Paulo Cartaxana

Fast cytoplasmic streaming enables extensive chloroplast movements in the giant cells of unicellular, siphonous macroalgae. We studied chloroplast movements by light microscopy, macro-photography and pulse modulated chlorophyll a fluorescence in two such algae: Dasycladalean Acetabularia acetabulum and Bryopsidales Bryopsis sp.. Chemical inhibitors of actin polymerization and microtubule assembly were used to confirm that the observed effects were controlled by the cytoskeleton. Macro-imaging suggest that A. acetabulum responded to high light by reversible chloroplast aggregation, and inhibition of the movements led to increased Photosystem II photoinhibition, probed by the fluorescence parameter FV/FM. In A. acetabulum, wounding caused by cutting or feeding by the sap-sucking sea slug Elysia timida triggered appearance of darker and lighter cell regions, presumably chloroplast aggregation, within minutes of incurring damage. Addition of media collected from vicinity of cut algae was sufficient to induce these aggregations in intact algae, suggesting that water-borne cues or signals triggered the response. On the other hand, only minimal cytoplasmic changes were observed in Bryopsis sp. in response to high light or cutting. The relevance of chloroplast movements in protection against abiotic and biotic stressors in A. acetabulum, and the potential reasons behind the different defence strategies of the algae, are discussed.

In Metazoa, long-term sequestration of photosynthetically active algal chloroplasts – kleptoplasts – is a distinctive physiological trait of sacoglossan sea slugs. In this study, we examined the effects of the light spectrum on the body weight and photosynthetic activity of the sea slug Elysia crispata. Laboratory-reared specimens were exposed to equivalent irradiances of white, red, or blue light during feeding and starvation experiments. Sea slugs fed under red light increased their weight at a faster pace than specimens fed under white or blue light. At the end of the feeding trial, chlorophyll a concentration – a proxy for kleptoplast abundance – was significantly higher under blue light. Progressive weight loss was observed in starved sea slugs under all light spectra, but an initial transient weight increase was observed under red light. Photosystem II activity and photosynthetic electron transport rate declined in starvation, with the decrease being fastest under red light and slowest under blue light. Results suggest a trade-off between increased photosynthetic rates and kleptoplast degradation, leading to increased growth (under red light) and enhanced kleptoplast longevity, possibly due to reduced photooxidative damage (under blue light). We hypothesise that the higher degree of parapodia closure observed under blue light shields kleptoplasts from light-induced damage, effectively extending their lifespan.

The capacity to retain long-term functional algal chloroplasts within animal cells is a singular trait of certain Sacoglossa sea slugs. The sequestered chloroplasts (kleptoplasts) confer photosynthetic capacity to the host. Photosynthetic organisms possess distinctive lipid classes that are essential for chloroplast membrane integrity and photosynthetic function. This study investigated how chloroplast lipidomes from two macroalgae ( Acetabularia acetabulum and Bryopsis sp.) are remodelled following sequestration by the photosynthetic sea slugs Elysia crispata , Elysia viridis , and Elysia timida . Pigments were analysed by HPLC, and lipidomic profiling of chloroplasts, focusing on glycolipids, betaine lipids and phytosterols, was conducted using C18-LC-MS/MS. Kleptoplasts preserved an intact algal pigment profile across hosts. Glycolipid signatures in sea slug tissues closely resembled those of their algal donors, although shifts in relative abundances suggested post-sequestration remodelling of plastidial membranes, with potential consequences on membrane curvature, stability and kleptoplast morphology. In contrast, betaine lipid composition diverged markedly between sea slugs and algal donors, with a set of dominant betaine species shared among all sea slugs. Phytosterol composition was better preserved in sea slugs feeding on Bryopsis sp. than on A. acetabulum . This study demonstrated that kleptoplast lipidomes retain strong algal identity while undergoing selective modifications within the animal host. Host-associated modifications likely tune membrane architecture to support long-term stability and photosynthetic functionality within the hosts’ cellular environment, facilitating the integration and performance of sea slug kleptoplasts.

