Sharein El-Tourky
Research Proposal
Spatial and Temporal Patterns in the Production, Abundance, and Distribution of
Farranula gracilis in the Florida Straits.
Key Words: Zooplankton, marine ecology, trophic dynamics, food web, bottom-up controls
Background: Effective fisheries management is necessarily dependent on the accuracy of fisheries
models, which can be limited if they omit critical elements. One critical element in the formulation of
these models is the trophic interactions at the larval stage of fish development. At this stage, fish
mortality rates are at their peak and survival is often determined by resource limitation1. Thus it is
crucial to identify and quantify essential prey resources and determine how they vary in abundance and
availability.2 Prey availability is the “bottom-up” control for larval fish survival, particularly as it
regulates growth rate; this contrasts with the ‘top down” control by predation on the adult and larval
fish. To identify factors essential to larval fish survival, it is essential to first identify the prey, and then
determine the factors that limit their availability. The main resources larval fish consume are
mesozooplankton, particularly secondary producers. Different larval fish species exhibit varying
degrees of prey specificity1. This specificity can be further complicated by the patchy distribution of
both larval fish predators and their mesozooplankton prey, whose spatial distribution is primarily
determined by physical processes, such as currents.
The copepod Farranula gracilis is an ideal model organism for studying bottom-up controls. F. gracilis
is the primary food source for larval billfish, particularly blue marlin and sailfish, in the Straits of
Florida (SOF).3 A crucial spawning ground for Atlantic Billfish stocks, 1.6% of blue marlin and 2.3% of
sailfish stock spawning occurs in the SOF.4 Larval survival rates of billfish in the SOF appear to
correlate with increasing rates of F. gracilis consumption.1 Gut content analysis of larval billfish guts
showed that fast growing larvae had higher proportions of F.gracilis in their gut. Faster growing larvae
commence piscivory earlier. Piscivory is the most significant factor in survival of larvae to sexual
maturity.3
Research Plan: While it is clear that F. gracilis is an important prey item, it’s not evident how changes
in abundance and distribution of F. gracilis relate to larval billfish growth. In this study, I will quantify
the spatial and temporal patterns of F. gracilis distribution from the same samples used to establish F.
gracilis as the primary prey of larval billfish. This relationship between F. gracilis and larval billfish
was established by scientists in the laboratory of my committee member, so the samples are readily
available to me. Due to my proximity to the Florida Straits, I also have access to the live samples I will
use to determine production rates. In order to quantify the carbon available for utilization by larval
billfish, respiration and egg production rates will be calculated from live samples collected from the
Florida Straits as indexes to the secondary production of F. gracilis. Primary production will be
simultaneously quantified. Additionally, molecular techniques will be employed to identify the prey
selectively consumed by F. gracilis. Finally, I will combine secondary production data with primary
production data from the Florida Straits in order to describe the flow of energy between trophic levels
from phytoplankton to larval billfish.
Aim 1 tests the hypothesis that abundance of F. gracilis establishes an upper limit on the survival of
larval billfish. I predict that known larval billfish abundance data will be positively related to
abundance of F. gracilis. I predict changes in larval fish survival will reflect changes in abundance and
distribution of F. gracilis due to upwelling and eddy formation. If valid, changes in physical
oceanographic factors in the SOF can be used as an indicator of larval success. I also predict that F.
Sharein El-Tourky
Research Proposal
gracilis exhibits a reverse daily vertical migration pattern. If true, the distribution of F. gracilis at the
surface of the water column could explain their high incidence in the guts of larval fish. If no
relationship is evident, billfish may select for F. gracilis solely due to greater capture success.
Distributions of F.gracilis will be determined using the same samples used to establish published
distributions of larval Billfish in Florida Straits. Abundance of F.gracilis will be calculated via visual
counting, and will be compared both to published abundance patterns of billfish and total abundance of
zooplankton.
Aim 2 tests the hypothesis that larval billfish survival is related to secondary production rates of F.
gracilis, rather than abundance, which is further hypothesized to be dependent on primary production. I
predict that secondary production rates of F. gracilis will reflect the magnitude of primary production
and the degree of prey selectivity of F. gracilis. I predict that there will be significant temporal and
spatial fluctuations in secondary and primary production. Furthermore, I predict that larval fish
distribution will reflect areas of highest production by F.gracilis. Prey selectivity of F. gracilis will be
determined using reverse blocking primers to block copepod DNA in conjunction with universal primers
to amplify the prey DNA in the copepod’s gut.5 Using the gut fluorescence method, grazing rates will be
calculated for F. gracilis in order to determine spatial and temporal patterns in utilization of primary
productivity. Egg production and respiration rates calculated from F. gracilis will be used as indexes to
secondary production. Primary and secondary production will be monitored at different stations over a
period of three years. The spatial and temporal patterns in rates that emerge will be used to explain
observed patterns in larval billfish abundance and mortality.
Intellectual Merit: My study will serve as a model for future zooplankton studies in crucial
spawning grounds of a variety of fish species, and will lead to superior management strategies.
Ideally, my research model will elucidate “hotspots” for ecosystem management, resulting in
economically stable fisheries.
Broader Impacts
The steady decline in fishing stocks, despite the implementation of fisheries management
strategies, indicates the necessity for more comprehensive ecosystem models that incorporate
energy flow dynamics. In the Florida Straits, Blue marlin and Sailfish are believed to be
overexploited.6 I have met with colleagues at the University of Miami to discuss the opportunity
to use my future data to develop a dynamic multispecies model or a whole ecosystem model such
as ECOPATH with ECOSIM. Ultimately, my study will benefit plankton ecologists, fisheries
modelers and communities that depend on sustainable fisheries. While I am conducting my
research in Miami, I will continue to share science with the public through the Miami Science
Museum Integrated Marine Program and College Training (IMPACT) program. The purpose of
the program is to prepare low-income, first-generation college bound students for a degree in
science or technology. As the first person in my family to earn a degree, I can easily identify
with these students. I am using my experiences to help develop the curricula for the marine
science summer program and as a mentor to offer advice on overcoming the obstacles to
education they might face. This proposal is original work.
References: 1Sponaugle et al. (2010) Mar Biol 157:839-849 2Young et al. (2009) J. Plankton Res. 31(6):687-700.
3
Llopiz and Cowen. (2008) Mar Ecol Prog Ser. 358:231-244. 4Richardson et al. (2009) Fisheries Ocean. 18(6):402418.5Vestheim and Jarman. (2008) Frontiers in Zool. 5:12. 6Die. (2006). Bulletin of Mar Sci. 79:529-54.