A Comparison of Copepoda (Order: Calanoida, Cyclopoida, Poecilostomatoida) Density in the Florida Current Off Fort Lauderdale, Florida

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6-1-2010 A Comparison of Copepoda (Order: Calanoida, Cyclopoida, Poecilostomatoida) Density in the Florida Current Off orF t Lauderdale, Florida Jessica L. Bostock Nova Southeastern University, [email protected]

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Nova Southeastern University Oceanographic Center

A Comparison of Copepoda (Order: Calanoida, Cyclopoida, Poecilostomatoida) Density in the Florida Current off Fort Lauderdale, Florida

By Jessica L. Bostock

Submitted to the Faculty of Nova Southeastern University Oceanographic Center in partial fulfillment of the requirements for the degree of Master of Science with a specialty in:

Marine Biology

Nova Southeastern University June 2010

Thesis of Jessica L. Bostock

Submitted in Partial Fulfillment of the Requirements for the Degree of

Masters of Science: Marine Biology

Nova Southeastern University Oceanographic Center

June 2010

Approved:

Thesis Committee

Major Professor :______

Amy C. Hirons, Ph.D.

Committee Member :______

Alexander Soloviev, Ph.D.

Committee Member :______

Jonathan Shenker, Ph.D.

Acknowledgements

The completion of this thesis and research would not have been possible without the hard work of many individuals. I would first like to thank my committee members, Dr. Amy C. Hirons, Dr. Alex Soloviev, and Dr. Jonanthan Shenker for their invaluable assistance during various stages of my project. Dr. Hirons, as my major professor, has provided many invaluable critiques and comments during the progression of the project to make it successful. I would also like to thank Dr. Alexander Soloviev and Dr. Jonathan Shenker for giving suggestions and constructive criticism along the way. I would also like to thank Dr. Jason Gershman, of the Division of Math, Science and Technology of Farquhar College of Arts and Sciences who assisted with the statistical portion of my research. I would like to thank my friends and family for supporting and encouraging me throughout this process. To my lab mates, Stephanie Healey, Gabriela Winiewski, and Maduhra Mokashi for their constant support and entertainment during the identification portion of my project. To my co-workers and friends, Kerry Boytin, Whitney Brown, Jamie Rodriguez, Zaibis Munoz, Sara Schilling, Kenrick Roberts, Lindy Wagner, and Anthony DeSantis. Your showed me what true friends are with willing ears to listen and offering advice when I was lost, thank you. Finally, I am indebted to my father and mother, Jay and Kathleen Bostock, for their unwavering love and unconditional support throughout my entire life. They have taught me the invaluable lessons of commitment, sacrifice, and perseverance. Without them I would not be where I am today and I thank you. I would also like to express my gratitude to my older sister, Virginia Bostock. She was able to show me there was a light at the end of the tunnel and that I can do this. And to my younger siblings, Meredith and Devon Bostock, who could always bring a smile to my face when I needed it the most. Thank you all for being my rock, I couldn’t have asked to for a better family.

Table of Contents

ACKNOWLEDGEMENTS ...... 3

TABLE OF CONTENTS ...... 4

LIST OF FIGURES ...... 6

LIST OF TABLES ...... 8

ABSTRACT ...... 10

I. INTRODUCTION...... 12

Copepoda ...... 12 Ecological Importance ...... 15 Life History ...... 16 Geographical Distribution: Latitudinal, Land Proximity, and Depth ...... 20 Latitude ...... 20 Land Proximity: Coastal and Pelagic Distribution ...... 22 Depth: Diel Vertical Migration ...... 23

Anatomy and Function ...... 24 Seta position ...... 24 Cephalosome ...... 24 Antennule and Antenna...... 27 Mandible, Maxillule, Maxilla, and Maxilliped ...... 29 Metasome ...... 32 Urosome ...... 35

Taxonomic Composition of South Floridian Waters ...... 35

Physical Environment ...... 37 Tropical Waters ...... 37 The Florida Current ...... 38

Statement of Purpose ...... 41

II. MATERIAL AND METHODS ...... 42

Study Site ...... 42

Zooplankton Collection ...... 44

Identification Analysis ...... 45

Laboratory Analysis ...... 45

Diversity and Statistical Analysis ...... 46

III. RESULTS ...... 49

Copepod Composition and Density Data ...... 50

Diversity Data ...... 69

Oceanographic Data ...... 71 CTD Data ...... 71 ADCP Data ...... 74

Density Statistical Analysis ...... 78

IV. DISCUSSION ...... 90

Gear Selectivity ...... 91

Sea surface temperature ...... 93

Salinity ...... 94

Fluorescence ...... 94

Copepod Composition and Density Distribution ...... 95

Spatial and Temporal Scales ...... 102

Biological Interactions ...... 103

Study Influence...... 106

V. CONCLUSION ...... 107

VI. REFERENCES ...... 111

APPENDIX A ...... 120

List of Figures

Figure 1. Calanoida nauplii ...... 18 Figure 2. General copepodite developmental stages...... 19 Figure 3. General morphology of Calanoida copepods ...... 25 Figure 4. Antennule (A1) ...... 28 Figure 5. Antenna (A2) ...... 30 Figure 6. Mandible (Md), Maxillule (Mx1), Maxilla (Mx2), and Maxilliped (Mxp) ...... 31 Figure 7. Pereipods ...... 34 Figure 8. Map of the Caribbean Sea ...... 39 Figure 9. Satellite image of zooplankton sampling stations located east of Port Everglades Florida, U.S.A ...... 43 Figure 10. Mean overall density distribution of copepod at Stations A and B in February 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 51

Figure 11. Mean overall density distribution of copepod at Stations A and B in July 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 52

Figure 12. Mean density distribution of copepod orders at Stations A and B in February 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 53

Figure 13. Mean density distribution of copepod orders at Stations A and B in July 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 54

Figure 14. Mean density distribution of the top four dominant genera at Stations A and B in February 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 57

Figure 15. Mean density distribution of the top four dominant genera at Stations A and B in July 2007 using the bongo net in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 58

Figure 16. Average genera population densities (organism m -3 ) captured in the bongo net for Stations A and B in February and July 2007...... 59

Figure 17. Mean overall density distribution of copepod at Stations A and B in February 2007 using the Tucker trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 60 Figure 18. Mean overall density distribution of copepod at Stations A and B in July 2007 using the Tucker trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 61

Figure 19. Mean density distribution of copepod orders at Stations A and B in February 2007 using the Tucker trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 63

Figure 20. Mean density distribution of copepod orders at Stations A and B in February 2007 using the Tucker trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 64

Figure 21. Mean density distribution of the top four dominant genera at Stations A and B in February 2007 using the Tuckler trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 66

Figure 22. Mean density distribution of the top four dominant genera at Stations A and B in July 2007 using the Tucker trawl in surface waters (0-25 m) transposed on acoustic Doppler current profile (ADCP) current velocity ...... 67

Figure 23. Average genera population densities (organism m -3 ) captured in the Tucker trawl for Stations A and B in February and July 2007...... 68

Figure 24. Sea surface temperature, density and fluorescence data results for Stations A and B in February 2007 ...... 75

Figure 25. Sea surface temperature, density and fluorescence data results for Stations A and B in July 2007...... 76

Figure 26. Acoustic Doppler current profile (ADCP) current velocity results for February 2007 at Stations A and B ...... 77 Figure 27. Acoustic Doppler current profile (ADCP) current velocity results for July 2007 at Stations A and B...... 79

Figure 28. Acoustic Doppler current profile (ADCP) current direction for February 2007 at Stations A and B ...... 80

Figure 29. Acoustic Doppler current profile (ADCP) current direction for July 2007 at Stations A and B ...... 81

List of Tables

Table 1. Definition and interpretations of alpha and beta diversity in relation to various diversity measures and indices used to examine zooplankton samples ...... 47 Table 2. Copepod genus mean densities (ρ) (organisms m-3) and percent Composition (%) for Stations A and B in February and July 2007. Zooplankton samples were collected with a bongo 202-μm net...... 56

Table 3. Copepod genus mean densities (ρ) (organisms m-3) and percent composition (%) for Stations A and B in February and July 2007. Zooplankton samples were collected with a Tucker 760-μm trawl...... 65

Table 4. Alpha diversity analysis. Used to determine different levels of diversity Of individual habitats (Stations A and B), months (February and July 2007) and equipment type (bongo 202-μm net and Tucker 760-μm trawl). Three different diversity measures were used on each zooplankton sample; species richness, Shannon Index, and Simpson’s Index of Diversity ...... 69

Table 5. SØrensen’s Similarity Index. Stations A and B represent the two ecosystems analyzed while the Florida Current acted as the environmental gradient. Both net types were assessed...... 71

Table 6. CTD data. Sea surface temperature, salinity and depth for all Zooplankton samples collected at Stations A and B for February and July 2007...... 73

Table 7. Mann-Whitney U results of overall copepod densities. Comparisons Were analyzed based on station in the same month and against station in different months. Analysis was based on zooplankton collection in the bongo net and Tucker trawl. Italics represent statistical significance among densities...... 83

Table 8. Mann-Whitney U results of copepod order densities. Comparisons were analyzed based on stations in the same month and against the same station in different months. Analysis was based on zooplankton collection in the bongo net. Italics represent statistical significance among densities...... 84

Table 9. Mann-Whitney U results of copepod order densities. Comparisons Were analyzed based on stations in the same month and against the same station in different months. Analysis was based on zooplankton collection in the Tucker trawl. Italics represent statistical significance among densities...... 86

Table 10. Mann-Whitney U results for the densities of copepod four most abundant genera. Comparisons were analyzed based on stations in the same month and against the same station of different months. Analysis was based on zooplankton collection from the bongo net. Italics represent statisticalsignificance among densities...... 87

Table 11. Mann-Whitney U results for the densities of copepod four most abundant genera. Comparisons were analyzed based on stations in the same month and against the same station of different months. Analysis was based on zooplankton collection from the Tucker trawl. Italics represent statisticalsignificance among densities...... 89

Abstract

Copepods, minute crustaceans, are vital constituents of marine food web dynamics in tropical ecosystems. Ecologically, copepods provide the link between primary production and tertiary consumers. Changes in population structure and densities may impact ecosystem stability and production on small to large spatial scales.

The present study examined the influence of the Florida Current on copepod population densities off the coast of Fort Lauderdale, Florida due to limited data in the area.

Samples were collected during February and July 2007 at two locations, Stations A and

B. Station A, dependent on current dynamics, fluctuated between the most western boundary and the inshore waters adjacent to the coast. Station B was typically located within the Florida Current showing great influence from the current’s physical factors.

The current, acted as a physical barrier, entrapping species at near shore stations, increasing population densities by increased nutrient loads through upwelling and land runoff. The movement of the current inshore showed a greater resurgence of oceanic species at each station. However, the western edge of the current, acting as a barrier, yielded the lowest population densities overall and among all copepod orders. The decrease can influence food web dynamics and the prey availability to higher tertiary consumers. Population dynamics were ascertained by relative copepod densities identified to the lowest possible taxa and enumerated. Calanoid copepods were dominant in zooplankton samples, showing high instances of Calanus and Undinula, followed by

Poecilostomatoida, highly represented by Corycaeus and Oncaea, and Cyclopoida.

Poecilostomatoid densities were numerically important, where in some samples

Corycaeus contributed to 42 % of overall copepod densities. Previous studies have led to

10 their underestimation, due to gear selectivity and extrusion directly related to their prosome length. Diversity levels revealed an overall diverse habitat, typical of tropical environments. However, there was greater diversity in coastal waters as compared to the

Florida Current which was only found oceanic species present.

Key Words: Copepoda, Calanoida, Poecilostomatoida, Cyclopoida, Florida Current, density

I. Introduction

Copepoda

Plankton are aquatic organisms, characterized by the inability to move against

currents. They inhabit both fresh and marine environments, occupying the pelagic realm

and the benthos. Plankton are grouped into three categories, phytoplankton, zooplankton,

and baterioplankton. Of these three, zooplankton are small heterotrophic protozoans and

metazoans. Copepods, minute holoplanktonic crustaceans, are dominant members of the

marine zooplankton community. Copepods are the most common and diverse members

of aquatic environments, with over 14,000 species, 2,280 genera, 210 families and 10

orders (Boltovoskoy 1999; Mauchline 1998). The majority of species are found within

four of the ten orders of copepods: Calanoida, Cyclopoida, Harpacticoida, and

Poecilostomatoida. These orders in marine ecosystems account for nearly 80% of the

carbon biomass in marine plankton samples (Turner 2004).

Orders

Calanoida

Calanoida contains over 43 families with over 1,800 marine species, nearly 40 %

in the suborder Clausocalanoidea (Mauchline 1998). They are characterized by long

first antennae extending to or beyond their metasome, articulation between the fifth

metasomal somite and the genital somite, a fifth biramous leg, and a generally oval body

shape. Calanoids inhabit both fresh water and marine environments, with mainly

holoplanktonic species. Many species are herbivorous yet some show omnivorous or

carnivorous tendencies. Reproductively, calanoids are both egg carriers and egg scatterers

in the pelagic environment.

Cyclopoida

Cyclopoida contains over 12 families, 80 genera and 450 marine species.

Cyclopoids are characterized with short first antennae that do not extend beyond the cephalosome, narrowed anterior and broadened posterior cephalosome, articulation between the fifth and sixth metasomal somite, and uniramous fifth legs. Cyclopoids inhabit fresh water and marine environments, with holoplanktonic, commensal, parasitic, on coral, tendencies (Humes 1962). These small organisms mainly feed on detritus but are also known to be both omnivores and carnivores. Reproductively, cyclopoids have developed and carry embryos in paired egg sacs attached to the female.

Harpacticoida

Harpacticoida contains over 54 families, 460 genera and 3,000 species. They are characterized by elongated bodies, short antennae, articulation between the fourth and fifth metasomal somite, and irregular body shape and appendage structures. They inhabit both fresh and marine environments, mainly with in the benthic realm. However, few species do inhabit the water column and are holoplanktonic. Many of these species are raptorial in their feeding strategy and will selectively seek prey. Reproductively, after insemination the female carried the brood in sacs located on the urosome.

