Daniel Leduc

Is the meiofauna a good indicator for climate change and anthropogenic impacts

Our planet is changing, and one of the most pressing challenges facing the scientific community revolves around understanding how ecological communities respond to global changes. From coastal to deep-sea ecosystems, ecologists are exploring new areas of research to find model organisms that help predict the future of life on our planet. Among the different categories of organisms, meiofauna offer several advantages for the study of marine benthic ecosystems. This paper reviews the advances in the study of meiofauna with regard to climate change and anthropogenic impacts. Four taxonomic groups are valuable for predicting global changes: foraminifers (especially calcareous forms), nematodes, copepods and ostracods. Environmental variables are fundamental in the interpretation of meiofaunal patterns and multistressor experiments are more informative than single stressor ones, revealing complex ecological and biological interactions. Global change has a general negative effect on meiofauna, with important consequences on benthic food webs. However, some meiofaunal species can be favoured by the extreme conditions induced by global change, as they can exhibit remarkable physiological adaptations. This review highlights the need to incorporate studies on taxonomy, genetics and function of meiofaunal taxa into global change impact research.

Description of Oncholaimus moanae sp. nov. (Nematoda: Oncholaimidae), with notes on feeding ecology based on isotopic and fatty acid composition

A new free-living marine nematode species, Oncholaimus moanae sp. nov., is described from intertidal fine sand in southern New Zealand. Oncholaimus moanae sp. nov. can be distinguished from other species of the genus by the presence of a pre-cloacal papilla bearing four pairs of short, stout spines, a post-cloacal papilla, long (>70 μm) spicules, and a demanian system with two openings situated laterally at level of uvette. The δ 13 C signature of O. moanae sp. nov. suggests that benthic micro-algae are the main carbon source for this species, but an elevated δ 15 N signature suggests predatory feeding habits. The fatty acid composition of O. moanae sp. nov. is rich in highly unsaturated fatty acids, which are likely to originate from heterotrophic protists (e.g. ciliates). The data obtained in this study suggest, for the first time, that marine nematodes can be a high quality food source (i.e. rich in highly unsaturated fatty acids) to predators. Large nematodes living near or at the sediment surface, in particular, may represent an important trophic link between heterotrophic protists and higher trophic levels in marine sediments.

Macroinvertebrate diet in intertidal seagrass and sandflat communities: a study using C, N, and S stable isotopes

Abstract Most seagrass community food‐web studies using stable isotopes have been carried out in subtidal habitats during one sampling event. We used C, N, and S stable isotopes to characterise the diet of the dominant macroinvertebrates found in intertidal Zostera capricorni and sandflat communities of southern New Zealand in late summer and winter. The range of ä13C and ä34S values for Z. capricorni was wide (>5‰), which highlights the importance of accounting for spatial and temporal variability in primary producer isotopic signatures. The range of ä15N values for Z. capricorni was comparatively small (<l‰). Mixing models based on ä13C and ä15N signatures suggested that Z. capricorni was a potentially important contributor (24–99%) to the diet of most consumers sampled at the seagrass site, whereas microphytobenthos dominated the diet of the same consumers at the sandflat site. The main exception was the bivalve Austrovenus stutchburyi, which had a diet consisting mostly (up to 85%) of Ulva and Polysiphonia spp. at both sites. S isotopes proved to be of limited use owing to the difficulty of sampling microphytobenthos and to potential non‐dietary sources of 34S‐depleted sulfur to consumers. Mixing models also suggested that Z. capricorni contributed more to the diet of deposit feeders in August (late winter) than in March (late summer).

Description of new species of Setosabatieria and Desmolaimus (Nematoda: Monhysterida) and a checklist of New Zealand free‐living marine nematode species

Abstract Two new marine nematode species are described from intertidal sediments in southern New Zealand. Setosabatieria australis sp. nov. is characterised by an amphideal fovea with 3.5 turns, 7–9 small pre‐cloacal supplements, and 2–5 sub‐cephalic setae per file. Setosabatieria australis sp. nov. differs from all known species of the genus in having L‐shaped spicules with a hollow median region, in contrast to the typical curved shape. Desmolaimus courti sp. nov. is characterised by the presence of four long (15 pan) cephalic setae, two cuticularised rings in the buccal cavity, and a lightly cuticularised pharyngeal lumen. It differs from other species of the genus by having eight sub‐cephalic setae. A total of 116 marine species are included in the checklist of New Zealand free‐living nematodes, with the majority of records from the coast of Campbell and Auckland islands from the early part of the 20th century. Most records were from habitats such as seaweed or sponge, which may explain the high proportion (>50%) of cosmopolitan species recorded in New Zealand to date. Little is known about the sediment nematode fauna, particularly in deeper waters (>120 m), from where there are no records to date.

