Gisela M. Figueiredo

Do protozoa contribute significantly to the diet of larval fish in the Irish Sea

This study evaluates the role of protozoa in larval fish feeding by describing protozoa in larval fish diets and testing the hypothesis that, in the Irish Sea, larval fish feed on protozoan prey at rates that potentially sustain their food requirements. Gut contents of 11 taxonomic groups of larval fish were examined, and protist prey occurred in the diet of all of them. Protozoan prey were identified, which provided an insight into their trophic role. Most of the protozoan prey were autotrophic or mixotrophic. In general, larval fish diets were constant over the spring/summer period, regardless of prey availability in the field and the composition of larval fish assemblage (taxonomy and size). A laboratory experiment on ingestion rates of flounder larvae as a function of ciliates concentration was conducted. Combined laboratory and field data showed that, in the Irish Sea, it is unlikely that ciliates are often the primary food source of flounder larvae, and, by implication, other larval fish as well. However, ciliates and other protozoa could be a substantial component of the larval fish diet, and they may potentially prevent food limitation.

The Protozooplankton-Ichthyoplankton Trophic Link: An Overlooked Aspect of Aquatic Food Webs

ABSTRACT. Since the introduction of the microbial loop concept, awareness of the role played by protozooplankton in marine food webs has grown. By consuming bacteria, and then being consumed by metazooplankton, protozoa form a trophic link that channels dissolved organic material into the “classic” marine food chain. Beyond enhancing energy transfer to higher trophic levels, protozoa play a key role in improving the food quality of metazooplankton. Here, we consider a third role played by protozoa, but one that has received comparatively little attention: that as prey items for ichthyoplankton. For >100 years it has been known that fish larvae consume protozoa. Despite this, fisheries scientists and biological oceanographers still largely ignore protozoa when assessing the foodweb dynamics that regulate the growth and survival of larval fish. We review evidence supporting the importance of the protozooplankton–ichthyoplankton link, including examples from the amateur aquarium trade, the commercial aquaculture industry, and contemporary studies of larval fish. We then consider why this potentially important link continues to receive very little attention. We conclude by offering suggestions for quantifying the importance of the protozooplankton–ichthyoplankton trophic link, using both existing methods and new technologies.

Morphological description of the gastropod Heleobia australis (Hydrobiidae) from egg to hatching

