Maurizio Ribera d’Alcalà

Exploring the molecular basis of responses to light in marine diatoms

Light is an essential source of energy for life on Earth and is one of the most important signals that organisms use to obtain information from the surrounding environment, on land and in the oceans. Prominent marine microalgae, such as diatoms, display a suite of sophisticated responses (physiological, biochemical, and behavioural) to optimize their photosynthesis and growth under changing light conditions. However, the molecular mechanisms controlling diatom responses to light are still largely unknown. Recent progress in marine diatom genomics and genetics, combined with well-established (eco) physiological and biophysical approaches, now offers novel opportunities to address these issues. This review provides a description of the molecular components identified in diatom genomes that are involved in light perception and acclimation mechanisms. How the initial functional characterizations of specific light regulators provide the basis to investigate the conservation or diversification of light-mediated processes in diatoms is also discussed. Hypotheses on the role of the identified factors in determining the growth, distribution, and adaptation of diatoms in different marine environments are reported.

Ecological-network models link diversity, structure and function in the plankton food-web.

A planktonic food-web model including sixty-three functional nodes (representing auto- mixo- and heterotrophs) was developed to integrate most trophic diversity present in the plankton. The model was implemented in two variants - which we named ‘green’ and ‘blue’ - characterized by opposite amounts of phytoplankton biomass and representing, respectively, bloom and non-bloom states of the system. Taxonomically disaggregated food-webs described herein allowed to shed light on how components of the plankton community changed their trophic behavior in the two different conditions, and modified the overall functioning of the plankton food web. The green and blue food-webs showed distinct organizations in terms of trophic roles of the nodes and carbon fluxes between them. Such re-organization stemmed from switches in selective grazing by both metazoan and protozoan consumers. Switches in food-web structure resulted in relatively small differences in the efficiency of material transfer towards higher trophic levels. For instance, from green to blue states, a seven-fold decrease in phytoplankton biomass translated into only a two-fold decrease in potential planktivorous fish biomass. By linking diversity, structure and function in the plankton food-web, we discuss the role of internal mechanisms, relying on species-specific functionalities, in driving the ‘adaptive’ responses of plankton communities to perturbations.

Unexpected Regularity in Swimming Behavior of Clausocalanus furcatus Revealed by a Telecentric 3D Computer Vision System

Planktonic copepods display a large repertoire of motion behaviors in a three-dimensional environment. Two-dimensional video observations demonstrated that the small copepod Clausocalanus furcatus, one the most widely distributed calanoids at low to medium latitudes, presented a unique swimming behavior that was continuous and fast and followed notably convoluted trajectories. Furthermore, previous observations indicated that the motion of C. furcatus resembled a random process. We characterized the swimming behavior of this species in three-dimensional space using a video system equipped with telecentric lenses, which allow tracking of zooplankton without the distortion errors inherent in common lenses. Our observations revealed unexpected regularities in the behavior of C. furcatus that appear primarily in the horizontal plane and could not have been identified in previous observations based on lateral views. Our results indicate that the swimming behavior of C. furcatus is based on a limited repertoire of basic kinematic modules but exhibits greater plasticity than previously thought.

Nutrient consumption and chain tuning in diatoms exposed to storm-like turbulence.

Current information on the response of phytoplankton to turbulence is linked to cell size and nutrient availability. Diatoms are considered to be favored by mixing as dissolved nutrients are more easily accessible for non-motile cells. We investigated how diatoms exploit microscale turbulence under nutrient repletion and depletion conditions. Here, we show that the chain-forming diatom Chaetoceros decipiens, continues to take up phosphorus and carbon even when silicon is depleted during turbulence. Our findings indicate that upon silica depletion, during turbulence, chain spectra of C. decipiens remained unchanged. We show here that longer chains are maintained during turbulence upon silica depletion whereas under still conditions, shorter chains are enriched. We interpret this as a sign of good physiological state leading to a delay of culture senescence. Our results show that C. decipiens senses and responds to turbulence both in nutrient repletion and depletion. This response is noteworthy due to the small size of the species. The coupling between turbulence and biological response that we depict here may have significant ecological implications. Considering the predicted increase of storms in Northern latitudes this response might modify community structure and succession. Our results partly corroborate Margalef’s mandala and provide additional explanations for that conceptualization.

Marine diatoms change their gene expression profile when exposed to microscale turbulence under nutrient replete conditions

Diatoms are a fundamental microalgal phylum that thrives in turbulent environments. Despite several experimental and numerical studies, if and how diatoms may profit from turbulence is still an open question. One of the leading arguments is that turbulence favours nutrient uptake. Morphological features, such as the absence of flagella, the presence of a rigid exoskeleton and the micrometre size would support the possible passive but beneficial role of turbulence on diatoms. We demonstrate that in fact diatoms actively respond to turbulence in non-limiting nutrient conditions. TURBOGEN, a prototypic instrument to generate natural levels of microscale turbulence, was used to expose diatoms to the mechanical stimulus. Differential expression analyses, coupled with microscopy inspections, enabled us to study the morphological and transcriptional response of Chaetoceros decipiens to turbulence. Our target species responds to turbulence by activating energy storage pathways like fatty acid biosynthesis and by modifying its cell chain spectrum. Two other ecologically important species were examined and the occurrence of a morphological response was confirmed. These results challenge the view of phytoplankton as unsophisticated passive organisms.

