Ecology of the marine copepod genus Oithona

Copepods have a crucial role in the pelagic marine ecosystem, for their participation in the nutrient cycling and carbon export in biogeochemical cycles, and their role as link organisms between primary producers and higher trophic levels. Historically, marine zooplankton studies have focused on large organism (> 1mm), due to the use of relatively large mesh sizes in plankton nets, which has resulted in an underestimation of the importance of small copepods such as the genus Oithona. The study of small copepods, and especiall of Oithona, has raised special interest in recent years due to its great abundance and ubiquitous presence in both coastal and oceanic regions, and with a distribution that extends from polar to tropical . Besides their numerical dominance, Oithona also makes up a significant fraction of the biomass of copepods in certain regions. Their described low metabolic rates, coupled with an ambush feeding behavior and low mortality, are considered the clue of their success and of their capacity to maintain active populations throughout the year. Although new insights on the ecology of Oithona have been acquired in the past decade, knowledge on their vital rates is still very scarce. The lack of studies on the ecophysiology of Oithona contrasts with the large amount of studies conducted on calanoid copepods on aspects related to feeding, growth, and egg production. The main objective of this thesis was to contribute to a better knowledge and understanding of some biological and ecological aspects of the genus Oithona. For that purpose, we carried out laboratory experiments with cultured specimens, and experimental lab and fieldwork with natural populations in polar and tropical regions. In the laboratory we studied the effect of food concentration on ingestion and fecundity rates of Oithona davisae. The results obtained indicate that Oithona davisae is able to feed at very low food concentrations, which indicates its ability to exploit oligotrophic environments. Oithona capacity to reproduce continuously throughout the year, even in environments or periods of low food availability, was confirmed by the relatively high fertility rates observed in laboratory experiments at low food concentrations. The trophic role of Oithona, their natural diet and ingestion rates were studied in different pelagic ecosystems; as well as the fecudity of adult females in these ecosystems, and their relationship with environmental factors. We also investigated some aspects of the population ecology Oithona in polar regions (abundance, vertical distribution and migration patterns). The results of the in situ investigations were carried out in order to compare life strategies between Oithona species of contrasting habitats. In polar environments, winter reproductive activity of the adult females was observed, which highlights the importance of small copepods in high-latitude environments, especially when large calanoid are not present in the productive zone of the water column. Moreover, the strategy of Oithona life in polar area is different from that of large calanoid, and it benefits from its independence from the spring blooms of phytoplankton to maintain active populations throughout the year. The ability of Oithona to successfully survive when unfavourable conditions are present in the water could explain the success of this genus of copepods in marine environments around the world.Postprint (published version

Molecular evidence of host-parasite interactions between zooplankton and Syndiniales

Although parasitism is one of the most prevalent interactions in nature, studies of aquatic food webs rarely include parasites. Syndiniales (Dinophyceae, Alveolata) is a diverse parasitic group of dinoflagellates, common in all marine environments, and are described as dominant components of pelagic ecosystems. However, their temporal dynamics, prevalence, and host-specificity are poorly known. Using DNA metabarcoding to explore trophic interactions of zooplankton, we found a high proportion of Syndiniales sequence reads associated with the targeted consumers. We observed the occurrence of Syndiniales in copepods, cladocerans, appendicularians, and polychaete larvae, ranging between 11 and 36% relative read abundance, encompassing 11 main putative clades. Zooplankton–Syndiniales interactions showed variability in occurrence across the taxa, but also certain host-specificity. The study suggests that the observed copepod–Syndiniales interactions can be both direct parasitic infections and the result of trophic transmission through potentially infected prey by Syndiniales. Given the quantitative importance of Syndiniales and zooplankton in marine environments, our findings emphasize that their interactions should be recognized as key players in the structure and connectivity of plankton food webs

DNA metabarcoding reveals trophic niche diversity of micro and mesozooplankton species

Alternative pathways of energy transfer guarantee the functionality and productivity in marine food webs that experience strong seasonality. Nevertheless, the complexity of zooplankton interactions is rarely considered in trophic studies because of the lack of detailed information about feeding interactions in nature. In this study, we used DNA metabarcoding to highlight the diversity of trophic niches in a wide range of micro- and mesozooplankton, including ciliates, rotifers, cladocerans, copepods and their prey, by sequencing 16- and 18S rRNA genes. Our study demonstrates that the zooplankton trophic niche partitioning goes beyond both phylogeny and size and reinforces the importance of diversity in resource use for stabilizing food web efficiency by allowing for several different pathways of energy transfer. We further highlight that small, rarely studied zooplankton (rotifers and ciliates) fill an important role in the Baltic Sea pelagic primary production pathways and the potential of ciliates, rotifers and crustaceans in the utilization of filamentous and picocyanobacteria within the pelagic food web. The approach used in this study is a suitable entry point to ecosystem-wide food web modelling considering species-specific resource use of key consumers

