On the 29th June 2019, The Guardian newspaper reported extremely high temperatures in California with researchers allegedly discovering scores of dead mussels which had been cooked alive. The claim is that the molluscs were exposed to temperatures of 37°C from the heatwave baking the rocks they were attached to and were slowly cooked alive in their shells. Take into account that the ambient temperature at the shore was more like 27°C.
Personally, something about this article does not seem to add up. In Gibraltar our coastline is adorned with mussels and we typically reach temperatures of over 30°C in the summertime. I have yet to see beds of mussels “cooked alive” in situ. It is not impossible, but on the scale of probability it seems rather unlikely. Further, a quick inspection of food cooking safety standards advises that the minimum temperature we cook our food at is around 60°C; a full 23°C difference.

In this case, it is the ecosystem which collapses!

It provoked me to ponder the consequences of the what-if scenarios. What if the increases in average global temperature reached a point where mussels started cooking in their shells at low tide? What would the environmental impacts be on our local ecosystem? In the first instance one suspects that the only viable habitat would be below the neap low tide mark. It is also true that sea level rise is associated with melting polar ice caps – perhaps this would mitigate the negative effects all round or even provide new habitats should the level rise sufficiently. But why is this even important? They are just mussels!

Mussels are bi-valves which form part of the Phylum Mollusca. They can be marine or fresh water and play an important role in hydrothermal vent habitats. As filter feeders they help maintain water clarity by filtering out turbidity causing particulates. In marine habitats they tend to form huge matts in high energy exposed zones along the coastline. The matts actually help to dissipate the force of the waves and can be considered a survival strategy for the organisms.

Mussels are considered a keystone species which means that they play a crucial role in the ecosystems they form part of. The term keystone species was first coined by an American zoologist Robert T. Paine in 1969. The reason for the term is that the effect is considered to be analogous to the keystone in an arch; it collapses without it but in this case, it is the ecosystem which collapses!

Within an ecosystem there can be complex interactions between various keystone species. By way of an example, sea stars are a keystone species which exert top-down control over mussels, limiting their populations. Sea stars and mussels are important prey items for other keystone species and consequently it is incredibly difficult to predict that a local extinction of one animal will play out throughout the system as a whole. The short answer is that it doesn’t usually end well.

The short answer is that it doesn’t usually end well.

Mussels are incredibly important to the aquaculture industry also, growing an impressive 40mm within 12-15 months. Their fast growth rate, and relative resilience to changing environmental conditions, makes them an ideal choice for farming. They don’t need much feeding too as much of their food is found in suspension within the water. Consequently, within the EU aquaculture produces around 20% of food productions and is presently growing at around 7% per year according to the EU Commission on Food, farming and fisheries.
With their importance both environmentally and commercially established, one has to cast their mind back to the article to see it in its full context. Wild mussels cooking alive would quickly decimate the local marine environment and would quickly be followed by increased levels of other species dying off. This event would also be news worthy and yet no article like that can be found on various permutations of google searches. Commercial mussels can be lowered and raised through the water column and consequently there would be less of an issue to them.

The worrying effect of climate change on our present food webs is very concerning indeed and the Guardian article certainly helps to raise this point into our collective consciousness. The loss of any species can often have dramatic and unforeseen consequences on the ecosystem which can all too often be irreversible. As with the mussel’s example, even a localised mass dying can knock a delicate balance off kilter with far reaching implications for us as a species. Whilst the example presented is almost certainly conflated the established scientific evidence would suggest that this kind of a future could be on the cards.

Consequently, society needs to work very hard at mitigating the effects of climate change on our biosphere because although our inactions will not directly impact us, they will have far reaching and devastating implications on our descendants. “How could I look my grandchildren in the eye and say I knew what was happening to the world and did nothing.” – David Attenborough

Intertidal rocky shorelines
Filter feeders
Interesting Fact:
Mussels have even colonised hydrothermal vents within the deep oceans