Light sensing and responses in marine microalgae

Marine eukaryotic phytoplankton are major contributors to global primary production. To adapt and thrive in the oceans, phytoplankton relies on a variety of light-regulated responses and light-acclimation capacities probably driven by sophisticated photoregulatory mechanisms. A plethora of photoreceptor-like sequences from marine microalgae have been identified in omics approaches. Initial studies have revealed that some algal photoreceptors are similar to those known in plants. In addition, new variants with different spectral tuning and algal-specific light sensors have also been found, changing current views and perspectives on how photoreceptor structure and function have diversified in phototrophs experiencing different environmental conditions.

TURBOGEN: Computer-controlled vertically oscillating grid system for small-scale turbulence studies on plankton

In recent years, there has been a renewed interest in the impact of turbulence on aquatic organisms. In response to this interest, a novel instrument has been constructed, TURBOGEN, that generates turbulence in water volumes up to 13 l. TURBOGEN is fully computer controlled, thus, allowing for a high level of reproducibility and for variations of the intensity and characteristics of turbulence during the experiment. The calibration tests, carried out by particle image velocimetry, showed TURBOGEN to be successful in generating isotropic turbulence at the typical relatively low levels of the marine environment. TURBOGEN and its sizing have been devised with the long-term scope of analyzing in detail the molecular responses of plankton to different mixing regimes, which is of great importance in both environmental and biotechnological processes.

Ecological Physiognomy of the Eastern Mediterranean

The Eastern Mediterranean (EMED) is connected with the open ocean through three different sills and a wide buffering basin such as the Western Mediterranean. It is in fact almost completely enclosed by land, with the exceptions of the Sicily Channel and the very shallow connections of Bosphorus with the Marmara Sea and the more recent one with the Red Sea, which dates 1869. Though, it is a large basin with a maximum depth of more than 5000 m. Because of these characteristics, many relevant processes took place in the past and others are occurring today. To quote a few, the frequent changes in the pelagic system ([1] and references therein), the introduction of exotic species through the Suez Canal [2], the recent changes in thermohaline circulation [3] and their implications. Many topics have been thoroughly analyzed in this workshop and elsewhere. Instead, we will comment on some basic features of the pelagic realm, and the main forcings that make the area as it is now and eventually differentiate one region from another. Our contribution will mostly focus on inputs and internal transfers, which indeed cover only partially the functioning of an ecosystem. However, we think that these basic processes deserve attention and our aim is to promote a discussion on them. Moreover we will restrict our comments to the EMED proper, i.e. Adriatic and Aegean Seas will be excluded, whenever possible, from our analysis.

Meiofaunal assemblages of the bay of Nisida and the environmental status of the Phlegraean area (Naples, Southern Italy)

Nisida is an islet of volcanic origin of the Phlegraean archipelago (Southern Italy) that has been included in the General Reserve of the Regional Park of Phlegraean Islands. The islet has been inaccessible both by land and by sea for a long time and, thus, has maintained its naturalistic value almost unchanged, in contrast with the close Bagnoli area, in which a steel industry has been active for several decades. An investigation was carried out in 2014–2015 at the bay of Nisida (Porto Paone). The main aims of our study were to document the structure of the meiofaunal assemblage, to identify the environmental factors that lead to its spatial and temporal variations, and to evaluate the ecological quality of this area, so bridging a gap in the scientific knowledge of Porto Paone. According to the diverse substrate typology and hydrodynamic regime, four stations were established to evaluate the meiofaunal assemblage over a period of one year. A high number of meiofaunal taxa (21) and a high biodiversity of meiofauna were recorded: the total meiofaunal density was higher in the eastern sector of the bay, where the effects of currents increase the abundance of temporary meiofauna in the sediment by increasing the supply of planktonic larvae of macrofauna (i.e., annelids, molluscs). PERMANOVA revealed significant differences of the assemblage structures at both the temporal and spatial scales. Summer conditions appeared to favor an increase of several taxa, which may be related to both an enhancement of the trophic sources, in turn promoting more trophic lifestyles, and to the biological cycles of individual taxa. Among the environmental variables, sediment variations, temperature, and chlorophyll-a (Chl-a) concentration appeared to be important in influencing the meiofaunal distribution. The results suggest that Porto Paone is characterized by a great richness (21 vs. 8 total taxa), especially if compared with the close, highly impacted area of Bagnoli. According to the current classification of environmental quality based on the meiofaunal richness, Porto Paone may be classified with a high ecological quality.

A Conceptual Framework for Developing the Next Generation of Marine OBservatories (MOBs) for Science and Society

In the field of ocean observing, the term of ‘observatory’ is often used without a unique meaning. A clear and unified definition of observatory is needed in order to facilitate the communication in a multidisciplinary community, to capitalize on future technological innovations and to support the observatory design based on societal needs. In this paper, we present a general framework to define the next generation Marine OBservatory (MOB), its capabilities and functionalities in an operational context. The MOB structure has four components (observatory infrastructure, cyberinfrastructure, human capacity and knowledge generation engine) that are constantly and adaptively interacting with each other. Therefore, MOB is a complex infrastructure focused on a specific geographic area with the primary scope to generate knowledge via data and information thus addressing scientific, societal and economical challenges. MOB long-term sustainability, is a key feature that should be guaranteed by strategic planning that incorporates governance feedbacks. Innovations and the overall reduced-cost of equipment and operations will allow the development in quality and quantity of the MOBs globally. Thanks to the desirable MOB’s proliferation, a deeper biological understanding of the marine ecosystem should be reached thus contributing to effective conservation of ecosystems and management of humankind activities in the oceans. In sum, we provide an actionable blue-print for the upgrade and development of a sustained marine observatory producing knowledge to support science-based economical and societal decisions.