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Estimates of carbon flux to the deep oceans are essential for our understanding of global carbon budgets. Sinking of detrital material (“biological pump”) is usually thought to be the main biological component of this flux. Here, we identify an additional biological mechanism, the seasonal “lipid pump,” which is highly efficient at sequestering carbon into the deep ocean. It involves the vertical transport and metabolism of carbon rich lipids by overwintering zooplankton. We show that one species, the copepodCalanus finmarchicusoverwintering in the North Atlantic, sequesters an amount of carbon equivalent to the sinking flux of detrital material. The efficiency of the lipid pump derives from a nearcomplete decoupling between nutrient and carbon cycling—a “lipid shunt,” and its direct transport of carbon through the mesopelagic zone to below the permanent thermocline with very little attenuation. Inclusion of the lipid pump almost doubles the previous estimates of deep-ocean carbon sequestration by biological processes in the North Atlantic.

This study examined the predator-prey interaction between Flaccisagitta enflata , a dominant chaetognath species, and copepods in the southwestern Gulf of Mexico to investigate the roles of environmental variables and predator-prey encounters in the feeding rate of F. enflata on copepods and to analyze the gut content of the predator throughout three seasons. Zooplankton samples were collected in summer, fall, and winter in both neritic and oceanic waters. Predator-prey encounters were examined under calm and turbulent conditions to test the influence of wind-induced turbulence. Results indicated that encounters varied across seasons and zones: under calm conditions, they ranged from 11 to 75 copepods/chaetognath.day; under turbulent conditions, encounters increased by 1.5 to 1.8 times at the surface. Statistical tests revealed significant differences in feeding rates across seasons and zones: in summer and fall, feeding rates were higher in neritic waters, whereas in winter, they were higher in the oceanic zone. The primary factors influencing feeding rates were temperature, encounter rates, and salinity. Higher summer and fall temperatures resulted in shorter digestion times and, consequently, higher feeding rates (0.44 to 0.74 copepods/chaetognath day). The encounter rates, strongly correlated with copepod density, positively influenced feeding rates, particularly in summer and fall, with the highest values in the neritic zone. The lowest salinity records, caused by river discharges and observed in winter in shelf waters, corresponded with the lowest feeding rates (0.30 copepods/chaetognath.day). Freshwater inflows carrying suspended sediments increase turbidity, which potentially interferes with the predatory mechanisms of F. enflata and diminishes its feeding rates. Specifically, the main ingested copepods were members of the genera Temora and Euaugaptilus. These findings improve our understanding of the predator-prey interaction between the most abundant zooplankton organisms.

Metazoan adaptation to global change relies on selection of standing genetic variation. Determining the extent to which this variation exists in natural populations, particularly for responses to simultaneous stressors, is essential to make accurate predictions for persistence in future conditions. Here, we identified the genetic variation enabling the copepod Acartia tonsa to adapt to experimental ocean warming, acidification, and combined ocean warming and acidification (OWA) over 25 generations of continual selection. Replicate populations showed a consistent polygenic response to each condition, targeting an array of adaptive mechanisms including cellular homeostasis, development, and stress response. We used a genome-wide covariance approach to partition the allelic changes into three categories: selection, drift and replicate-specific selection, and laboratory adaptation responses. The majority of allele frequency change in warming (57%) and OWA (63%) was driven by shared selection pressures across replicates, but this effect was weaker under acidification alone (20%). OWA and warming shared 37% of their response to selection but OWA and acidification shared just 1%, indicating that warming is the dominant driver of selection in OWA. Despite the dominance of warming, the interaction with acidification was still critical as the OWA selection response was highly synergistic with 47% of the allelic selection response unique from either individual treatment. These results disentangle how genomic targets of selection differ between single and multiple stressors and demonstrate the complexity that nonadditive multiple stressors will contribute to predictions of adaptation to complex environmental shifts caused by global change.

