Question: Calanus get lipid from algae, store it and herring eat the calanus. Menhaden get the lipid directly from algae. What is the percentage energy loss difference between the herring and menhaden?
There is no single measured “percentage energy-loss difference” for these two fish. You can still bound it from trophic levels and typical transfer efficiencies.
### The two pathways are not equally long
A useful rule of thumb is that **about 10% of energy becomes new production at the next trophic level** (roughly 90% lost to respiration, feces, and unconsumed production). Marine averages are often a bit lower, around **8%**, and productive coastal food webs can be higher, **10–15%** or more for some steps. Lipids and omega-3s often transfer better than bulk carbon. (LINK)
Food-web models and isotopes put the fish at different heights:
| Group | Typical trophic level | Meaning ||—|—|—|
| Phytoplankton | 1 | Algae |
| *Calanus* | ~2.1–2.3 | Mostly herbivorous copepod |
| Juvenile menhaden | ~2.5–2.6 | Still heavily algal / detrital |
| Adult menhaden | ~2.8–3.4 | Mix of algae + zooplankton |
| Herring | ~3.5 | Mostly zooplankton (*Calanus*, krill) |
So herring sit about **0.5–1 full trophic step above menhaden**, not a clean “algae→fish” versus “algae→copepod→fish” contrast. Adult menhaden already eat a lot of zooplankton. Only young menhaden are close to a one-step algal pathway. (LINK)
### What that means in energy terms
If you treat the difference as **one extra trophic step** at 10% efficiency:
– Extra step keeps ~10% of the energy that entered that step.
– About **90%** of the energy that reached *Calanus* never becomes herring flesh.
Relative to a short algal→menhaden path, the herring path then yields on the order of **one-tenth** as much fish biomass per unit of algal production.
Using the actual trophic-level gap (menhaden ~2.6, herring ~3.5) and 10% transfer per level:
– Algae → menhaden: \(0.10^{1.6} \approx 2.5\%\) of primary production ends up as menhaden production.
– Algae → *Calanus* → herring: \(0.10^{2.5} \approx 0.3\%\) ends up as herring production.
That is about an **8-fold difference**: the herring pathway delivers roughly **10–15% as much fish production per unit algae** as the shorter menhaden pathway. Equivalently, **about 85–90% more of the original algal energy is dissipated** before it becomes herring than before it becomes young menhaden.
At a more optimistic 15% transfer efficiency the gap shrinks but stays large (herring still on the order of **15–20%** of the menhaden yield per unit algae).
A Norwegian herring bioenergetics study found that feeding herring convert only **~17% of consumed prey energy into growth**; the rest is metabolism and waste. That is the fish’s own conversion efficiency, on top of whatever *Calanus* already lost converting algae. (LINK)
### Why the textbook 90% figure is too clean
1. **Menhaden are not pure algae-eaters.** Adults sit closer to herring than the cartoon implies, so the real gap is smaller than a full extra 90% loss.
2. **Transfer efficiency is not a fixed 10%.** Phytoplankton→copepod can be ~12–23%; copepod→small pelagic fish ~10–14%. Omega-3 transfer from algae to copepods is often higher than carbon transfer (~20% in some studies). (LINK)
3. **Calanus concentrates lipids.** Much of what herring get is stored wax esters, not bulk copepod protein. Lipid transfer can be more efficient than total-energy transfer even though an extra animal is in the chain.
4. **Not all algae are available to menhaden.** They filter poorly on the smallest cells. *Calanus* can use some of that production, then pass a packed lipid store to herring. The “wasted” extra step sometimes packages energy that menhaden never capture.
### Practical takeaway
For **total energy / biomass from a given amount of algae**, the extra *Calanus* step typically costs on the order of **one extra 85–90% loss**, so herring production per unit primary production is often **about an order of magnitude lower** than production of young, more herbivorous menhaden.
For **omega-3 lipids specifically**, the gap is smaller than that bulk-energy gap, because copepods retain and upgrade EPA/DHA better than they retain total carbon. That is why herring can still be extremely oily even though they sit higher on the food chain.