Characteristics of meiofauna in extreme marine ecosystems: a review

Extreme marine environments cover more than 50% of the Earth’s surface and offer many opportunities for investigating the biological responses and adaptations of organisms to stressful life conditions. Extreme marine environments are sometimes associated with ephemeral and unstable ecosystems, but can host abundant, often endemic and well-adapted meiofaunal species. In this review, we present an integrated view of the biodiversity, ecology and physiological responses of marine meiofauna inhabiting several extreme marine environments (mangroves, submarine caves, Polar ecosystems, hypersaline areas, hypoxic/anoxic environments, hydrothermal vents, cold seeps, carcasses/sunken woods, deep-sea canyons, deep hypersaline anoxic basins [DHABs] and hadal zones). Foraminiferans, nematodes and copepods are abundant in almost all of these habitats and are dominant in deep-sea ecosystems. The presence and dominance of some other taxa that are normally less common may be typical of certain extreme conditions. Kinorhynchs are particularly well adapted to cold seeps and other environments that experience drastic changes in salinity, rotifers are well represented in polar ecosystems and loriciferans seem to be the only metazoan able to survive multiple stressors in DHABs. As well as natural processes, human activities may generate stressful conditions, including deoxygenation, acidification and rises in temperature. The behaviour and physiology of different meiofaunal taxa, such as some foraminiferans, nematode and copepod species, can provide vital information on how organisms may respond to these challenges and can provide a warning signal of anthropogenic impacts. From an evolutionary perspective, the discovery of new meiofauna taxa from extreme environments very often sheds light on phylogenetic relationships, while understanding how meiofaunal organisms are able to survive or even flourish in these conditions can explain evolutionary pathways. Finally, there are multiple potential economic benefits to be gained from ecological, biological, physiological and evolutionary studies of meiofauna in extreme environments. Despite all the advantages offered by meiofauna studies from extreme environments, there is still an urgent need to foster meiofauna research in terms of composition, ecology, biology and physiology focusing on extreme environments.

Differences in meiofauna communities with sediment depth are greater than habitat effects on the New Zealand continental margin: implications for vulnerability to anthropogenic disturbance

Studies of deep-sea benthic communities have largely focused on particular (macro) habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. Compared to mega-epifauna and macrofauna, much less is known about habitat-related variation in meiofaunal community attributes (abundance, diversity and community structure). Here, we investigated meiofaunal community attributes in slope, canyon, seamount, and seep habitats in two regions on the continental slope of New Zealand (Hikurangi Margin and Bay of Plenty) at four water depths (700, 1,000, 1,200 and 1,500 m). We found that patterns were not the same for each community attribute. Significant differences in abundance were consistent across regions, habitats, water and sediment depths, while diversity and community structure only differed between sediment depths. Abundance was higher in canyon and seep habitats compared with other habitats, while between sediment layer, abundance and diversity were higher at the sediment surface. Our findings suggest that meiofaunal community attributes are affected by environmental factors that operate on micro- (cm) to meso- (0.1–10 km), and regional scales (> 100 km). We also found a weak, but significant, correlation between trawling intensity and surface sediment diversity. Overall, our results indicate that variability in meiofaunal communities was greater at small scale than at habitat or regional scale. These findings provide new insights into the factors controlling meiofauna in these deep-sea habitats and their potential vulnerability to anthropogenic activities.

Northern New Zealand rhodoliths: assessing faunal and floral diversity in physically contrasting beds

Rhodolith beds are recognised internationally as unique ecosystems, harbouring a high diversity and abundance of marine biota. Beds typically occur in environments of moderate exposure and coarse sandy sediments, in which individual rhodoliths are not moved away from the beds, and do not get buried by fine sediments. For the first time in New Zealand, we have physically and biologically characterised selected rhodolith beds in order to document the marine biota within and beneath them. Three beds at two locations in the Bay of Islands, northern New Zealand, were sampled in February and September 2010; two beds were located in a typical rhodolith habitat (a sandy channel), and one in an atypical habitat (a muddy bay). In each bed, rhodolith species and abundance were analysed along with environmental characteristics (sediment granulometry, light environment, temperature, current speed and direction). Characterisation of biological diversity associated with the rhodolith beds included assessment of macroalgae, invertebrates (surface and subsurface) and fish. Sampling within the beds produced a total of 238 taxa: 197 invertebrates, 37 algal and four fish taxa, indicating that a high diversity of biota occur within these northern New Zealand rhodolith beds. We found significant differences in the abundance, taxon richness, and community structure of the biota among rhodolith beds, and surprisingly, the highest abundance and taxon richness occurred in a bed in a highly sedimented environment. In addition, two adjacent and physically similar beds were significantly different from each other in terms of community structure. This finding points to the importance of sampling individual rhodolith beds and suggests that it would be risky to extrapolate findings to other beds, even those in close proximity.

