Sa. Woodin et al., PROCESS-SPECIFIC CUES FOR RECRUITMENT IN SEDIMENTARY ENVIRONMENTS - GEOCHEMICAL SIGNALS, Journal of marine research, 56(2), 1998, pp. 535-558
The most biologically and geochemically active marine sediments are ch
aracterized by steep chemical gradients within the top centimeters of
sediment (Berner, 1980). A common feature of these environments is dis
ruptions of surface sediments by both physical and biotic forces. Grow
th and mortality rates for new recruits are affected by many of these
surface perturbations. At the same time, these disturbances also impos
e a discontinuity in concentration across the sediment-water interface
, and accordingly, a change in surface chemistry. In this paper we pre
sent evidence that the cue used by juveniles to distinguish between re
cently disturbed and undisturbed surfaces may be disruption of geochem
ical gradients that are typical of nearshore benthic systems. New juve
niles exposed to ammonium concentrations typical of disturbed surface
sediments exhibit behaviors consistent with rejection of the habitat.
Conversely, new juveniles placed onto sediments containing ammonium le
vels typical of undisturbed surficial sediments rapidly initiate burro
wing activity, a sign of ''acceptability.'' We also present a numerica
l model, which assesses the dynamics of small-scale chemical shifts th
at accompany sediment disruption, to determine (a) what is the magnitu
de of surface chemistry changes associated with disturbance (i.e. what
is the signal strength)? and (b) what are the spatial and temporal sc
ales associated with the return to the undisturbed condition (''recove
ry'')? Model results show that the signal strength, and the return to
''acceptable'' conditions, are strongly influenced by the initial grad
ient. Model predictions of the time required to ''recover'' indicate t
hat times to recovery are longer than the interval between disturbance
events, but are of the same temporal scale (minutes to hours). Thus,
our results suggest that the dynamics of surficial gradients provide a
strong signal over appropriate time scales that may reveal the intens
ity of disturbance and the likelihood of mortality for juveniles. As s
uch, transport-reaction processes which govern porewater concentration
s in surficial sediments may also play a role in recruitment processes
.