Poecilostomatoida

Poecilostomatoida, previously classified in Cyclopoida, contain over 1500 marine species and are generally parasitic copepods as seen on the gills of Mugil cephalus (Ho and Do 1981). Poecilostomatoids are characterized but long uniramous first antennae extending the length of the prosome and articulation between the fourth and fifth

13 metasomal somite. Like cyclopoids, poecilostomatoids are also selective raptorial feeders and carry embryos in paired egg sacs.

Order Contribution

The dominant copepods collected in zooplankton samples come from the order

Calanoida. However, there has been speculation to the contribution of Calanoida copepods in biomass to the zooplankton community. Cyclopoida, like Calanoida, is ubiquitous in nature with 19 families and 63 genera. However, there is relatively little information known about the biology and physiology of the order. Due to small body size, it is difficult to taxonomically distinguish certain species (Ferrari 1975). Species differentiation may be based on the number of external setae on the exopod of the pereipod as seen in the family Oithonidae (Ferrari and Bowman 1980). Some specific families, genera, and species within the order are well known and documented, such as

Oithona spp. and Oncaea spp. The genus, Oithona, could be greatly underestimated due to the mesh size used to capture small copepods. A 202 micrometer (µm) mesh net was used as the smallest mesh net, catching only 7% of the organisms ranging from 200 µm to 20 millimeter (mm) (Galliene and Robins 2001). However, the size of Oithona spp., ranging from 0.45 to 0.80 mm, and other species can be significantly smaller, leading to assumptions of underestimation of specific genera or species (Grice 1960).

Nevertheless, these two genera are comparable to calanoids in environmental habitat as both are present in both coastal and oceanic environments and appear in high densities within zooplankton samples (Gonzalez and Smetacek 1994, Uye and Sano

1995). Through recent studies it has been found that smaller copepods may play a larger role and have a greater impact on community structure than previously thought. Hopcroft

14 and Roff (1998) hypothesized that smaller species such as Oithona spp. have higher growth rates which in turn produce a higher yield of the organisms.

Ecological Importance

Copepods are vital constituents in the marine food webs, as secondary producers, providing the link between primary production, phytoplankton, and tertiary consumers, such as fish larvae (Sommer and Stibor 2002). Copepod trophic interactions include grazing on phytoplankton, helping maintain the chemical composition of the ocean in the microbal loop, and being prey to other planktonic carnivores (Turner 2004). However, the most important function of a copepod is transferring energy from the primary trophic level to the tertiary level, supporting higher tropic levels with 10 % trophic efficiency through secondary production (Sander and Moore 1978).

The ecological importance of copepods may be influenced by oceanic and atmospheric conditions, resulting in changes to community structure, biomass, density, and diversity (Lia et al. 2006). Differences in diversity and copepod biomass result from alteration in the physical and biological parameters of oceanic conditions (Ashjian 1993;

Ashijian and Wisher 1993). Physical parameters can include temperature, salinity, oxygen content, velocity, depth and geographical position. Tolerance to the physical environment plays a major role in the retention of individuals and species in specific environments. Temperature and salinity are two factors that have a large impact on species; these affect growth rate, reproductive success, and environmental tolerance.

Species have specific temperature and salinity ranges in which they inhabit. If the environmental conditions change drastically outside the copepods environmental range, it could have detrimental effects. Acartia tonsa showed high mortality rates in salinity

15 greater than 10 – 15 parts per thousand (‰) (Cervetto et al. 1999). Temperature can directly affect reproductive success. As the temperature increases generation time decreases exponentially, thus increasing growth rate and decreasing the size of the individual.

Life History

The life history of copepods can be divided in to four distinctive stages: egg, nauplius, copepodite and adult terminal stage. These stages can vary greatly depending on species, habitat and food source availability. The eggs of copepods can either be carried by the female or scattered in the water column. Dispersion of eggs differs among orders. Calanoida generally scatter eggs; however some species retain the eggs.

Retention is also found in Cyclopoida, Poecilostomatoida and Harpacticoida.

The breeding behavior and timeline of copepods are dependent on latitude and seasonality. Tropical species are hypothesized to have continuous breeding cycles throughout the year, which may correlate to short generation times and high egg production rates, ranging from 3.2 to 88 eggs per female per day with increased temperatures, approximately 28ºC (McLaren et al. 1969; Hopcroft and Roff 1998). In temperate and polar regions, a fixed breeding period occurs consistently with the onset of phytoplankton blooms. Breeding is timed to optimal food resource availability to ensure survival of the offspring (Bathmann et al. 1993).

The production of offspring is a mechanism of sexual reproduction where the male transfers one or more spermatophore to the female genital somite (Mauchline 1998).

The spermatophore is attached the male’s fifth leg that is modified for copulatory processes. The female has a single ovary located between the cephalosome and the first

16 thoracic segment dorsal laterally to the gut. The ovary leads to the oviducts located at the genital somite of the urosome where fertilization is achieved by the transfer of spermatozoa via spermatophore to the female genital opening (Buskey 1998).

After the release or hatching, the offspring enters the naupliar stage (N) (Figure

1). This developmental stage is divided into six sub groups, NI – NVI. However, the number of stages may vary among species; there are only five naupliar stages of

Pseudodiaptomas coronatus (Allan 1976). The nauplius has three pairs of multipurpose appendages, two sets of antenna and one or two maxillipeds. All appendages are used for locomotion and/or feeding (Mauchline 1998). As the nauplius grows and progresses through the different stages, body complexity increases with the addition of thoracic segments and appendages (Ianiva 1998). As the complexity increases, the nauplius transitions into a copepodite.

The first copepodite stage is distinguished by the fusion of the first thoracic segment and the cephalosome. The second through the fourth somite of the metasome are present along with the anal segment and the telson of the urosome. As the naupliar stage was dictated by six subgroups, the copepodite (C) has five subgroups, CI – CV.

The growth of the copepodite is seen in the addition of some metasomal and urosomal segments along with the development of pereipods. The presence of pereipods can indicate the copepodite stage. CI may only have one or two pereipods while CV can have well developed pereipods on four or five somites. The last stage of the copepodite is also referred to as adult terminal stage or CVI. In the adult stage, all metasomal and urosomal segments are fully developed with appendages (Figure 2) (Mauchline 1998).

Figure 1.Calanoida nauplii. The general naupliar body structure of Calanoida copepods consisting of three appendages; two sets of antenna and one or two maxillipeds. Appendages are used for feed and location (modified from Mauchline 1998).

Figure 2. General copepodite developmental stages. The sequential segmentation of copepodites from CI to adult male and female. The dashed line indicated the division of metasome and urosome. The darkened segment indicates the new segment after the previous molt. C+1, cephalosome and first metasomal somite; 2-7 represent thoracic somites; A, anal somite (modified from Mauchline 1998).

Geographical Distribution: Latitudinal, Land Proximity, and Depth

Copepods have ubiquitous distribution that allows them to inhabit various habitats and depths as well as freshwater, semi-terrestrial, estuarine and marine environments.

Copepods can either be commensal, parasitic or free living in the water column. In the marine setting, free living copepods can inhabit the benthos, epipelagic, and mesopelagic regions while some can venture into the upper bathypelagic zone. The latitudinal distributions of copepods demonstrate variability in both species diversity and density among polar, temperate, and tropical regions. Diversity can be attributed to various environmental factors such as temperature, salinity, and pressure. Temperature can have a great effect and influence on the level of species’ diversity latitudinally.

Latitude

Polar regions are characterized by extremely low water temperature ranging from below freezing to 10˚C (Colling 2004). The extreme environmental conditions limit species diversity due to physiological and anatomical adaptations and modifications. In high latitude regions oxygen consumption and metabolism are increased in comparison to temperate and tropical regions (Lonsdale and Levin 1985). These modifications allow specific species to survive.

Various copepod densities are greatly interconnected to phytoplankton aggregations in association with latitudinal seasonality. A substantial phytoplankton bloom occurs during the spring in high latitude regions. The seasonal variation of the solar irradiance is a result of the obliquity of the Earth’s rotational axis in comparison to the perpendicular plane (Gaidos and Williams 2004). The extreme declination of the

20 polar regions away from the sun during the winter causes less solar radiation and a decrease in phytoplankton production. During the spring, solar irradiance increases, contributing significantly to primary production (Ohlmann et al. 1996). The spring phytoplankton bloom solicits a delayed and mimicked response in copepod densities.

These copepod aggregations are a product of the adults attempting to coincide spawning with the greatest abundance of food sources, thereby trying to increase and insure the survivorship of the offspring (Smith 1990).

Temperate regions show a moderate level of copepod diversity and species density which will vary dependent on seasonality (Ohlmann et al. 1996). Temperatures vary throughout the year and allow for a wider variety of species that can adapt to both cool and warm waters. Temperate regions also exhibit two main phytoplankton blooms, one during the spring and the other in late summer followed by an increase in copepod abundance (KiØrboe and Vielsen 1994).

Tropical regions, unlike polar latitudes, have high species diversity levels while species densities are minimal. Low latitudes have a fairly consistent temperature range,

25 ˚C to 30˚ C, which is more conducive to a greater number of species (Colling 2004).

Physiological adaptations and modified anatomical structures evolved due to increased competition, food acquisition, and predator avoidance. These adaptations, along with suitable environmental conditions, can increase species diversity of organisms vying for a specific niche. As species diversity increases, species density decreases. However, the greatest abundance is seen in the upper photic layer, 100 m and decreases drastically with depth (Longhhurst 1976). The lack of seasonality, with no specific phytoplankton bloom, result in low primary production (Hopcroft and Roff 1998). Constant solar

21 irradiance produces year round uniform phytoplankton blooms with no deviations as seen in other regions (Sheldon 1989).

Land Proximity: Coastal and Pelagic Distribution

Sander and Moore (1978) stated that copepods account for 70% of many zooplankton samples and their densities will increase in relation to proximity to shore.

This can have a great influence on species diversity when comparing inshore and offshore sites. It has been shown that inshore copepod numbers can dramatically increase and can account for as much as ninety percent of a zooplankton sample. The same pattern was observed off Kingston, Jamaica where higher rates of secondary production occurred near-shore compared to offshore (Moore and Sander 1979).

The stability of inshore waters may be significantly higher than offshore waters. It allows to be a prime environment for increased phytoplankton productivity due to greater nutrient input from land drainage due to rainfall (Hopcroft and Roff 1990; Moore and

Sander 1979; Webber et al. 1992). A study conducted by Sander and Moore (1978) showed that there was an increase in copepod distribution to the proximity to land showing high incidence of one or two species rather than the increase of the entire population and community of copepods. The island mass effect or nearness of land masses is produced by tidal induced mixing, wind driven currents, benthic or topography interactions, and phytoplankton distribution (Alvarez-Cadena et al. 1998; Danonneau and

Charpy 1985; Leichter et al. 1998; Moore and Sander 1979). It was also found that through the land mass effect there were high percentage contributions by copepods inshore which accounted for nearly 90% of the zooplankton community in neritic waters

(Sander and Moore 1978).

Depth: Diel Vertical Migration

A unique characteristic of zooplankton is mass vertical movement in the water column, from depth to surface waters or vice versa. During nocturnal migrations, organisms ascend into nutrient rich waters where organisms have a greater metabolic advantage and predator avoidance. The migration of copepods occurs within the first few hundred meters of the water column (Lampert 1989; Stich and Lampert 1981). Depth ranges of copepods can be determined from vertical migration observations. The depth ranges as studied by Roehr and Moore (1965) in Floridia varied from coastal to pelagic waters. Moore and O’Berry (1957) examined the influence of vertical migrations of shallow and deep water copepods in the Gulf Stream and hypothesized that the distance of migrations was related to light exposure. Deep water species have a greater tolerance for temperature and pressure fluctuations, along with light intensity, in comparison to shallow water species. Pleuromma spp. and Rhincalanus spp. in Floridian waters have a vertical range of 200 m (Roehr and Moore 1965).

Copepods are commonly thought to have fixed depth ranges based on environmental factors. Paffenhofer and Mazzocchi (2003) examined diurnal migration patterns of copepods within the upper 100 m to assess potential factors that attributed to variation of migration, such as sex, age, water temperature, food resources, feeding behavior, and predation. The findings could only relate food availability and feeding behavior as a major influence on diel migration and depth ranges. Food predetermines depth range due to particulate matter sinking in the water column. Copepods will exploit and utilize all resources available within a certain locale and the location is dependent mainly on food and temperature.

Anatomy and Function

Copepod identification is based on morphological variation of the general body structure (Figure 3). The general body structure is comprised of three main segments; the cephalosome, metasome, and the urosome. Each body segment aids in either mobility, food acquisition, and or sensory and copulatory processes with help of various appendages. The modification of the general structure of each segment, somite and appendage along with seta number and placemen can distinguish between different taxonomic levels from order to species.

Seta position

While the taxonomic identification of copepods is established through body tagmosis, seta position and other various projections can help identify species (Boltovskoy 1999). The arrangement of hooks, spines, spinules and rami of various appendages helps in the identification of specific taxonomic levels. A spine is defined as a firm, broad-based projection, either curved or straight with no protrusions.

A spinule is a minor version of a spine. A seta is a long and slender version of a spine that tapers at the apex and is either naked or plumose, with smaller projections (Owre and Foyo 1967). The order of these projections on the interior or exterior of specific segments of an appendage can help distinguish families and other lower taxonomic levels.

Cephalosome

The cephalosome is the most anterior region of the copepod and is a combination of the head fused with one or more thoracic somites (Owre and Foyo 1967). The head

LIST OF ABBREVIATIONS A1 first antenna Md mandible A2 second antenna Mx1 first maxilla Abd abdomen Mx2 second maxilla Ansgm anal segment Mxp maxilliped Gnsgm genital segment P1-P5 first pereipod – fifth pereipod

Figure 3. General morphology of Calanoida copepods. The cephalosome contains antennae and all oral appendages. The metasome contains five somites with five pairs of swimming legs. The urosome contains the anal somite and caudal ramus (modified from Owre and Foyo 1967).

contains the five cephalic somites and the fusion of the first thoracic segment may be complete or partial. These somites bear optical and sensory organs, oral appendages and antennae. The cephalic somites may contain eyes or optical lenses ranging from pronounced to primitive development. Eyes are used to differentiate between light and dark and can be related to kinesis and or taxis. The change in speed and guided direction change can be associated with diel vertical migration and the distinction between night and day with in the photic zone (Land 1998).