Spatial patterns and environmental drivers of benthic infaunal community structure and ecosystem function on the New Zealand continental margin

To investigate regional drivers of spatial patterns in macro- and meio-faunal community structure (abundance, biomass and taxonomic diversity) and ecosystem function (sediment community oxygen consumption [SCOC]), we sampled two regions in close proximity on New Zealands continental margin—the Chatham Rise and the Challenger Plateau. Sites (n = 15) were selected in water depths ranging from 266–1212 m to generate a gradient in sedimentary properties and, in particular, surface pelagic productivity. Both macro- and meio-fauna abundance and biomass was 2–3.5 times higher on the Chatham Rise than on the Challenger Plateau, reflecting regional differences in pelagic primary production. We also found significant inter- and intra-regional differences in macro-fauna taxonomic diversity with two distinctive site groupings in each region. Univariate and multivariate measures of macro-fauna community attributes were most strongly correlated with sediment photosynthetic pigment (explaining 24%–59% of the variation). Sediment pigment content was as equally important in explaining meio-fauna community structure (36%–7%). Unlike community structure, SCOC was most strongly correlated with depth (44%), most likely reflecting temperature effects on benthic metabolism. Our results highlight the importance of a benthic labile food supply in structuring infaunal communities on continental margins and emphasise a tight coupling between pelagic and benthic habitats.

One new genus and two new free-living nematode species (Desmodorida, Desmodoridae) from the continental margin of New Zealand, Southwest Pacific Ocean.

One new genus and two new species of the family Desmodoridae are described from the upper continental slope of New Zealand, at 350-1240 m water depths. Onepunema gen. n. is characterised by a striated head capsule, small buccal cavity without teeth, and presence of two testes. Onepunema gen. n. can be differentiated from all other genera of the family by the presence of two testes, which is an exception to the holapomorphic character (i.e. monorchic males) of the Desmodoroidea. Onepunema enigmaticum gen. et sp. n. shares characters typical of the subfamilies Spiriniinae (small buccal cavity without distinct teeth) and Desmodorinae (presence of head capsule). Onepunema gen. n. is placed within the Desmodorinae based on the latter trait, which is never found within the Spiriniinae. The type species, Onepunema enigmaticum gen. et sp. n., is characterised by the presence of two laterodorsal and two lateroventral rows of pores with conspicuous ducts, slender pharynx with rounded terminal bulb, presence of two types of cells in intestinal epithelium, and presence of four or five pre-cloacal supplements consisting of thickened areas of cuticle in males. The genus Pseudonchus is recorded for the first time from the deep sea (1240 m water depth) and from the New Zealand region. Pseudonchus virginiae sp. n. is characterised by its stout body, short cephalic setae, monospiral amphideal fovea, short arcuate spicules with capitulum, five regularly-spaced precloacal setae, and short conical tail. A key to all known valid species of the genus Pseudonchus is provided.

Three new species of free-living nematodes from inter-tidal sediments in southern New Zealand

Three new species are described from sheltered intertidal sediments of Papanui Inlet, southern New Zealand. Microlaimus falciferus n. sp. is characterised by a cuticle with two lateral alae, the presence of pores between the cephalic setae, a strongly sclerotised and non-compartmentalised mouth cavity and scythe-shaped spicules with two sub-lateral pre-cloacal setae. This is the first species of the family Microlaimidae described as having lateral differentiation of the cuticle. Microlaimus falciferus n. sp. can also be differentiated from other Microlaimus species by the presence of two types of porids, i.e. , pores and short hollow setae, as all other species of the genus possess only one type of porid (when present). Aponema subtile n. sp. is characterised by its slender form, relatively long tail, presence of longitudinal bars and lateral grooves on the cuticle and groups of short setae in the pre- and post-cloacal regions. It is similar to A. torosum in the structure of the male sexual organs but differs from the latter in the following ways: higher a values (30-40 vs 17-27); longer tail (5.4-7.8 vs 4-5 anal body diam. long) and a weakly sclerotised pharyngeal bulb that is never angular in appearance. Sabatieria annulata n. sp. is most similar to the cosmopolitan species S. punctata , the main difference being the absence of punctations in S. annulata n. sp. Sabatieria annulata n. sp. also has shorter spicules (34-36 vs 41-54 μ m) and shorter gubernacular apophyses (14-16 vs 20-24 μ m) than S. punctata .