While community ecologists have traditionally focused on local-scale
processes, it has become apparent that a broader perspective, which explores the
community-level ramifications of material fluxes within and between ecosystems, is
necessary to effectively evaluate bottom-up influences on community structure and
dynamics. In this dissertation, I employed ecosystem principles to understand these
processes in rocky intertidal communities. I specifically examined the roles of sessile
invertebrates in mediating the transfers and transformations of carbon and nitrogen in
intertidal ecosystems.
First, I quantified the links between nearshore pelagic and rocky intertidal
systems. By assimilating suspended particulate organic material (seston), mussels and
other sessile invertebrates serve as mediators of material exchange from pelagic to
benthic ecosystems. I evaluated these trophic linkages along productivity gradients on
the coasts of New Zealand and Oregon, which allowed me to address the influences of
seston quality and quantity on the growth and ammonium excretion rates of mussels.
My results highlight the necessity of simultaneously considering both seston quantity
(total organic particulates) and quality (phytoplankton availability) in evaluating
benthic-pelagic coupling.
Second, I assessed the utilization of invertebrate-excreted ammonium by
macroalgae in high-intertidal pools. Sessile invertebrates not only serve as mediators
of material transfer into intertidal ecosystems, they also chemically transform that
material, converting particulate organic nitrogen, which is unusable by macroalgae,
into ammonium, which algae readily assimilate. l showed that especially in high-zone
pools, which are isolated from the ocean for 80% of the time, invertebrate-excreted
ammonium is an important nitrogen source for macroalgae. Ammonium accumulated
in tide pools and was subsequently taken up by algae. This novel positive interaction
influenced community structure: macroalgal species richness increased with the rate of
invertebrate-mediated ammonium loading in pools.
Finally, by experimentally manipulating macroalgae and invertebrates in
laboratory mesocosms, I quantified the effect of ammonium loading on algal growth. I
demonstrated that algal nitrogen assimilation rates increased with the rate of
ammonium accumulation in tide pools, which resulted in enhanced growth when
invertebrates were present. Together, these studies suggest that by merging
community and ecosystem perspectives we can gain unique and important insights
into the bottom-up processes influencing intertidal systems. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30478 |
| Date | 12 May 2003 |
| Creators | Bracken, Matthew E. |
| Contributors | Menge, Bruce A., Lubchenco, Jane |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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