Raquel A. F. Neves ¹*, Jean Louis Valentin and Gisela M. Figueiredo ¹Universidade Federal do Rio de Janeiro Programa de Pos-Graduacao em Ecologia (PPGE-UFRJ) Laboratorio de Zooplâncton Marinho Av. Professor Rodolpho Rocco 211, Cidade Universitaria, Rio de Janeiro, RJ, Brasil. CEP: 24949-900 *Corresponding author: raquelneves@ufrj.br Hydrobiidae family (Caenogastropoda) has a global distribution in the intertidal zones of lagoons and estuaries (KABAT; HERSHLER, 1993). They constitute a diverse group of gastropods consisting of more than 1000 species (BOSS, 1971) and they play an important role in the benthic food web (KABAT; HERSHLER, 1993). In South America, Heleobia australis (Orbigny, 1835) is the dominant species of the Hydrobiidae family and it is an important food source for many species (ALBERTONI et al., 2003). Heleobia australis occurs in estuarine systems and coastal lagoons from Rio de Janeiro, Brazil to the Rio Negro, Argentina (SILVA; VEITENHEIMER-MENDES, 2005), and it forms dense populations that reach up to 40,000 ind./m² (BEMVENUTI et al., 1978). It is a gonochoristic species with internal fertilization and the sperm may be stored for some time before fertilization, as described for other Gastropoda (KOHN et al., 1987). As protostomes, H. australis has spiral and determinate cleavage. Their eggs have an animal-vegetal polarity that defines the anterior-posterior axis of the embryo (COLLIER, 1997; NIELSEN, 2004). Related species deposits their egg masses from which pelagic veligers develop (SOLA, 1996), and H. australis has been observed to present a similar development (pers. observation). In order to better understand ecological, behavioral and taxonomic aspects of organisms it is important to know their morphological characteristics throughout their life cycle. However, studies of Hydrobiidae life cycles are still rare, particularly as regards their development from eggs to veliger larvae. For H. australis, despite its abundance, no stage of development has yet been described. This is thus the first study to describe the development of this species from egg to hatching by continuous observation. The characterization of this stage may help in the identification of the species. KOHN et al. (1987) suggested using pigmentation and velar lobe shape to identify living specimens. Heleobia australis was sampled in two areas of Guanabara Bay (Rio de Janeiro, Brazil) (22°84’S 043°20’W; 22°76’S 043°20’W) using a Van-veen grab (0.05 m²) in May and September, 2009. The sediment in the regions sampled was muddy (silt-clay), without any vegetation, and had a low dissolved oxygen concentration (VALENTIN et al., 1999). Egg masses were separated from thirty adults and kept in covered 150-ml Petri dishes with filtered (0.07 µm) sea water at 23°C, the same temperature as that recorded in the natural habitat. Then the eggs were isolated and classified according to their stage and maintained under the same conditions. A few eggs in each stage were observed daily and photographed using a Canon camera attached to a Zeiss Axiostar optic microscope. The images were then analyzed and the embryos measured using the Carl Zeiss imaging solutions program Axio Vision (V 4.5). The egg masses were observed attached to the adult shells (Fig. 1A), which is typical of the Hydrobiidae. Breeding seems to occur year-round in Guanabara Bay. As with other species of Hydrobiidae, mature females lay their fertilized eggs in capsules (or egg masses), preferably on live shells of their own species (FISH; FISH, 1974), but they may also be laid on dead shells, shells of other species, on sand grains, or algae (ANDERSON, 1971). The egg masses of H. autralis were yellow and consisted of capsules, each one containing one white egg that developed into a veliger larva. The number of eggs per egg mass varied between 10 and 15 (n=30). Some eggs had not completed their development and different development stages were to be found in the same egg mass; embryos in the initial stage of development and post-hatching capsules were observed in the same egg mass. Despite not being possible to determine the timing of development of each stage, the stages were classified in accordance with the development proposed by Russo and Patti (2005). A. Pre-division phase: egg before the cleavage. The capsules are of spherical shape and compact. The egg diameter was of about 80 µm and the capsule about 120 µm (Fig. 1B; n = 15).

Evaluation of the complexity and performance of marine planktonic trophic models

Planktonic models represent a powerful tool for creating hypotheses and making predictions about the functioning of marine ecosystems. Their complexity varies according to the number of state variables and the choice of functional forms. We evaluated plankton models during the last 15 years (n =145) with the aims of understanding why they differ in complexity, evaluating model robustness, and describing studies of plankton modelling around the globe. We classified models into four groups: Nutrient-Phytoplankton-Zooplankton (NPZ), Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD), Size-Structured (SS) and Plankton-Functional-Type (PFT). Our results revealed that the number of state variables varied according to the question being addressed: NPZ models were more frequently applied in physical-biological studies, while PFT models were more applied for investigating biogeochemical cycles. Most models were based on simple functional forms which neglect important feedback related to control of plankton dynamics. Modelling studies sometimes failed to describe sensitivity analysis, calibration and validation. The importance of testing different functional forms was commonly overlooked, and the lack of empirical data affected the verification of model robustness. Lastly, we highlight the need to develop modelling studies in the Southern Hemisphere, including Brazil, in order to provide predictions that assist the management of marine ecosystems.

Immunological and physiological responses of the periwinkle Littorina littorea during and after exposure to the toxic dinoflagellate Alexandrium minutum.

