"Discussion":Limacina helicina and Marine foodweb

Fig 2: Limacina Helcina (a pteropod). www2.cnrs.fr/en/1544

Background

The pteropod Limacina helcina (above image), otherwise known as “Sea butterflies” (due to the shape of their parapodia) (close relatives of snails and clams), are an important species in marine ecosystem. In fact, they make up for “50% of all total zooplankton population”. They are filter-feeders that uses mucusy web-like structures to feed on “phytoplankton ,other small zooplankton or their own juveniles”. By “filter-feeders”, we meant that they leave their presumptive mouth open so that large volume of sea water can rush in and in the process, food materials get trapped in their mucusy web-like structure, and ultimately get swallowed. They are known to inhabit relatively deeper levels of the open ocean ( which has significant consequences when it comes to acidification-discussed later). They are one of many calcifying organisms that make up the zooplankton, and they use a polymorph of calcium carbonate called aragonite to make their shells (Acker et al 1989). Pteropods calcify their outer shell to make it hard for predators to bite on them, in other words, they use calcification as a defense mechanism.

Marine food Web: Who are these “…Planktons”?

            The marine food web is composed of phytoplankton and zooplankton plus other organisms that feed on the zooplankton , such as salmon. Phytoplankton forms the base of the marine food web because of their photosynthetic nature. They are single-celled plants that are able to use the carbon absorbed by the ocean to make their own food. In essence, these species play an important role in being a food source for primary marine consumers but also play a crucial role in mitigating carbon accumulation in the ocean (http://marinebio.org/oceans).  Zooplankton are tiny marine animals that also form a very basal part of the marine food web, getting their energy from the aforementioned phytoplankton. They are weak swimmers that usually just move along with the water current. Pteropods are a member of a subdivision of zooplankton known as holoplankton, meaning that they spend their entire life cycle in the plankton (http://marinebio.org/oceans).

            Ultimately though, we are really worried about the effect of ocean acidification on some of these zooplankton species because of the effect it may have on secondary marine consumers such as salmon. Since salmon depend on these pteropods for food, a decrease in their population could lead to a dramatic decrease in salmon population. This has some serious economic consequences given the amount of revenue generated by salmon farming in the US. It has been reported that “Of the total $USD 3.0 billion personal income generated from the salmon fishing industry in 2007, 43 percent was in the US..” (www.wildsalmoncenter.org). On the other hand, a decrease in the population of calcifying organisms would allow for a phytoplankton bloom, and thereby causing an increase in the use of carbon that is fed into the ocean by these plant species. From the above argument, it is obvious that the fate of pteropods has some very important policy implications: Do we let them die off so that the phytoplankton can continue using up the CO2 that is absorb by the ocean (hoping that would fix the ocean acidification problem in the long run) or do we find other ways of mitigating ocean acidification, safe the pteropods, and thereby salvaging the economy that is depended on the salmon industry?