Are they important or not?

A new research paper looks at the role of jellyfish and menhaden in the ecosystem of the northern Gulf of Mexico.

Jellyfish can be gorgeous, but they're rarely considered charismatic like tuna or swordfish or marine mammals.  And menhaden -- well, they're in the middle of the trophic levels, very very very important to the food chain as a food source and also as filter feeders, but beautiful?  Handsome? Charismatic?  Not really.

So it's good to see these important cogs in the oceanic wheel getting their just due, as done in this research.

So what did they do in the study?   Here's a couple of excerpts from the following article:


Tampering with the food web: what do changes in jellyfish and menhaden populations mean for the ecosystem?

Importance:  "Some of the most important groups in marine food webs are forage fish. Forage fish are small, schooling fish that are critical in transferring energy from low to high trophic levels; they often serve as the link between planktonic primary producers and organisms higher in the food web (e.g., tunas, marine mammals and seabirds). For many years, jellyfish have been overlooked in food webs, and were previously considered “trophic dead ends”. However, in reality, they play a very similar role to forage fish in the food web, with the same prey types and large predators."

So they want to find out what happens to the ecosystem if there are significant changes in the population of jellyfish and menhaden.

Modeling:

"Four scenarios were tested with the food web model:
(1) increase large jellyfish consumption of plankton prey by 50%,
(2) remove menhaden by increasing forage fish fishing pressure by 50% and decreasing the menhaden population by 59%,
(3) reduce forage fish fishing by 50% and increase menhaden stock by 41%,
(4) close of all fisheries, increasing populations for fish groups."

Summary of results:
For (1), total ecosystem productivity decline, major effects on higher trophic levels (top predators/consumers).

For (2), about a 10% decline in total ecosystem productivity.

For (3), not much change.

For (4), big increases for some things (like menhaden, as would be expected if they aren't fished for), but jellyfish and other forage fish populations declined.


So, I'd say that the study shows jellyfish and menhaden are pretty important to the ecoystem.  The concern is that increasing jellyfish populations, which could be happening both due to climate change and as the jellyfish fill ecological niches that have been vacated by other species due to overfishing, could cause real adverse effects, such as seen in Scenario 1.

The menhaden fishery should therefore be protected vigorously.  Even if they aren't beautiful.