrogates (microspheres) revealed maximum ingestion (Imax) of 1.63 × 10³ zoospores d–1, with a half saturation constant (k) of 5.75 × 10³ zoospores ml–1. Using these growth and grazing data we developed and assessed a population model that incorporated chytrid-host and micrograzer dynamics. Simulations using our data and realistic parameters obtained from the literature suggested that micrograzers could control Bd and potentially prevent chytridiomycosis (defined as 10⁴ sporangia host–1). However, simulated inferior micrograzers (0.7 × Imax and 1.5 × k) did not prevent chytridiomycosis, although they ultimately reduced pathogen abundance to below levels resulting in disease. These findings indicate how micrograzer responses can be applied when modeling disease dynamics for Bd and other zoosporic fungi.