The majority of reef zooplankton is demersal, and rises into the water column from the benthos at night when levels of predation are lower. But, perhaps the degree to which variations in the relative amounts of zooplankton occur at night by comparison with levels during the day might be surprising (Table 2). While some corals feed during the day, and some feed day and night, the majority feed at night. This corresponds to when zooplankton is most abundant. In this way, corals can gain energy from light during the daytime and feed at night when zooplankton is most abundant. This is the most energy efficient way for corals to maximize their energy intake. Of course, exceptions arise over time, and even night feeding corals may feed during the day, although it is likely they will only do this if there is sufficient prey to warrant the considerable energy expense of prey capture. In aquariums, since there is such a relative paucity of zooplankton and a concurrent lack of nightly migration, coupled with the normal daytime feeding of the tank, many normally night-feeding corals extend to feed during the day. Tentacle extension, it should be noted, is not always related to food capture, and may also be indicative of competition or to expose corals with zooxanthellae in the tentacles to light. Generally, corals with transparent tentacles (tentacles lacking zooxanthellae), are night feeders.
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]Taxonomic group[/SIZE][/FONT][FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]day (mg/m-3) [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]night (mg/m-3)[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]copepods [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]174[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]1574[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]appendicularians[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]4[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]34[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]chaetognaths [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]2[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]70[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]amphipods [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]0[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]26[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]ostracods [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]2.5[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]138[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]decapods [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]0.7[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]43[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]veligers[/SIZE][/FONT][FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]15[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]382[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]foraminferans [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]4[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]10[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]fish larvae[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]13[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]70[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]mysids [/SIZE][/FONT][FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]6[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]701[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]crab zoe[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]0[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]237[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]polychaetes [/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]4[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]38[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]Total Haloplankton/Meroplankton[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]130[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]2346[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]Total Microplankton [/SIZE][/FONT]
[SIZE=-1][FONT=Georgia, Times New Roman, Times, serif](zooflagellates, ciliates, nauplii) [/FONT][/SIZE]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]11[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]181[/SIZE][/FONT]
[FONT=Georgia, Times New Roman, Times, serif][SIZE=-1]Table 2. Composition and amounts of zooplankton by time of day.[/SIZE][/FONT]
Because it is not known what the energy budgets of corals in aquariums are, it is difficult to say whether or not there is an advantage or disadvantage to the often abnormal feeding behaviors in aquariums. If corals meet their energy needs through various combinations available at various times of the day, there is probably little disadvantage. Nor am I comfortable suggesting the feeding at night is "better" than feeding during the day. However, it is more natural, and it may be stressful for those corals that feed almost exclusively at night in the wild to feed during the day. The possible deleterious effects of strong lighting on normally withdrawn tentacles may also be injurious since they probably lack the photoprotective pigments of the rest of the tissue and the zooxanthellae.