Comparative techniques to quantify cyanobacteria dominated epilithic biofilms on tropical rocky shores

Abstract

ABSTRACT-The epilithic biofilm of troplcal shores is dominated by cyanobacteria with only a sparse cover of diatoms. Geographical comparison of biofilms is difficult, however, due to variation in enumeration techniques. This paper describes techniques to quantify the biofilm in an attempt to standardize comparative studies. Spec1c.s rlchness and relative abundance were best enumerated using scanning electron microscope (SEM) images of air d r~e d rock chips, as compared to light, epifluorescence and confocal laser mlcroscopy. SEM preparations provided cleal-lmages and allowed identification of most specles Alr d r~e d and Cryo-stage preparations prov~ded the least damaged images of species whereas the harsh dehydration process in crit~cal-point dried specimens damaged morphology and removed loosely dttached species resulting in unclerest~mation of specles richness and abundance A combination of SEh4 techniques (e.g. Cryo-stage, air d r~e d and critical-po~nt dried san~ples) is reconimended for initial species identificdtion. Chlorophyll a extraction from rock chips, as an indirect estlmate of biomass, was more eff~cient using methanol or ethanol a s compared to acetone. Methanol heated for 2 min and cooled for 12 h ylelded 100% chlorophyll a extraction while cold methanol, methanol heated for 2 min and cooled for 3 and 6 h, and ethanol heated for 5 min, extracted greater than 95% chlorophyll a. No significant loss of chlorophyll a was recorded in rock samples stored in moist or dry conditions at 4°C or room temperature for 24 h or at -20°C for a month, but in samples stored at 4°C or room temperature for a week, 60 to 75% loss occurred. Chlorophyll a, once extracted. can b e stored for a week in the dark prior to measurement without significant loss. To standardize techniques for tropical, cyanobacteria-rich epilithic biofilms, chlorophyll a extraction of rock chips using cold methanol 1s recommended.

Variability and community organization in moderately exposed tropical rocky shore algal communities as influenced by different consumer groups

“…In this study colonization of space starts from bare rock surface of encrusting algae followed by biofilms, green turfs, brown turfs and then Ulva and Porphyra or foliose algae. Microscopic examinations show that during succession from a bare space to colonization of a foliose algae, a coat of protein polysaccharides cover the surfaces of bare patches which prepares it to be colonized by various microalgae and then turfing algae (Nagarkar and Williams 1997;Williams et al 2000). This predictable pattern of biofilm to macroalgal succession is an evidence of reduced stress from grazers as well as from other physical factors (Underwood 1980;Kaehler and Williams 1998;Freidenburg et al 2007).…”

“…Various studies on consumer driven effects (Williams 1993a(Williams , 1993b(Williams , 1994Kaehler and Williams 1996;Kennish et al 1996;Nagarkar and Williams 1997;Hutchinson and2003a) were already conducted in Hong Kong rocky shores but not to site level and shore level replications which can allow us to generalize on a much broader scale. In addition, although it is mentioned in most of the previous studies done in the area that fishes have no effect on these shores (see Kaehler and Williams 1996;Hutchinson and Williams 2001), caging experiments separating the effects of molluscs and fishes have not been demonstrated in the area.…”

“…Comparison between the mid shore treatments of Williams 1993b and this study showed inconsistent results; whereas his study did not produce differential impacts of grazing in the mid shore, this study recorded differential impacts of grazing in the four study sites. Microalgal abundances measured using chl a concentration represents the microalgal standing stock (Nicotri 1977;Nagarkar and Williams 1997;Jenkins et al 2001). This is primarily represented in the epilithic algal biofilm that covers most rock surfaces in temperate and tropical rocky shores.…”

“…A more direct examination of grazing effects other than chl a (Nicotri 1977;Underwood 1984;Williams 1993b) and wax discs (Thompson et al 1997;Hutchinson and Williams 2003) can be done by microscope examinations using dissecting scopes or SEM (Nagarkar 1996;Nagarkar and Williams 1997;Williams et al 2000;Jenkins et al 2001) although this can be more labor intensive. Results from this study (Table 10 and Figs.…”

“…The Hong Kong rocky shores have been much studied on grazer-alga interaction such as on the effects of seasonality (Williams 1993(Williams , 1994, recruitment of erect and encusting algae (Kaehler and Williams 1997), grazer pressure (Harper and Williams 2001;Hutchinson and Williams 2003a;Wai and Williams 2006), typhoon (Hutchinson and Williams 2003b), cyanobacteria (Nagarkar and Williams 1997), and succession (Williams et al 2000). However the system was much studied, scale up of these previous studies remains rare and effects of processes at work at the scale of tens of meters to hundreds of meters may not work in the scale of thousands of meters; the findings remain limited to the areas of study.…”