Empty bucket

Sieving sediment with Kharis. Photo by Alexa Elliott, 
Changing Seas/South Florida PBS.

"Empty bucket!" I crooned. 

"Empty bucket!" Kharis echoed. 

Standing shoulder-to-shoulder at the lab bench, both of us diligently washed sediment through our sieves. Reaching the bottom of a bucket meant that we had almost finished a sample. This small event was enough cause for celebration and levity. 

One of the chapters Kharis designed for her thesis involves looking at juvenile clams and snails on the Arctic ocean floor. In the Arctic, ice scours the seafloor, and this impacts the animals that live there. Ice floes bang against the coast; icebergs bash into the seafloor; and in the intertidal zone, the sediment freezes solid. Ice makes it very dangerous to live in shallow water, so there's a cline in biodiversity with depth. More individuals and more species live deeper, because the deeper you go, the less likely you are to be brutally murdered by frozen water. 

Kharis is trying to figure out what stage in the life-history sets up that cline. We know the adults primarily occur deeper, but what about the juveniles? Do larvae know that ice could scour their life away when they pick a place to settle? Maybe the juveniles occur evenly across the habitat until the ice comes along and kills all the ones in the shallows. That's what we're trying to figure out. 

In ecology, where and how an organism lives is called its niche. Most species have a functional niche - where they could live in theory, based on the temperature and other environmental conditions - and a realized niche - where they actually live. A large functional niche can be dramatically shrunk to a small realized niche because of predators, storms, fishing, or any number of factors. While clams could theoretically survive in the shallows, ice could be that factor that comes along and shrinks their niche. 

Kharis preserving a sediment sample. Photo by Alexa Elliott,
Changing Seas/South Florida PBS.

The other layer to this study is that ice scour patterns in the Arctic are changing. Kongsfjorden, once a seasonally ice-covered fjord, now has open water year-round. Meanwhile, the two glaciers at the head of the fjord are calving off increasing numbers of icebergs as they slowly shrink. These two factors could actually have opposite effects on the seafloor - there are fewer ice floes but also more icebergs. Which one has a stronger impact on the community? We're collecting our samples in the same area as a similar study 20 years ago, so we should be able to tell. Besides revealing the fundamental ecology of molluscan niches in the Arctic, we should be able to document the impacts of long-term climatic change. 

It's been a lot of work, but I'm excited to see Kharis's study move forward!