The Seascapes

The Seascapes

Saturday, January 1, 2011

What makes some parts of the ocean sticky to fish? Ocean Observing for marine habitat science & ecosystem management

(The following is a short white paper we drafted for publication in a NOAA Technical Memorandum that will serve as the proceedings of a workshop that was hosted by the Mid-Atlantic Fisheries Management Council in December, 2010 on Habitat and Ecosystem Approaches to Management in the Mid-Atlantic Bight)

We often use our experiences as terrestrial organisms
inhabiting landscapes to draw inferences about the ways
marine organisms use and are constrained by seascapes. 
 In the sea the properties and dynamics of the fluid are
critical habitat features that control the vital rates of most
organisms while most terrestrial animals have evolved
mechanisms to at least partially decouple many of their
 vital rates from the dynamics and properties of the 
atmospheres fluid.
Marine organisms have evolved in an aqueous environment, with a high viscosity, high heat capacity, and solute concentrations similar to those in the spaces of their living cells.  The organisms are exposed to motions and environmental conditions in the sea that are dramatically slower and less variable than similar motions and conditions in the atmosphere. Furthermore, since the density of seawater is only slightly less than the density of living tissues, drag rather than gravity is the dominant force controlling movements in the sea.  The oceans are inhabited by nearly neutrally buoyant organisms that grow in direct contact with the “hydrosphere” throughout life cycles that usually include egg and larval stages a few millimeters long and adults with body sizes that can range from 10's of centimeters to meters.  Rates of metabolism, growth, survival, dispersal, and reproduction in marine organisms are tightly coupled to many scales of variability (millimeters to 1000s of kilometers, seconds to decades) in the water column as well as the seabed as the organisms make the dramatic habitat transitions usually required to complete their life cycles. In contrast, early development in most terrestrial animals is internal (or external, but aquatic in amphibians and some insects); while juveniles and adults are exposed to the atmosphere over a range of body sizes an order of magnitude smaller than marine organisms. Terrestrial organisms are largely constrained to two spatial dimensions by gravity and have evolved elaborate mechanisms to decouple metabolism and other physiological rates from the short-term variability of the atmosphere.  Despite these profound differences, we often use terrestrial frameworks to think about and investigate the ways marine organism use and are affected by their habitats.  We treat seascapes as analogues of landscapes; as two-dimensional matrices of habitat patches with slow spatial dynamics.  We use our own experiences as terrestrial organisms inhabiting landscapes to draw inferences about the constraints seascapes impose on the forms and ecologies of marine organisms, often overlooking the dynamic water column processes that define habitats, even for organisms strongly associated with the seabed.  Further, even when we do recognize that the vital rates of marine organisms and dynamics of their populations are strongly regulated by the ocean's “hydrosphere”, the absence of data describing the dynamics and structure of the water column at ecologically relevant space-time scales has made it difficult to consider the ocean's fluid explicitly in the design and analyses of relationships between species and their habitats in the sea.

MARACOOS remotely sensed ocean data and several
assimilation circulation models.
Index of divergence derived from vertical current velocities
 measured with HF radar and frontal boundaries indentified
using classification of satellite data.  The plots on the right
show abundance responses of squid and butterfish to 
divergences and fronts.
However, the state of the art, Integrated Ocean Observing Systems (IOOS), now monitor and model the physical and primary production dynamics of the ocean at the broad spatial but fine time scales required to understand the ways water column processes affect the vital rates of marine organisms and dynamics of their populations.  IOOS is an intergovernmental/inter-agency effort focused on the development of ocean observing and forecasting systems.  IOOS themes range from public health and safety to marine operations and natural resource conservation.  As part of the US IOOS program, partners in the Mid-Atlantic region along the US East Coast have developed a regional scale ocean observing network. The footprint of the Mid Atlantic Regional Ocean Observing System (MARACOOS=MARCOOS=MACOORA) stretches along 1000 km of coastline from Cape Hatteras, North Carolina to Cape Cod, Massachusetts and offshore to the continental shelf break.  MARACOOS uses a multi-platform approach to characterize the fine scale structure and dynamics of the coastal ocean. The platforms include US and foreign satellites in space, a network of high-frequency (HF) radars deployed along the shore, and a fleet of robotic gliders flying beneath the ocean's surface (for more data see here).  Satellites provide time series maps of surface temperature, chlorophyll A, and other ocean color products describing light absorption and backscatter.  Ensemble clustering is applied to the satellite information to objectively identify and visualize water masses and the surface fronts between them. The HF radar network provides hourly surface current measurements from the edge of the continental shelf into estuaries.  These current measurements can be processed to show near-real time and statistical forecasts of horizontal surface flows, upwelling and downwelling dynamics, and the evolution of surface fronts.  Robot gliders that carry sensors measuring temperature, salinity, chlorophyll-A, and particle backscatter describe seasonal to inter-annual changes in the vertical structure of the ocean.  Satellite, HF radar, and glider data are assimilated into an ensemble of numerical circulation models (UMD-HOPS, NYHOPS, ROMS) that are evaluated by comparing model realizations to field measurements. MARACOOS data and model forecasts provide spatially and temporally explicit descriptions of the physical forcing, flows of materials, and primary productivity that structures and regulates the mid-Atlantic Bight ecosystem. In addition to an extensive data archive, MARACOOS makes these data freely available in real time via Internet portals managed by trained operational oceanographers. Developments in high speed wireless communications and internet infrastructure now permit real time virtual collaboration between marine habitat and ecosystem ecologists in the field and operational oceanographers with expertise in IOOS data streams and forecasts.  Access to IOOS data and expertise allows ecologists to easily consider processes in the water column as well as on the seabed in studies of the life history processes that ultimately determine recruitment and the dynamics of populations of ecologically and economically organisms in the mid-Atlantic Bight ecosystem.
Analysis of deviance derived from Generalized Additive
Modeling describing the proportions of variation in the 
abundance of four species explained by IOOS ocean data, water 
column (pelagic) and bottom data (benthic) data measured 
on surface ships (=insitu), as well as abundance of prey for 
two predators strongly associated with the seabed. 

