The rate and intensity of algal blooms has increased over the last two decades. Sponges are efficient filter feeders and are thought to be powerful bioactive controls of algal blooms. However, very little research has explored the effect of large concentrations of algae on the ability of sponges to filter effectively. In this study the filtration and clearance rate before and after being introduced to algae rich seawater was measured to explore the effect of large algae concentrations on filtration rate. This study found that while there was a linear decrease in algae concentration there was no significant difference in the filtration rate of the study species, Amphimedon queenslandica. This raises further questions regarding the efficiency of filtering across greater periods of time and across different species of demospongiae.  

Sponges are one of the oldest extant metazoan phyla, and live in almost all marine environments (Frost, 1978).  Within a reef ecosystem they play a prominent role in nutrient cycling by filtering particulate matter, which prevents oversaturation of phytoplankton and algal blooms (Simpson, 1984). It has been estimated that in warm water, a sponge population inhabiting a reef slope between 20 and 40m would filter the surrounding water column every 24hrs (Reiswig, 1974). Sponges utilize filter feeding via the rapid beating of flagella attached to choanocytes (Thomassen and Riisgård, 1995).They then trap organic particles for consumption and expel inorganic particles back into the water column (Thomassen and Riisgård,1995).

Clearance rate and filtration rate are the two main measurements used to understand the filter feeding of sponges. Clearance rate is a measure of the microsphere concentration over time, and is usually measured as a difference in particle concentration in water surrounding a sponge in a closed area over time (Reiswig,1974). Filtration rate is the measurement of the rate at which water is pumped through the sponge, and it usually measured by tracking the flow of a fluorescent dye (Richter, 2001).

Filtration rate and clearance rate have been used interchangeably in the literature when discussing filtration of sponges (Thomassen and Riisgård,1995; Reiswig, 1974),however there is little research on the effect of filtration and clearance rates over time. Specifically, there is little to no research regarding the effect of overexposure of algae on the ability for sponges to filter effectively.
This is a growing concern as the past decades have seen a vast increase in algal blooms that exceeds the expected increase as a result of the development of powerful mapping and tracking tools (Min et al., 2001). Hypothesised influences of increasing frequency of blooms include; increasing costal development and resulting increase in coastal pollution, increasing aquaculture,increasing global temperatures and decreasing benthic cover (Min et al., 2001;Peterson et al., 2006).

Thus the aim of this research was to explore the influence of overexposure to algae, that is algae at a greater concentration than is seen in nature, on the filtration rate of Amphimedon queenslandica overtime. The clearance rate will be used as a control to ensure the sponge is effectively ingesting particles.

If the filtration rate decreases over time due to a large number of particles being trapped in the choanocytes this will have implications for future research as filtration rate and clearance rate will no longer be able to be used interchangeably.Furthermore, it will have implications regarding the effect of algal blooms on the health and ecological function of sponges.

Amphimedon queenslandica was selected as the study species for this research. The sponges were collected from the Moreton Bay region on 21/12/15, and kept in the Degnan Aquariums until the commencement of research. The three individuals used were of similar sizes with a similar number of functional ostia (~3).

6 sponges were initially used to explore filtration rate in the absence of algae,however only 3 were pumping effectively so the sample size was reduced to the 3 functional organisms. To measure the filtration rate fluorescein dye was pumped into the water surrounding the ostia of the sponges. The sponge was then recorded for 30-40 seconds and the video was analysed using the ‘Tracker video analysis and modelling tool’.

Once the initial filtration was measured the sponges were introduced to algae rich water. The algae selected had cell sizes 0f 1-2 µm, this cell size is cleared most effectively by demospongiae (Reiswig 1971; Turin 1997). Algae was mixed with seawater, then introduced to Amphimedon to ensure the algae concentration was consistent. The water was stirred and a 1ml sample was taken from the water to be analysed using a spectrophotometer at OD 550nm. This was repeated at 30 minutes, 60 minutes and 90 minutes. Finally, the sponges were placed back into tanks and the filtration rate was measured again using fluorescein dye. 

This study determined that there is very little difference in the filtration rate of Amphimedon queenslandica before and after introduction of algae-rich seawater. The results also indicated that the clearance rate of algae was consistent over time. This is contrary to the literature, which suggests that the clearance rate over time fits an exponential curve, due to a decline in algae concentration (Pile et al., 1997). Thus, this research does not agree with current scientific knowledge. The limited time frame across which samples were taken, the lack of replicates or the use of a novel sponge species could all have contributed to this.

