The effect of the salinity, light regime and food source on carbon and nitrogen uptake in a benthic foraminifer
<p>Foraminifera are unicellular organisms that play an important role in marine organic matter cycles. Some species are able to isolate chloroplasts from their algal food source and incorporate them as kleptoplasts into their own metabolic pathways, a phenomenon known as kleptoplastidy. One sp...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-02-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/18/1395/2021/bg-18-1395-2021.pdf |
| Summary: | <p>Foraminifera are unicellular organisms that play an important role in marine
organic matter cycles. Some species are able to isolate chloroplasts from
their algal food source and incorporate them as kleptoplasts into their own
metabolic pathways, a phenomenon known as kleptoplastidy. One species showing
this ability is <i>Elphidium excavatum</i>, a common foraminifer in the Kiel
Fjord, Germany. The Kiel Fjord is fed by several rivers and thus forms a
habitat with strongly fluctuating salinity. Here, we tested the effects of
the food source, salinity and light regime on the food uptake (via <span class="inline-formula"><sup>15</sup>N</span>
and <span class="inline-formula"><sup>13</sup>C</span> algal uptake) in this kleptoplast-bearing foraminifer. In
our study <i>E. excavatum</i> was cultured in the lab at three salinity
levels (15, 20 and 25) and uptake of C and N from the food source
<i>Dunaliella tertiolecta</i> (Chlorophyceae) and <i>Leyanella arenaria</i> (Bacillariophyceae) were measured over time (after 3, 5 and 7 <span class="inline-formula">d</span>). The species was very well adapted to the current salinity of the
sampling region, as both algal N and C uptake was highest at a salinity of 20. It seems that <i>E. excavatum</i> coped better with lower than with
higher salinities. The amount of absorbed C from the green algae
<i>D. tertiolecta</i> showed a tendency effect of salinity, peaking at a
salinity of 20. Nitrogen uptake was also highest at a salinity of 20 and
steadily increased with time. In contrast, C uptake from the diatom
<i>L. arenaria</i> was highest at a salinity of 15 and decreased at higher
salinities. We found no overall significant differences in C and N uptake from
green algae vs. diatoms. Furthermore, the food uptake at a light–dark rhythm
of <span class="inline-formula">16:8</span> <span class="inline-formula">h</span> was compared to continuous darkness. Darkness had a
negative influence on algal C and N uptake, and this effect increased with
incubation time. Starving experiments showed a stimulation of food uptake
after 7 <span class="inline-formula">d</span>. In summary, it can be concluded that <i>E. excavatum</i>
copes well with changes of salinity to a lower level. For changes in light
regime, we showed that light reduction caused a decrease of C and N uptake by
<i>E. excavatum</i>.</p> |
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| ISSN: | 1726-4170 1726-4189 |