Determination of prey capture rates in the stony coralGalaxea fascicularis: a critical reconsideration of the clearance rate concept

Abstract

In order to determine optimal feeding regimes for captive corals, prey capture by the scleractinian coral Galaxea fascicularis was determined by measuring clearance of prey items from the surrounding water. Colonies of G. fascicularis (sized between 200 and 400 polyps) were incubated in 1300 ml incubation chambers. Nauplii of the brine shrimp Artemia sp. were used as the prey item. A series of incubation experiments was conducted to determine the maximal capture per feeding event and per day. To determine maximal capture per feeding event, total uptake of nauplii after one hour was determined for different prey item availabilities ranging from 50 to 4000 nauplii per polyp. To determine maximal capture per day, the corals were subjected to four repetitive feeding events at three different prey item densities (50, 100 and 150 nauplii per polyp). Alongside these quantitative experiments, it was tested to what extent the feeding response of corals is triggered by chemical cues. One hour after food addition, extract of Artemia nauplii was added to the incubation chambers to test its effect on subsequent prey capture rates. In all experiments, prey capture was expressed as the number of nauplii consumed per coral polyp. Total capture of Artemia nauplii by G. fascicularis after a single feeding event increased linearly up till a prey item availability of 2000 nauplii per polyp. Maximal capture per feeding event was estimated at 1200 nauplii per polyp, which is higher than rates reported in previous studies. It became apparent that at high densities of Artemia nauplii, the clearance rate method does not discriminate between active capture and passive sedimentation. Repetitive feeding with 50 nauplii per polyp resulted in a constant total prey capture per feeding event. At a supply of 100 nauplii per polyp, total capture decreased after the first feeding event, and remained constant during the subsequent feeding events at a level comparable to the lower food availability. However, at a supply of 150 nauplii per polyp, total capture per event was higher throughout the entire four-hour incubation period, which obfuscates an accurate estimation of the maximal daily food uptake. In all incubations, a decrease in capture efficiency was observed within the course of the feeding event. In all repetitive feeding experiments, capture efficiency increased immediately upon addition of a new batch of food. This increase in efficiency was not caused by a priming effect of extract of Artemia. The inconsistencies in the data show that estimates of prey capture based on clearance rates should be interpreted with caution, because this method does not take into account potential dynamics of prey capture and release.

Water Flow Affects Zooplankton Feeding by the Scleractinian CoralGalaxea fascicularison a Polyp and Colony Level

“…These findings fit well with the long-term effects of zooplankton feeding on corals, which show that heterotrophy can be a limiting factor to growth [1,6]. Several factors may affect coral feeding rates, including bleaching status [4], prey density [7], symbiotic organisms such as epizoic flatworms [8], water flow rate [9][10][11][12][13][14][15][16], and colony size [12,16]. Water flow is a key parameter in this respect, as sessile organisms including corals depend on water movement to provide them with prey items [17].…”

Management of marine resources; combining industry and research

“…Improved husbandry of captive corals is the key to a more sustainable coral trade; investigating the optimal feeding regimes for captive corals (Osinga et al , 2012b) or determining the effect of light, food supply and water flow will provide a better insight into the growth of corals in captivity (Kimokeo et al , 2012). Experiments performed in captivity provide opportunities by which conditions can be adapted to simulate future seawater conditions based on climate change and ocean acidification for example (Toonen et al , 2012) and for the fertilization success of corals in areas that have increased turbidity (Erftemeijer et al , 2012).…”