Periphyton
Part 2
Aufwuchs
In a previous article, we discussed the formation
processes and structure of biofilm in aquatic environments. We now turn to
aufwuchs….its formation and composition, and the functions of the member flora
and fauna.
As biofilm approaches its final stages of growth, which is
determined by both organic and inorganic nutrients, algae begins to colonize
the biofilm surface. Diatoms are usually first to colonize but are quickly
followed by other sessile forms of algae including filamentous. The biofilm and
algae form a mutually beneficial partnership. The biofilm supplies nutrients to
the algae and the algae in turn supplies much needed Oxygen to the biofilm
bacteria.
Earliest algal colonization cells excrete mucilage then
organized into pads, stalks with contribution of other organisms (Goldsborough,
2005). There are different adaptations changing with different taxonomic composition
such as stalks with sticky ends, sticky capsules, muscular suction pads, glue
or simply clinging to the substrate (Reid and Wood, 1976) later, chemical and
physical factors develop the assemblage and make it denser.
Two of the factors that influence the algae growth and
colony population are light and temperature.
Light had no important effect on abundance of algae, different
light intensities form different algae taxa in aufwuchs structure (Vermaat J.
E., 1995). For example if sufficient light is available, the community will be
microalgae dominated. If there is light penetration, the aufwuchs community
will be heterotroph dominated (Goldsborough, 1993). Although in very low light
regimes (12 μmol) algae growth is minimal (Hill and Fanta, 2008), aufwuchs
structure can support high irradiance (800 μmol) exposure
(Nofdianto, 2010). Photosynthesis occurs at levels far below
maximum daily irradiance and photoinhibition is typically rare (Goldsborough et
al., 2005). Temperature has effects on aufwuchs taxonomic structure like light
regime (Vermaat J. E., 2005). For example, while high temperatures make the algae
Scenedesmus dominate, low temperatures favored the algae Navicula in Vermmat
and Hootsmans (1994)’ and Bothwell’s (1988) study. Besides it is same for
season differences that diatoms are dominant in spring and green algae or
cyanobacteria are dominant in summer (Meulemans and Roos, 1985).
Temperature and light often show strong parallelism because
if there is sunlight, it will provide light for phytosynthesis of macrophytes
and warm up the environment (Vermaat J. E., 2005). Therefore separation of temperature
and light interaction and impacts on algae growth is not very common (Bothwell,
1988). Still there are some studies (Vermaat and Hootsmans, 1994; Nofdianto,
2010) which showed the interaction of low temperature and high irradiance or
vice versa. Both of these studies determined the maximum growth at 20°C and
200-225 μmol. This degree of temperature and light is optimum for all organisms
groups. Above or below these levels taxa and abundance is changing.
Nutrient effect on algae development has been studied many
times. These studies (Marcus, 1980; Hansson, 1992; Jones and Sayer, 2003; Liboriussen et al., 2005, 2006; Smith and Lee,
2006; Becares et al., 2008; Özkan et al., 2010; Rosemond et al., 1993, 2000;
Chételat et al., 1999; Sharifi and Ghafori, 2005; Greenwood and Rosemond, 2005;
Bowes et al., 2010) generally concluded that higher nutrient caused higher
algal biomass in aquatic ecosystems.
Substrates greatly influence aufwuchs population diversity
and richness. Sand and silt
provide the poorest habitat, because of few attachment sites for algae and
consumers. Boulders, rocks and gravel are
better because of larger surface area, more attachment sites, providing cover
and refuge, and divert the force of moving water. Organic substrates such as logs,
stumps, and tree branches are known to provide the best substrate for
supporting taxa richness because of the immediate availability of carbon and
other organic compounds. Twigs and leaf litter also support an abundant
community but are not long-lived in the aquatic environment thus providing only
temporary benefit. Aufwuchs are classified by substrate (all of the epi’s
mentioned in Part 1 of this article) and by certain water quality parameters (pH
range, nutrient levels of N and P, the Halobian spectrum - chloride
concentrations or conductivity, and the Saprobien system - based on organic
pollution).
It is a well known fact that diversity in any ecosystem is
the ultimate key to the stability of that ecosystem. This especially holds true
within aquatic ecosystems. Mixed populations have the advantage of being able
to perform more complex transformations (for example, those requiring multiple
steps), and they are more resistant to environmental stress. (Brenner,
K., You, L. & Arnold, F. H.) The more diversity and abundance an aufwuchs algae
population can sustain the more diverse and abundant will be the population of
the various micro-, meio-, and macro-organisms within the aufwuchs. In
addition, the potential for diversity also increases the community’s ability in
remediating pollution, organic and inorganic. The types of algae within an
aufwuchs community are also indicators of, not only form but also, level of
pollution. In a typical garden pond N and P are usually the two pollutants of concern;
however other pollutants may be encountered, such as heavy metals, herbicides
and pesticides.
Living upon, and within, the diverse aufwuchs
algae colony is a variety of animal life ranging in size from the micro-
(amoeba, protists, ciliates, flagellates etc.) through the meio- (nematodes, rotifers, harpacticoid, cyclopoid
and calanoid copepods, ostracods, oligochaetes, tardigrades and gastrotrichs.
Nemotodes being most populous). Meiofaunal organisms play an important role
in the aquatic food web complex since they consume bacteria, other microfauna
and flora, and detritus,
and they are, in turn, consumed by many larger macrofaunal invertebrates
and juvenile finfish
(Stickney et al. 1975, Bell and Coull 1978, Alheit and Scheibel 1982, Kennish
1986, Smith and Coull 1987, Coull 1990), and macro-organisms (Insect
larvae, nymphs, and adults; crustacean, amphibian larvae and fish larvae).
Each, to some degree, relies on the aufwuchs as a source of food. These
organisms are classified by method of feeding: raspers, grazers, scrapers,
piercers and gatherers. Larger organisms such as herbivore and omnivore fish
also look to aufwuchs as a source for food. Nemotodes, copepods and
turbellarians comprise more than 95% of the meiofauna in most aufwuchs.
Since aufwuchs is
sedentary, it is sensitive to changes in water quality. A diverse community can
be found in healthy streams and ponds. Nuisance blooms are usually symptoms of a system
stressed by factors such as elevated nutrients and high temperatures.
In conclusion, the
periphyton community, biofilm and aufwuchs, can be considered to be the
recycling center for any aquatic eco-system. It is here that the food chain
begins. It is here that organics and inorganics are converted to other forms
that serve as nutrients for various organisms, both small and large. It is here
that feces from the various inhabitants of the ecosystem are turned back into a
nutrient source. It is here that nitrification (and denitrification) occurs. It
is here that inorganic pollutants such as heavy metals and chemicals may be
rendered less harmful through biological processes and absorption. It is here
that a large portion of total water column oxygenation takes place. It is here
that the greatest mechanisms and processes for maintaining water quality exist.
It is usually green. It is almost always slimy. It is seldom
attractive. It is universally cursed and derided by many Pond Keepers. It is,
however, the most important grouping of organisms in any aquatic eco-system. It
is generally called Periphyton.
