Grantee Research Project Results

2001 Progress Report: Top-Down Trophodynamics

EPA Grant Number: R828020C003
Subproject: this is subproject number 003 , established and managed by the Center Director under grant R828020
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Children's Environmental Health and Disease Prevention Center - Dartmouth College
Center Director: Karagas, Margaret Rita
Title: Top-Down Trophodynamics
Investigators: Cowen, Robert , Paddack, Michelle , Sponaugle, Susan
Institution: University of Miami
EPA Project Officer: Packard, Benjamin H
Project Period: December 15, 1999 through December 14, 2003
Project Period Covered by this Report: December 15, 2000 through December 14, 2001
RFA: National Center for Caribbean Coral Reef Research (1999) RFA Text |  Recipients Lists
Research Category: Congressionally Mandated Center , Targeted Research

Progress Summary:

As planned, two cruises were conducted during 2000 (May and August-September). All data have been entered into an Access database and edited. Preliminary data analysis examined differences in abundances and size frequencies of species and groups of species among sites. Size frequencies were combined with weight-length relationships (both published and obtained during this study) to obtain biomass estimates for select species at each site. Consumption rates were calculated for a single species for which sufficient data were available (Sparisoma viride). Results are presented in question #5.

We have collected a total of 172 individual fishes (1-2 species representative of each of the 4 families) in order to establish weight-length and gut volume-length relationships and to conduct stomach content analysis. Some of these samples have been collected during dawn hours in order to determine gut fill time for two species (Sparisoma viride and Acanthurus bahianus). Grazing observations have been conducted for 183 individual fishes representing 3 families.

Biomass and feeding rate values from the above sampling efforts are being combined with published values on algal bite yield (Bruggemann et al. 1994) in order to obtain consumption rate. This analysis has been completed for one species of parrotfish (Sparisoma viride) for which the bite yield data are available.

Aims of the project have not changed from the original application.

· Field collections are only conducted when minimum ocean conditions are met (underwater visibility at least 4 m).
· Data collectors are kept the same as much as possible. Divers undergo at least 3 training sessions in a swimming pool before each sampling period. In these sessions, divers practice underwater size estimation of fishes using plastic models. Values from a final swim are kept in order to compare bias among divers.
· Data collectors use a CD database of fish pictures to test knowledge of species before each sampling period.
· Divers carry laminated sheets with pictures of relevant fish species to refer to if needed while underwater.
· Data sheets are reviewed with each diver following each dive.
· Field notes are taken on each dive recording sea conditions and incidental observations.
· Results are compared with any published values and causes of any discrepancies are examined.
· Collected Fishes are placed in coolers and processed (size and weight, guts excised) immediately upon returning to shore. Fish are assigned unique numbers and placed in labeled plastic bags. Samples are then frozen and brought to lab for analysis. A complete lab log is maintained.
· Copies of database are kept on two different computers.

We compared density of fish (by species and groups of species) among sites and between seasons (May vs. September; Figure 1). Examining Sparisoma viride in particular, we found that our estimates of were up to 5 times greater at most of our sites compared to those of other studies in the Caribbean for this species (Our values: 0.024 - 0.25 fish m-2 in Key Largo; Bruggemann et al 1996: 0.0488 fish m-2 in Bonaire; Lewis & Wainwright 1985: 0.02 - 0.03 fish m-2 in Belize). Several potential factors may be the cause of this discrepancy: our counts include the smallest size classes whereas other studies have not included estimates of juveniles; herbivorous fishes are not fished in the Florida Keys although they are elsewhere in the Caribbean; regional differences in reef structure or food availability may create differences among areas.

Analyses to date suggest a difference in biomass of S. viride between at least two of the three strata, with high relief offshore reefs containing higher biomass than patch reefs (Figure 2). Low relief sites appear to be more similar to high relief sites than to patch reefs. These biomass differences are a result of differences in length frequencies of the populations among the different reefs, as differences in density among the strata are small. Seasonal differences (May versus September) in length frequency can be seen in some cases (e.g., larger size classes of Sparisoma viride are more abundant at Turtle Rocks, a patch reef, in September compared to May) (Figure 3). This is consistent with Carpenter (1986) who found fish abundances to fluctuate over time, mainly due to new scarid recruits in late summer.

Consumption rates calculated for spotlight parrotfish (Sparisoma viride) indicate algal consumption rates at high relief sites are double that of patch reefs. Mean values listed are for May and September, respectively: 2.701 and 2.533 g algae (ash free dry wt) consumed m-2 day-1 at high relief sites; 1.983 and 1.868 g algae (ash free dry wt) consumed m-2 day-1at low relief sites; 0.835 and 1.139 g algae (ash free dry wt) consumed m-2 day-1at patch reefs. The major factor driving this gradient is size structure differences among reef types. The need for accurate size structure data is emphasized by these results.

Figure 1. Comparison of spotlight parrotfish density among sites and between seasons. Sites are grouped according to reef type (blue=high relief offshore reefs, pink=low relief reefs, green=patch reefs).

Figure 2. Biomass of Sparisoma viride at each site in May and September.

Figure 3. Length frequency histograms for Sparisoma viride for two seasons at a single site.

Future Activities:

Two cruises are planned for 2001 (February and May). Spectrophotometric techniques are being explored as a tool for determining algal diet composition of selected species. In accordance with the spectrophotometric technique, laboratory experiments are being designed in order to determine photosynthetic degradation products of different types of algae. Laboratory experiments also will be conducted to determine gut processing time and gut fill time of selected parrotfishes.

Grazing rate observations will be extended to determine daily variation and differences among depths, habitat types, and season. Dawn observations and collections will be repeated to determine gut fill time and number of bites to fill gut. These values will be used as a comparative method of calculating consumption rate.

Supplemental Keywords:

RFA, Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Geographic Area, Water, ECOSYSTEMS, algal blooms, Aquatic Ecosystem, Aquatic Ecosystems & Estuarine Research, Ecological Risk Assessment, State, Terrestrial Ecosystems, estuarine research, Watersheds, Aquatic Ecosystems, Ecological Monitoring, Nutrients, Water & Watershed, Ecology and Ecosystems, Environmental Monitoring, estuarine integrity, nutrient flux, FLA, coastal resources, environmental indicators, coastal watershed, marine biology, nutrient stress, Florida, water quality, watershed assessment, coastal ecosystem, coral reefs, nutrient sensitive ecosystems, estuaries, coastal ecosystems, watershed restoration, ecosystem response, ecosystem stress, nutrient kinetics, Florida Keys, bloom dynamics, wetlands, coastal environments, environmental stress, algal growth, nutrient concentrations, trophic interactions, ecological indicators, ecological research, nutrient transport, coral reef ecosystem integrity, nutrient cycling, nutrient supply, watershed sustainablity, marine ecosystem, esturarine eutrophication, watershed sustainablility

Progress and Final Reports:

Original Abstract

2000

2002

Final

Main Center Abstract and Reports:

R828020    Children's Environmental Health and Disease Prevention Center - Dartmouth College

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828020C002 Nutrient Cycling and Algal Productivity in the Florida Keys
R828020C003 Top-Down Trophodynamics
R828020C004 Physical Oceanographic Studies
R828020C005 Impacts of Nutrients on Reefs in the Florida Keys