14
G.R. Carvalho et al.
restriction length polymorphism (RFLP), amplified fragment length polymorphism
(AFLP) or microsatellites are appropriate methodologies. These well established
methods are suited to resolve the degree of biodiversity within populations of certain
species, and the utility of fingerprinting methods for microbial biodiversity assessment has been demonstrated in numerous publications (e.g. Adachi et al. 2003, John
et al. 2004, Iglesias-Rodriguez et al. 2006, see review in Medlin 2007). In all studies to date, microbial populations in the oceans have been shown to have a distinct
structure and gene flow can be restricted between geographically close areas. The
oceans are far more fragmented in terms of population structure and gene flow than
would have been believed decades ago.
1.2.3 Diversity and Ecological Analyses of Benthic Meiofaunal
Communities
Soft-bottom benthic meiofauna are a ubiquitous, highly abundant community
assemblage (ranging between 45 and 500 μm in size) that play a crucial role in
marine ecosystem functioning and services. Comprised of between 50 (shallow
water) and 90% (deep water) nematodes, meiofaunal assemblages contribute significantly to bentho-pelagic coupling in the form of nutrient cycling, water column
processes, pollutant distribution, secondary production and stability of sediments
(Snelgrove et al. 1997, Smith et al. 2000, Snelgrove et al. 2000). Despite their
pivotal role in ecosystem functioning (Danovaro et al. 2008), our ability to construct mechanistic links between biodiversity and ecosystem services is significantly
impeded by a poor understanding of global marine meiofaunal taxonomy and diversity. For example, a current estimate of global nematode diversity (c. 1 million
species) remains a matter of conjecture (Lambshead and Boucher 2003). Only about
20,000 species have been described, around 4,000 of which are marine (Platt and
Warwick 1983), and contemporary studies routinely recover between 30 and 40%
of sampled taxa that are new to science (Lambshead and Boucher 2003). Such a
knowledge gap is undoubtedly the result of the small size and apparent morphological conservatism of nematodes, rendering identification a considerable challenge
to non-specialists. Indeed, even for experts, many male- or female-specific diagnostic morphological characters exhibit intraspecific variation and are restricted to
mature individuals that can only be appraised using combinations of traditional light
and electron microscopy combined with informed knowledge from specialist literature (Floyd et al. 2002, DeLey et al. 2005). From a logistical perspective, surveys
have additionally shown that 120 times more scientific effort has to be expended
in assigning only 10% of nematodes to known species, compared to parallel studies
that successfully assigned all vertebrate morphospecies to known taxa (Lawton et al.
1998). The finding that more than 5,000 nematodes comprising up to 50 species can
be recovered from a single 38 cm 3 temperate benthic fine sand sample, highlights
the formidable challenge that meiobenthologists face when analyzing environmental
samples.
G.R. Carvalho et al.
restriction length polymorphism (RFLP), amplified fragment length polymorphism
(AFLP) or microsatellites are appropriate methodologies. These well established
methods are suited to resolve the degree of biodiversity within populations of certain
species, and the utility of fingerprinting methods for microbial biodiversity assessment has been demonstrated in numerous publications (e.g. Adachi et al. 2003, John
et al. 2004, Iglesias-Rodriguez et al. 2006, see review in Medlin 2007). In all studies to date, microbial populations in the oceans have been shown to have a distinct
structure and gene flow can be restricted between geographically close areas. The
oceans are far more fragmented in terms of population structure and gene flow than
would have been believed decades ago.
1.2.3 Diversity and Ecological Analyses of Benthic Meiofaunal
Communities
Soft-bottom benthic meiofauna are a ubiquitous, highly abundant community
assemblage (ranging between 45 and 500 μm in size) that play a crucial role in
marine ecosystem functioning and services. Comprised of between 50 (shallow
water) and 90% (deep water) nematodes, meiofaunal assemblages contribute significantly to bentho-pelagic coupling in the form of nutrient cycling, water column
processes, pollutant distribution, secondary production and stability of sediments
(Snelgrove et al. 1997, Smith et al. 2000, Snelgrove et al. 2000). Despite their
pivotal role in ecosystem functioning (Danovaro et al. 2008), our ability to construct mechanistic links between biodiversity and ecosystem services is significantly
impeded by a poor understanding of global marine meiofaunal taxonomy and diversity. For example, a current estimate of global nematode diversity (c. 1 million
species) remains a matter of conjecture (Lambshead and Boucher 2003). Only about
20,000 species have been described, around 4,000 of which are marine (Platt and
Warwick 1983), and contemporary studies routinely recover between 30 and 40%
of sampled taxa that are new to science (Lambshead and Boucher 2003). Such a
knowledge gap is undoubtedly the result of the small size and apparent morphological conservatism of nematodes, rendering identification a considerable challenge
to non-specialists. Indeed, even for experts, many male- or female-specific diagnostic morphological characters exhibit intraspecific variation and are restricted to
mature individuals that can only be appraised using combinations of traditional light
and electron microscopy combined with informed knowledge from specialist literature (Floyd et al. 2002, DeLey et al. 2005). From a logistical perspective, surveys
have additionally shown that 120 times more scientific effort has to be expended
in assigning only 10% of nematodes to known species, compared to parallel studies
that successfully assigned all vertebrate morphospecies to known taxa (Lawton et al.
1998). The finding that more than 5,000 nematodes comprising up to 50 species can
be recovered from a single 38 cm 3 temperate benthic fine sand sample, highlights
the formidable challenge that meiobenthologists face when analyzing environmental
samples.