1. SHALLOW SUMMIT/CONTINENTAL SHELF
CONNECTED
• High habitat fragmentation
 Able to disperse long distances
BATHYAL
DISCONNECTED
• High habitat fragmentation
• Dispersal ability limited
ABYSSAL
CONNECTED
• Dispersal ability severely limited
 Habitat homogeneity
Larval Dispersal Potential Decreases with Depth
- Implications for open ocean connectivity
The Depth Differentiation Hypothesis is the observation of a peak in population divergence in the bathyal region with a decline in divergence towards the
abyssal depths (reviewed in Rex & Etter 2010). If levels of population divergence vary with depth, then does population connectivity also vary with depth?
And could a connectivity pattern provide a mechanism for population isolation in the bathyal and an explanation for the observed patterns of gene-flow?
KERRY L. HOWELL1, REBECCA E. ROSS1, IAN KIRBY1, W. A. NIMMO SMITH1, JANE READ2
1 School of Marine Science & Engineering, Plymouth University, UK. 2 National Oceanography Centre, Southampton, UK.
Method: Dispersal modelling
Model: Connectivity Modelling System (Paris et al 2013)
Hydrography: HYCOM + NCODA Global 1/12° model daily output files
Setup: We ran the CMS as a simple Lagrangian particle tracer tracking
neutrally buoyant particles released from 5 seamounts
worldwide. Theoretical particles were released daily for a year
(2012) from 16 equally spaced positions at each depth band
and tracked for 100 days. Depth bands were every 500m and
the summit to the nearest 100m.
The maps (right) show all recorded particle trajectories at all seamounts.
Depth bands are coloured from yellow (shallowest) to navy blue (deepest)
and layered in reverse depth order to show the deepest release on top.
CS – Cross Seamount, Hawaii (1500, 2000, 2500 ,3000m);
AD – Anton Dohrn, UK(700,1000,1500m);
HG – Hotspur Guyot, Brazil (500, 1000, 1500, 2000, 3000, 3500m);
GB – Geroevka Bank Seamount, Indian Ocean (500, 1000, 1500, 2000m);
CG – Cascade Guyot, Tasmania (1200, 1500, 2000, 2500m).
Dispersal vs. Depth
Maps
Analysis
All 500m depth bands are compared here in a boxplot which shows the
maximum straight line distance travelled (SLD) against depth with the
bold horizontal lines representing the median.
The plotted smooth component of a Generalised Additive Model of SLD as
a function of depth shows the distinct relationship observed above
1300m
A B
A
B
Discussion
This study shows a relationship between depth and
passive dispersal which may provide a mechanism for
population isolation in the bathyal as observed in the
Depth Differentiation Hypothesis.
• Little is known of deep sea larval behaviour but there
is a suggestion that there is limited vertical gene
flow within many species (due to e.g.
temperature/pressure tolerances, water mass
boundaries).
• There is a decrease in habitat fragmentation with
depth as the bathyal exhibits differing terrain,
substrate and environmental conditions while the
abyssal presents a more homogenous habitat with
limited variation in substrate and conditions.
Larvae which are restricted vertically may therefore
experience greater reproductive isolation in the bathyal
(as shown in the diagram left) leading to greater
opportunity for adaptive radiation and population
differentiation as is repeatedly observed.
Paris CB, Helgers J, van Sebille E, Srinivasan A (2013) Connectivity Modeling System: A probabilistic modeling tool for the multi-scale tracking of biotic and abiotic variability in the ocean. Environmental Modelling &
Software 42: 47-54.
Rex MA & Etter RJ (2010) Deep-sea biodiversity: pattern and scale. Cambridge, MA: Harvard University Press. pp233-240
References