Assess the Effects of Climate Change on the Host Distribution and Over-Wintering Patterns of Parasitic Sea Lice

Project Description

Sea lice are a major parasitic burden on aquaculture. Most fish species are parasitized by members of the Siphonostomatoida order of copepods, containing around 75% of those that infect fish. Characteristically, they have siphon-like jaws and a filament to allow attachment to the fish. Although native to Maine, these parasites were not a major aquaculture issue until the early 2000s. Since 2008, the salmon louse Lepeophtheirus salmonis has become a seasonal parasite in the state, causing an estimated $50 million burden on the US aquaculture industry. A vast majority of this loss occurs in Maine.

Like green crabs, their range is limited by temperature and they are not found north of the July 10°C isotherm. It is proposed that lice numbers affecting both wild and farmed fish will increase as water temperatures rise. It is important to understand the overwintering strategies of Lepeophtheirus salmonis. Its wild host, the Atlantic salmon (Salmo salar), has severely declined, yet the parasite still appears on newly transferred salmon smolts, often within four weeks of sea transfer. Lepeophtheirus salmonis in the Pacific uses the stickleback as an overwintering host. This is not the case in the Atlantic.

The strategy of sea lice for overwintering in Maine is currently unknown. They could be using another peripatetic host or warming water could lead to increased survival of the larval stages. Researchers are investigating these overwintering strategies using Lepeophtheirus salmonis as a model for other marine ectoparasites. Lepeophtheirus salmonis is particularly suitable, as it has a Palearctic distribution and is directly relevant to the finfish aquaculture industry in Maine.

Results and Accomplishments

A new area of research looked at the density of larval sea lice at different temperatures. At colder temperatures, sea lice larvae were distributed much higher in the water column than expected. A proposed hypothesis is this could be related to the larvae actively osmoregulating (rather than osmoconforming), maintaining a specific osmotic pressure within their bodies. Ocean water becomes denser when it cools but sea lice maintain a constant density and float higher in the water column.

A second hypothesis being tested suggests that lice are actively controlling their buoyancy in the same way planktonic cnidarians do. They may be actively pumping sulphate ions into their coelom to maintain their higher position in the water column. This may give them the ability to control their position in the water column by changing their density and not osmolality independently of each other.

This project also investigates the oxygen consumption of sea lice in summer and winter conditions. It has been observed that sea lice swim faster in colder water than warmer water. This is a bit counterintuitive, as poikilothermic organisms often decrease their metabolism as they cool. Faster swimming in cold water strongly suggests there is something novel about sea lice physiology at cold temperatures. A collaboration with Dr. Nishad Jayasundara (UMaine) has been established to further investigate these findings. Seahorse oxygen consumption equipment was adapted for sea lice use and project personnel are calibrating it to investigate the different pathway of oxygen in order to see if the underlying physiology can be understood.

Summary of Data Being Collected

Data	Type	Quantity	Location
Sea lice swimming speeds	Video	GBs	Bricknell Lab, UMaine
Stable isotope values	Biochemical	1,000s	Bricknell Lab, UMaine; Byron Lab, UNE
Molecular data	Biochemical	1,000s	Bricknell Lab, UMaine