[Coral-List] coral feeding questions
szmanta at uncw.edu
Fri Jun 2 10:08:48 EDT 2006
I have been standing by reading the discussion about feeding by corals, an old discussion indeed which has been on-going within the coral community for ca. 40 years or more. Thus it seems we learn slowly! I think the reason for that is that for some odd reason we seem to have a greater tendency to be polarized than some other disciplines of science: everything has to be black or white, we don't like shades of grey (or gray either). As one who has worked with both autotrophic and heterotrophic aspects of coral nutrition, I never felt that I had to characterize corals as belonging to either camp, but rather I wanted to provide some quantitative information about such phyiological activities of the corals I studied. My opinion is that corals are blessed with very adaptable and varied trophic abilities that have served the group well over hundreds of millions of years. While there is no doubt that some reef species are quite dependent on their algal symbionts, others are apparently less so and thus do well at depth and in shaded areas where the zoox may be just passengers looking for a good shelter to live in. My first studies were on Astrangia danae (or A. poculata) a facultatively zooxanthellate species where the dark brown colonies were found deeper and under overhangs, while the white ones were more in the open...go figure.
More to the present ping-pong match: some old and recent references that (a) show that the multiple nutritional sources for reef corals has been long known and appreciated (Yonge 1973), and (b) some more recent studies that have shown that it's not just zooplankton that needs to be considered as heterotrophic food sources for corals. I remember being surprised in 1985 or 88 (getting old, can't remember which reef meeting) when Clive Wilkinson presented a paper showing data for coral filtration rates of phytoplankton (comparing them with sponges): I think he chose phytoplankton because he didn't realize the literature of the time told us that corals can't eat and digest such plant matter.
Yonge, C.M. 1973. The nature of reef-building (hermatypic) corals. Bulletin of Marine Science 23: 1- 15.
Wellington, G.M. 1982. An experimental analysis of the effects of light and zooplankton on coral zonation. Oecologia 52: 311-320.
Rosenfeld et al. 1999. Sediments as a possible source of food for corals. Ecol Letters 2: 345-348
Anthony k. and K. Fabricius. 2000. Shifting roles of heterotrophy and autotrophy in coral energetics under varying turbidity. JEMBE 252: 221-253
Houbreque et al 2004. Importance of a micro-diet for scleractinian corals. MEPS 282: 151-160
Houbreque et al. 2004. Interactions between zooplankton feeding, photosynthesis and skeletal growth in the scleractinian coral Stylophora pistillata. J Exp Biol 207: 1461-1469
As a final anecdote: back in the early '80s when I was doing nightly dives trying to pin-point coral spawning, I kept seeing the corals bulge their oral disks and then spit out stuff just at dusk as they expanded their polyps. The first few times I got all excited thinking it was the beginning of spawning. But syringe samples I collected, when observed under the microscope, showed the stuff to be made of : sponge spicules, zooplankton carapace parts, lots of marine snow like material that was totally unrecognizable, zooxs, foram tests etc etc. In other words, anything they could get their little tentacles on but couldn't digest.
As as a second final anecdote: a few years back a woman started a discussion on Coral-List suggesting that one reason corals were doing poorly was because as we overfish the world's oceans, we reduce the amount of N being cycled through these ecosystems. She suggested that corals may be mroe starved than they used to be when fishes living over the corals were more abundant. Judy Meyer showed back in 80s that corals grew faster when they had resident fish schools (Meyer, J.L. and E.T. Schultz. 1985. Migrating haemulid fishes as a source of nutrients and organic matter on coral reefs. Limnol. Oceanogr. 30:146-156.). In 1998 the worst bleaching year to date in the Florida Keys, inshore corals with large schools of grunts living on them bleached white as sheets in mid-June and were 100 % recovered by mid-September while more offshore corals that bleached later in the summer (temperatures heated up sooner inshore) suffered much death and tissue loss. These are the facts and I cannot tell you for sure why these two populations responded/recovered so differently to bleaching, but I suspect it was the high nutritional state of the corals due to fish feces as a food source.
Dr. Alina M. Szmant
Coral Reef Research Group
UNCW-Center for Marine Science
5600 Marvin K. Moss Ln
Wilmington NC 28409
Tel: (910)962-2362 & Fax: (910)962-2410
email: szmanta at uncw.edu
Web Page: http://people.uncw.edu/szmanta
From: coral-list-bounces at coral.aoml.noaa.gov on behalf of Zac Forsman
Sent: Fri 6/2/2006 4:13 AM
To: coral-list at coral.aoml.noaa.gov
Cc: grottoli.1 at osu.edu
Subject: [Coral-List] coral feeding questions
Great comments Charles!
-I have one question though: the tanks at the
Waikiki Aquarium all have live rock/sand/gravel.
Might these serve as refugia for populations of all
kinds of micro organisms that the corals could feed
on? Increased nutrients might be used by the coral..
but they could also cause a bottom up trophic cascade
that benefit the coral. Might also increase the
detritus or 'marine snow' in the tank.
I have one other question for Andrea:
For the studies you mentioned that looked at
zooplankton, did they arrive at those conclusions by
looking at gut contents? Would that bias the counts
towards critters with a hard carapace?
Is anyone aware of any other controlled feeding
studies out there?
-Just curious, Zac
Zac Forsman, Ph.D.
Department of Biology
2450 Campus Rd.
Honolulu HI, 96822
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