ASSESSING ECOSYSTEM BALANCE IN PREDATOR-LIMITED SOUTHERN HEMISPHERE KELP FORESTS
(DUKE UNIVERSITY - NICHOLAS SCHOOL OF THE ENVIRONMENT)
Ecosystems worldwide maintain equilibrium through a series of checks and balances. In
1960, a team of scientists sought to explain the verdancy of Earth, despite abundant herbivory.
They attributed greenness to trophic cascades ecosystem-wide, predicting top-down linear effects
between trophic levels. However, modern ecology has shown cascading effects across trophic
levels can be multidirectional. While most studies on trophic cascades are conducted locally, the
range of kelp species Macrocystis pyrifera spans continents, offering a unique opportunity to
track fluctuations in trophic cascades within kelp systems over vast latitudinal ranges.
Kelp forests create habitat structure in temperate seas circumglobally, hosting productive
and dynamic communities. These structurally significant brown algae thrive in mid-high
latitudes, where long photo periods facilitate rapid growth, and upwelling replenishes nutrientrich
seawater. Historically, a trophic cascade in NE Pacific kelp forests triggered by the removal
of sea otters results in significant increase of algal grazers (urchins, echinoid species), and
subsequent decrease in kelp. A slow increase in sea otter populations in these regions over the
last century, however, has resulted in fewer algivore urchins and more abundant kelp forests,
demonstrating effective top-down control. This paradigm has been described in Pacific kelp
systems, but while the sea otter’s range does not extend to South America, Macrocystis co-exists
with echinoid grazers throughout Patagonia.
Though this predation disparity has not been investigated through the range of Macrocystis, research in austral kelp forests confirms macroalgae Ecklonia display high
phlorotannin content. These defensive chemical compounds reduce palatability and grazing success. Plasticity in chemical defense production among Macrocystis across a predator gradient would suggest novel flexibility between top-down and bottom-up control in one foundation species across latitudes. I will study Macrocystis in Patagonia, investigating structural and chemical defense as the ecosystem moves southerly and echinoid grazers persist.