Over the past six years we have been developing an approach to integrate IOOS remotely sensed data and short-term model forecasts into regional scale habitat studies.  Our approach has included the development of distribution based habitat models for resource species that are also ecologically important in the mid-Atlantic Ecosystem, as well as adaptive surveys designed to measure habitat specific distributions and life history processes rates for these species.  We are nearing completion of a NOAA Fisheries and the Environment Funded project in which we have used multivariate and single species modeling to evaluate the power of IOOS data to describe distributions of organisms with different vertical habitat preferences in the mid-Atlantic Region using abundance data collected on North East Fisheries Science center bottom trawl surveys 1,2.  In analyses targeted at species important in the Mid-Atlantic Bight food web, we have found that our models, built using remotely sensed surface measurements, explain more of the abundance variation for pelagic species (longfin inshore squid and butterfish ~73%) than demersal species (spiny dogfish and summer flounder ~50%).  However, bottom habitat variables (e.g. rugosity & depth) and surface pelagic features measured by IOOS remote sensing (e.g. surface fronts, vertical & horizontal current velocities) were equally important for all species, while in-situ shipboard measurements of water column stability and structure were more useful for modeling pelagic species.  All species were associated with specific surface current flows, regions of upwelling, and/or surface fronts identified with IOOS remote sensing, indicating that pelagic processes affecting energy costs of movement, prey production and prey aggregation influenced distributions of the animals regardless of their vertical habitat preference.  We found that most of our IOOS informed habitat models had greater explanatory power and out of sample prediction capabilities than previously published models built using the same analytical technique, but without the benefit of access to IOOS data streams.  
Industry and scientific collaborators involved in finding a
solution for the bycatch mortality of butterfish in the longfin
inshore squid fishery.
We have begun to extend IOOS our informed habitat studies in two directions.  In a project recently funded by the NOAA/NEFSC Cooperative Network, we are collaborating directly with members of the Garden State Seafood Association to use the ecological knowledge of fishers to refine our habitat models in an effort to develop tools to reduce the bycatch of butterfish in the longfin inshore squid fishery.  The goodwill required for this close collaboration between the fishing industry, government and academic scientists was developed in IOOS regional association meetings that serve as “neutral ground” for many stakeholders with diverse and sometimes competing interests in the services of the ecosystem.  
Ongoing analysis of adult summer flounder abundance
responses during autumn migration and spawning to
features measured with IOOS remote sensing.

Spatial part of summer flounder egg habitat model, tracks
of simulated particles released in surface currents measured
during the early fall 2009.  Circle shows locations of
simulated particles near the mouth of New York harbor.
Plot on the bottom right shows the relative abundances of
summer flounder larvae collected in adaptive plankton
surveys off the mouth of New York Harbor.

