Sponge Bleaching

Why in News?

New Zealand recorded the largest-ever sponge bleaching event off tits southern coastline caused by marine heatwaves earlier this year.

Sponges are more resilient to ocean warming and marine heat waves than other organisms.
But in this event only a single species of cup sponge Cymbastella lamellata was affected.
- The bleaching turned millions of the normally dark brown sponges bright white.
Instances of tissue loss, decay and death of other sponge species across parts of New Zealand had also been reported.

One of the most ancient and abundant animals on rocky reefs across the world.
Sponges contain symbiotic relationships like the corals.
In New Zealand, they occupy up to 70% of the available seafloor.
- They are found extensively in mesophotic ecosystems at depths of 30-150m.
Functions of Sponges
- Filter large quantities of water.
- Capture small food particles.
- Moving carbon from the water column to the seafloor.
  - It provides food for bottom-dwelling invertebrates.
- Sponges add 3-dimensional complexity to the sea floor.
  - It provides habitat for various species such as crabs, shrimps and starfish.

Unlike other species Cymbastella lamellata hosts dense populations of diatoms which give the sponge its brown Color.
These diatoms live within the sponge tissue, exchanging food for protection.
When the sponge bleaches, it expels the diatoms, leaving the sponge skeleton exposed.
This leads to tissue loss or tissue decay which are amplified with increased heat stress.