Bryopsidales green macroalgae can induce non-photochemical quenching (NPQ) only slowly, presumably due to the lack of the proton gradient-induced component (qE) of NPQ and xanthophyll cycle. Here, two morphologically rather similar siphonous macroalgae, a Bryopsidales alga Bryopsis sp. and a Dasycladales alga Acetabularia acetabulum , latter of which is capable of qE, were given high light treatments with both constant and fluctuating intensity. No differences in the rate of photoinhibition of Photosystem II (PSII), estimated with the chlorophyll a fluorescence parameter F _V /F _M , in the absence or presence of lincomycin, were observed between constant and fluctuating light, nor between the two algae. Bryopsis sp. showed slower PSII recovery than A. acetabulum , possibly reflecting a regulatory response rather than increased oxidative stress, as the recovery rates increased with increasing amounts of PSII photoinhibition in both algae. In Bryopsis sp., however, high light treatments led to decreased electron transfer rates, estimated by both chlorophyll a fluorescence and net oxygen production, whereas a stimulation was observed in A. acetabulum . Nigericin, which prevents the formation of qE, increased photoinhibition in A. acetabulum but not in Bryopsis sp. Microoxic conditions as well as inhibitors of plastid terminal oxidase and mitochondrial respiration, on the other hand, enhanced photoinhibition only in Bryopsis sp., suggesting that, in the absence of qE, oxygen-dependent pathways (including flavodiiron proteins) are important for photoprotection. Near-infra-red absorption measurements suggest decreased Photosystem I (PSI) donor side limitation in Bryopsis sp., compared to A. acetabulum , and a lower capacity to keep P700 oxidised.

Caulerpa lentillifera is an edible green macroalga with increasing commercial importance in seaweed aquaculture and functional food markets. The seaweed thallus is composed of stolons and fronds that bear globular structures resembling grapes. After harvesting and sorting, the majority of C. lentillifera biomass is rejected as waste, and only selected fronds are considered food-grade. This study provides an integrated analysis of lipids, fatty acids, and photosynthetic pigments in fronds and stolons of C. lentillifera. Lipidomic analysis by liquid chromatography high-resolution mass spectrometry (LC-HR-MS/MS) revealed similar lipid profiles in fronds and solons, with glycolipids as major lipid components, followed by phospholipids, betaine lipids, and neutral lipids. Fatty acid composition was also similar in fronds and stolons, showing high proportions of polyunsaturated fatty acids (PUFA), including nutritionally valuable omega-3 PUFA. High-performance liquid chromatography (HPLC) analysis identified eight photosynthetic pigments, with siphonaxanthin and its ester siphonaxanthin dodecenoate as the predominant carotenoids, alongside chlorophylls a and b, violaxanthin, neoxanthin, neochrome, and β,ε-carotene. No significant effect of short-term high light stress on pigment composition was observed. Overall, stolons showed nutritional value comparable to that of food-grade fronds, supporting the valorisation of C. lentillifera as a sustainable source of bioactive lipids and carotenoids for food and nutraceutical applications.

Fast cytoplasmic streaming enables extensive chloroplast movements in the giant cells of unicellular, siphonous macroalgae. Here, we studied chloroplast movements in two such algae: the Dasycladalean Acetabularia acetabulum and the Bryopsidales Bryopsis sp.. We hypothesised that chloroplast movements function as a protective avoidance mechanism under excess light, particularly in Bryopsis sp., which lacks capacity for fast induction of photoprotective non-photochemical quenching (NPQ) and state transitions. In addition, we also investigated whether chloroplast movements are involved in responses to wounding and herbivory. The movements were studied by light microscopy, photography and pulse modulated chlorophyll a fluorescence quenching analysis. Chemical inhibitors of actin polymerization and microtubules assembly were used to confirm that the observed effects were active responses controlled by the cytoskeleton. A. acetabulum responded to high light by reversible chloroplast aggregation, probed by macro-imaging; and chemical inhibition of chloroplast movements led to an enhancement of Photosystem II photoinhibition, as probed by the fluorescence parameter F _V /F _M . No chloroplast movements were observed in Bryopsis sp. in response to high light. In A. acetabulum , wounding caused either by cutting or due to feeding by the sap-sucking sea slug Elysia timida triggered aggregation of chloroplasts within minutes of incurring the damage. Interestingly, the aggregation also occurred in intact cells away from the cutting site. Furthermore, the addition of media collected from the vicinity of cut algae was sufficient to induce chloroplast aggregation in intact algae, suggesting that water-borne cues or signals triggered the aggregation response in A. acetabulum . Bryopsis sp., however, responded to cutting by only local chloroplast aggregation. The relevance of chloroplast movements in protection against both abiotic and biotic stressors in A. acetabulum, and the potential reasons behind the different defence strategies of the algae, are discussed.