Developed eyes are uncommon and are a tool to distinguish between various taxonomic levels. While the structure of the eyes can be highly complex and specialized, some species such as Pareuchaeta norvegica and Calanus finmarchinus do not have lenses (Mauchline 1998). Cyclops spp. have a single medial eye; Copilia spp. have two primitive compound eyes while Cephalophanses refulgens have distinct lenses located on the dorsal anterior position of the cephalosome as a result of highly modified ocelli

(Mauchline 1998; Owre and Foyo 1967; Wolken 1969). Sensory and neurological organs appear to have neurosecretions which may be related to photosensory cells that are regulated by light (Maucline 1998). This regulation of light can be directly related to copepod vertical movement in the water column. Another function of the eye can be related to mate identification and location as seen in Pontellidae. This family has three eyes, two dorsal and one ventral. The size of the eye shows sexual dimorphic characteristics with the enlarged dorsal eyes in the male Labidocera and ventral eyes in

Pontella and Anomalocera. Studies show that the enlarged eyes may help in mate location (Land 1998).

Antennule and Antenna

The cephalosome contains two anterior appendages, the antennules, and antennae that aid in sensory, motility, and copulatory processes. The antennules, also referred to as the first antennae (A1), are bilateral, uniramous, symmetrical appendages that vary in number of segments and seta location among species and sex (Figure 4) (Mauchline

1998). The generalized structure is based on twenty-eight segments of the antennules; the variation of the number of segments and fusion helps to differentiate between species

(Boxshall and Huys 1998). Xanthocalanus paraincertus has twenty-four segments on the first antennae with fusion between the VIII-IX segments (Grice and Halsemann 1965).

However, Epischura shows only the distal fusion between XXI-XXIII and XXIV-XXV in the male of the geniculate antennule and no fusion in the female (Boxshall and Huys

1998). In addition, the male and female differentiation of antennules is further distinguished by the number of seta projections. The male can double the number of aesthetsacs on each segment to detect female pheromones pre-mating (Ohtsuka and Huys

2001). The geniculate antennule is used to grasp the female abdomen or caudal ramus during mate guarding and spermatophore transfer (Boxshall and Huys 1998; Katona

1975).

While antennules are used during copulation, other studies showed antennule setae are mechanoreceptors and can detect spatial disturbances through movement and chemical stimuli, and they are used to sense prey and predators as seen in Cyclops scutifer (Lenz and Yen 1993; Stickler and Bal 1973). Seta organization on the proximal, middle and distal segments receive different chemical and mechanical stimuli based on proximity to the body, which suggests distal segments receive stimuli with little

(a)

(b)

Figure 4. Antennule (A1). (a. Neocalanus gracilis ♀ b. Centropages typicus ♂) The first appendage of the cephalosome. The shape and number of the antennules segments are species specific and gender dependent. They can vary from 27 segments in the family Epacteriscidea to 26 segments in Ridgewayiidae (modified from Owre and Foyo 1967; Mauchline 1998).

interference from other copepod motor functions (Yen and Nicoll 1990). This allows the copepod to detect various fields of disturbances, from short to long distances.

The antenna, also referred to as the second antenna (A2), is the next posterior appendage (Figure 5). Unlike the antennule, the antenna is biramous with the presence of an endopod and exopod. The articulation of the antenna helps with the collection and manipulation of food particles towards the mouth. The number of seta and arrangement help in identification of species. In the family Calanidae the exopod has seven segments with I-II having two setae and III-VI having one seta (Bradford and Jillett 1974).

Mandible, Maxillule, Maxilla, and Maxilliped

Other cephalic appendages that aid in food manipulation surround the mouth. The labrum and labium are the lateral margins of the mouth with seta projections that secrete compounds that aid in the digestion of food (Mauchline 1998). Surrounding the margin of the mouth are the mandible, maxillule, maxilla and maxilliped (Figure 6). The structure of these appendages, along with seta position, shows species variation as a result of different feeding strategies.

The main differences among these four true oral appendages are that the mandible and maxillule are biramous while the maxilla and maxilliped are uniramous (Mauchline

1998). Other differences are present in seta location and arrangement, which may aid in species’ identification. In Calanidae the mandible’s blade shows well-defined teeth and a developed lope on the endopod. The maxilla consists of fourteen spines and setae on the

Figure 5. Antenna (A2). (Corycaeus limbatus ♀) The second appendage of the cephalosome. The antenna is biramous with an endopod, the inner most branch, and an exopod, the outer most branch (Mauchline 1998; Owre and Foyo 1967).

(a) (b)

Figure 6. Mandible (Md), Maxillule (Mx1), Maxilla (Mx2), and Maxilliped (Mxp). (a. Pleuromamma abdominalis ♀ b. Bradycalanus typicus ♀ c. Megacalanus princeps ♀ d. Valdvivella insignis ♀). (modified from Owre and Foyo 1967).

31 first inner lobe. The maxilla also has four setae on the second and third inner lobes, the basipod, and the first and second endopodal segments. The third endopodal segment shows seven setae, the endopod has eleven setae with the second outer lobe having one and the first inner lobe having nine setae. The maxilliped contains five segments that have from proximal to distal position four, four, three, four and four setae (Bradford and

Jillett 1974).

Metasome

The cephalosome is followed by the medial thoracic region, also referred to as the metasome. The metasome consists of generally six somites but is variable among species. Aegisthis aculeatus has six distinct thoracic segments while Gaidius tenuisspinus show a fusion between the fourth and fifth segment (Owre and Foyo 1967). The last thoracic somite is called the genital segment (gnsgm) which bears the genital aperture.

The aperture is adorned with spines, hairs and is either symmetrical or asymmetrical. The articulation of the thoracic somites is one of the main characteristics of differentiating between specific orders. In Calanoida and Cyclopoida, differentiation is based on gymnoplean tagmosis, the prosome and urosome boundary established by the last pedigerous somite and the genital segment. Calanoida is generally classified by having a movable articulation between Pd5 and genital somite while Cyclopoida has articulation between Pd 4 and 5 (Boltovskoy 1999).

Pereipods

Each somite contains one pair of pereipods, or swimming legs. The metasome has one to five pairs of pereipods depending on the sex and species of the copepod

(Figure 7). The pereipods are biramous appendages that vary in seta arrangements. In the family Calanidae the first four legs in both males and females are nearly the same with the exopod’s first basipod segment having setae on the inner edge and the second basipod with spines on the outer edge. The distinction of legs is seen in the seta arrangement of the terminal endopod segment. The first leg has one outer, one terminal and four inner setae. The second and third legs have two outer, one terminal and five inner setae. The fourth leg shows two outer, one terminal and four inner setae (Bradford and Jillett 1974).

The family Calanidae is represented by the presence of no spine or setae on the coxa of the fifth leg. One seta is located on the exterior portion of the basis while one exterior spine is on the first exopodal segment. The second exopodal segment has one exterior spine and one interior seta. The terminal exopodal segment has two exterior spines, one terminal seta, and four interior setae. The endopodal segments do not have any spines. This segment does have one seta on the interior of the first segment, one interior seta on the second segment, and either zero, one or two setae on the exterior of the ramus which has two setae on the terminal section and on the interior. As compared to the family Heterohabdidae, the differentiation is on the second exopodal segment that has both exterior and interior spines instead of an exterior spine and an interior seta

(Boltovskoy 1999).

The fifth legs have distinct characteristics and show sexual dimorphism.

Commonly, one of the male’s fifth legs is modified for copulation grasping during the reproduction (Figure 7). The fifth leg is also used for spermatophore placement and

(a) (b) (c)

Figure 7. Pereipods. (a, Canthocalanus pauper ♀ P1 b. Mesocalanus tenuincornis ♂ P5 c. Undinula vulgaris ♂ P5). P1 – P4 are paired swimming legs similar in both sexes. P5 is usually absent in females but is highly modified in the male for copulatory processes (modified from Bradford and Jillett 1974; Mauchline 1998).

transfer. The fifth leg is adorned with fine setae on the terminal position of the leg to aid in the transfer of the spermatophore (Ohtsuka and Huys 2001). Acartia hongi has rod like projections on the distal segment of the male’s left fifth leg with long setae on the first exopodal segment (Soh and Suh 2000).

Urosome

The abdominal region of copepod is the most posterior body segment of the copepod, commonly referred to as the urosome. Like the metasome, this abdominal region has one to five somites. However, unlike the cephalosome and the metasome, the urosome does not contain any jointed appendages. The somites can be further broken down into sub segments based on function. There is an anal segment, caudal ramus or furca and telson. The telson in most species becomes forked at the most posterior end creating the caudal ramous, which can also be referred to as the furca (Mauchline 1998).

Taxonomic Composition of South Floridian Waters

The anticylonic gyre of the North Atlantic Ocean creates a western boundary current along the eastern Florida coast known as the Florida Current; a subsidiary of the

Gulf Stream (Charney 1955). These two currents have similar physical characteristics and are often reported as the Gulf Stream. Western boundary currents are characterized as being narrow and fast moving; Gulf Stream has a velocity of 150 cm s -¹ in some areas

(Bowman 1971). Due to the rotation of the gyre, water is fed into this region from waters near the Bahamas, Cuba, Haiti, Dominican Republic, Jamaica, Puerto Rico and the Gulf of Mexico (Ulanski 2008). All the surrounding waters can contribute to the composition and abundance of copepods seen off of South Florida’s coast.

Bowman (1971) examined the distribution of calanoid copepods along the U.S.

Eastern Seaboard from Florida to North Carolina. Two species within the family

Calanidae were identified as the most abundant in pelagic waters, Undinula vulgaris and

Calanus minor. Eucalanidae was identified as the most abundant Family within the shelf and coastal regions associated with the Gulf Stream. In another study conducted by

Grice (1960), there were six abundant species Paracalanus crassirostris, Paraclanus parvus, Oithona nana, Acartia tonsa, Oithona brevicorni, and Oithina simplex.

However, the prevalence of certain species changes continuously due to the discovery of new species. Twenty-eight new species have been found in the Caribbean Sea since 1970

(Park 1970).

Youngbluth (1979) examined the copepod distribution in Puerto Rican waters and identified 69 copepod species, with only 9 species contributing to 75 % of the sample.

Dominate species were Undinula vulgaris, Paracalanus aculeatus, P. uasimodo,

Clausocalanus furatus, Temora turbinate, Acartia spinata, Oithona plumifera and O. setigera. The water temperature remained fairly constant over the course of a year, varying between 25.5 ˚C and 29.0 ˚C from January to August, respectively. Salinity ranged from 31.96 ‰ in the winter months to 36.04 ‰ in the summer. The increase of salinity during the summer can be attributed to the increase of daylight leading to increased evaporation and a change in physical environment. The alternation of abiotic factors can either increase, decrease, or not affect population densities.

Moore and Sander (1977) examined the copepod taxonomic composition in offshore waters near Barbados over a 28 month period from 1967 to 1969. A total of 141 copepod species were identifiable. Of the species, 92 were calanoids, 38 cyclopoids, and

9 harpacticoids. Twelve species accounted for 75 % of all copepods found: Farranula gracilis, Undinula vulgaruis, Oncaea venusta, Oncea mediterranea, Euchaeta marina,

Oithona nana, Calocalanus pavo, Oithona setigera, Oithona plumifera, Paracalanus aculeatus, Macrosetella gracilis, and Corycaeus speciosus. From the twelve species identified, the most common was Undinula vulgaris.

Physical Environment

Tropical Waters

Marine waters located within the tropical equatorial region (23.5 ˚ N and 23.5 ˚S) account for nearly half of the world’s oceans and one-third of all continental shelf waters.

These oceans are characterized by annual sea surface temperatures exceeding 20 ˚C, high evaporative environments, and heavy rainfall. The warm waters, in conjunction with the planet’s cooler latitudes, play a vital role in the global heat transfer and regulation of climate (Huskin et al. 2001; Turner et al. 1998).

The tropical coastal regions supply nearly 80% of global oceanic production while tropical oceanic waters have limited nutrients, such as nitrate, phosphate, and silica decreasing primary production (Huskin 2001; Karl et. al. 1996; Longhurst and Pauly

1987). The nutrient deficiency in tropical oceanic waters is due to a lack of thermocline variability. The thermocline hinders vertical mixing, which brings nutrients up from lower depths. The oligotrophic waters are then dominated by microflagellates and cyanobateria in the phytoplankton assemblages (Turner et al. 1998). However, tropical coastal regions have increased primary production due to enriched waters from upwelling events, seen along the western coast of continents, and land run-off (Twilley et al. 1992).

Low nutrients loads produce a reduction in homogenous environments, creating

37 greater biodiversity as a result of increased species competition (Braakhekke and

Hooftman 1999; Harpole 2007; Herbert et al. 2004). Species’ competition for niche space, food, and mating, while yielding high diversity levels, also affects the organisms’ physiological adaptations. Unique species’ adaptations, along with general body structure, produce smaller organisms as compared to higher latitudes. A decrease in species biomass is also attributed to tropical sea surface temperatures, decreasing generation time and increasing growth rates (Piontkovski and Landry 2003). Tropical waters have consistent, annual abiotic factors creating stable environments; a slight variation may have a significant impact on the community structure or dynamics of the copepod populations.

The Florida Current

The Florida Current, a subsidiary feature of the Gulf Stream, has similar physical properties of the well-known western boundary current (Figure 8). The Gulf Stream plays a significant role in the transport of heat northward, regulating global climate stability. However, it also affects zooplankton and larval transport. The interactions of the current with coastal waters influence local and distant population distribution and recruitment processes (Cha et al. 1994).

The Florida Current originates in the Gulf of Mexico composed of waters from the Loop and the Antilles currents (Cha et al. 1994: Gyrory et al. 2006). The Florida

Current flows through the Straits of Florida, a long narrow trough between Florida and

Bahamas banks, and moves northward over the continental shelf to Cape Hatteras, -75

ºW, 35 º N (Hurley et al. 1962; USCG 2008). The central axis of the Florida Current is located 25 km offshore of Miami and 80 km off shore of Key West (Cha et al. 1994;

Figure 8. Map of the Caribbean Sea. Arrows indicate major direction of major current systems that contribute to the Florida Current off the east coast of Florida (Ulanski 2008).