Interactions among microscopic planktonic organisms underpin the functioning of open ocean ecosystems. With few exceptions, these organisms lack advanced eyes and thus rely largely on chemical sensing to perceive their surroundings. However, few of the signaling molecules involved in interactions among marine plankton have been identified. We report a group of eight small molecules released by copepods, the most abundant zooplankton in the sea, which play a central role in food webs and biogeochemical cycles. The compounds, named copepodamides, are polar lipids connecting taurine via an amide to isoprenoid fatty acid conjugate of varying composition. The bloom-forming dinoflagellate Alexandrium minutum responds to pico- to nanomolar concentrations of copepodamides with up to a 20-fold increase in production of paralytic shellfish toxins. Different copepod species exude distinct copepodamide blends that contribute to the species-specific defensive responses observed in phytoplankton. The signaling system described here has far reaching implications for marine ecosystems by redirecting grazing pressure and facilitating the formation of large scale harmful algal blooms. Significance We report the chemical basis for a critical question in ocean science: how do single-celled algae, which are responsible for almost half of Earth's photosynthesis, sense their environment to respond appropriately to the lethal threat of predation? The increasing frequency of toxic algal blooms, with worldwide consequences to human health, fisheries, and marine ecosystem functioning, has garnered much attention in recent years, but it has remained unclear how algal toxicity is regulated. With the current paper, we show that substantial (20×) induction of toxicity occurs when one species of algae is exposed to a family of previously unknown chemical cues from predatory zooplankton (copepods). The copepodamides represent the first discovery, to our knowledge, of chemical cues mediating interactions between marine zooplankton and their prey.

Interactions between planktonic organisms, such as detection of prey, predators, and mates, are often mediated by fluid signals. Consequently, many plankton predators perceive their prey from the fluid disturbances that it generates when it feeds and swims. Zooplankton should therefore seek to minimize the fluid disturbance that they produce. By means of particle image velocimetry, we describe the fluid disturbances produced by feeding and swimming in zooplankton with diverse propulsion mechanisms and ranging from 10-µm flagellates to greater than millimeter-sized copepods. We show that zooplankton, in which feeding and swimming are separate processes, produce flow disturbances during swimming with a much faster spatial attenuation (velocity u varies with distance r as u ∝ r ⁻³ to r ⁻⁴) than that produced by zooplankton for which feeding and propulsion are the same process (u ∝ r ⁻¹ to r ⁻²). As a result, the spatial extension of the fluid disturbance produced by swimmers is an order of magnitude smaller than that produced by feeders at similar Reynolds numbers. The “quiet” propulsion of swimmers is achieved either through swimming erratically by short-lasting power strokes, generating viscous vortex rings, or by “breast-stroke swimming.” Both produce rapidly attenuating flows. The more “noisy” swimming of those that are constrained by a need to simultaneously feed is due to constantly beating flagella or appendages that are positioned either anteriorly or posteriorly on the (cell) body. These patterns transcend differences in size and taxonomy and have thus evolved multiple times, suggesting a strong selective pressure to minimize predation risk.

Understanding how populations adapt to heterogeneous thermal regimes is essential for comprehending how latitudinal gradients in species diversification are formed, and how taxa will respond to ongoing climate change. Adaptation can occur by innate genetic factors, by phenotypic plasticity, or by a combination of both mechanisms. Yet, the relative contribution of such mechanisms to large-scale latitudinal gradients of thermal tolerance across conspecific populations remains unclear. We examine thermal performance in 11 populations of the intertidal copepod Tigriopus californicus, ranging from Baja California Sur (Mexico) to British Columbia (Canada). Common garden experiments show that survivorship to acute heat-stress differs between populations (by up to 3.8°C in LD50 values), reflecting a strong genetic thermal adaptation. Using a split-brood experiment with two rearing temperatures, we also show that developmental phenotypic plasticity is beneficial to thermal tolerance (by up to 1.3°C), and that this effect differs across populations. Although genetic divergence in heat tolerance strongly correlates with latitude and temperature, differences in the plastic response do not. In the context of climate warming, our results confirm the general prediction that low-latitude populations are most susceptible to local extinction because genetic adaptation has placed physiological limits closer to current environmental maxima, but our results also contradict the prediction that phenotypic plasticity is constrained at lower latitudes.

Copepods are small crustacean zooplankton that closely follow Bergmann's rule, which states that larger organisms will be found at higher latitudes. While thermally driven metabolic effects and food availability are often stated to be the major drivers behind this trend, temperature affects multiple variables within the copepod and its environment, a key variable to copepod ecology being viscosity. To test the effects of viscosity on copepod body size, two lineages of subtropical, freshwater Mesocyclops sp. copepods were grown for five generations in cultures of differing temperatures, 30°C and 18°C, and viscosities, natural and altered to mimic 18°C while at 30°C. Copepods grown at 30°C were, on average, 13.20% smaller than those grown at 18°C, regardless of viscosity. Copepods grown in 30°C cultures with a viscosity of 18°C had no body size differences when compared to copepods grown at 30°C and a natural viscosity. Copepods reached sexual maturity after 10 days while grown at 30°C and after 13 days while grown at 18°C, with viscosity playing no role in maturation time. As such, this study provides further support for temperature driving copepod body size, with the viscosity of the environment playing no discernible role in the body size of these small organisms.