Photosynthetic sacoglossan sea slugs sequester the chloroplasts of the algae they feed upon and keep these organelles functional in the cells of their ramified digestive system. Whether the stolen chloroplasts – kleptoplasts – influence animal behavioural responses towards light is uncertain. To address this matter, we: (1) determined the light preferences of the photosynthetic sea slug Elysia crispata when offered different light spectra (450, 517, 520–650 and 665 nm) and intensities (60, 180, 425 and 1400 µmol photons m–2 s–1); and (2) established whether the light intensity preferences of E. crispata were different when fed algae acclimated to low (40 µmol photons m–2 s–1) and high irradiance (425 µmol photons m–2 s–1). Sea slugs were collected from a coral reef in the Gulf of Mexico and transported to the laboratory to perform controlled experiments. During trials, sea slugs exhibited marked exploratory behaviour. However, results show that E. crispata avoids red light (665 nm) and prefers low irradiance (60 µmol photons m–2 s–1), showing that both light spectrum and intensity are relevant to their behaviour. Furthermore, sea slugs increased their selection for high irradiance after being fed algae acclimated to high light. These results support our hypothesis that the acclimation state of the acquired kleptoplasts affects sea slug behaviour towards light. Light perception and photobehaviour in photosynthetic sea slugs seem to depend not only on animal photoreceptors, but also on a communication network between the endosymbiotic chloroplasts and the animal host.

Some Sacoglossa sea slugs are capable of stealing and maintaining functional intracellular chloroplasts—kleptoplasts—from their macroalgal prey for periods of up to several months, a process known as kleptoplasty. Although the cultivation of these marine invertebrates under laboratory conditions is crucial for research in various fields (e.g., endosymbiosis, animal physiology, discovery of new marine natural products), rearing protocols are scarce. This study presents a standardized protocol for the laboratory rearing of large numbers of the sacoglossan tropical sea slug Elysia crispata. The detailed protocol successfully facilitated embryonic development, larval metamorphosis, and juvenile-to-adult transition, allowing the rearing of multiple generations. Two groups, characterized by acquiring different kleptoplasts, were obtained by feeding the sea slugs with two different prey macroalgae: Bryopsis sp. and Acetabularia acetabulum. Usually referred to as lettuce sea slug among marine aquarium hobbyists, E. crispata is a highly valued organism for its striking appearance and ability to control nuisance algal growth in reef aquariums. This protocol allows experimental reproducibility and access to specimens under different development stages, potentially boosting research on kleptoplasty while also contributing to reducing the impact of the marine aquarium trade on natural populations.

Marine heatwaves (MHW) are intensifying, causing mass bleaching events in coral reefs. While their ecological and socioeconomic impacts are well documented, their cascading effects on specialized organisms remain understudied. Here, we investigate the impact that MHW and feeding on bleached prey have on a stenophagous tropical nudibranch, Berghia stephanieae , by analyzing its survival, reproduction, cellular stress response (CSR) and the photosynthetic activity of its endosymbionts. Thermal stress significantly reduced the number of eggs laid by B. stephanieae , while parental investment per egg was maintained. Moreover, exposure to a combination of MHW and bleached prey, impaired this nudibranch’s CSR and reduced survival, indicating a performance breakdown. These findings highlight the vulnerability of such specialized predators to MHW and the need to integrate them in marine conservation strategies. With extreme climate events becoming more frequent and prolonged, species featuring specialized diets can be amongst those paying the highest toll.