Molinari and Learman 1987). While the axis has a relative position, the width of the

Florida Current increases with latitude; approximately 80 km at 27 ˚N, 120 km at 29 ˚N and 145 km at 73 ˚W (USCG 2008).

However, the relative position of the Florida Current is variable and dependent on numerous factors, such as meanders, eddies, upwelling, and seasonal oscillations. When the Loop and Antilles currents converge, this may change the position of the Florida

Current which is dependent on the intensity of the two water masses. The convergence, along lateral meanders, still results in a north to northeast water flow (USCG 2008).

While northward flow is prevalent, there is a southward countercurrent along the continental shelf which transports about 29 x 106 m3 s-1 of water (Richardson 1985;

Soloviev et al. 2007). The mean transportation can also be measured in a Sverdrup (Sv),

1 million cm 3 s -1. The average transport for the Florida Current is 31.5 Sv (at 27˚N) and increases to 45.9 Sv at Cape Hatteras, 35˚N (Gyrory et al. 2006; USCG 2008) However, the dynamic nature of the current changes the average transport seasonally, annually and decadal. A seasonal difference as great as 10 Sv has been recorded with winter records of

25.4 Sv and summer records of 33.6 Sv (Niiler and Richardson 1973; Schott et al. 1988).

While the Florida Current transport shows variation with time, it may be influenced by current velocity. Near surface velocity, within 30 meters of the surface, measures 1 m s-1 and has reached 2.1 m s-1 . As depth increases, current velocity decreased to 0.7 m s-1 at 100 m and 0.5 m s-1 at 200 m. Differentiation is also seen horizontally where currents are strongest on the western edge and weaken further offshore. Variation is also seen seasonally, with surface velocity records of 1.8 m s-1 in

May and 0.9 m s-1 in February (USCG 2008).

The Florida Current, at Cape Hatteras, transitions into the Gulf Stream, traveling along the Eastern Seaboard and eventually colliding with the Labrador Current (Wishner and Allison 1986). The Gulf Stream is characterized by water temperatures, generally

80˚ F (27˚C), and a meandering flow (Ulanski 2008). The position of the stream shifts north, reaching higher latitudes, in the fall, while winter and spring see a decrease in the latitude position. The Florida Current also shows decade oscillation (USCG 2008).

Statement of Purpose

Copepods, dominant crustaceans in marine zooplankton communities, play a significant role in oceanic food web dynamics and ecosystem stability. Copepods as secondary producers provide a vital link in marine food webs, connecting primary producers, which convert solar power into usable energy, to tertiary consumers (Sommer and Stibor 2002). A disruption in copepod community structure, species diversity and population density due to oceanic and atmospheric conditions can influence food web dynamics.

Analyses of copepod density and diversity in tropical latitudes have focused on the surrounding waters of the Gulf of Mexico, Caribbean and Sargasso seas in the Atlantic

Ocean. However, the western boundary current of the Atlantic Ocean, the Gulf Stream and its subsidiary current the Florida Current, have limited data. A comprehensive study conducted by Owre and Foyo in 1967 wan an in-depth examination of copepod identification and community structure. The study illustrated a relative baseline for common species in the Gulf Stream, as seen today. The physical nature of the current, salinity, temperature, and velocity, in association with density and diversity have yet to be examined.

Copepod population density and species diversity were assessed at two locations

along the western edge of the Florida Current during February and July 2007. The two

site locations, Stations A and B, were chosen for their proximity to the Florida Current.

Station A showed a fluctuation of the most western boundary of the Florida Current

approaching the location the throughout the sampling periods. Station B was typically

located within the current, showing the greatest influence from the current’s physical

factors. A statistical comparison among location and month highlighted variations in

copepod community structure, species diversity, and population densities. The variations

were a direct result of the physical aspects of the Florida Current at each location.

II. Material and Methods

Study Site

Zooplankton samples were collected on a University National Oceanographic

Laboratory System (UNOLS) vessel, R/V F.G. Walton Smith, located at the Rosenstiel

School of Marine and Atmospheric Science (RSMAS) in Miami, Florida to compare

copepod community structure and population. Zooplankton samples examined in the

study were collected in the Atlantic Ocean at two locations, Station A and Station B, east-

northeast of Port Everglades, Florida located 6 miles and 12 miles offshore at -80.0º W,

26.11º N and -79.56ºW, 26.11ºN, respectively (Figure 9). Sample locations were chosen

due to their proximity to the Florida Current. Station A’s proximity to the Florida

Current was dependent on the month; the current shifts offshore during winter months

and inshore during summer. Station B showed a continuous position within the Florida

Current for both months. Samples were collected in February and July 2007 to assess and

compare population densities and species’ diversity.

Figure 9. Satellite image of zooplankton sampling stations located east of Port Everglades Florida, U.S.A. (Modified from Google Earth 2010).

Zooplankton Collection

Samples were collected using a 202-μm bongo net and 760-μm Tucker trawl net.

Both nets were chosen to cover a large spectrum of copepods sizes. The bongo net was used to capture smaller copepods, due to their under sampling and underestimation of diversity in previous studies (Hopcroft et al. 2001; Woodd-Walker et al. 2002) Flow meters were attached to each net to calculate water volume. The bongo net was towed for 15 minutes at 0-25 m depths while the Tucker trawl net was towed for 10 minutes at

0-25. All zooplankton samples were collected at night due the organisms diel vertical movement. The samples were preserved in 5% seawater buffered formalin in the field. and transferred to 70% ethanol in the laboratory for long-term preservation. A sub- sample was taken from the known sampled volumes, using a Folsom plankton splitter.

Zooplankton densities were calculated using individual counts, split ratios and water volumes; densities are represented as number of individuals m-3. Replicate counts were conducted to assure accurate results and to account for any anomalies found.

Physical Data Collection

The physical oceanographic data were collected simultaneously with zooplankton tows. The conductivity, temperature, and density meter was attached to each zooplankton net. Sea surface temperature (SST) (˚C), salinity (‰) and depth (m), were measured every 30 seconds during each tow using an Idronaut Ocean Seven 304 CTD. A shipboard acoustic Doppler current profiler (ADCP) collected water velocity and direction at both stations during each cruise.

Identification Analysis

Copepods were identified to the lowest identifiable taxonomic classification using published classification literature (Boltovoskoy 1999, Boxshall 1977, Ferrari and

Bowman 1980, Owre and Foyo 1967, Rose 1938) and an Olympus SZ X 7 dissecting microscope with an Olympus DF PL 1.5x lens. Genus was chosen as the most appropriate lowest taxonomic classification level for the study. Species levels were unable to be determined based on copepods sizes and specimen damage. Using genera and higher taxonomic levels is not uncommon in density and diversity studies, and they have been shown to be highly associated with species richness (Williams and Gaston 1994;

Williams et al. 1994; Roy et al. 1996; Woodd-Walker et al. 2002). An Internet Protocol

(IP) Capture 3.3 MPX Camera was used to photograph images. RINCON Simple Image

Analysis software was used to count and measure species-specific identification features.

Laboratory Analysis

Three subsamples were examined and enumerated for each sampling location, using a Folsom plankton splitter. The subsamples were split to contain at least 200 organisms. During identification analysis, abundance counts were recorded for each order, family, and genus. The abundance counts were transferred into density calculations reporting the number of organisms per cubic meter. Microcrustacean densities were calculated using the equation:

D = N x S V

45 where D is the density of organisms in numbers per cubic meter, N is the number of organisms, S is the split factor, and V is the volume of water filtered. The split factor was the fraction of the total sample used for analysis (NOAA 2003).

Diversity and Statistical Analysis

Two measures of biodiversity were calculated to gain a greater understanding of the sampled copepod populations, alpha (α) and beta (β) diversity. Alpha diversity referred to diversity within an individual habitat or ecosystem, mainly expressed as the number of taxa or species’ richness (S). Shannon-Weiner Index (H’) and Simpson’s

Index of Diversity (1-D) also measured individual habitat diversity. Beta diversity calculated the change in species’ diversity between habitats (Table 1).

The Shannon-Weiner Index measured the similarity of abundances of various species and assumed all species were represented at random selection. This index took into account species’ richness and equitability. However, the index was highly sensitive to the number of species and was greatly influenced by rare species, resulting in difficult interpretations. The formula to interpret data:

H’= - Σ pi ln (pi) i = 1

where S is the number of species and pi is the relative abundance of each species. High

H’ values indicated a diverse community. A qualitative comparison was used to determine how much more diverse one station’s community was to the other station.

Typical communities typically fall between 1.5 and 3.5. The Shannon Index checked

Table 1. Definition and interpretations of alpha and beta diversity in relation to various diversity measures and indices used to examine zooplankton samples (modified from DeTroch et al. 2001).

Diversity Definitions Interpretation in Present Study

Alpha Diversity (α)

(S) Species Richness S is the number of species within a given area, inventory diversity

(H’) Shannon-Weiner H’ is the measurement of the For individual habitats, Index similarity of random selection Stations A and B

(1-D) Simpson’s Index of 1-D is the measurement of Diversity similarity of random selection of organisms that are not of the same species

Beta Diversity (β)

SØrensen’s Similarity The comparison of species The change in species Index diversity between different diversity between Stations A ecosystems or along an and B in comparison with the environmental gradient Florida Current

47 species diversity while Simpson’s Index was used to measure the relative abundance of species at each station (Beaugrand et al. 2002).

The Simpson’s Index (D) measure of diversity assumed two selected organisms were chosen at random and did not belong to the same species and was less sensitive to species’ richness. ∑ n(n-1) D = N(N-1)

where n is the total number of organisms of a specific species and N is the total number of organisms within a sample. The Simpson’s Index (D) calculation ranges from 0 to 1.

Zero indicated infinite diversity while one showed homogeneity. However, Simpson’s

Index can be translated into and easier interpretation of the data, Simpson’s Index of

Diversity (1-D). This index showed that as diversity increases the value will increase towards 1.

Beta diversity compared species’ diversity between different ecosystems or along an environmental divide. The environmental divide in the samples sites was the Florida

Current. The diversity was determined by the number of taxa unique to each ecosystem.

Beta diversity can be interpreted using SØrensen’s Similarity Index, calculating the overlap between communities. 2c β = S1 + S2

where c is the number of species shared by the two locations, S1 and S2 are the respectful populations from each station. The similarity index measurements range from 0 to 1, 0

indicating no species overlap between communities and 1 showing the same species were

in both communities.

Statistical analysis, performed with SYSTAT (Statistical and Graphical

Software Package) software (Systat Software, Inc., Chicago, IL, USA) examined the

differences of population densities for all months and locations, using the equation,

n2 (n2 + 1) n2 U = n1n2 + 2 - Σ Ri i = n1 +1

where U is the Mann-Whintney U test result, n1 is the sample size of one population, n2 is

the sample size of a second population, and Ri is the rank of the sample size. Mann-

Whitney U, a non-parametric test, was used to assess and determine statistical

significance between population means for five different comparisons; Stations A and B

in February, Stations A and B in July, Station A in February and July, Station B in

February and July, and Station B in February and Station A in July. This test made no

assumption about the distribution and was used due to zooplankton patchiness. All

Mann-Whitney U tests rendered significant findings if the p values were less than 0.05.

III. Results

Population density and species’ diversity were analyzed by studying the

community structure and overall composition in collected samples. The goal of the

analysis was to determine if there was a significant difference between the copepod

population densities at two different locations among different taxonomic levels:

order,and genera. An analysis of the physical data collected from the two locations

49 during different months were examined to determine if there was a significant seasonal variation that could attribute to the changes in copepod population density and diversity.

Copepod Composition and Density Data

In 8 samples a total of 6,489 copepods were identified with a representatives of 20 genera, 18 families and 4 orders of copepods; 13 genera of Calanoida, 1 genus of

Cyclopoida, 2 genera of Harpacticoida, and 4 genera of Poecilostomatoida. Calanus spp., Undinula spp., Candacia spp., Eucalanus spp., Euchaeta spp, Temora spp., Oithona spp., Corycaeus spp., and Oncaea spp. were found at all stations and months in the bongo net. The bongo net collected 9 genera found at only one station and month; Centropages spp., Lucicutia spp., Bathycalanus spp., Pontella spp., Pontellina spp., Rhincalanus spp.,

Clytemnestra spp., Microsetella spp., and Copilia spp. Calanus spp., Undinula spp.,

Euchaeta spp., Rhincalanus spp., and Copilia spp., were found at all stations and months in the Tucker trawl. The Tucker trawl collected 2 genera found only at one station and month; Microsetella spp. and Oncaea spp. All species’ identifications were found in

Appendix A.

Bongo net

The overall population density for each sample showed an increase in copepod densities at Station A in February as compared to Station B (Figure 10). July showed a decrease at Station A as compared to Station B (Figure 11) The highest population density was in the order Calanoida, accounting for 56% of total copepod density collected in the bongo net, followed by Poecilostomatoida (40%), Cyclopoida (3%), and

Harpactacoida (<1%) for all months and locations combined. Individual sampling month and location showed the same hierarchy of orders (Figures 12 and 13). Calanus spp.

February 2007 using the 2007 February

oppler current profile (ADCP) profile oppler current current

coustic D coustic

25 m) transposed m) 25 a on

density distribution of copepod at Stations B at and A distribution density copepod of

waters (0 waters

overall

surface surface

Mean Mean

in in

. .

Figure Figure net bongo from (modified USCGvelocity 2008)

2007 using 2007 the

July

coustic Doppler current profile (ADCP) profile current current Doppler coustic

25 m) transposed m) 25 a on

density distribution of copepod at Stations B at and A distribution density copepod of

all all

waters (0 waters

over

surface surface

Mean Mean

in in

. .

