The fact that biomass, species composition and seasonal duration of aquatic vegetation determine the composition and abundance of macroinvertebrates, have long been established (Kornijow, 1996). But one thing that is not yet clear enough is, understanding the degree to which plant associated macroinvertebrates play key roles in regulating the dynamics of micro algal biomass in fresh water vegetation. Several studies have reported the fundamental importance of grazers in maintaining the health of some specific aquatic vegetation such as seagrass meadow (Nickles et al., 1993; Jernakoff and Nielsen, 1997). More so, the regulation of abundance and growth of epiphytic algae which competes for light availablility with aquatic vegetation by invertebrate grazers have been reported (Montfrans et al., 1984). It is also very important to mention that earlier studies have shown the modification effects of invertebrates grazing on periphyton and epiphyton composition (Mazzella and Russo, 1989) which in turn provides a connection in the aquatic food web between primary producers and higher trophic levels (Orth, 1984).
In contrast to most reports on the regulatory functions of grazing on abundance and density of microalgal species, some recent studies indicates that invertebrate grazing might not have the most reported potential to reducing microalgal abundance in highly eutophic lakes (Lotze and Worm, 2002; Lapointe et al., 2004). This conclusion was based on the explanation that eutrophication modifies the diversity, species richness and species composition of plant communities (Korpinen et al., 2007). Another explanation to the conclusion was that invertebrate grazing effects on plant communities rely on productivity (Hillebrand et al., 2000), even as it was reported that in unproductive lakes, plant species richness was decreased by grazing pressure, but when compared to productive lakes, grazing suppressed dominant algae, hence an increase in algal diversity and species richness (Korpinen et al., 2007). However, Hillebrand et al.,(2000) shed more light on this conclusion by reporting that grazing increased microalgal diversity and species richness only in productive conditions especially at the ambient nutrient level where grazing impact was negative on both diversity and species richness.
Possible reasons given to explain the difference in grazing effects of invertebrate species on microalgae was the probable preferences of grazers to a variety of microalgal species (Jernakoff and Nielsen, 1997). This is because little knowledge exist about the difference in functional roles of invertebrate species in controlling macroalgal growth, for example, comparing a species functional roles with another as in the case of gastropod and amphipod species respectively (Jernakoff and Nielsen, 1997).
It is however, very important to remind our readers that studies on mesograzers, vis-a-vis herbivory on algae species have predominantly centered on examining the roles of eukaryotic algae as food and habitat for marine grazers (as viewed by Paul et al., 2001). A clear-cut reason for this view was given by Cruz-Rivera (2006) who further explained that many community studies which described algae species in fresh water systems have concentrated particularly, on explaining the factors underlying the control of algal blooms because it is usually linked to eutrophication, disturbance and anthropogenic habitat degradation, hence the continuous existence of algae in aquatic ecosystems is seen as “abnormal” instead of normal component of the community.
In tune with the view expressed above, feeding preferences of mesograzers in relation to macroalgal species have been widely reported (Cornwell et al., 2009). For example, the study of the large molluscan grazer – Abalone, feeding on macroalgae species of marine origin indicates that species of Abalone from the northern hemisphere prefer the brown algae species as their feeding habits (Guzman del Proo et al., 2003), while their counterparts from South-East Asia tend to feed on red algae species (Tahil and Junio Menez, 1999).
More so, some studies have suggested that benthic blue-green algae species from tropical regions, could play great ecological roles by serving as sources of food and habitat to marine meso-grazers (Cruz-Rivera and Paul, 2002, Paul et al., 2001). For instance, these studies described the feeding preferences of the small sea hare Stylocheilus striatus and concluded that this organism; which lives in Marine blue-green algae mats, could feed preferentially on the blue-green algae species of the genus Lyngbya, at the same time that the organism has the choice of other algae species, particularly macroalgae and cyanobacteria species as food sources.
Given the stated claims of varying tendencies among mesograzers with regards to their preferences of algae species as food sources, it is reasonably important to suggest that mesograzers has the potential to feed on alternative food sources other than algae species. Supporting this hypothesis, several studies have shown that some aquatic invertebrates feed on a variety of food sources (Dangles, 2002; Mihuc and Mihuc, 1995; Friberg and Jacobsen, 1994). For example, Hirabayashi and Wotton, (1999) reported that chironomid larvae has the ability to feed on many food types including algae, detritus and associated microorganisms, macrophytes, and woody debris.
Similarly, Baker et al., (2010) conducted a laboratory study to quantify the rates of consumption of native and non-indigenous aquatic plants in Florida using the snail Pomacea insularum (Gastropoda: Ampillariidae). The authors concluded that more than 50% of the plants were consumed by the snail. In the same vein, study showing the efficient consumption rates of decayed Alnus glutinosa leaves by Asellus aquaticus have long been reported (Adcock, 1982); even as another study showed the feeding ability of the decapod Cambous bartonii on leaf litter (Huryn and Wallace, 1987). More recently, Callisto et al., (2007) conducted an investigation to show the possible use of head water stream leaf litter as food source for chironomids and concluded that some chironomids can use leaf litter of riparian vegetation as a complementary food source.
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Last updated:
06/09/10