Temperature affects the use of storage fatty acids as energy source in a benthic copepod (Platychelipus littoralis, Harpacticoida)

The utilization of storage lipids and their associated fatty acids (FA) is an important means for organisms to cope with periods of food shortage, however, little is known about the dynamics and FA mobilization in benthic copepods (order Harpacticoida). Furthermore, lipid depletion and FA mobilization may depend on the ambient temperature. Therefore, we subjected the temperate copepod Platychelipus littoralis to several intervals (3, 6 and 14 days) of food deprivation, under two temperatures in the range of the normal habitat temperature (4, 15 degrees C) and under an elevated temperature (24 degrees C), and studied the changes in FA composition of storage and membrane lipids. Although bulk depletion of storage FA occurred after a few days of food deprivation under 4 degrees C and 15 degrees C, copepod survival remained high during the experiment, suggesting the catabolization of other energy sources. Ambient temperature affected both the degree of FA depletion and the FA mobilization. In particular, storage FA were more exhausted and FA mobilization was more selective under 15 degrees C compared with 4 degrees C. In contrast, depletion of storage FA was limited under an elevated temperature, potentially due to a switch to partial anaerobiosis. Food deprivation induced selective DHA retention in the copepod's membrane, under all temperatures. However, prolonged exposure to heat and nutritional stress eventually depleted DHA in the membranes, and potentially induced high copepod mortality. Storage lipids clearly played an important role in the short-term response of the copepod P. littoralis to food deprivation. However, under elevated temperature, the use of storage FA as an energy source is compromised

The early life history of the clam Macoma balthica in a high CO₂ world

This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis were severely diminished: successful fertilization was reduced by 11% at a 0.6 pH unit decrease from present (pH 8.1) conditions, while hatching success was depressed by 34 and 87%, respectively at a 0.3 and 0.6 pH unit decrease. Under acidified conditions, larvae were still able to develop a shell during the post-embryonic phase, but higher larval mortality rates indicate that fewer larvae may metamorphose and settle in an acidified ocean. The cumulative impact of decreasing seawater pH on fertilization, embryogenesis and survival to the benthic stage is estimated to reduce the number of competent settlers by 38% for a 0.3 pH unit decrease, and by 89% for a 0.6 pH unit decrease from present conditions. Additionally, slower growth rates and a delayed metamorphosis at a smaller size were indicative for larvae developed under acidified conditions. This may further decline the recruit population size due to a longer subjection to perturbations, such as predation, during the pelagic phase. In general, early life history processes were most severely compromised at similar to pH 7.5, which corresponds to seawater undersaturated with respect to aragonite. Since recent models predict a comparable decrease in pH in coastal waters in the near future, this study indicates that future populations of Macoma balthica are likely to decline as a consequence of ongoing ocean acidification

Natural stable isotope ratios and fatty acid profiles of estuarine tidal flat nematodes reveal very limited niche overlap among co-occurring species

The high local-scale species diversity of marine meiofauna, and of nematodes in particular, has puzzled ecologists for decades. Both pronounced niche differentiation and neutral dynamics have been suggested as mechanisms underlying that high diversity. Differential resource use is the most plausible basis for niche differentiation, yet the vast majority of studies demonstrating that this is prominent in marine nematodes are based on laboratory experiments on single species or highly simplified assemblages. Only a small number of studies have investigated resource differentiation under natural conditions. Here we use natural stable-isotope ratios of carbon and nitrogen, as well as fatty-acid profiles, to assess differential resource use and trophic structure in nine abundant estuarine tidal flat nematode species, comprising different presumed feeding modes (deposit feeders, epistratum feeders, predators) and resource guilds (herbivores, carnivores) based on buccal cavity morphology. Nematodes comprise up to three different trophic levels (from primary to tertiary consumers), yet with the exception of some herbivores, omnivory is prominent. Bivariate isotopic niche spaces were of similar size among most species, irrespective of their trophic level. Herbivory not only contributed importantly to the nutrition of suspected herbivores, but also to that of species that were previously considered carnivores based on the morphology of their buccal cavity. Herbivory mainly targets diatoms in some nematode species, yet includes dinoflagellates in others. Bacteria, in contrast, appear to be of limited nutritional importance. Odontophora setosus is identified as a predator/omnivore (possibly of heterotrophic protists) with a trophic level in between that of secondary and tertiary consumers. Our study thus demonstrates that resource differentiation is pronounced among as well as within nematode feeding modes and resource guilds. However, this study included only the most abundant species of the in situ community, hence it remains to be established whether and to what extent its conclusions can be extrapolated to entire, often highly species-rich communities