Figure Figure net bongo from (modified USCGvelocity 2008)

the the

February 2007 using 2007 February

coustic Doppler current profile (ADCP) profile current current Doppler coustic

25 m) transposed m) 25 a on

waters (0 waters

surface surface

. Mean density distribution of copepod orders at Stations B at and A density orders Mean . distributioncopepod of

Figure Figure in net bongo from (modified USCGvelocity 2008)

2007 using 2007 the

in July in

coustic Doppler current profile (ADCP) profile current Doppler coustic

25 m) transposed m) 25 on

waters (0 waters

surface surface

. Mean density distribution of copepod orders at Stations B at and A density orders Mean . distributioncopepod of

net in net

igure igure

F bongo velocity USCG (modified 2008) from current

54 and Undinula spp. dominated the order Calanoida; other numerically important calanoids were Euchaeta spp. and Temora spp. Poecilostomatoida showed high incidences of

Corycaeus spp. and Oncaea spp. Cyclopoida was represented by only one genus, Oithona spp. which was present at all locations and months. Rare species, Clytemnestra spp. and

Microsetella spp. were present at one station during one month.

The four most abundant species, Calanus spp., Undinula spp., Corycaeus spp. and

Oncaea spp., accounted for 85% of the total copepod density collected in the bongo net for all months and stations. Corycaeus spp. represented a total of 27%, followed by

Undinula spp. (23%), Calanus spp. (22%), and Oncaea spp. (13%). The remaining 16 genera accounted for 15 % of the total copepod density (Table 2). The four most abundant genera, percent of total density, varied dependent on station and month (Figure

14 and 15). They accounted for 90% of the sample in February at Station A, 76% of the sample in February at Station B, 91% of the sample in July at Station A, and 83% of the sample in July at Station B. However, the dominant genus and its percent contribution to the sample varied across month and station. Undinula was the dominate genus in

February at Station A comprising 29% of the sample. Calanus was the dominate genus in February at Station B comprising 20% of the sample. Corycaeus was the dominate genus in July at Stations A and B comprising 39 % and 42 % of the sample, respectively.

Genera composition for all stations and months are seen in Figure 16.

Tucker trawl

The overall population density for each sample showed an increase in copepod densities at Station B in both February and July as compared to Station A (Figure 17 and

18 )The Tucker trawls showed the same hierarchy in copepod orders. Calanoida

Table 2. Copepod genus mean densities (ρ) (organisms m-3) and percent composition (%) for Stations A and B in February and July 2007. Zooplankton samples were collected with a bongo 202-μm net.

Station Station A Station B Station A Station B Month February February July July Depth (m) 12.60 9.85 15.64 12.58 Temp (ºC) 25.0 25.5 28.9 29.2 Salinity (‰) 36.28 36.34 36.03 36.18 ρ % ρ % ρ % ρ % Calanoida Calanidae Calanus 58.96 25 31.16 20 30.07 20 59.71 22 Undinula 68.85 29 29.13 19 38.40 26 48.41 18 Candaciidae Candacia 2.45 1 1.01 1 0.25 0.2 3.39 1 Centropagidea Centropages - - - - 0.75 0.5 - - Eucalanidae Eucalanus 0.73 0.3 2.37 2 0.25 0.2 0.11 0.04 Euchaetidae Euchaeta 8.35 4 5.75 4 0.76 0.5 24.67 9 Lucicutiidae Lucicutia 0.24 0.1 ------Megacalanidae Bathycalanus - - 1.35 - - - - - Pontellidae Pontella 0.24 0.1 ------Pontellina 0.24 0.1 ------Rhincalanidae Rhincalanus - - - - 0.25 0.2 - - Scolecitrichidea Scolecithrix 0.98 0.4 2.37 2 - - 10.73 4 Temoridea Temora 4.66 2 6.43 4 4.04 3 4.52 2 Total 145.75 62 79.60 52 74.80 51 151.57 56

Cyclopoida Oithonidae Oithona 5.58 2 12.87 8 4.80 3 0.75 0.3 Total 5.58 2 12.87 8 4.80 3 0.75 0.3

Harpacticoida Clytemnestridae Clytemnestra - - 0.33 0.2 - - - - Ectinosomatidae Microsetella - - - - 0.25 0.2 - - Total - - 0.33 0.2 0.25 0.2 - -

Poecilostomatoida Corycaeidae Corycaeus 19.16 8 28.11 18 56.85 39 112.83 42 Oncaeidae Oncaea 66.09 28 29.81 19 8.59 6 3.38 1 Sapphirinidae Copilia - - 1.01 1 - - - - Sapphirina - - 0.33 0.2 0.75 0.5 0.18 0.07 Total 85.25 36 59.28 39 66.20 45 116.40 43

February 2007 February2007

at Stations B at and A

coustic Doppler current profile current (ADCP) Doppler coustic

)a on transposed

25 m 25

the top four dominant genera genera dominant four top the

waters(0

surface surface

bongo net in net bongo

Mean density density Mean distribution of

. .

Figure Figure using the velocity USCG (modified 2008) from current

in July in

coustic Doppler current profile current Doppler coustic

at Stations B at and A

25 25 on transposed m)

the top four dominant genera genera dominant four top the

m USCG m 2008)

waters(0

surface surface

Mean density density Mean distribution of

. .

e e

Figur in using 2007 net bongo the velocity fro (modified current (ADCP)

Figure 16. Average genera population densities (organism m -3 ) captured in the bongo net for Stations A and B in February and July 2007.

February 2007 using the 2007 February

coustic Doppler current profile (ADCP) current profile current (ADCP) Doppler coustic current

25 m) transposed m) 25 a on

density distribution of copepod at Stations B at and A distribution density copepod of

waters (0 waters

overall

surface surface

in in

Mean Mean

. .

Figure Figure trawl Tucker from (modified USCGvelocity 2008)

2007 using 2007 the

July

coustic Doppler current profile profile (ADCP) Doppler coustic current

25 m) transposed m) 25 a on

density distribution of copepod at Stations B at and A distribution density copepod of

waters (0 waters

overall

surface surface

in in

Mean Mean

. .

Figure Figure trawl Tucker velocity USCG (modified 2008) from current

accounted for 97% of total copepod density in the Tucker trawl, followed by

Poecilostomatoida (2%) and Harpacticoida (<1%) in all months and stations combined individually (Figure 19 and 20). However, Cyclopoida was not represented in the samples. Calanoida showed high incidences of Euchaeta spp. and Undinula spp. in all stations and months. Other Calanoida copepods that were numerically important included Candacia spp., Eucalanus spp., and Rhincalanus spp. Rare species, represented at one sampling station with one individual collected, were limited to order Harpacticoida with Microsetella spp.

The four most abundant species, Eucalanus spp., Undinula spp., Rhincalanus spp. and Euchaeta spp., accounted for 91% of the total copepod density collected in Tucker trawls for both months and stations. Undinula spp. represented a total of 42%, followed by Euchaeta spp. (37%), Eucalanus spp. (8%), and Rhincalanus spp. (4%). The remaining 11 genera accounted for 9 % of the total copepod density (Table 3). The four most abundant genera, percent of total density, varied dependent on station and month

(Figures 21 and 22). They accounted for 90% of the sample in February at Station A,

92% of the sample in February at Station B, 83% of the sample in July at Station A, and

97% of the sample in July at Station B. The dominate genus for all samples was

Undinula. This genus accounted for 50% of the sample in February at Station A, 40% of the sample in February at Station B, 51% of the sample in July Station A, and 57% of the sample in July Station B. Genera composition for all stations and months are seen in

Figure 23.

Tucker Tucker

February 2007 using the 2007 February

coustic Doppler current profile (ADCP) current velocity profile current (ADCP) current Doppler coustic

25 m) transposed on on transposed m) 25

waters (0 waters

Mean density distribution of copepod orders at Stations B at and A density orders Mean distributioncopepod of

surface surface

n n

Figure Figure trawl USCG 2008) from (modified

in in

Tucker trawl Tucker

February 2007 using the 2007 February

in in

coustic Doppler current profile (ADCP) current velocity profile USCG (modified current from (ADCP) current Doppler coustic

25 m) 25 a on transposed

Mean density distribution of copepod orders at Stations at and A density B orders Mean distribution copepod of

aters(0

Figure Figure surface 2008)

Table 3. Copepod genus mean densities (ρ) (organisms m-3) and percent composition (%) for Stations A and B in February and July 2007. Zooplankton samples were collected with a Tucker 760-μm trawl.

Station Station A Station B Station A Station B Month February February July July Depth (m) 22.21 24.28 24.36 23.25 Temp (ºC) 24.9 25.3 28.7 29.2 Salinity (‰) 36.36 36.33 36.07 36.24 ρ % ρ % ρ % ρ % Calanoida Calanidae Calanus 0.18 5 1.55 2 0.11 3 0.11 0.8 Undinula 1.63 50 37.43 40 1.82 51 8.08 57 Candaciidae Candacia 0.10 3 4.19 4 0.07 2 0.09 0.6 Eucalanidae Eucalanus 0.05 2 9.23 10 - - 0.03 0.2 Euchaetidae Euchaeta 1.04 32 34.91 37 1.11 31 5.71 40 Rhincalanidae Rhincalanus 0.19 6 4.43 5 0.03 1 0.01 0.07 Total 3.19 98 91.74 98 3.14 88 14.03 99

Harpacticoida Ectinosomatidae Microsetells 0.004 0.1 ------Total 0.004 0.1 ------

Poecilostomatoida Corycaeidae Corycaeus 0.004 0.1 0.59 0.6 - - Oncaeidae Oncaea - - - 0.03 0.2 Sapphirinidae Copilia 0.060 2 1.19 1 0.30 8 0.1 0.7 Sapphirina - 0.35 0.4 0.11 3 0.07 0.5 Total 0.064 2 2.13 2 0.41 11 0.2 1

coustic coustic

at Stations B at and A

25 m) transposed m) 25 a on

waters (0 waters

surface

in in

the top four dominant genera genera dominant four top the

current velocity USCG (modified 2008) from current

Tuckler trawl Tuckler

Mean density density Mean distribution of

. .

Figure Figure using the 2007 February profile (ADCP) current Doppler

July

current current

cousticDoppler

at Stations B at and A

25 m) transposed on on transposed m) 25 a

waters (0 waters

the top four dominant genera genera dominant four top the

surface surface

in in

Tucker trawl Tucker

Mean density density Mean distribution of

. .

Figure Figure using 2007 the USCG velocity from (modified current (ADCP) 2008) profile

Figure 23. Average genera population densities (organism m -3 ) captured in the Tucker trawl for Stations A and B in February and July 2007.

Diversity Data

Alpha Diversity

Species richness (S) denoted the overall number of genera counted in each sample

(Table 4). The bongo net captured an average of 320. 3 copepods in February at Station

A, 150 copepods in February at Station B, 193 copepods in July at Station A, and 475.6 copepods in July at Station B. The Tucker trawl had 236.3 copepods in February at

Station A, 252 copepods in February at Station B, 131 copepods in July at Station A, and

262 copepods in July at Station B.

The Shannon Index (H’) indicated the similarity of various species within each sample and assumed all species are represented at random selection (Table 4). The

Shannon Index, for the bongo net was H’=2.703 for February at Station A, H’= 2.742 for

February at Station B, H’= 1.747 for July at Station A, and H’= 1.839 for July at Station

B. The Shannon Index, for the Tucker trawl was H’=1.775 February at Station A, H’=

1.921 February at Station B, H’= 1.804 July at Station A, and H’= 1.232 for July at

Station B.

Simpson’s Index of Diversity (1-D) was used to measure the relative abundance of species at each station (Table 4) (Beaugrand et al. 2002). The Simpson’s Index of

Diversity for the bongo net was 1-D = 0.769 for February at Station A, 1-D = 0.821 for

February at Station B, 1-D = 0.734 for at July at Station A, 1-D = 0.743 for July at

Station B. The Simpson’s Index of Diversity for the Tucker trawl was 1-D = 0.616 for

February at Station A, 1-D = 0.669 for February at Station B, 1-D = 0.639 for July at

Station A, 1-D = 0.573 for July at Station A.

Table 4. Alpha diversity analysis. Used to determine different levels of diversity of individual habitats (Stations A and B), months (February and July 2007) and equipment type (bongo 202-μm net and Tucker 760-μm trawl). Three different diversity measures were used on each zooplankton sample; species richness, Shannon Index, and Simpson’s Index of Diversity

Month Station Species Shannon-Weiner Simpson’s Index Richness(S) Index (H’) of Diversity (1-D) Bongo net Station A 320 2.703 0.769 February Station B 150 2.742 0.821 Station A 193 1.747 0.734 July Station B 477 1.839 0.743 Tucker trawl Station A 236 1.775 0.616 February Station B 252 1.921 0.669 Station A 131 1.804 0.639 July Station B 262 1.232 0.573

Beta Diversity

SØrensen’s Similarity Index (β) was used to compare species diversity between different ecosystems or along an environmental divide. The different environments compared where, February Station A and B, July Station A and B, Station A February and July, and Station B February and July for both the bongo net and Tucker Trawl

(Table 5). β = 0.740 and β = 0.833, comparing Station A and B in February and July respectively in the bongo net. β = 0.880 and β = 0.875, comparing Station A and B in

February and July respectively in the Tucker trawl. β = 0.692 and β = 0.888, comparing

Station A during February and July and Station B during February and July respectively in the bongo net. β = 0.750 and β = 0.770, comparing Station A during February and July and Station B during February and July respectively in the Tucker trawl.

Oceanographic Data

CTD Data The Idronaut Ocean Seven 304 CTD probe collected sea surface temperatures

(˚C), salinity (‰), and depth (m) readings every 30 seconds during each zooplankton tow. A summary of average sea surface temperatures for each zooplankton sample are reported in Table 6. The sea surface temperature ranged from 24.9 ºC to 25.5 ºC in

February and 28.7 ºC to 29.2ºC in July. The data showed no significant difference between temperatures among stations of the same month and compared to other months.

The CTD data also collected salinity reading ranging from 36.28 ‰ to 36.36 ‰ in

February and 36.0.3‰ to 36.24 ‰ between stations within the same month or seasonally.

There was a slight decrease from winter to summer months. Summer months

Table 5. SØrensen’s Similarity Index. Stations A and B represent the two ecosystems analyzed while the Florida Current acted as the environmental gradient. Both net types were assessed.

SØrensen’s Similarity Bongo net Tucker trawl Index

Stations A and B in 0.740 0.880 February

Stations A and B in 0.833 0.875 July

Station A in February 0.692 0.750 and July

Station B in February 0.888 0.770 and July

Table 6. CTD data. Sea surface temperature, salinity and depth for all zooplankton samples collected at Stations A and B for February and July 2007.