In another project, we are using archived IOOS data along with NEFSC bottom trawl survey data of adults and egg collections from NEFSC MARMAP surveys made during the 1970s and 1980s to identify the characteristics of summer flounder spawning grounds in the mid-Atlantic region.  Our preliminary analyses indicate that autumn spawning may be concentrated outside the mouths of several large estuaries where processes of nutrient enrichment from estuarine outflows and coastal upwelling, high phytoplankton productivity, and processes of particle concentration along water mass convergences may create pelagic habitats promoting the survivorship and growth of summer flounder larvae.  Furthermore, we have been using MARACOOS assimilative circulation model nowcast and short-term forecasts to adaptively route surveys investigating habitat quality for fish larvae.  On these cruises we have collected large numbers of summer flounder larvae that appear, based on estimates of larval age and particle tracking in surface currents measured with HF radar, to be derived from a specific spawning ground identified in the analysis of summer flounder spawning grounds described above.  While this study is still in its infancy, we believe our IOOS informed approach that combines regional scale habitat analysis and modeling with adaptive process based field studies will allow us to develop broad scale habitat models that couple ontogenic habitats and important life history processes for this and other species in the mid-Atlantic region.  This is just the kind of approach required for effective space based ecosystem management.
Habitat science in the service of ecosystem management
could focus on processes that affect many species rather
than just a few.  Andrew Bakun described the triad physical
of physical processes in his book "Patterns in the Ocean".
We are finding that distributions of summer flounder adults
during autumn migration and spawning and eggs appear to
be associated with these processes and they are likely to be
important to many species.

We believe our IOOS informed approach to habitat science will be most useful for the development of tactical tools for ecosystem assessment and management.  There are several pathways toward the development of habitat science in the service of ecosystem management in the region.  The first of these is to develop single species models focused on ecosystem keystone species indentified in ecosystem modeling efforts in the Northwest Atlantic 3,4.   The rational behind this an approach is that the identification and conservation of habitats maintaining the resilience of ecosystem keystone populations should be translated across a level of ecological organization to promote the resilience of the ecosystem as a whole.  By resilience we mean the tendency of populations and ecosystems to return relatively rapidly to healthy states following significant perturbations 5.  One potential flaw with this approach is that rapid changes in climate are producing rapid changes in the distributions of animals, particularly in regions of faunal transition like the mid-Atlantic Bight 6,7.  If this is the case, the identity of ecosystem keystones may also be changing and thus targeting at a few individual species could fail to meet the goal of promoting ecosystem resilience. What is most intriguing about our study of summer flounder spawning grounds is that the hydrographic processes and structures we have identified that may promote nutrient enrichment, concentration, and larval delivery are the same “triad” of processes that appear to define important spawning grounds for pelagic species in the eastern Pacific Ocean and Mediterranean Sea 8,9.  Thus, we may be able to shift focus from habitat studies of individual keystone species, toward investigations of “keystone habitats” where physical and biological processes in the water column and on the seabed promote the survival of critical life history stages of many species rather than just a few.  This approach focused on habitat processes will be essential if the ecosystem is changing rapidly with climate change.  No matter what approach we take, habitat science in support of ecosystem assessment and management will require close, honest and open collaboration between physical and chemical oceanographers, habitat ecologists and ecosystem scientists, as well fisherman who arguable have the most intimate and practical understanding of the ecosystem as a whole.

1 Manderson J, L Palamara, J Kohut, MJ Oliver.  (in review) Using an ocean observatory to identify habitat associations of species with different vertical habitat preferences in the coastal ocean.

2 Palamara L, Manderson J, J Kohut, Oliver MJ & J Goff (in review) Improving Models of Covariation Between Marine Communities and their Habitats by Incorporating Pelagic Features Captured by Coastal Ocean Observatories

3 Link J, Overholtz W, O'Reilly J, Green J, Dow D, Palka D, Legault C, Vitaliano J, Guida V, Fogarty M, Brodziak J, Methratta L, Stockhausen W, Col L, Griswold C (2008) The Northeast U.S. continental shelf Energy Modeling and Analysis exercise (EMAX): Ecological network model development and basic ecosystem metrics. Journal of Marine Systems 74:453-474

4 Link JS, EA Fulton, RJ Gamble (2010) The northeast US application of ATLANTIS: A full system model exploring marine ecosystem dynamics in a living marine resource management context. Progress In Oceanography 87: 214-234

5 Levin SA & J Lubchenco. (2008) Resilience, Robustness, and Marine Ecosystem-based Management. BioScience 2008 58 (1), 27-32

6 Sorte CJB, SL Williams, JT Carlton (2010). Marine range shifts and species introductions: comparative spread rates and community impacts. Global Ecology and Biogeography
19(3): 303–316.

7 Nye JA, Link JS, Hare JA, Overholtz WJ (2009) Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf. Marine Ecology Progress Series 393:111-129

8 Bakun A.(1996) Patterns in the ocean: Ocean processes and marine population dynamics.  California Seagrant System

9 Agostini VN & Bakun A. (2002) ‘Ocean triads’ in the Mediterranean Sea: physical mechanisms potentially structuring reproductive habitat suitability (with example application to European anchovy, Engraulis encrasicolus).  Fisheries Oceanography 11(2): 129-142