Spatial aggregation patterns of free-living marine nematodes in contrasting sandy beach micro-habitats

Abstract

In the absence of chemical or physical gradients, random displacement of organisms can result in unpredictable distribution patterns. In spite of a limited locomotive capability, marine nematodes may choose where to settle after re-suspension and may maintain their position in the sediment under calm conditions, leading to small-scale (,1 m) spatial variability. However, in more energetic environments, nematodes become re-suspended with sediments and re-distributed at distances dependent on prevalent hydrodynamic regimes, from metre-to decametre-scale or more. In this study, we tested the hypothesis that micro-habitats (i.e. runnels and sandbars) in a macrotidal sandy beach influence the distribution patterns of freeliving marine nematodes by exhibiting contrasting hydrodynamic regimes. Specifically, we predicted patchier distributions in the calmer environment (runnel). We sampled nematodes in each habitat from ,1 m to decametre scales. Our results show more heterogeneous spatial distributions in the runnel, presumably owing to a predominance of active displacement under calmer conditions and sediment cohesion by algal films. Biological similarity among runnel replicates was low, whereas replicates from the sandbar exhibited higher similarity, presumably because of homogenization of the sediment and inhabiting fauna by tidal currents. A significant negative correlation between biological similarity and sampling distance was found in the runnel, but not in the sandbar. The most similar samples were the closest in the runnel and the most distant in the sandbar. More patchily distributed taxa were found in the runnel and a larger fraction of homogeneously or randomly distributed taxa in the sandbar. We conclude that different hydrodynamic regimes in contrasting intertidal micro-habitats significantly influenced the nematofaunal distribution, resulting in different spatial patterns next to one another in the same beach. This has significant implications for sampling and monitoring designs and begs the need for detailed studies about the physical and biological processes governing meiobenthic communities.

Nematodes as indicators of environmental quality in seagrass (Posidonia oceanica) meadows of the NW Mediterranean Sea

“…The increase in Epsilonema may be explained as an opportunistic response due to its ability to exploit the food released from sewage discharge. Epsilonema is a small and short Nematode, with a strong tendency towards clumped distributions [83] and is a good competitor adhering to sediments around food patches [84]. It constitutes an aberrant morphotype, called ''stout'', characterised by a length/width ratio 515 [85] and is heavily cuticularized, all features that make this genus more stable and less vulnerable to disturbance [86].…”

Dispersal and gene flow in free-living marine nematodes

“…Similar active dispersal abilities have been observed in the deep sea [43-45], but here nematodes are far less abundant in the water column than in shallow-water habitats. The complex interactions between habitat, hydrodynamics and species-specific traits lead to high variation in dispersal patterns through space and time [41,46], which in turn may lead to a high degree of patchiness in nematode community composition [45,47]. …”

A functional and morphological approach to evaluate the vertical migration of estuarine intertidal nematodes during a tidal cycle

“…These short-scale variations in horizontal distribution may reflect distinct aggregation and dispersal patterns among the species (Somerfield et al 2007). Distribution patterns can be modified by the erosive potential of the waves and tide currents (Gallucci and Netto 2004), chemical changes caused by the death and decomposition of organisms (Ó lafsson 1992), bioturbation and bioirrigation engineering (Pinto et al 2006;Braeckman et al 2011a, b), competition with the macrofauna for food (Ó lafsson 2005), preferential selection of food dos Santos et al 2008;Franco et al 2008), and the differing locomotion ability of the species (Gingold et al 2011). Fig.…”

“…Nematode locomotion behavior is described as undulating, with the length and frequency of body waves varying as a function of viscosity (Gray and Lissmann 1964;Wallace 1968). Tail shape (Thistle and Sherman 1985;Thistle et al 1995), size and shape of the body (Soetaert et al 2002;Vanaverbeke et al 2004;Schratzberger et al 2007), and presence of caudal glands (Gingold et al 2011) may be related to the ability to move and eventually explain differences in distribution patterns. Nematode feeding strategies are also rather variable, and their locomotion behavior may be conditioned by the ''mobility'' of the food itself, as diatoms and other microorganisms, mainly in the case of nematodes classified as epistrate feeders.…”