There are lots of processes that create waste in the ocean. Organisms excrete organic matter as waste, have organic matter fall out of their mouths when trying to feed (a process called “sloppy feeding”), molt their exoskeletons, and leak organic matter through diffusion. Additionally, organisms die and their carcasses remain in the water. In total, these processes creates a large supply of organic matter that varies from very small materials (Dissolved Organic Matter) to much larger materials (Particulate Organic Matter/Detritus). However, if you go snorkeling you will quickly realize that there is not a dead body sight (or we hope so!). What is happening to all this organic matter?
Decomposers are organisms that break down non-living organic matter into smaller molecules. Decomposers are responsible for releasing carbon dioxide and inorganic nutrients (like nitrate and phosphate) that can be used again by primary producers to stimulate growth! In the ocean, microorganisms like Bacteria and Archaea are the primary decomposers; they break down organic matter externally to their bodies and feed by absorbing on a molecular scale. Fungi can also be decomposers in marine ecosystems, and are notable for their ability to decompose woody substrates.
There is also a subset of decomposers known as detritivores (also referred to as “bottom-feeders” or “scavengers”) that feed on dead particulate matter and feces by oral ingestion. Marine detritivores include organisms like crustaceans, sea stars, sea cucumbers, and worms. As both detritivores and microbial decomposers can feed on particulate matter, detritivores often end up eating dead material that is covered by the microbial decomposers! These microbes are thus an extra source of energy for our detritivores.
Today, we are going to look at a really big and really cool example of marine decomposition: a whale fall! A whale fall is when a whale dies and its body sinks to the sea floor. This large carcass then becomes a food oasis in an otherwise food-limited desert, supporting a host of wacky and amazing organisms!
Read the information about a whale fall, upwelling, and phytoplankton abundance provided in the Supplement Packet.
1) Name the three stages of whale decomposition. Describe what occurs in each of those stages.
1) If you consider all stages of decomposition, how many years does it take for a whale carcass to decompose?
*Fun Fact! Because whale carcasses take so long to decompose, it is estimated that there may be as many as 690,000 whale carcasses decomposing in the ocean at any one moment!*
3 ) Identify four detritivores found at a whale fall.
4) Whale carcasses are especially lipid rich, containing 2000-3000 kg of bone lipids! Which organisms are primarily responsible for the decomposition of the bone lipids?
During what stage does the majority of bone decomposition occur?
5) Deep water is full of nutrients that are released from the decomposition of organic matter (carcasses, feces, etc.). How do these nutrients re-enter surface waters?
6) Explain the relationship between upwelling and phytoplankton abundance in the ocean.