Phytoplankton plays a vital role in marine ecosystems. Apart from being a food source for marine animals, it removes carbon dioxide from the atmosphere through photosynthesis. Phytoplankton needs iron to grow. Whale poo is very rich in iron, containing 10 million times as much as seawater. Over the last century, commercial whaling has reduced the number of whales dramatically, starving the oceans of the necessary iron and decreasing the plankton’s capability to remove carbon dioxide from the atmosphere. Protecting whales and restoring their populations should therefore be an important goal for governments.

http://www.abc.net.au/news/2014-10-08/whale-poo-vital-to-southern-ocean-health/5798118

Over the last decade, bed bugs have re-emerged in the developed world. They can now be found even in 5-star hotels. They live in bedding and under mattresses and feed on blood. They hide during the day but emerge during the night to feed on their sleeping host. Their faeces appear as clusters of tiny spots and contain histamine, a chemical known to cause allergic reactions such as asthma, itchiness, sneezing and watery eyes. There are treatments available to get rid of bed bugs, but their poo can remain in mattresses, carpets and furniture upholstery long after the bugs are gone.

https://www.sciencenewsforstudents.org/article/yuck-bedbug-poop-leaves-lingering-health-risks

Every year, around 236,000 tonnes of microplastics (tiny fragments of plastic from broken down plastic bags, bottles and other plastic products) end up in our oceans. Researchers have long feared that these microplastics could enter the food chain, eventually being ingested by humans eating fish and other seafood. A 2017 study in the UK examining poo samples of seals and mackerel found proof that microplastics are indeed transferred from prey to predator. Scientists at Ghent University in Belgium claim that shellfish lovers eat up to 11,000 plastic fragments in their seafood every year. Plastic in our oceans has become a global crisis. It is expected to outweigh fish by 2050.

https://www.nature.com/articles/d41586-018-02649-z

Outbreaks of the crown-of-thorns starfish are a major threat to the health of reefs. The masses of starfish eat the corals and cause their destruction. One way to tackle the problem is to try to cull them, which is not an easy task. Another option is to identify the fish species that feed on the starfish and protect them to increase their numbers. Previously, fish were caught and cut open to inspect the content of their intestine to see whether they contained any crown-of-thorns starfish remains. A new, non-invasive and non-lethal approach is to collect fish poo and examine it to see whether it contains starfish DNA.

http://www.abc.net.au/news/2018-02-15/fish-poo-could-be-the-key-in-tackling-crown-of-thorns-problem/9447528