Distribution of faecal indicator bacteria in tropical waters of Peninsular Malaysia and their decay rates in tropical seawater.

We investigated the appropriateness of faecal indicator bacteria in tropical waters. We compared total coliform (undetectable to 7.2 × 105 cfu 100 mL-1), faecal coliform (undetectable to 6.1 × 105 cfu 100 mL-1) and enterococci (undetectable to 3.1 × 104 cfu 100 mL-1) distribution in Peninsular Malaysia. Faecal indicator bacteria was highest in freshwater, and lowest in seawater (q > 4.18, p < 0.01). We also measured the decay rates of Escherichia coli and Enterococcus faecium in microcosms. In seawater, average decay rate for E. coli was 0.084 ± 0.029 h-1, and higher than E. faecium (0.048 ± 0.024 h-1) (t = 2.527, p < 0.05). Grazing accounted for 54 % of both E. coli and E. faecium decay. E. coli decayed in the <0.02 µm seawater fraction (0.023 ± 0.012 h-1) but E. faecium sometimes grew. Seawater warming further uncoupled the response from both E. coli and E. faecium as E. faecium grew and E. coli decayed with warming. Our results suggested that the prevalence of faecal indicator bacteria in tropical waters was not due to faecal pollution alone, and this will have serious implications towards the use of these faecal indicator bacteria.

The impact of eutrophication towards selected bacterial process rates in tropical coastal waters.

The dissolved organic nutrient conditions and bacterial process rates at two tropical coastal sites in Peninsular Malaysia (Port Klang and Port Dickson) were initially studied in 2004-2005 period and later revisited in 2010-2011. We observed that dissolved organic nitrogen (DON) increased about two- and ten-fold at Port Klang and Port Dickson, respectively and resulted in a significant change in DOC:DON ratio (t ≥ 2.077, p < 0.05). Among the bacterial processes measured, bacterial respiration (BR) was lower in the 2010-2011 period at both stations (t ≥ 3.390, p < 0.01). BR also correlated to the DOC:DON ratio (R2 ≥ 0.259, p < 0.01). The increase in substrate quality enabled the bacteria to respire less in the dissolved organic matter degradation. As a result, the average bacterial growth efficiency increased slightly in the 2010-2011 period.

Influence of elevated river flow on hypoxia occurrence, nutrient concentration and microbial dynamics in a tropical estuary.

We sampled the Klang estuary during the inter-monsoon and northeast monsoon period (July-Nov 2011, Oct-Nov 2012), which coincided with higher rainfall and elevated Klang River flow. The increased freshwater inflow into the estuary resulted in water column stratification that was observed during both sampling periods. Dissolved oxygen (DO) dropped below 63 µM, and hypoxia was observed. Elevated river flow also transported dissolved inorganic nutrients, chlorophyll a and bacteria to the estuary. However, bacterial production did not correlate with DO concentration in this study. As hypoxia was probably not due to in situ heterotrophic processes, deoxygenated waters were probably from upstream. We surmised this as DO correlated with salinity (R2 = 0.664, df = 86, p < 0.001). DO also decreased with increasing flushing time (R2 = 0.556, df = 11, p < 0.01), suggesting that when flushing time (> 6.7 h), hypoxia could occur at the Klang estuary. Here, we presented a model that related riverine flow rate to the post-heavy rainfall hypoxia that explicated the episodic hypoxia at Klang estuary. As Klang estuary supports aquaculture and cockle culture, our results could help protect the aquaculture and cockle culture industry here.

Environmental control of Vibrio spp. abundance and community structure in tropical waters.

We measured Vibrio spp. distribution and community profile in the tropical estuary of Port Klang and coastal water of Port Dickson, Malaysia. Vibrio spp. abundance ranged from 15 to 2395 colony forming units mL-1, and was driven by salinity and chlorophyll a (Chl a) concentration. However, the effect of salinity was pronounced only when salinity was <20 ppt. A total of 27 Vibrio spp. were identified, and theVibrio spp. community at Port Dickson was more diverse (H' = 1.94 ± 0.21). However species composition between Port Dickson and Port Klang were similar. Two frequently occurring Vibrio spp. were V. owensii and V. rotiferianus, which exhibited relatively higher growth rates (ANCOVA: F > 4.338, P < 0.05). Co-culture experiments between fast- and slow-growing Vibrio spp. revealed that fast-growing Vibrio spp. (r-strategists) were overwhelmed by slower-growing Vibrio spp. (K-strategists) when nutrient conditions were set towards oligotrophy. In response to resource availability, the intrinsic growth strategy of each Vibrio spp. determined its occurrence and the development of Vibrio spp. community composition.

Distributions of particulate and dissolved phosphorus in aquatic habitats of Peninsular Malaysia.

Particulate phosphorus was the dominant phosphorus species and accounted for 72 ±â€¯5% of total phosphorus in coastal habitats, 63 ±â€¯4% in estuaries, 58 ±â€¯6% in lakes and 80 ±â€¯7% in aquaculture farms whereas dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) were minor components. Correlation analyses (DIP vs Chl a; R2 = 0.407, df = 31, p < 0.001) suggested phosphorus limiting conditions in lakes, which was corroborated with the highest alkaline phosphatase activity (APA) that fluctuated from 0.38 to 41.14 nmol L-1 min-1. In contrast, APA was elevated in coastal habitats and estuaries only when DIP concentration decreased below 0.9 µM. Moreover size-fractionation experiment showed that the highest APA was detected in the 0.2-2 µm pico-size fraction. Our results suggested that the main APA in coastal habitats and estuaries was from phototrophic pico-eukaryotes and heterotrophic bacteria, and regulated largely by DIP availability.