Month Station Tow Depth (m) Temperature (˚C) Salinity (‰) Bongo net February Station A 12.36 25.0 36.28 Station B 9.85 25.5 36.34 July Station A 15.64 28.8 36.03 Station B 12.58 29.2 36.18 Tucker trawl February Station A 22.21 24.9 36.36 Station B 24.28 25.3 36.33 July Station A 24.56 28.7 36.07 Station B 23.25 29.2 36.24

73 are characterized by an increase in precipitation, which decreases salinity with the addition of freshwater. A summary of the average salinities for each zooplankton sampled are reported in Table 6.

Fluorescence data, which measured photosynthetic activity, provided information on the level phytoplankton primary productivity at each location and month (Figures 24 and 25) (Falkowski and Kiefer 1985). February had five times greater amount of primary production as compared to July (USCG 2008). The increase of fluorescence in February was an indication of a phytoplankton bloom which would likely be followed by a zooplankton bloom in March. This was confirmed with an increase in zooplankton abundance, though not significant (USCG 2008).

ADCP Data

The ADCP data provided information regarding current velocity and direction, giving insight to the location of different water masses. The data followed the movements of the Florida Current over the sampling period of February and July. The general location of the current was an approximation due to the boundaries having wide distributions and the constant dynamic nature of the stream (USCG 2008). In February the current was less centralized over the sampling locations and flowed northward.

Station A, located shoreward, did not show direct presence of the Florida Current but a strong jet was found at approximately at 100 meters depth. The current velocity, at sampling depth, 25 meters, was a 600 mm s -1 and 1000 mm s -1at 100 meters, where the jet of water from the Florida Current was located. The current was present at Station B, approximately 12 miles offshore, from 0 – 100 meters depth, and flowing at approximately 1100 mm s -1 (Figure 26).

Figure 24. Sea surface temperature, density and fluorescence data results for Stations A and B in February 2007 (modified from USCG 2008).

Figure 25. Sea surface temperature, density and fluorescence data results for Stations A and B in July 2007 (modified from USCG 2008).

ruary 2007 2007 at ruary

08).

USCG20

(modified from (modified

. Acoustic Doppler current profile (ADCP) current velocity results velocity profile Feb (ADCP)current Doppler for Acoustic . current

Figure Figure B Stationsand A

The ADCP data for July showed a more intensified current at both Stations A and

B. The E-W vertical transect showed the current’s migration into coastal waters. Station

A, approximately 6 miles offshore, was in the Florida Current to a depth of 100 meters.

Station A showed two distinct water masses, the Florida Current from 0 - 100 m and coastal waters from 100 – 200 m. At Station B the Florida Current reached 150 m depth.

There was a distinct decrease in current velocity from 0-100 m to 100 – 150m. The upper velocity of the current is 1650 mm s -1 and it was reduced to 1100 mm s -1 at depth.

Station A did not show a distinct differentiation in current velocity but rather a consistent velocity of 1200 mm s -1 (Figure 27).

The ADCP data also recorded current direction. February samples showed both

Stations A and B with a north-northeast flow along the E-W transect at sampling depth

25 m (Figure 28). As depth increased, the current direction became more pronounced northward at 100 meters. A monthly comparison showed an anomaly in July. Inshore waters near the coastline, west of Station A, illustrated a reverse flow southward. Water at Stations A and B in July illustrated a pronounced northward movement of the current, as compared to the northeast flow in February (Figure 29).

Density Statistical Analysis

Mann-Whitney U, a non-parametric test, was used to assess and determine statistical significance between population means(overall, order, and genera densities for both the bongo net and tucker trawl for five different comparisons; Stations A and B in

February, Stations A and B in July, Station A in February and July, Station B in February and July, and Station B in February and Station A in July. The western edge of the

Florida Current was located at Station B in February and Station A in July. The

G 2008) G

USc

Acoustic Doppler current profile (ADCP) current velocity results velocity A profile Stations July (ADCP)at 2007 current Doppler for Acoustic current

. .

Figure Figure from B (modified and

007 at Stations at 007 and A

USCG2008)

Acoustic Doppler current profile (ADCP) current direction for February 2 direction for profile February (ADCP)current Doppler Acoustic current

. .

modified from from modified

(

Figure Figure B

USCG2008)

Acoustic Doppler current profile (ADCP) current direction for July 2007 at Stations A and and direction for Stations profile July at 2007 (ADCP)current Doppler A Acoustic current

. .

Figure Figure from B(modified

81 comparison between these two samples was used to see if there were any deviations in the densities when the physical environment was very similar. The Mann-Whitney U results for the overall copepod densities in the bongo net showed statistical significance between Stations A and B in February, Stations A and B in July, Stations A in February and July, Stations B in February and July (U = 9.000, df = 1, p = 0.046; U = 0.000, df =

1, p = 0.05; U = 9.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.046, respectively) .

There was no statistical significance between Station B in February and Station A in July

(U = 2.000, df = 1, p = 0.268) (Table 7).The results for the overall copepod densities in the Tucker trawl showed statistical significance between Stations A and B in February,

Stations A and B in July, Station B in February and July, and Station B in February and

Station A in July (U = 0.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.05: U = 9.000, df

= 1, p = 0.05; U = 9.000, df = 1, 0.050 respectively). There was no statistical significance between Station A in February and July as seen in Table 7.

The Mann-Whitney U results were used to determine the statistical significance of each order in relation to the variation among stations in the same month, stations between months and Station B in February and Station A in July (Table 8). In looking at the bongo net, Calanoida showed statistical significance between Stations A and B in

February, Stations A and B in July, Station A in February and July, and Station B in

February and July (U = 9.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.05; U = 9.000, df

= 1, p = 0.05; U = 0.000, df = 1, p = 0.05, respectively). Cyclopoida showed statistical significance between Stations A and B in July and Station B in February and July (U =

0.000, df =1, p = 0.043; U = 0.000, df = 1, p = 0.046 respectively). There was no

Table 7. Mann-Whitney U results of overall copepod densities. Comparisons were analyzed based on station in the same month and against station in different months. Analysis was based on zooplankton collection in the bongo net and Tucker trawl. Italics represent statistical significance among densities.

Copepod Density Comparison U df p-value Bongo net Stations A and B in February 9.000 1 0.046

Stations A and B in July 0.000 1 0.050

Station A in February and July 9.000 1 0.050

Station B in February and July 0.000 1 0.046

Station B in February and Station A in July 2.000 1 0.268

Tucker trawl Stations A and B in February 0.000 1 0.050

Stations A and B in July 0.000 1 0.050

Station A in February and July 2.000 1 0.275

Station B in February and July 9.000 1 0.050

Station B in February 9.000 1 0.050 and Station A in July

Copepod Orders U df p-value Stations A and B in February Calanoida 9.000 1 0.050 Cyclopoida 6.000 1 0.513 Harpacticoida 3.000 1 0.317 Poecilostomatoida 7.000 1 0.275 Stations A and B in July Calanoida 0.000 1 0.050 Cyclopoida 9.000 1 0.043 Harpacticoida 6.000 1 0.317 Poecilostomatoida 0.000 1 0.050 Station A in February and July Calanoida 9.000 1 0.050 Cyclopoida 6.000 1 0.507 Harpacticoida 3.000 1 0.317 Poecilostomatoida 9.000 1 0.050 Station B in February and July Calanoida 0.000 1 0.050 Cyclopoida 9.000 1 0.046 Harpacticoida 6.000 1 0.317 Poecilostomatoida 0.000 1 0.050 Station B in February and Station A in July Calanoida 4.000 1 0.827 Cyclopoida 3.000 1 0.507 Harpacticoida 5.000 1 0.796 Poecilostomatoida 3.000 1 0.513

significant difference found between Stations A and B in July and Station A in February and July. Harpacticoida did not show an statistical significance in any comparisons.

Poecilostomatoida showed statistical significance between Stations A and B in July,

Station A in February and July, and Station B in February and July (U = 0.000, df = 1, p

= 0.05; U = 9.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.05 respectively). There was not statistical significance found between Stations A and B in February. All orders in the bongo net did not show any statistical significance between Station B in February and

Station an in July.

The Tucker trawl showed variation from the bongo net (Table 9). Calanoida showed statistical significance between Stations A and B in February, Stations A and B in July,

Station B in February and July, and Station B in February and Station A in July (U =

0.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.05; U = 9.000, df = 1, p = 0.05; U =

9.000, df = 1, p = 0.05 respectively). There was no statistical significance between

Station A in February and July. Cyclopoida was not capture in the Tucker trawl and thus could not be analyzed. Harpacticoida did not show any statistical significance when comparing any stations or months. Poecilostomatoida showed statistical significance between Stations A and B in February, Stations A and B in July, Station A in February and July, Station B in February and July, and Station B in February and Station A in July

(U =0.000, df = 1, p = 0.046; U = 9.000, df = 1, p = 0.046; U = 0.000, df = 1, p = 0.046;

U = 9.000, df = 1, p = 0.046; U = 9.000, df = 1, p = 0.05 respectively).

Further analysis looked at all the genera of each sample for all comparison in both the bongo net and Tucker trawl. Additional analysis looked at the four most abundant genera, comprising over 50 % of each sample in the bongo net (Table 10). The bongo net

Table 9. Mann-Whitney U results of copepod order densities. Comparisons were analyzed based on stations in the same month and against the same station in different months. Analysis was based on zooplankton collection in the Tucker trawl. Italics represent statistical significance among densities.

Copepod Orders U df p-value Stations A and B in February Calanoida 0.000 1 0.050 Harpacticoida 6.000 1 0.317 Poecilostomatoida 0.000 1 0.046 Stations A and B in July Calanoida 0.000 1 0.050 Harpacticoida 4.500 1 1.000 Poecilostomatoida 9.000 1 0.046 Station A in February and July Calanoida 5.000 1 0.827 Harpacticoida 6.000 1 0.317 Poecilostomatoida 0.000 1 0.046 Station B in February and July Calanoida 9.000 1 0.050 Harpacticoida 4.500 1 1.000 Poecilostomatoida 9.000 1 0.046 Station B in February and Station A in July Calanoida 9.000 1 0.050 Harpacticoida 4.500 1 1.000 Poecilostomatoida 9.000 1 0.050

Copepod Genera U df p-value Stations A and B in February Calanus 9.000 1 0.046 Undinula 9.000 1 0.050 Corycaeus 0.000 1 0.034 Oncaea 9.000 1 0.050 Stations A and B in July Calanus 0.000 1 0.050 Undinula 2.000 1 0.275 Corycaeus 0.000 1 0.050 Oncaea 9.000 1 0.050 Station A in February and July Calanus 9.000 1 0.046 Undinula 8.000 1 0.127 Corycaeus 0.000 1 0.037 Oncaea 9.000 1 0.050 Station B in February and July Calanus 0.000 1 0.050 Undinula 0.000 1 0.050 Corycaeus 0.000 1 0.046 Oncaea 9.000 1 0.050 Station B in February and Station A in July Calanus 5.000 1 0.827 Undinula 0.000 1 0.050 Corycaeus 0.000 1 0.046 Oncaea 8.000 1 0.127

87 showed dominance of Calanus spp., Undinula spp., Corycaeus spp., and Oncaea spp.

Calanus spp. showed statistical significance between Stations A and B in February,

Stations A and B in July, Station A in February and July, and Station B in February and

July (U = 0.000, df =1, p = 0.046; U = 0.000, df = 1, p = 0.05; U = 9.000, df = 1, p =

0.046; U = 0.000, df = 1, p = 0.05 respectively). There was no statistical significance between Station B in February and Station A in July. Undinula spp. showed statistical significance between Stations A and B in February, Station B in February and July, and

Station B in February and Station A in July (U = 9.000, df = 1, p = 0.05; U = 0.000, df =

1, p = 0.05; U = 0.000, df = 1, p = 0.05 respectively). There was no statistical significance between Stations A and B in July and Station A in February and July. Corycaeus spp. showed a statistical significant between Stations A and B in February, Stations A and B in July, Station A in February and July, Station B in February and July, and Station B in

February and Station A in July (U = 0.000, df = 1, p = 0.034; U = 0.000, df = 1, p = 0.05,

U = 0.000, df = 1, p = 0.037; U = 0.000, df = 1, p = 0.046; U = 0.000, df = 1, p = 0.046 respectively). Oncaea spp. showed statistical difference between Stations A and B in

February, Stations A and B in July, Station A in February and July, and Station B in

February and July (U = 9.000, df =1, p = 0.05; U = 9.000, df = 1, p = 0.05; U = 9.000, df

= 1, p = 0.05; U = 9.000, df = 1, p = 0.05 respectively). There was no statistical significance between Station B in February and Station A in July.

Further analysis looked at all the genera of each sample for all comparison in both the Tucker trawl. Analysis looked at the four most abundant genera, comprising over 90

% of each sample for the Tucker trawl (Table 11). The four most abundant genera were

Eucalanus spp., Euchaeta spp., Rhincalanus spp., and Undinula spp. Eucalanus spp.