Phytoplankton employ a variety of defence mechanisms against predation, including production of toxins. Domoic acid (DA) production by the diatom Pseudo-nitzschia spp. is induced by the presence of predators and is considered to provide defence benefits, but the evidence is circumstantial. We exposed eight different strains of P. seriata to chemical cues from copepods and examined the costs and the benefits of toxin production. The magnitude of the induced toxin response was highly variable among strains, while the costs in terms of growth reduction per DA cell quota were similar and the trade-off thus consistent. We found two components of the defence in induced cells: (i) a ‘private good’ in terms of elevated rejection of captured cells and (ii) a ‘public good’ facilitated by a reduction in copepod feeding activity. Induced cells were more frequently rejected by copepods and rejections were directly correlated with DA cell quota and independent of access to other food items. By contrast, the public-good effect was diminished by the presence of alternative prey suggesting that it does not play a major role in bloom formation and that its evolution is closely associated with the grazing-deterrent private good.

The Canary Current Large Marine Ecosystem (CCLME) is one of the most productive Large Marine Ecosystems worldwide. Assessing the abundance, biomass and distribution of zooplankton in the southern part of this system, off the coast of West Africa, remains challenging due to limited sampling efforts and data availability. However, zooplankton is of primary importance for pelagic ecosystem functioning. We applied an inversion method with combined analysis of acoustic and biological data for copepod discrimination using a bi-frequency (38 and 120 kHz) approach. Large copepods with equivalent spherical radii > 0.5 mm were identified using differences in the mean volume backscattering strength (MVBS). Regarding abundance measured by net sampling, copepods strongly dominated the zooplankton community and the large fraction account for 18%. This estimate correlated significantly with MVBS values that were obtained using an inverse algorithm. We confirmed the utility of using 38 kHz for large copepod detection. An epipelagic biomass of large copepod was estimated at 120–850 mg m -2 in March during upwelling season. It is worth noting that this estimation likely underestimates the true biomass due to inherent uncertainties associated with the measurement method. We recommend future investigations in the interest of using only nighttime data to improve the sampling pattern, particularly on the upper part of the water column (< 10 m) as well as on the shallow part of the continental shelf (< 20 m depth) not covered by fisheries vessel. Nevertheless, such high copepod biomass supports high fish production underlining the key role of copepod in the CCLME. Our results open the way to the analysis of the fluctuation and trend of copepod biomass, along with three decades of fisheries acoustics data available in the region. This helps to determine ecosystem changes, particularly under climate change, and to investigate the role of copepods in the southern CCLME carbon pump at the fine scale.

Sea lice infestations cause significant economic losses in the Atlantic salmon aquaculture industry. To biologically control sea lice at farming sites, cleaner fish such as lumpfish are employed. However, the efficacy of lumpfish is under constant debate, primarily due to limited knowledge of digestion times, which makes it difficult to interpret the number of salmon lice found in the stomach contents of dissected lumpfish. The aim of this study was to provide quantitative estimates of the degradation of salmon lice over a period of 12 days. After an acclimation period of approximately one week, batches of eight lumpfish (average weight 94.3 g, SD ± 33.2) were fed salmon lice and arranged in tanks. Each batch received six large mobile lice and two adult female lice. Samplings were conducted at 24-hour intervals during the first four days and at 48-hour intervals over the remaining eight days. The experiment was conducted twice, each at a different temperature regime (6°C and 9°C), using live lice in both trials. To investigate if the freshness of the louse influenced degradation and digestion, the setup was replicated in the 9°C experiment with lice that had been stored frozen at -80°C, with an additional 12-hour sampling point for comprehensive observation. The analysis of salmon lice revealed expected digestion times of 6.4 days and 12.9 days for large mobile and adult female salmon lice, respectively. Temperature and lice freshness did not seem to influence digestion times, but the developmental stage of the lice did. The findings of this study can be used to estimate the cleaning efficacy of lumpfish based on the stomach contents.