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Publication year : 0
Thematic : Coastal Biodiversity
Language : English
Note
Hypoxia is often associated with increasing nutrient loadings and has clear mortality effects on sessile
organisms, but its population effects on mobile organisms in coastal environments are uncertain. The evidence
for hypoxia having population level effects is laboratory experiments, many examples of localized effects in
nature, a few population-level examples, fish kills, and intuition. Despite the perception by many people, none
of these provide conclusive evidence of widespread population responses to hypoxia.We synthesize the results
from seven ecological simulation models that examined how low dissolved oxygen (DO) affected fish at the
individual, population, and community levels. These models represent a variety of species, simulate the
dynamics at a range of temporal scales and spatial scales, and impose a variety of subsets of possible DO effects.
Several patterns emerged from the accumulated results. First, predicted responses were large in simpler
models, and small to large in more complex models. Second, while the main effects of increased hypoxia were
generally small to moderate, there were instances of relatively large indirect effects and interaction effects.
Indirect effects involved growth and mortality responses due to altered spatial distribution (rather than due
directly to DO) and food web interactions. Interaction effects were larger responses to hypoxia when other
factors were at certain levels (e.g., responses at low versus high fish densities). Interactions also occurred when
the predicted responses were larger than would be expected by the sum of the separate effects. Third, accurate
information on exposure and degree of avoidance of low DO were critical unknowns. Our interpretations
should be viewed as suggestive rather than definitive. The patterns described were based on a collection of
modeling results that were not designed to be compared to each other. A quick look at other models seems to
confirm our patterns, or at minimum, does not contradict our patterns. Quantifying the effects of hypoxia on
fish populations, whether large or small, is critical for effective management of coastal ecosystems and for costeffective
and efficient design of remediation actions. The potential for interaction and indirect effects
complicates field study and management. Improving our predictions of the effects of hypoxia on fish
populations and communities has moved from a computational issue to a biological issue. We seem to be
making progress on monitoring and modeling movement behavior, but progress is slower in food web theory
and empirical research and in quantifying interspecific interactions and habitat quality in terms of process rates
that relate to population dynamics.
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Keywords : Podocarpus rotundus
Encoded by : Pauline Carmel Joy Eje
