Photosynthesis versus feeding

[ATJ]

We know from a number of studies on anthozoans that, generally, feeding provides more nutrition than the products of photosynthesis. Some studies have even shown that some anthozoans will "starve" in full light without food, but "thrive" in darkness with food. We also know that photosynthesates are a good source of carbon but not as good for nitrogen.

What I was wondering was the nitrogen requirements of the zooxanthellae. If they normally benefit from having a supply of nitrogen from the host as result of food digested and metabolised by the host, but the host is deprived of food, will the zooxanthellae then be deprived of nitrogen (assuming very low nutrient water)? That is, will they be limited in their own metabolism due to a shortage of nitrogen which may be another reason that most anthozoans need to feed.

I think, also, that many anthozoans that can rely less on feeding and more on the products of photosynthesis live in waters with a higher nutrient content which may be utilised by either the host or the zooxanthellae.

 

[rshimek]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote

Originally posted by ATJ:

Hi ATJ,

We also know that photosynthesates are a good source of carbon but not as good for nitrogen.

Photosynthates are not "not as good for nitrogen."
Photosynthates LACK nitrogen totally. A photosynthetic organism may build proteins, but they do NOT do this by photosynthesis. They use the photosynthate as fuel to build nitrogen containing compounds in separate biochemical pathways.

What I was wondering was the nitrogen requirements of the zooxanthellae. If they normally benefit from having a supply of nitrogen from the host as result of food digested and metabolised by the host, but the host is deprived of food, will the zooxanthellae then be deprived of nitrogen (assuming very low nutrient water)?

Absolutely.

I think, also, that many anthozoans that can rely less on feeding and more on the products of photosynthesis live in waters with a higher nutrient content which may be utilised by either the host or the zooxanthellae.

This is actually not the case. The marine areas with much dissolved nutrient are typically temperate or boreal, and the anthozoan fauna in these areas is dominated by non-zooxanthellate anemones.

 

[ATJ]

Ron,
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by rshimek:
<strong>Photosynthates are not "not as good for nitrogen."
Photosynthates LACK nitrogen totally. A photosynthetic organism may build proteins, but they do NOT do this by photosynthesis. They use the photosynthate as fuel to build nitrogen containing compounds in separate biochemical pathways.</strong><hr></blockquote>
Sorry, I worded it badly, I meant the products the host receives from the zooxanthellae.
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by rshimek:
<strong>This is actually not the case. The marine areas with much dissolved nutrient are typically temperate or boreal, and the anthozoan fauna in these areas is dominated by non-zooxanthellate anemones.</strong><hr></blockquote>
I was thinking of turbid and/or lagoonal areas within or adjacent to reef areas which may be subject to higher nutrients due to run-off, etc. For example, Goniopora spp. are frequently found in turbid lagoonal environments. Also note that relatively high nitrate and phosphate levels have been found in areas of the Indonesian Archipelego during upwelling periods (Southeast Monsoon) (Tomascik et al, 1997).

It is interesting to note that according to Fabricius and Alderslade (2001), Xenia (which have reduced guts) are typically found in clear water habitats and may be common below depths of 10m. This appears to go against my idea of increased nutrients decreasing the importance of feeding.

[ November 24, 2001: Message edited by: ATJ ]</p>

 

[rshimek]

Hi Andrew,

Regarding lagoonal areas and diversity... They are diverse enough, but the diversity of anthozoan life - is really a lot higher in the high nutrient areas of some boreal regions. In the Oregonian biome of NW North America, there are maybe 30-35 common sea anemones including several that get over 50 cm in diameter, and one can often find dozens of species and thousands of individuals in a small area.

One of the larger ones is Metridium gigantea, large individuals of which will stand 1.5 m high when fully inflated. In areas of high currents these form huge clonal (I presume) beds. I once had a diving partner who claimed the most sensual thing he had ever done was roll through one of these beds while wearing a thin wet suit. (My comment was that the 1960's were REAL good to him....).

Anyway, both the diversity and biomass is probably far higher in these temperate areas than in lagoonal ones, and virtually none of the anemones found there are zooxanthellate.