Santa Cruz Island Reserve

13 Oct, 05 PM - 21 Oct, 05 PM

This trip will be taken in order to set-up field experiments that will be maintained for two years. Likely only one site will be set up at this time. The objective of these experiments is to determine rocky intertidal macroalgal community response (in terms of diversity and relative abundances of functional forms) to nutrient enrichment, and its dependence on initial nutrient regime and initial consumer community. The first experiment will test the conditions maintaining diversity as both nutrient addition and consumer density are altered. To do so, I will concurrently address how 1) increased bottom-up forcing through enrichment affects macroalgal growth, abundance, and diversity (primary effect); and 2) variable magnitude of top-down consumer control may alter these primary effects. The second experiment will determine how changes in macroalgal assemblages affect consumer communities (primary response cascades upward to secondary response). Both experiments will quantify how the above processes and community consequences vary with baseline nutrient supply. This study will utilize plots of natural communities, where the majority of previous studies have utilized either cleared or already bare substrate (e.g. Worm et al. 2000a, 2002; Worm and Lotze 2006; Freidenburg et al. 2007; Masterson et al. 2008) or mesocosm communities (Bokn et al. 2003; Kraufvelin et al. 2006; but see Guerry et al. 2009). Plots will be 0.75m x 0.5m in size. Treatments will cross nutrient addition (+/-) with grazer density (none, intermediate, and natural density) to give 6 treatments. Treatments will be applied in a block design (5 replicates) to account for natural heterogeneity at the scale of 10?s of meters. One replicate of each treatment will be randomly arranged in each block, with approximately 1m between treatments to prevent cross contamination of enriched vs. ambient plots, where nutrients levels have been shown to be no different beyond 1m from the source (M. Bracken, pers. comm.). Slow-release fertilizer (OsmocoteTM, in N:P ratios of 10:1 as in lab experiments) will be used to diffuse nutrients to plots (Worm et al. 2000b). Fertilizer will be placed in nylon stockings within PVC endcaps attached to the rock with eye bolts in the center of each plot. Empty nylons and endcaps will be placed in ambient treatments. Incoming tides cause nutrient release from the diffusers and simulate pulsed supply typical of rocky intertidal ecosystems (Nielsen 2001). Previous studies have shown Osmocote continuously enriches for 6 weeks (Worm et al. 2000b); thus nutrients will be replaced roughly every 3 weeks (M. Bracken, pers. comm.). All plots will be surrounded by Z-spar marine epoxy and painted with copper anti-fouling paint to deter immigration and emigration of limpets and chitons (Cubit 1984; Freidenburg et al. 2007). The addition of tanglefoot gum resin will prevent movement of littorinids (Geller 1991). All benthic macroherbivores will be removed from the exclusion plots (chitons, limpets, snails, crabs). In intermediate density plots, approximately ? of all grazers will be removed. High grazer treatments will have natural herbivore abundances. A second experiment will be conducted to test for secondary upward cascading effects of enrichment on consumer communities. This 2-factor experiment will compare grazer community changes with and without enrichment between plots controlling consumer densities and those that allow free movement in and out. The two ambient grazer treatments (+/- nutrients) from the first experiment will be utilized, and I will add two treatments (+/-) nutrients in which herbivore immigration and emigration is unconstrained. In these two treatments, I will apply epoxy, copper paint, and tanglefoot gum resin to all four corners to control for toxicity or other effects. Otherwise the design will be as indicated above. At the onset of both experiments, all benthic grazers will be counted and recorded in terms of functional groupings. Size classes of all snails and limpets will be recorded for 3 random subquadrats of each replicate (see Chapter 1.2.3). I will also record the number of identifiable species observed within each group. Photographs will be taken of each plot and analyzed for percent cover of algal forms (see Chapter 1.2.3). Water samples will be collected, filtered, and analyzed for NO3 and NH4. Every ~3 weeks, when exchanging nutrient diffusers, I will take photographs, count grazers, maintain the gum resin, and collect water samples (Worm et al. 1999, 2000b). Recent studies in rocky intertidal systems have initiated a shift in the paradigm of top-down control on rocky shores; yet, the timing, scale, and magnitude of these effects have varied widely among studies. This inconclusive evidence for highly vulnerable rocky intertidal ecosystems necessitates further investigation into the mechanisms underlying larger community response, and suggests that knowledge of baseline conditions may be critical to predicting the effects of nutrient enrichment.

Visit #19257 @Santa Cruz Island Reserve

Approved

Under Project # 10408 | Research

Anthropogenic nutrient loading on rocky intertidal biodiversity: baseline-dependent effects

graduate_student - University of California, Los Angeles

Reservation Members(s)

Rachel Clausing Oct 13 - 21, 2009 (9 days)
Rachel Clausing Oct 13 - 21, 2009 (9 days)

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Dorm 2 Oct 13 - 21, 2009
Jeep 2 Oct 13 - 21, 2009