Effects of eutrophication on diatom abundance, biovolume and diversity in tropical coastal waters.

Diatom abundance, biovolume and diversity were measured over a 2-year period along the Straits of Malacca at two stations with upper (Klang) and lower (Port Dickson) states of eutrophication. Diatom abundance, which ranged from 0.2 × 104 to 21.7 × 104 cells L-1 at Klang and 0.9 × 103- 41.3 × 103 cells L-1 at Port Dickson, was influenced partly by nutrient concentrations. At Klang, the diatoms were generally smaller and less diverse (H' = 0.77 ± 0.48) and predominated by Skeletonema spp. (60 ± 32% of total diatom biomass). In contrast, diatoms were larger and more diverse (H' = 1.40 ± 0.67) at Port Dickson. Chaetoceros spp. were the most abundant diatoms at Port Dickson but attributed only 48 ± 30% of total diatom biomass. Comparison of both Klang and Port Dickson showed that their diatom community structure differed and that eutrophication reduced diatom diversity at Klang. We also observed how Si(OH)4 affected the abundance of Skeletonema spp. which in turn influenced the temporal variation of diatom community at Klang. Our results highlighted how eutrophication affects diatom diversity and community structure.

Synechococcus production and grazing loss rates in nearshore tropical waters.

Temporal variation of Synechococcus, its production (µ) and grazing loss (g) rates were studied for 2 years at nearshore stations, i.e. Port Dickson and Port Klang along the Straits of Malacca. Synechococcus abundance at Port Dickson (0.3-2.3 × 105 cell ml-1) was always higher than at Port Klang (0.3-7.1 × 104 cell ml-1) (p < 0.001). µ ranged up to 0.98 day-1 (0.51 ± 0.29 day-1), while g ranged from 0.02 to 0.31 day-1 (0.15 ± 0.07 day-1) at Port Klang. At Port Dickson, µ and g averaged 0.47 ± 0.13 day-1 (0.29-0.82 day-1) and 0.31 ± 0.14 day-1 (0.13-0.63 day-1), respectively. Synechococcus abundance did not correlate with temperature (p > 0.25), but nutrient and light availability were important factors for their distribution. The relationship was modelled as log Synechococcus = 0.37Secchi - 0.01DIN + 4.52 where light availability (as Secchi disc depth) was a more important determinant. From a two-factorial experiment, nutrients were not significant for Synechococcus growth as in situ nutrient concentrations exceeded the threshold for saturated growth. However, light availability was important and elevated Synechococcus growth rates especially at Port Dickson (F = 5.94, p < 0.05). As for grazing loss rates, they were independent of either nutrients or light intensity (p > 0.30). In nearshore tropical waters, an estimated 69 % of Synechococcus production could be grazed.

Temporal variation of phytoplankton growth and grazing loss in the west coast of Peninsular Malaysia.

Phytoplankton growth (µ) and grazing loss (g) rates were measured monthly by the Landry-Hassett dilution method over a 2-year period at both estuarine (Klang) and coastal water (Port Dickson) systems along the Straits of Malacca. Chlorophyll a (Chl a) concentration ranged from 0.20 to 4.47 µg L(-1) at Klang except on two occasions when Chl a spiked above 10 µg L(-1). In contrast, Chl a concentrations were relatively stable at Port Dickson (0.14 to 2.76 µg L(-1)). From the rate measurements, µ was higher (t = 2.01, df = 43, p < 0.05) at Klang (0.30 to 2.26 day(-1)) than at Port Dickson (0.18 to 1.66 day(-1)), but g was not significantly different (p > 0.80). g ranged from 0.30 to 1.50 and 0.21 to 1.51 day(-1) at Klang and Port Dickson, respectively. In this study, grazing loss was coupled to phytoplankton growth, and the ratio of g/µ or grazing pressure which estimates the proportion of primary production grazed was 50% at Klang and lower than at Port Dickson (68%; t = 2.213, df = 36, p < 0.05). We found that the higher growth rates in a eutrophic system, i.e., Klang, were not matched by higher grazing loss, and this may have implications for the biogeochemical cycling in coastal waters.

Investigating the spatial distribution of phototrophic picoplankton in a tropical estuary.

We sampled extensively (29 stations) at the Klang estuarine system over a 3-day scientific expedition. We measured physical and chemical variables (temperature, salinity, dissolved oxygen, total suspended solids, dissolved inorganic nutrients) and related them to the spatial distribution of phototrophic picoplankton (Ppico). Multivariate analysis of variance of the physicochemical variables showed the heterogeneity of the Klang estuarine system where the stations at each transect were significantly different (Rao's F18, 36 = 8.401, p < 0.001). Correlation analyses also showed that variables related to Ppico abundance and growth were mutually exclusive. Distribution of Ppico was best explained by the physical mixing between freshwater and seawater whereas Ppico growth was correlated with temperature.