Meiofauna with special reference to nematodes in trawling ground of subtropical Hong Kong

Abstract

Bottom trawling is one type of large-scale, anthropogenic dis-turbances in many of the world’s most productive marine environ-ments. The most evident effects of trawling on bottom sedimentare the alteration of distribution and abundance of target andnon-target species by means of non-selective, destructive trawlingmethods (Jennings and Kaiser, 1998; Hall, 1999; Kaiser and deGroot, 2000) and the strong collateral impacts on physical and bio-logical habitats(Freeseet al., 1999;Chuenpagdee et al., 2003).Suchdisturbance affects the diversity, abundance, size structure andproduction of benthic communities in our oceans (Kaiser andSpencer, 1996; Bergmann and Moore, 2001; Jennings et al., 2001,2002; Hermsen et al., 2003).In general, studies have suggested that frequent trawling dis-turbances may lead to the proliferation of smaller benthic species,with faster life histories, because they can withstand the mortalityimposed by trawling and benefit from reduced competition orpredation as populations of larger species are depleted (Jenningset al., 2001). In some areas, trawling has led to significant de-creases in infaunal biomass and production, and the abundanceof larger individuals is reduced more than smaller ones (Kaiserand Spencer, 1996). However, different benthic animals and sea-floor types are affected to different degrees. The greatest damageoccurs when animals come into contact with the hard parts of thefishing gear. Larger body-sized infauna are more susceptible todamage, particularly shallow burrowing species (Bergman andHup, 1992). Gilkinson et al. (1998) demonstrated that smallerbody-sized fauna are less susceptible to physical damage, as theyare pushed aside with fluidized sediments generated by the pres-sure wave that occurs in front of the moving trawl. Many ecolog-ical processes, such as production, are functions of body mass(Dickie et al., 1987). The smaller organisms that are less vulnera-ble to trawl disturbances generally have a higher annual repro-ductive output and higher intrinsic rates of natural increase,both of which decrease with increasing body size within a popu-lation (Brey, 1999; Collie et al., 2000; Duplisea et al., 2002). Bot-tom trawling can therefore lead to changes in communitycomposition and size structure through removal of large body-sized species and the largest individuals within populations (Ballet al., 2000).Meiofauna have been regarded as an important component inbenthic ecosystems due to their small size, high abundance andfast turnover rates (Heip et al., 1985; Coull, 1999). They are highquality food sources for fish, shrimp and mollusc larvae and impor-tant components in benthic food chains (Bell and Coull, 1978; Ellisand Coull, 1989; Gee, 1989; Coull, 1990). Hence, they play animportant role in trophic transfer in the marine ecosystem (War-wick, 1989). They also make use of organic detritus in sedimentsand are grazers of benthic bacteria and microalgae. Their grazingrate on bacteria is almost similar to the production of bacteria, sothey can regulate the productivity of bacteria (Montagna et al.,1995). Hence, they are important to the process of biological, geo-chemistry recycling. Compared with macrofauna, the easier fieldsampling, higher species richness, shorter life-cycles (3–5 genera-tionsper year) and lack of larval stages, make meiofauna importantin environmental assessment and ecosystem health monitoring(Coull and Chandler, 1992; Kennedy and Jacoby, 1999; Bongersand Ferris, 1999). In particular, they respond rapidly to environ-mental changes such as grain size, redox potential and food avail-ability (Soyer, 1985; Danovaro, 1996). They can resist disturbancesdue to trawling because they may be resuspended during thetrawling operation owing to their small body size (Gilkinsonet al., 1998). Their short life-cycles (Schwinghamer et al., 1986)would also allow them to withstand high mortality due totrawling.Although, there are numerous reports on the effects of bottomtrawling on sediment parameters and macrobenthic communi-ties, there were limited studies about meiofauna and nematodes(Pranovi et al., 2000; Schratzberger et al., 2002; Schratzbergerand Jennings, 2002; Lampadariou et al., 2005). Schratzbergerand Jennings (2002) revealed that the total nematode abundancewas significantly higher in an area exposed to medium level oftrawling disturbance in the North Sea. In temperate waters, Sch-ratzberger et al. (2002) found that seasonality may impact thenematode community structure, rather than caused by trawling,in a study in the North Sea. This study aimed to examine the sea-sonal changes of meiofauna with special reference to nematodesin trawling ground of Hong Kong, which is located in subtrophicwaters. The H