Species of the dinoflagellate genus Alexandrium produce phycotoxins responsible for paralytic shellfish poisoning. Blooms of Alexandrium minutum reach very high concentrations of vegetative cells in the water column; and when these blooms occur, large numbers of toxic cysts can be produced and deposited on sediments becoming available to benthic species. The present study investigated the potential effect of exposure to toxic cysts of A. minutum on the periwinkle Littorinalittorea. Snails were exposed for nine days to pellicle cysts of toxic and non-toxic dinoflagellates, A. minutum and Heterocapsa triquetra, respectively, followed by six days of depuration while they were fed only H. triquetra. Toxin accumulation, condition index, immune and histopathological responses were analyzed. Histological alterations were also monitored in snails exposed to a harmful A. minutum bloom, which naturally occurred in the Bay of Brest. Snails exposed to toxic cysts showed abnormal behavior that seems to be toxin-induced and possibly related to muscle paralysis. Periwinkles accumulated toxins by preying on toxic cysts and accumulation appeared dependent on the time of exposure, increasing during intoxication period but tending to stabilize during depuration period. Toxic exposure also seemed to negatively affect hemocyte viability and functions, as ROS production and phagocytosis. Histological analyses revealed that toxic exposure induced damages on digestive organs of snails, both in laboratory and natural systems. This study demonstrates that an exposure to the toxic dinoflagellate A. minutum leads to sublethal effects on L. littorea, which may alter individual fitness and increase the susceptibility of snails to pathogens and diseases.

Do the changes in temperature and light affect the functional response of the benthic mud snail Heleobia australis (Mollusca: Gastropoda)?

The aim of this study was to determine the influence of temperature increase combined to conditions of light incidence on functional response of Heleobia australis. Experiments were conducted using nine to ten food concentrations for each treatment: 20°C without light; 30°C without light and, 30°C under low light intensity. For each experiment, the functional response type III (sigmoidal) was fitted and equation parameters were determined. Results suggest that, if the sediment temperature increases, H. australis will not have its ingestion rates affected negatively, whilst its feeding behavior seems to be negatively affected by light. Ingestion rates estimated for organic content in the Guanabara Bay were: 0.34 µgC ind-1h-1 at 20°C without light, 1.44 µgC ind-1h-1 at 30°C without light and 0.64 µgC ind-1h-1 at 30°C under light incidence. Higher ingestion rates were estimated at the high temperature, even under light incidence, and temperature seems to have outweighed the light effect. In contrast, if higher carbon content is considered, despite high temperature, the experiment conducted with light incidence showed lower ingestion rates than those from the experiment at 20°C without light. This study provides the first quantification of H. australis ingestion rates and the effects that changes in temperature and light have on its feeding behavior.

Reproduction and structure of the population of the Chaetognath Parasagitta friderici in Guanabara Bay (Brazil) based on short term sampling

The aim of this study was to describe the total density, densities of developmental stages and the reproduction period of Parasagitta friderici. Weekly samples were collected at one station in the channel of Guanabara Bay, Rio de Janeiro, during one year. Three vertical hauls were made for each sample, and P. friderici was separated, the developmental stages were identified, and body length (BL), ovary length (OL) and seminal vesicle width (SVW) were measured. Throughout the year P. friderici was the most abundant chaetognath species occurring in all four developmental stages, the densities of which varied from week to week. Higher densities of adults occurred in the spring, followed by peaks of juveniles in the summer. Although P. friderici seems to reproduce continuously in Guanabara Bay, a reproductive peak was apparent during the spring. The intensification of reproduction during the spring, with juveniles occurring in the summer, seems to be related to the period of higher food supply during the rainy season and intrusions of the South Atlantic Central Water.

Suspended microplastics in a highly polluted bay: Abundance, size, and availability for mesozooplankton

Microplastic ingestion by mesozooplankton may be an important pathway for the microplastics to enter the food web. To determine microplastic abundance in Guanabara Bay, samples were collected by neustonic haul with a 64-μm-net and oblique hauls using 64- and 200-μm nets. Microplastic size and abundance as well as copepod, fish-larvae, and chaetognath sizes, densities, and preferential prey sizes were determined. Microplastic abundance was higher in samples collected with fine nets (average 4.8 microplastics m-3, maximum 11 microplastics m-3) than in those collected with coarse net. Microplastic abundance in Guanabara Bay was higher than that in other marine ecosystems. Microplastics >100 μm were too large to be ingested by copepods. However, for fish larvae and chaetognaths, the abundance of microplastics, at the corresponding prey size range, were, respectively, ~9000- and 14,400-folds lower than the preferential copepod prey, in the same size range. Thus, in Guanabara Bay, microplastics were available, but too diluted to be frequently ingested by fish larvae and chaetognaths.