EFFECTS OF FLOW VELOCITY AND SETTLEMENT LOCATION ON GROWTH RATES OF EARLY JUVENILES OF THE PEDUNCULATE BARNACLE, POLLICIPES POLYMERUS, SOWERBY 1833
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Date
2021-11-10
Authors
Everson, Hannah N.
Journal Title
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Publisher
University of Oregon
Abstract
The intertidal lepadomorph barnacle, Pollicipes polymerus, is known for its propensity to
aggregate in rosette-shaped or irregular clusters. The gregarious lifestyle is ensured by the
species’ settlement preference. Cyprids of P. polymerus settle almost exclusively on the peduncle
of adult conspecifics, while settlement in cracks and crevices and on acorn barnacles is rare. For
gregarious settlement behavior to evolve and persist, individuals should gain some benefit that
would otherwise not be achieved with a solitary lifestyle - such as defense against predators
(Riipi et al. 2001) or to facilitate cross-fertilization (Wu 1981) Due to increasing demand for P.
polymerus in culinary markets, the gregarious settlement behavior makes them particularly
susceptible to overharvesting. This study examines whether gregarious settlement results in
higher growth rates of juveniles compared to growth of solitary individuals. I asked if and how
P. polymerus gains in overall fitness from gregarious settlement. I address two questions: 1) Is
the growth rate of early juveniles dependent on the velocity of water in which they feed? and 2)
Does settlement on conspecifics benefit early juveniles by increasing growth rate? Two treatment
groups (solitary and gregarious) were studied, with individuals ranging in size from 1mm - 3mm
rostro-carinal length. An apparatus, utilizing a rotating disc, was constructed to create a range of
experimental velocities. For two trials carried out in a marina environment (trial 1 and 2), growth
rates ranged from 0.1mm - 1.2mm/wk at any given velocity. For two trials in a tank environment
(trials 3 and 4) individual growth never exceeded 0.6mm/wk. Overall results indicate that neither
current velocity nor settlement location had consistent effects on early juvenile growth rates. In
the tank environment, where food concentrations were lower, velocity had a significant negative
effect on the growth rate of gregarious but not solitary juveniles. In only 1 of 4 trials, settlement
on a conspecific had a significant positive effect on average juvenile growth. The absence of
consistent trends within and across trials together with few significant results indicate that
velocity and settlement location for early juveniles may not be primary factors in gregarious
settlement of this barnacle. Other factors or these factors at different life stages may account for
settlement behavior. My findings also suggest that aquaculture of these barnacles does not
require specific flow speeds or adult substrata to cultivate newly settled barnacles.
Description
18 pages