Demospongiae are acknowledged to have vast diversity in their functional ecology (Reiswig, 1974; Turon, 1997). As Amphimedon queenslandica has not been examined in depth before, it is possible that the deviation from current scientific knowledge is due to unknown species specific characteristics. If filtration and clearance rate are consistent across time and for differing concentrations of algae and other organic suspended particles, Amphimedon queenslandica could play an important role in the regulation of algal blooms and water clarity in the Great Barrier Reef, and the Moreton Bay region. Particularly in light of increasing temperatures and coastal pollution (Peterson et al., 2006). It would be useful to explore this hypothesis with different local species of demospongiae.

Alternatively,this research suffered due to a lack of replicates. This is due largely to the lack of healthy sponges of an appropriate size. This effects the statistical analysis in a number of ways; a small sample size may not fully represent the diversity found in the structure and resulting filtration rates of the sponges.Furthermore, a low sample size can decrease the significance of a p-value, thus rendering it more difficult to reject the null hypothesis. Future research would benefit from having a significantly larger sample size.

Finally,the clearance rate was measured at 30 minute intervals four times for a total of 90 minutes. The filtration rates were measured before the introduction of algae (0 minutes) and at the conclusion of the clearance rate trial (90 minutes). During this time the filtration rate did appear to decrease, however a Students T-Test determined that this was not a significant decrease. I propose that this lack of significance was a result of a limited time measurement, and if the trial was extended the p value would decrease to allow rejection of the null hypothesis.

This research demonstrated that Amphimedon queenslandica maintains a consistent filtration rate when exposed to high concentrations of algae. This indicates that there is potential for Amphimedon queenslandica to be capable of clearing algal blooms if there is a significant population size, however more research needs to be done to support this hypothesis. 

Frost, T. (1978). In situ measurements of clearance rates for the freshwater sponge Spongilla lucustris. Limnol.Oceangr., 23(5), pp.1034-1039.

Min, X., Yijun, Z. and Kai, C. (2001). Algal Toxins of Blooms, Red Tides and Their Analysis Methods. Journal of Lake Sciences, 13(4), pp.376-384.

Peterson, B., Chester, C., Jochem, F. and Fourqurean, J. (2006). Potential role of sponge communities in controlling phytoplankton blooms in Florida Bay. Marine Ecology Progress Series,328, pp.93-103.

Pile, A., Patterson, M., Savarese, M.,Chernykh, V. and Fialkov, V. (1997). Trophic effects of sponge feeding within Lake Baikal's littoral zone. 2. Sponge abundance, diet, feeding efficiency, and carbon flux. Limnol. Oceangr., 42(1), pp.178-184.

Reiswig, H. (1971). Particle Feeding in Natural Populations of Three Marine Demosponges. Biological Bulletin,141(3), p.568.

Reiswig, H. (1974). Water transport,respiration and energetics of three tropical marine sponges. Journal of Experimental Marine Biology and Ecology, 14(3), pp.231-249.

Reiswig, H. (1975). Bacteria as food for temperate-water marine sponges. Can. J. Zool., 53(5), pp.582-589.

Richter, C., Wunsch, M., Rasheed, M., Kotter,I. & Badran, M.I. (2001). Endoscopic exploration of Red Sea coral reefs reveals dense populations of cavity-dwelling sponges. Nature, vol. 413,no. 6857, pp. 726-30. 

Riisgård, H., Thomassen, S., Jakobsen, H.,Weeks, J. and Larsen, P. (1993). Suspension feeding in marine sponges Halichondria panicea and Haliclona urceolus: effects of temperature on filtration rate and energy cost of pumping. Marine Ecology Progress Series,96, pp.177-188.

Simpson, T. (1984). The cell biology of sponges. New York: Springer-Verlag.

Thomassen, S. and Riisgård, H. (1995). Growth and energetics of the sponge Halichondria panicea. Marine Ecology ProgressSeries, 128, pp.239-246.

Turon, X., Galera, J. and Uriz, M. (1997). Clearance rates and aquiferous systems in two sponges with contrasting life-history strategies. The Journal of Experimental Zoology, 278(1),pp.22-36.