Feeding and egg production of Oithona spp. in tropical waters of North Queensland, Australia

Despite the acknowledged importance of small copepods of the genus Oithona in marine pelagic ecosystems, there is little information about their ecological role, potential food resources and egg production rates (EPR) in tropical environments. In the present study, feeding and EPR of adult females of two species of Oithona were determined in two different tropical marine food webs in North Queensland, Australia, during the 2011 austral autumn. Oithona attenuata was studied in the waters of the Great Barrier Reef lagoon, and Oithona dissimilis was studied in a mangrove area. Oithona spp. ingested dinoflagellates and ciliates preferentially to other prey items of the nano- and microplankton assemblage. Oithona spp. clearance rates on dinoflagellates and ciliates ranged from 3.7 to 10.4 mL female^−1 day^−1, and from 4.3 to 18.1 mL female^−1 day^−1, respectively. The daily body carbon ingested per female was <1% when feeding on dinoflagellates, and varied from 1 to 10% when feeding on ciliates. Our results suggest that Oithona spp. feed on small flagellates (5–20 μm), although the contribution of carbon to the diet was low (2.5–3.2% body carbon). Egg production and weight-specific EPR ranged from 0.22 to 3.34 eggs female^−1 day^−1, and 0.2–4.5% day^−1 respectively. The ingestion rates measured in all the feeding experiments were too low to sustain metabolic and egg production costs, indicating that other food resources, not considered in this study, might contribute significantly to the diet of Oithona spp. in tropical environments

Plankton community structure and role of Oithona similis on the western coast of Greenland during the winter-spring transition

The cyclopoid copepod Oithona similis is one of the most abundant copepods in the oceans and has a potentially important role in pelagic food webs. However, there is a lack of knowledge on aspects of its biology and function in planktonic communities. In the present study, we aimed to assess and compare the species’ trophic role in Greenlandic coastal waters during the winter-spring transition, with a focus on its winter behaviour, when large calanoids are not present in the surface layer. Two locations were studied: waters offshore from Godthåbsfjord (Nuuk) in winter, and Qeqertarsuaq (Disko Bay) in spring (bloom and post-bloom period). The potential prey of adult females of O. similis was quantified, and grazing experiments were conducted to determine the feeding rates of adult females on phytoplankton and protozooplankton >10 µm. The abundance, stage composition, and egg production of O. similis was also investigated. Ciliates were the preferred prey for O. similis, which confirms its importance as a link between the microbial food web and higher trophic levels. We observed high egg production rates and efficiencies of O. similis in winter, confirming that it is active and successfully reproductive in food-limited winter conditions. Our results stress that O. similis is a key component of Arctic and subarctic marine communities throughout the year

Population dynamics and production of the small copepod Oithona spp. in a subarctic fjord of West Greenland

13 pages, 9 figures, 1 tableThe small cyclopoid copepod Oithona is widely occurring in polar areas; however, knowledge of its biology and ecology is very limited. Here, we investigate the population dynamics, vertical distribution, and reproductive characteristics of Oithona spp. from late winter to summer, in a subarctic fjord of West Greenland. During winter-early spring, the abundance of Oithona spp. was low (1.8 × 103 ind. m-2) and the population was mainly composed of late copepodites and adults, whereas in summer, abundance peaked and younger stages dominated (1.1 × 106 ind. m-2). In general, all stages of Oithona spp. remained in the upper 100 m, with nauplii exhibiting a shallower distribution. Although no general seasonal migration was found, a deeper distribution of the adult females in winter was observed. The mean clutch size of Oithona spp. varied from 16 to 30 eggs per female, peaking in summer. Egg production rates (EPR) were low in winter-early spring (0.13 ± 0.03 eggs female-1 day-1) and reached maximum values in summer (1.6 ± 0.45 eggs female-1 day-1). EPR of Oithona spp. showed a significantly positive relationship with both temperature and protozooplankton biomass, and the development of the population seemed to be appreciably affected by temperature. Oithona spp. remained active throughout the study, stressing the key importance of these small copepods in high-latitude ecosystems, especially in periods when larger copepods are not present in the surface layer. © 2014 Springer-Verlag Berlin HeidelbergThis study was supported by the Greenland Climate Research Centre through the project 6505 to T.G. Nielsen. The research leading to these results has received funding from the European Commission FP7 EURO-BASIN (Grant Agreement: 264 933), and from the Spanish Ministry of Economy and Competitiveness through a Ph.D. fellowship (BES-2008-004231) to S. Zamora-Terol, and the project CTM2007-60052 to E. SaizPeer Reviewe