Author – Jim Waymer, Dec 1, 2020
Too much of our errant sewage and fertilizer feeds algae that die, rot, and then the bacterial fallout robs fish of oxygen. So when thousands of dead fish lined stretches of the Indian River Lagoon this week, many feared a repeat of 2016’s “fish-apocalypse” when tons of carcasses of sea life fouled waterways from Titusville to Melbourne.
For months, biologists had been discussing — and fearing — that the lagoon’s ongoing algae blooms would eventually kill marine life and seagrass en masse. Ongoing warmer-than-usual temperatures worsened the situation.
But biologists say this latest die-off is nowhere near the levels of dead fish the 156-mile lagoon region saw in 2016. In the short term, they say, this week’s cold, windy weather should stir up enough oxygen in the water to bring some temporary relief for fish and the coastal dwellers who must bear the odor of their collective demise.
Fish die-offs in the Lagoon tend to happen more often during warm summer months, when algae blooms are more frequent and more severe.
During daylight, algae produce oxygen through photosynthesis, replenishing oxygen levels in the water. But at night, the algae consume oxygen. This, coupled with the normal demand for oxygen from fish, crabs and other marine life can cause dips in dissolved oxygen in the lagoon, with the lowest levels just before dawn.
When dense clusters of fish die and rot, bacteria increase, further diminishing the available oxygen in the water.
Winds help aerate the water, but stagnant days pose more of a threat.