Recruitment Dynamics, how settlement choices affect barnacle abundance and distribution.
My graduate research focused on the transition between the
pelagic larval and the benthic adult stages in the barnacle
lifecycle. Semibalanus balanoides
reproduces once yearly during the winter. The cohort of larvae
attaches to hard surfaces in the rocky intertidal between January and
May. Larvae encounter a variety of environmental conditions when
they attach including seasonally variable characteristics like air
temperature and spatially variable characteristics like rock
topography. The environmental conditions experienced during
larval settlement will in part cause the barnacle’s survival or
mortality during the ensuing development to adulthood. Other
causes of mortality include biotic interactions like predation, but
they are also dependent on the environmental conditions that direct
barnacle attachment. Therefore, the time and place where
individuals attach could be valuable information for understanding
barnacle recruitment, and this data is summarized from daily
photoquadrats of barnacle habitat during the settlement season.
|Enlarge ImageFor my graduate studies I primarily studied recruitment patterns in the intertidal barnacle Semibalanus balanoides at Gardiner beach in Woods Hole. Here I am taking a photo of a tiny quadrat (1.5X2cm!!) using the macro setting on a Nikon Coolpix camera. Just to my left is a white settlement plate for a transplant experiment.
|Enlarge ImageA quadrat that I photographed daily in 2006.
|Enlarge ImageThe diamonds are ploted for values of first settlement day and total
cumulative settlement among twelve settlement plates monitored over 140
consecutive days in 2006. The negative correlation suggests two
possible explanations: first that larval supply is variable between the
haphazardly located settlement plates spaced over Gardiner beach in
Woods Hole. Alternatively, barnacle larvae exhibit settlement behavior
that descriminates between these settlement plates, though the surface
of plates are standardized to minimize the contact based habitat cues
to barnacle larvae. It is likely some combination of these two
factors, as indicated by various other lines of evidence.
|I compiled a timeseries of photographs to depict settlement on PVC plates that I monitored in 2006.|
|» View Video (Media Player) |
Recruitment of the intertidal barnacle Semibalanus balanoides;
metamorphosis and survival from daily to seasonal timescales
Jonathan N. Blythe
Submitted to the MIT/WHOI Joint Program in Applied Ocean Science and Engineering
on August 27, 2008, in partial fulfillment of the requirements for the Degree of
Doctor of Philosophy in Biological Oceanography
The benthic habitat is the terminal destination for marine animals in terms of their reproductive lifecycle. Recruitment dynamics relating to seasonal changes in the benthic habitat may be the best source of information for predicting recruit abundance and for marine resources management. The transition from the pelagic to the benthic phases is the last stage in the connectivity between benthic populations. The transition to the benthos may be a process that dominates recruitment dynamics to the exclusion of other characteristics of larvae such as their quality and their density. Recruitment of benthic marine animals is influenced by two seasonally varying factors of the benthic habitat. First, the availability of suitable habitat for recruitment can in large part determine the survival probability for settlers, a trend that is most pronounced for low or no survival when the settlement substrate is saturated by conspecifics from a recruitment cohort. Preemption is caused by the presence of current occupants from a recruit cohort, and it influences the settlement rate or the survival probability of conspecifics. Descriptive statistics (Chapter 2) and a field experiment (Chapter 4) highlight the role of preemption on barnacle recruitment. The second factor results from seasonal changes in environmental conditions that settlers experience in the benthic habitat, which could affect the physiology and survival probability of barnacle settlers. Highly unpredictable features of recruitment dynamics also play a role, such as wind that enhances wave action in the rocky intertidal that has been linked to the rate of settlement. Day to day variability in wind may cause patterns of settlement to be highly unpredictable. Predator induced mortality is spatially aggregated, and the random pattern of mortality in space is highly unpredictable. In contrast to these high frequency sources of recruitment variability, seasonal factors that vary at lower frequencies and that often change monotonically lend great predictive ability for recruitment dynamics. It appears that barnacles have evolved to compete for suitable habitat and have mechanisms to cope with seasonally varying environmental conditions in the benthic habitat, which may be the basis for why these features dominate the barnacle recruitment dynamic.
Thesis Supervisor: Jesús Pineda
Settlement video and Ph.D. dissertation Introduction ChapterSee links at the bottom of this webpage.