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THE QUEBEC REGION BULLETIN
DÉCEMBRE 2011 - JANVIER 2012/VOLUME 14/NUMÉRO 6
An international team of researchers has shown that regardless of where they live—in the Gulf of St. Lawrence, the Gulf of Maine or all the way north in the Barents Sea—northern shrimp have adapted to their environment to provide their larvae with optimal conditions for survival. This little shrimp is a master strategist!
The team with researchers from Canada, the United Kingdom, the United States, Denmark and Iceland have put together a series of projects designed to document the link between inter-annual and inter-regional variations in the northern shrimp's reproductive cycle and the oceanographic conditions in which northern shrimp larvae evolve. The team also compared isolated populations remote from one another.
Since the 1990s, Patrick Ouellet and Louise Savard, of Fisheries and Oceans Canada, have been interested in the population dynamics of northern shrimp (Pandalus borealis) in the Gulf of St. Lawrence. This crustacean is of major socio-economic importance to the region. Because shrimpers’ catches are closely linked to population abundance and the annual recruitment of juvenile shrimp, the researchers sought to understand the factors that influence these elements.
A singular reproductive cycle
Female northern shrimp lay their eggs in early fall and carry their fertilized eggs under their abdomen until the following spring, at which point their larvae will hatch. Ocean water temperature influences the eggs' incubation time. For instance, colder waters will delay hatching. Larvae then migrate towards the surface to feed on plankton for the first few weeks of their lives. This early phase can be crucial to their survival and therefore to the recruitment of future populations.
The researchers wondered whether adult shrimp were synchronizing larval hatch with phytoplankton bloom. When hatching is synchronized with phytoplankton bloom, the larvae have a better chance of finding enough of the food that is essential to their survival and development. In contrast, if hatch time is not synchronized with the phytoplankton production, the larvae face food shortages and as a result, many larvae will die, which will have a direct impact on recruitment in subsequent years.
Phytoplankton bloom occurs at approximately the same time every year, with the duration of daylight and luminosity probably influencing the onset of bloom more than water temperature. And yet, the abundance of northern shrimp varies from one year to the next. If this synchronism is indeed responsible for inter-annual variations in the crustacean’s population, how does this occur throughout the territory inhabited by the species, where deep-water temperatures vary from place to place?
The research team successfully showed that there is in fact a remarkable synchronism between the time of larval hatch and phytoplankton bloom across the northwest Atlantic, from the Gulf of Maine in the south to the Barents Sea in the north. This finding is a particularly innovative contribution. The synchronism is seen as an adaptation of the northern shrimp's reproductive cycle to the local water temperatures, so that mating time, egg laying and incubation generally correspond to phytoplankton bloom in a given region.
The researchers also found that the duration of phytoplankton bloom had a positive influence on larval survival, but that water temperatures also affected the survival and growth rate of juvenile shrimp.
These research efforts show that northern shrimp have been able to adapt over time to the oceanographic conditions in which they exist. Will the anticipated era of climate change force northern shrimp to adapt once again?
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