Much of my research has focused on the intertidal amphipod Corophium volutator. This species is a tube-dweller common to mudflats in the Bay of Fundy, Canada and Maine, USA (A), where densities can exceed 60,000 amphipods per square meter! When the tide ebbs across a mudflat, males (B) frequently emerge from their burrows to crawl in search of mates (C), with which they co-habit.
 

(A) Mudflat at Starrs Point, Nova Scotia.

(B) Male Corophium voluator.

(C) Female Corophium volutator.

Corophium volutator is a very important prey item for migrating shorebirds. In late summer, over a million semipalmated sandpipers, Calidris pusilla stage on mudflats in the Bay of Fundy, on their way from breeding grounds in the Arctic to Wintering areas in South America. At major roosting sites (e.g., [D]) more than 150,000 can be seen between mid-July and the end of August.

Sandpipers forage on the edge of the tide, feeding almost entirely on C. volutator (>90% of their diet). During their 2-week stop-over, each bird may consume >30,000 amphipods per day, nearly doubling in mass before flying non-stop to Wintering areas. By following the edge of the tide, sandpipers are able to easily capture amphipods as they emerge from their burrows to crawl. However, even after amphipods stop crawling (5-15 minutes), sandpipers continue to forage on burrowed amphipods until the tide forces them off of the mudflat (2-6 hours later). In one study (McCurdy et al. 1997), I found that sandpipers forage day and night on Corophium, possibly to ensure that they acquire sufficient fat reserves to complete their migration. Amphipods appear to respond to the increased risk of predation on the ebb tide by reducing their crawling activity during the day, beginning immediately after sandpipers arrive each year. At night, however, amphipods continue to crawl on the ebb tide, likely because sandpipers do not forage visually at night (McCurdy et al. 1999b).
 

(D) Roosting site at Evangeline Beach, Nova Scotia.

(E) Semipalmated sandpiper, Calidris pusilla.

Most of my research on sandpipers and Corophium has dealt with understanding the role parasites may play in this predator-prey interaction and investigating how individual amphipods respond to parasitism. I have found that Corophium serve as intermediate hosts for 2 parasites; a nematode (Skrjabinoclava morrisoni) (F) and a trematode (Gynaecotyla adunca) (G). Both of these parasites must pass through an amphipod in order to sucessfully complete their life-cycles in shorebirds (transmission to shorebirds occurs when an infected amphipod is eaten by a shorebird). Both parasites interfere with 'normal' anti-predator behavior of amphipods, in that infected amphipods frequently crawl on the surface, making them more susceptible to predation by sandpipers. I have argued (McCurdy et al. 1999a, 2000b, 2000c) that increased crawling is a parasite adaptation in that it occurs only once parasites reach their infective stages (the point of development where they can be sucessfully transmitted to a sandpiper) and because increased frequency of crawling associated with parasitism only occurs during the day (when sandpipers are likely to detect crawling amphipods).
 

(F) Scanning electron micrograph of a Stage-III nematode, Skrjabinoclava morrisoni. At this stage, the nematode is able to infect a semipalmated sandpiper.

(G) Cercaria of the trematode Gynaecotyla adunca. This form contacts and infects amphipods.

(H) Encysted metacercaria of the trematode Gynaecotyla adunca. This form ready to be transmitted to a final-host shorebird.

In addition to testing the idea that parasites 'manipulate' behavior of amphipods, I have investigated how amphipods respond to parasitism. In several studies (McCurdy et al. 1999a, 1999b, 2000b), I have found that male and female amphipods minimize the impact of parasites on their lifetime reproductive success by hastening their onset of reproduction and by expending additional effort when first infected. Although parasitized amphipods suffer reduced reproductive success, by in mating before parasites reach a large size (and before they alter behavior) they appear to achieve higher fitness than if they waited to reproduce at the 'usual' time (McCurdy et al. 2001).

Finally, in addition to the impacts that parasites have on individual amphipods, parasite impacts may translate to the population and community levels. For example, epizootics of trematodes frequently causes crashes in populations of C. volutator. The role of parasites in causing recent declines in populations of C. volutator (e.g., [I]) is, as yet, unknown.
 

(I) Mudflat at Grande Anse, New Brunswick where densities of C. volutator have declined in recent years (note the difference in the texture of the mud compared to the mudflat at Starrs Point).

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