Copepod Genera U df p-value Stations A and B in February Eucalanus 0.000 1 0.050 Euchaeta 0.000 1 0.050 Rhincalanus 0.000 1 0.050 Undinula 0.000 1 0.050 Stations A and B in July Eucalanus 9.000 1 0.034 Euchaeta 0.000 1 0.050 Rhincalanus 6.000 1 0.456 Undinula 0.000 1 0.050 Station A in February and July Eucalanus 9.000 1 0.034 Euchaeta 3.000 1 0.513 Rhincalanus 9.000 1 0.046 Undinula 1.000 1 0.127 Station B in February and July Eucalanus 9.000 1 0.046 Euchaeta 9.000 1 0.050 Rhincalanus 9.000 1 0.046 Undinula 9.000 1 0.050 Station B in February and Station A in July Eucalanus 9.000 1 0.037 Euchaeta 9.000 1 0.050 Rhincalanus 9.000 1 0.046 Undinula 9.000 1 0.050

showed statistical significance between Stations A and B in February, Stations A and B

in July, Station A in February and July, Station B in February and July, and Station B in

February and Station A in July (U = 0.000, df = 1, p = 0.05; U = 9.000, df = 1, p = 0.034;

U = 9.000, df = 1, p = 0.034; U = 9.000, df = 1, p = 0.046; U = 9.000, df = 1, p = 0.037

respectively). Euchaeta spp. showed statistical significance between Stations A and B in

February, Stations A and B in July, Station B in February and July, and Station B in

February and Station A and July (U = 0.000, df = 1, p = 0.05; U = 0.000, df = 1, p = 0.05;

U = 9.000, df = 1, p = 0.05; U = 9.000, df = 1, p = 0.05 respectively). There was no

statistical significance between Station A in February and July. Rhincalanus spp. showed

statistical significance between Stations A and B in February, Station A in February and

July, Station B in February and July, and Station B in February and Station A in July (U

= 0.000, df = 1, p = 0.05; U = 9.000, df = 1, p = 0.046; U = 9.000, df = 1, p = 0.046; U =

9.000, df = 1, p = 0.046). Rhincalanus did not show any statistical significance between

Stations A and B in July. Undinula spp. showed statistical significance between Stations

A and B in February, Stations A and B in July, Station B in February and July, and

Station B in February and Station A in July ( U = 0.000, df = 1, p = 0.05; U = 0.000, df =

1, p = 0.05; U = 9.000, df = 1, p = 0.05; U = 9.000, df = 1, p = 0.05 respectively).

IV. Discussion

The presence of the Florida Current affected the copepod population densities and

genera diversity, which can lead to a distribution in energy transfer in marine food web

dynamics and ecosystem stability. It was assumed that the stations located within the

current did not vary significantly from one another in population structure, density or

diversity. The stations located outside the current were then assumed to show variation

90 when compared to those in the Florida Current. The western edge of the current acted as a barrier separating coastal waters from the Florida Current and oceanic waters. The horizontal movement of the current inshore and offshore transported zooplankton aggregations, increasing or decreasing the population densities at the two locations.

However, other factors can affect distribution, density and species diversity, such as gear selectivity and abiotic factors; sea surface temperature, salinity, and fluorescence.

Gear Selectivity

A 202 μm and a 760 μm mesh nets were deployed to collect zooplankton samples, limiting bias of only using one mesh size which captured a specific size range of copepods. The use of both nets allowed for an array of copepods to be collected, allowing for a more in-depth analysis of population dynamics. From the study, there were greater populations densities found in the bongo net as compared to the Tucker trawl. The bongo net collected copepods that ranged in size from 0.7 to 2.5 mm, for all of the orders. However, there were instances of larger organisms, 3.5 mm, but were limited to one or two individuals of a specific genera, such as Pontellina. The majority of copepods found in the bongo net were within 1.0 to 1.5 mm. The Tucker trawl collected larger organisms with size ranges of 1.0 to 3.5 mm. Copepod composition in the Tucker trawl was limited to mainly calanoids, comprising nearly 95 % of the copepod populations in every sample. The high occurrence of calanoids can be attributed to the size of the order and external anatomy. Calanoids are generally characterized and identified by long antennules that extend to or beyond the urosome. The length of the anntenule increased the surface area of the copepod, rendering higher incidences of collection in the 760 μm mesh net while smaller copepods were extruded from the net.

All genera identified in the Tucker trawl were present in the bongo net. However, the main difference was in the size distribution of copepod genera, leading to variation in populations densities between the two nets. This was seen in the collection of Undinula and Euchaeta. The bongo net collected these two genera ranging from 1 to 1.75 mm while the Tucker trawl collected slightly larger individuals ranging from 1.75 to 2.5 mm.

Population densities were the greatest in the bongo net as compared to the Tucker trawl.

Yet, there was one instance where the Tucker trawl showed higher copepods densities at

Station B in February. The differentiation in size distribution between these two nets indicated a slightly larger copepod present during this time period and location. This may be a result of oceanic waters being brought into Station B from the Florida Current.

The same results would be expected at Stations A and B in July, which also have the

Florida Current present, however, the bongo nets have the highest densities. The increase in Tucker trawl densities at Station B in February may be a result of patchiness of larger organisms or an indication of the onset of spawning.

Spawning events are indicated by the onset of males and females gathering in large quantities to increase reproductive success. Copepods are sexually dimorphic with females being typically larger than males. The increase in the Tucker trawl may indicate higher instances of females during this time. However, the reproductive cycle of copepods in tropical waters are generalized to be continuous throughout the year as compared to higher latitudes with peak spawning periods in association with phytoplankton blooms. However, the reproductive periods, patterns and strategies are species specific and are difficult to determine due to limited information known of tropical copepods reproductive strategies.

Generally, the reproductive patterns of tropical copepods lack synchronization and seasonal regularity, of which can be classified into two main categories: continuous or sporadic spawning with or without long periods of activity (Moore and Sander 1976)

The reproductive nature of copepods is also dependent on the type of reproductive strategy the females partake in, either carrying the egg sac or scattering the eggs in the water column. Carrying the egg sac requires invested energy input of the female and limits reproductive succession as compared to scattering the egg. Undinula vigularis scatters the eggs and while some species of Euchaeta have egg sacs, produced thirty days after inseminations, as indicated by Euchaeta norvegica and Paraeuchaeta antarctica

(Alonzo et al. 2000). However, the breeding patterns of these two genera have limited information in tropical environments and no conclusive result can be determined based on the large aggregations of females in relation assuming a spawning events.

Sea surface temperature

Sea surface temperate each station was assessed to determine if the change from station and month had any effect on the densities. According to the United States Navy’s

(USN) General Digital Environmental Model (GDEM), the Florida Current’s surface sea water temperatures ranged from 25 ˚C to 28 ˚C, decreasing with depth, and varied seasonally, 23 ˚C in February and 30 ˚C in August (USCG 2008). The data collected followed the same pattern as reported by the USN. The temperature within the same month did not vary significantly between stations. And even though there were slight increases and decreases between months the level of variation did not warrant a statistical level of significance. The difference in SST between months was explained by the increase of solar irradiance and heat capture in surface waters during summer months.

Ergo, the temperature was not a variable affecting changes in copepod population densities and species’ diversity. It should be noted that Station B in all months did show a slightly higher average SST. This increase could have been the result of the Florida

Current transporting warmer waters northward from the Loop and Antilles currents.

Salinity

In addition to temperature, the salinity at each location was recorded. The average water salinity of the Atlantic Ocean varies between 34 to 37 ‰, while the subsurface waters of the Florida Current are characterized by salinities approximately closer to 36.2 to 36.6 ‰ (USCG 2008). All salinities recorded during this study fell within the range recorded by the United States Coast Guard’s (USCG) findings. The changes between stations and months were not statistically significant. It should be noted that the tropics show minimal changes in seasonal precipitative and evaporative processes which would not greatly influence changes in salinity.

Fluorescence

Fluorescence data, which measured photosynthetic activity, provided information on the level phytoplankton primary productivity at each location and month (Falkowski and Kiefer 1985). February had five times greater amount of primary production as compared to July, an order of magnitude (USCG 2008). The increase of fluorescence in

February was an indication of a phytoplankton bloom which would likely be followed by a zooplankton bloom in March. This was confirmed with an increase in zooplankton abundance, though not significant (USCG 2008). However, the subsequent months before sampling were not assessed and no conclusive finding could have been made in relation to fluorescence activity influence on copepod densities.

Copepod Composition and Density Distribution

Bongo net

Stations A and B in February

Stations A and B showed dominance in the orders Calanoida and

Poecilostomatoida, together representing over 90% at each station. Both orders saw a decline in the density from Station A to Station B. However, Calanoida was the only order that illustrated a statistical significance among densities of these two stations. The two stations also showed similar copepod assemblages, with 11 genera in common.

Station A had three genera absent at Station B; Lucicutia spp., Pontella spp., and

Pontellina spp. Station B had four genera absent at Station A; Bathycalanus spp.,

Clytemnestra spp., Copilia spp. and Sapphirina spp. However, the top four genera at each station were the same; Calanus spp., Undinula spp., Corycaeus spp., and Oncaea spp., with similar percent contributions. The main difference between the four genera was their densities. Calanus spp., Undinula spp., and Oncaea spp. densities declined while Corycaeus spp. densities increased. All density differences were statistically significant, as indicated by the Mann-Whitney U test for each genus.

Diversity was examined within each sample using the Shannon Index. Normal communities typically fall between 1.5 and 3.5. Both Stations A and B fell within the range of 2.703 and 2.742, respectively. There was a slight increase in diversity at Station

B, however, it was not statistically significant. The Simpson’s Index of Diversity showed relativity the same findings, with no statistical significance between the two locations.

The increase in diversity at Station B was due to an increase in the number of genera contributing to the sample. Biodiversity was compared between stations using the

Sørensen’s Similarity Index. The index revealed that generic composition of each station was very similar with a calculation of 0.740.

The main difference between each location was the positioning of the Florida

Current. The ADCP data revealed no presence of the Florida Current at Station A and the western edge of the Florida Current at Station B. The absence or presence of the

Florida Current in correlation with copepod densities could explain the significant differences between these two stations. The absence of the current at Station A yielded higher copepod densities of Calanoida and Poecilostomatoida in Calanus spp, Undinula spp, and Corycaeus spp. The increase in density was influenced by proximity of the

Florida Current and land. The Florida Current acted as a barrier separating coastal waters from the Florida Current and oceanic waters, limiting the flow between the two stations

(USGS 2008). This separation caused greater influence of coastal runoff from rainfall at

Station A. Coastal runoff increased nutrient input, increasing phytoplankton productivity and zooplankton aggregations (Hopcroft and Roff 1990; Moore and Sander 1979;

Webber et al. 1992). The Florida Current also caused downwelling offshore and upwelling near shore. Upwelling brought deep oceanic nutrient rich waters moving them shoreward, increasing nutrient loads and availability for coastal species. Increased food availability would cause increased copepod aggregations.

Station A and B in July

Stations A and B showed dominance in the orders Calanoida and

Poecilostomatoida, each contributing nearly 50% to each station. Both orders and

Cyclopoida showed significant differences between these two locations in their densities.

The two stations in July showed similar copepod assemblages, with 10 genera in

96 common. Station A had three genera absent at Station B; Centropages spp., Rhincalanus spp., and Microsetella spp. Station B had one genus absent at Station A; Scolecithrix spp.. However, the top four dominant genera at each station were the same; Calanus spp., Undinula spp., Corycaeus spp., and Oncaea spp., with similar percent contributions.

Corycaeus was the dominant genus showing higher percent contributions in each sample.

The main difference between the four genera was their densities. Calanus spp., Undinula spp., and Corycaeus spp. saw an incline decline in density while Oncaea spp. saw a decline from Station A to Station B. The differences in densities were only statistically significant for Calanus spp., Corycaeus spp., and Oncaea spp.

Diversity was examined within each sample using the Shannon Index. Normal communities typically fall between 1.5 and 3.5. Both Stations A and B fell within the range of 1.747 and 1.839, respectively. There was a slight increase in diversity at Station

B however it was not statistically significant. The Simpson’s Index of Diversity showed relativity the same findings, with slightly higher biodiversity at Station B. Biodiversity was compared between stations using the Sørensen’s Similarity Index. The index revealed that the generic composition of each station was very similar with each other,

0.833.

The main difference between each location was the positioning of the Florida

Current. The ADCP data showed the western edge of the Florida Current was at Station

A and the central axis of the Florida Current was found at Station B. The positioning of the Florida Current in correlation with copepod densities could explain the significant differences between these two stations. Station B had higher copepod densities and this may be a result being located in the central axis of the current bringing in more oceanic

97 species. It may also be a results of mixing and resurging of zooplankton at the site due to upwelling. During July, there was a southbound flow along the coast. The inshore flow and the Ekman transport indicated downwelling inshore and upwelling offshore.

Upwelling along the western boundary of the Gulf Stream south of Cape Hatteras has shown an increase in primary production, enhancing phytoplankton blooms followed by subsequent zooplankton aggregations (Flierl and Davis 1993). The transfer of water offshore towards the current could indicate and account for the increase in total copepod densities for Station B in July.

Station A in February and July

Station A in February and July showed dominance in Calanoida and

Poecilostomatoida, with increased densities in February. Both orders showed a statistical significance of their densities between months. Station A in February and July had a total of 8 genera in common. In February there were four genera absent in July; Lucicutia spp., Pontella spp., Pontellina spp., and Scolecithrix spp. In July there were four genera absent in February; Centropages spp., Rhincalanus spp., and Microsetella spp. However, the top four most abundant genera at each station were the same; Calanus spp., Undinula spp., Corycaeus spp., and Oncaea spp. The percent contribution the dominant genera was relatively the same for Calanus spp. and Undinula spp. in each month. The percent contribution increased in July for Corycaeus spp. and decreased for Oncaea spp. A clear distinction among these genera was their densities at each month. Calanus spp.,

Undinula spp., and Oncaea spp. densities decreased while Corycaeus spp. increased.

The densities at Station A for February and July were statically significant only for

Calanus spp., Corycaeusspp. and Oncaea spp.

Diversity was examined within each sample using the Shannon Index. Stations A in February and July fell within the range of 1.747 and 2.703, of a normal community.

February had a higher level of diversity than July. This was also evident in the

Simpson’s Index of Diversity. Biodiversity was compared between stations using the

Sørensen’s Similarity Index. The index showed similarity among months.

The main difference between months was the positioning of the Florida Current.

The ADCP data showed the absence of the Florida Current at Station A in February and the western edge of the Florida Current in July. The absence or presence of the Florida

Current in correlation with copepod densities could explain the significant differences between these two stations. The positioning of the current was similar to the position found at Stations A and B in February. The same influences of the current from Station

A and B in February can be directly related to comparing Station A in February and July.

The current created a barrier causing coastal upwelling and increasing copepod densities in February. In July the current caused downwelling decreasing nutrient availability and copepod densities.

