Ecology of the burrowing amphipod, Pontoporeia affinis, in Lake Michigan / by Wayne Paul Alley.

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relationships are attributable to either biological or environmental
phenomena.
It is often difficult to interpret the implications of biological association because the term itself is a loose definition which makes no distinction between relationships derived from mutualism, parasitism,
symbiosis, and predation with those based on similar or dissimilar habitat requirements. The patterns of association are also influenced by
the size of the units from which the samples are obtained. The relationships between organisms may vary from time to time.
SegerstrRle (1965), in an investigation of the Baltic Sea, found an
inverse relationship between the successful recruitment of the bivalve
Macoma baltica and the abundance of Pontoporeia affinis. He also found
a significant negative relationship between the abundance of the priapulid
worm Halicryptus spinulosus and P. affinis. Segerstrale concluded that
Pontoporeia ingested the spat of Macoma and the eggs of Halicryptus as
it fed on detrital material. Although in Lake Michigan the larvae of the
Sphaeriidae develop within the mantle cavity of the adult clam, the immature individuals, when released from the marsupia, are often small
enough to be ingested by large amphipods. Because little is known about
the complete feeding habits of Pontoporeia it is difficult to determine if
this amphipod actively seeks small clams and the eggs of the oligochaetes.
The positive associations between total Pontoporeia and the other
macrobenthic groups of the long-term study area probably reflect the