PhDThis study on the littoral of Crosemere has shown that complex
direct and indirect interactions exist between larvae of the gallery-building
caddis Tinodes waeneri, the filamentous macro-alga
Cladophora glomerata, and the larvae of several species of retreat-building
chironomids. Co-existence between these species is
facilitated by spatial and temporal patchiness in dispersal ability
and behaviour by the dominant grazer/competitor Tinodes waeneri.
Tinodes eats Cladophora and thus indirectly controls the
abundance of chironomids which associate with the Cladophora
mat. Adult oviposition under trees determines the initial
distribution of Tinodes and several chironomids. While these latter
can probably rapidly disperse by swimming, Tinodes dispersal is
more limited. This creates spatial refugia for Cladophora and
chironomids in areas of the littoral away from trees. Local-scale,
temporal refugia are created by Cladophora being able to 'grow
away' from Tinodes during periods in spring when Cladophora
colonizes more vigorously than Tinodes. Local-scale spatial refugia
are also created by modes' apparent reluctance to colonize taller
stones.
This spatial and temporal patchiness in species interactions in the
littoral is set against a background of lake-wide, temporal variation
which appears to constrain the entire littoral habitat. The summer
stratification of Crosemere into upper and lower layers causes the
surface waters, probably including also the littoral, to be seasonally
nutrient-limited, particularly in nitrogen. This in turn will limit
primary production in the littoral and thus also secondary
production. The epilithic species studied all appeared to be food-limited
in summer. The dominance of the Crosemere littoral by
retreat-dwelling species may partly be due to their ability to recycle
limited nutrients within or on their retreats and so to consume
more algae than is otherwise available to mobile species.Natural Environment Research council (NERC