Seawater carbonate chemistry and early life history processes of the Baltic tellin (Macoma balthica)

This study investigated the effects of experimentally manipulated seawater carbonate chemistry on several early life history processes of the Baltic tellin (Macoma balthica), a widely distributed bivalve that plays a critical role in the functioning of many coastal habitats. We demonstrate that ocean acidification significantly depresses fertilization, embryogenesis, larval development and survival during the pelagic phase. Fertilization and the formation of a D-shaped shell during embryogenesis were severely diminished: successful fertilization was reduced by 11% at a 0.6 pH unit decrease from present (pH 8.1) conditions, while hatching success was depressed by 34 and 87%, respectively at a 0.3 and 0.6 pH unit decrease. Under acidified conditions, larvae were still able to develop a shell during the post-embryonic phase, but higher larval mortality rates indicate that fewer larvae may metamorphose and settle in an acidified ocean. The cumulative impact of decreasing seawater pH on fertilization, embryogenesis and survival to the benthic stage is estimated to reduce the number of competent settlers by 38% for a 0.3 pH unit decrease, and by 89% for a 0.6 pH unit decrease from present conditions. Additionally, slower growth rates and a delayed metamorphosis at a smaller size were indicative for larvae developed under acidified conditions. This may further decline the recruit population size due to a longer subjection to perturbations, such as predation, during the pelagic phase. In general, early life history processes were most severely compromised at ~pH 7.5, which corresponds to seawater undersaturated with respect to aragonite. Since recent models predict a comparable decrease in pH in coastal waters in the near future, this study indicates that future populations of Macoma balthica are likely to decline as a consequence of ongoing ocean acidification

Fatty acid recovery after starvation : insights into the fatty acid conversion capabilities of a benthic copepod (Copepoda, Harpacticoida)

Benthic copepods (Harpacticoida) are key members of the meiofauna community, and potentially important conveyers of energy from primary producers to higher trophic levels. However, little is known on their capability for trophic upgrading of food quality (essential fatty acids). Therefore, Platychelipus littoralis copepods were subjected to famine (3 days) and subsequent refeeding (6 days) on high (Thalassiosira weissflogii) and low (Dunaliella tertiolecta) quality food at 4, 15 and 24 C-omicron, and their resilience for recovery of structural and storage fatty acids was determined. Additionally, stable isotope probing of fatty acids gave insight into the copepods' ability to synthesize ARA (20:4 omega 6), EPA (20:5 omega 3) and DHA (22:6 omega 3) from low quality food under different temperatures. High intraspecific variability (among copepod replicates) in fatty acid composition and C-13 enrichment was observed when copepods were exposed to heat (24 C-omicron) and food quality stress, and operated therefore as an indicator of environmental stress. Synthesis of the essential fatty acids ARA, EPA and DHA from dietary precursors increased with temperature. However, despite the capability for synthesis, no fatty acid accumulation was observed, which suggested substantial fatty acid turnover, especially under heat stress. Moreover, synthesis rates were not sufficient to restore the omega 3 pools and ensure survival, at least for the duration of the experiment. Therefore, the question rises whether copepods of this local P. littoralis population will be able to cope with the reduced dietary supply of essential omega 3 fatty acids, as predicted under global warming, given that the physiological need for these essential compounds likely increases with temperature

Antarctic harpacticoids exploit different trophic niches : a summer snapshot using fatty acid trophic markers (Potter Cove, King George Island)

Unraveling food webs is a first step toward understanding of ecosystem functioning and a requirement to forecast climate-induced ecosystem responses. In this study, the organisms under examination were benthic copepods (order Harpacticoida) inhabiting a fjord-like environment on the southern coastline of King George Island at the northwestern tip of the Antarctic Peninsula, one of the most rapidly warming regions on Earth. Despite increased understanding of Antarctic food web structures, little is known about the feeding ecology of benthic copepods in these systems. A fatty acid trophic marker strategy was used to unravel the diet composition of Antarctic harpacticoid copepod species or assemblages collected from distinct habitats in summer. Their diverse storage fatty acid composition revealed the occupation of different trophic niches associated with their specific lifestyles, i. e. endobenthic or epiphytic with (Alteutha spp.) or without (Harpacticus sp.) frequent water column excursions. Moreover, the prevalence of biosynthesized.7 long-chain monounsaturated fatty acids in Harpacticus sp. and.9 fatty acids in Alteutha spp. further suggested adaptations to particular habitats in polar ecosystems, as different dietary precursors-16: 1 omega 7 (microphytobenthos, epiphytic diatoms) or 18: 1.9 (flagellates)-fuel these elongation pathways