Station B in February and July

Calanoida and Poecilostomatoida were the dominate orders of each month. There was an increase in their densities in July. Both orders and Cylopoida showed statistical significance between their densities among these months. Station B in February and July had 11 genera in common. In February there were three genera not seen in July;

Bathycalanus spp. Clytemnestra spp., and Copilia spp. The top four most abundant genera at each station were the same; Calanus spp., Undinula spp., Corycaeus spp., and

Oncaea spp. The percent contribution of each dominant genera was relatively the same

99 for Calanus spp. and Undinula spp. in each month. The percent contribution of

Corycaeus spp. increased in July while Oncaea spp. percent contribution decreased. A clear distinction among these genera was in their densities at each month. Calanus spp.,

Undinula spp., and Corycaeus spp. increased in density in July while Oncaea spp. decreased. The density differences at Station B in February and July were statistically significant for all four genera.

Diversity was examined within each sample using the Shannon Index. Stations B in February and July fell within the typical range of a community, 1.839 and 2.742.

February had a higher level of diversity than July. This was also evident in the

Simpson’s Index of Diversity. All diversity indices did not show any statistical significance. Biodiversity was compared between stations using the Sørensen’s Similarity

Index. This revealed that generic composition of each station was very similar with,

0.888.

The main difference between months was the positioning of the Florida Current.

The ADCP data showed the western edge of the Florida Current at Station B in February and the central axis of the Current in July. The positioning of the Florida Current in correlation with copepod densities could explain the significant differences between these two months. The position of the current is similar to that in July at Stations A and B. The same influences of the current from Station A and B in July can be directly related to comparing Station B in February and July. In February Station B experienced downwelling while in July Station B was a site of upwelling brining in nutrient waters helping to increase copepod aggregations.

Station B in February and Station A in July

100

The dominant orders in each sampling locations were Calanoida and

Poecilostomatoida, each comprising nearly 90 % of the zooplankton samples. However the differences in densities did not show any statistical significance for any order.

Station B in February and Station A in July had 10 genera in common. In February at

Station B there were four genera not found at Station A in July; Bathycalanus spp,

Scolecithrix spp., Clytemnestra spp., and Copilia spp. In July at Station A there were three genera not found at Station B in February; Centropages spp., Rhincalanus spp., and

Microsetella spp. The top four most abundant genera at each station were the same;

Calanus spp., Undinula spp., Corycaeus spp., and Oncaea spp. The percent contribution of each dominant genus was relatively the same for Calanus spp. and Undinula spp. The percent contribution for Corycaeus spp. increased in July at Station A while Oncaea spp. percent contribution decreased. Station B in February and Station A in July showed similar densities, which were not statistically significant for Calanus spp. and Oncaea spp. The diversity of each location was examined. Station B in February showed higher levels of diversity, Shannon Index and the Simpson’s Index of Diversity, than at Station

A in July. The similarity between sites, SØrensen’s, was high, indicating homogeneity.

The similarity among densities and species’ diversity could be influenced by the position of the Florida Current. The western edge of the current was at each station. The western boundary was synonymous with downwelling events, decreasing densities in the same proportions. There were no significant differences between densities and this led to the assumption that the western boundary is characterized by a decrease in copepod densities.

Tucker trawl

101

The Tucker trawl showed dominance of the order Calanoida, which comprised over 85% of the samples collected at each station and month. Poecilostomatoida contributed less than 10% to each sample, while Harpacticoida was only present in one sample (Station A in February). Cyclopoida was not collected at any sampling location.

This was due to the relatively small size of the order and the large mesh of the net. All copepod densities were significantly smaller than those in the bongo net. This indicated that the contribution of smaller copepod is greater than larger ones. However, there were only a couple of instances where specific genera densities saw a spike, mainly at Station

B in February. All other densities stayed fairly the same with no significant difference between them.

Station B in February was the only location of the Tucker trawl to see a drastic increase in copepod densities. The top four dominant genera were Undinula spp.,

Eucalanus spp., Euchaeta spp., and Rhincalanus spp. All of these genera together contributed to over 90% of the sample. This spike in densities accounted for most of the significant differences when comparing stations. Another factor for statistical significance was the relatively low abundance of copepods. The increased densities of the larger copepods did not seem to be related to the positioning of the Florida Current as the smaller copepods were.

Spatial and Temporal Scales

This study only examined the effect of Florida Current on copepod population densities and species’ diversity. However, aggregations or patches of copepods could be a direct influence of spatial and temporal variation of physical processes, generated by climatic and hydrodynamic influences, and or biological interactions. Spatial variability

102 may occur over a broad or small range of scales between 10 m – 100 km to 0.1 - 50 m. In finer scales species’ behavior could have a greater influence on densities, seen in swarming behavior of copepods gathering in local eddies limiting dispersion by major current, than physical processes (Alvarez-Cadena 1998; Avois-Jacquet et al. a; Emery

1968; Hammer 1979; Haury et al. 1978; Mackas et al. 1985; Lewis and Boers 1991).

The physical processes appear on different spatial-temporal scales and change. While one process could show a positive influence on a fine scale it could also show a negative influence on another broad scale (Allen and Hoekstra 1991; Wiens 1989). For example, smaller scales that involve predator and prey dynamics could show negative correlations while broader scales show a positive interaction. (Fiedler 1983;Rose and Leggett 1990).

Physical processes and interactions also vary in scale but also in environment. Tropical oceanic waters are more stable environments with minimal seasonal changes. However, coastal tropical areas are prone to more physical factors interacting with topography such as wind-induced currents and rainfall patterns influencing life cycle, swarming and reproduction, all affecting destiny and diversity.

Biological Interactions

Biological interactions play a significant role in finer spatial scales, as in this study, and attribute to the patchy behavior of copepods. The four main biological interactions are diel vertical migration (DVM), predator avoidance, food aggregation, and mate seeking behavior. Diel vertical migration is the vertical ascent or descent of zooplankton in the water column at various periods during the day, creating large aggregations (Folt and Burns 1999). The migration of copepods occurs within the first few hundred meters of the water column and depth ranges vary from coastal to pelagic

103 waters (Lampert 1989; Stich and Lampert 1981; Roehr and Moore 1965). Migration patterns, based on physical and biological cues, are species specific and dependent on the developmental stage of the organism (Folt and Burns1999). The main physical attribute ensuing migration is light exposure. Light is a cue based on the optical properties of water and change in intensity from dawn to dusk. The light will trigger the vertical ascent or decent. However, the vertical movement is not limited to light properties.

Zooplankton also accumulate based on predator avoidance, food availability, mating behavior, current velocity and turbulence (Folt and Burns 1999; Avois-Jacquet et al. a)

Predator avoidance is another biological influence, affecting copepod abundance by removing individuals from the environment. Predators can have even greater effects on zooplankton distributions by triggering DVM, which in turn results in large scale aggregations. While large scale aggregations occur, they are also seen in the small scale with known responses of escape hops increasing swimming speeds and vertical movement. However, some responses are species specific, where species from more energetic physical regimes require larger mechanical stimuli from a predator to elicit an escape reaction and or respond when only closer together (Folt and Burns 1999; Avois-

Jacquet et al. a).

While predator avoidance elicits escapes responses, food availability and concentration also play a significant role in zooplankton patchiness and can be based on phytoplankton aggregations. Physical mechanisms may passively gather phytoplankton and zooplankton if they have similar characteristic such as size, shape, and buoyancy.

However, active zooplankton mobility does aid in the location of food patches and the retention within the phytoplankton aggregations (Deibel 2001). It has been noted that at

104 different food concentrations copepods can change swimming speeds, turning angles, or hopping rate; the interspersed movements of jumping by alternating resting and sinking with active movement. Acartia tonsa remains within food patches by decreasing motility and horizontal movement. Physical mobility in the location of food resources is also spurred biological interactions. Chemoreception, a response to odor, and physical stimulate, disturbances in the water column help copepods locate food patches (Folt and

Burns 1999).

However, zooplankton patchiness differs dependent on temporal and spatial scales and species specific response to food concentrations. Species specific differences is seen in a study conducted by Dagg (1977) where Acartia tonsa is sensitive to small scale patchiness due to the need for constant food availability. However, the reverse trend was detected with Calanus finmarchicus, where scarce food availability did not hinder it’s abundance. The tolerance of low food concentrations was in direct correlation to lipid storage. Physiologically food is stored is lipid reserves that can be tapped when food availability is scare. The fatty energy reserve is not prevalent in all copepods; some are more apt to draw energy from tissue a smaller energy reserve and are prone to starvation. High lipid content allows for longer periods of starvation and higher levers of survival during food scarcity. Food concentration varies dependent on spatial and temporal scales and survival or success of the organism depends on the length of time the food is available (Dagg 1977).

Zooplankton and copepod aggregations can be further linked to mate seeking, resulting in swarms. Copepods dispersion is sparse and locating a mate is difficult without a large aggregation of individuals. The movement of zooplankton can be on

105 large scale, through wind driven currents to diel vertical migrations, generating a chance encounter in the patches. Copepods can track mates on smaller scales over short distances by chemoreception. Water-borne pheromone detection and mechanoreception following fluid disturbances allows for the detection of specific species in a diverse environment

(Folt and Burns 1999).

Study Influence

Inconstancies in data and interpretation could be a result in during various aspects of the study. The main source of inconsistency would be from identification to the lowest taxonomic level. Identifications were determined based on anatomical and morphological differences. Species specific differences lie within the setae ordainmention on specific appendages, such as the mandible or antenna. However, through collecting and the preservation of species individuals no longer had intact anatomical markers for direct identification towards the species level. The collection of copepods with the bongo net and Tucker trawl used specific mesh sized nets that that were subjected to escapement and net clogging, which may cause damages appendages.

The rigorous force and pressure of oceanic waters to collect the specimens could have lead to ripping and loss of anatomical parts, mainly seen in the antenna, pereipods, caudal ramus setae and other decorative setae (Bradford and Jillette 1974). Damage to the organism would render the identification to species level difficult. However, genus identification was based on basic body structure and unique characteristics, such as the anchored rostrum of the Rhincalanus spp. which indicated that it was Rhincalanus cornutus.

106

Zooplankton sampling was further affected by collection periods, net avoidance

by organisms and cogging, and copepod patchiness in the horizontal spatial plane (Wiebe

and Holland 1968). Samples were collected and analyzed for February and July 2007,

which relayed only a snap shot of ecosystem and population structure. The sampling

only looked at a single day with in the month and assumed population structure, density

and diversity were consistent for the entire month. Analysis of all months in 2007 could

help gain a greater understanding of the copepod populations throughout the year and

insight to the connection of the Florida Current to populations densities and species’

diversity. The snap shot of community structure could be influenced by the patchiness

of plankton. Plankton patchiness vary in time, daily, seasonally and vertically within the

water column and cold be affected by both physical and biological factors. The physical

factors may include upwelling, influence of gyres and fronts of nutrient concentration.

Biological factors may also be influenced by predator and grazing capabilities (Collins

2002). The variation in patchiness could influence copepod concentrations and diversity

data.

V. Conclusion

Copepod population densities and species diversity were examined to determine the

effect of the Florida Current off the coast of Fort Lauderdale, Florida in 2007. A

comprehensive study conducted by Owre and Foyo in 1967 show an in-depth

examination of copepod community structure. The study illustrated a relative baseline

for common species in the Florida Current, as seen today. The physical nature of the

current; salinity, temperature, and velocity, in association with density and diversity have

yet to be examined.

107

Copepods were collected from two stations, east of Port Everglades, Florida located

6 miles and 12 miles offshore. Densities were calculated using individual counts and water volume sampled; densities are represented as individuals m -3. Replicate counts were conducted to assure accurate results. Species were identified to the lowest identifiable taxonomic classification based on published classification literature.

Copepod species diversity was typical of a standard tropical community showing dominance in only a couple of species; Calanus, Undinula, Corycaeus, and Oncaea. The different levels of diversity, alpha and beta, demonstrated that there was slightly higher instances of diversity is coastal waters in February as compared to July. This can be a direct effect of increased nutrient loads from upwelling and land runoff. Diversity levels decrease as the current moves shoreward in July cutting off the coastal input and only showing oceanic species.

Copepod population densities revealed several patterns based on different spatial and temporal scales. Overall copepod densities showed a dominance of Calanoida and

Poecilostomatoida dependent throughout the entire sampling period. Poecilostomatoida species are numerically important to population dynamics, even though previous studies have lead to the underestimation due to the relatively smaller size. The presence of these species is also an attribute of the current brining oceanic waters where they are normally distributed.

The dominant genera, Calanus, Undinula, Corycaeus, and Oncaea followed the same general pattern of increased coastal densities without the current, decreased densities at the western boundary of the current, and increased densities fully submerged in the current. The western edge of the current, for both months, had roughly the same

108 current velocity and direction. This would lead to the assumption that the western edge of the current could be identified through relatively low concentrations of these species throughout the entire year. The increase in overall density inshore was due to the current, acting as a physical barrier, trapping species at inshore stations increasing population densities by increased nutrient loads through upwelling and land runoff. Within the current, Station B in July, population densities increased due to the current bringing in oceanic waters, showing a greater resurgence of oceanic species and the significant increase in Poecilostomatoida species.

However, the population densities needed to consider the patchy nature of zooplankton samples. The physical processes, such as meteorological and hydrodynamic interactions, could have affected sampling densities. The same physical interactions experienced in one location did not hold the same for another location due to different environments. Coastal tropical areas are prone to more physical factors interacting with topography such as wind-induced currents and rainfall patterns which can influence life cycle, swarming, reproduction. Thus coastal tropical waters, such as Station A, were not controlled by the same physical and biological factors as tropical oceanic waters, Station

B (Avois-Jacquet et al. a).

While the physical environment plays a role in the patchiness of zooplankton, biological interactions play a much more significant role on finer spatial scales. The four main biological interactions that could change population densities are diel vertical migration (DVM), predator avoidance, food aggregation, and mate seeking behavior.

DVM, species specific, could bring aggregations to the surfaces based light identification and optical properties of the environment. Predator avoidance could decrease

109 populations at a sampling site due to escape behaviors. Food concentrations could either increase or decrease densities due to its presence or lack thereof. Mate seeking could lead to large swarms for reproductive purposes.

Additional studies are recommended to further test the influence of the physical and biological processes that could influence the overall population densities and species’ diversity. Studies examining food availability, reproductive cycles, diel vertical migration ranges, and predator densities could show a greater insight to the copepod populations. The influence of the Florida Current throughout the entire year needs to be assessed to determine if the position affects population densities.

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