Habitat Selection Among Fishes and Shrimp in the Pelagic Sargassumcommunity: the Role of Habitat Architecture
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HABITAT SELECTION AMONG FISHES AND SHRIMP IN THE PELAGIC SARGASSUMCOMMUNITY: THE ROLE OF HABITAT ARCHITECTURE by Chelsea O. Bennice A Thesis Submitted to the Faculty of The Charles E. Schmidt College ofScience in Partial Fulfillment of the Requirements for the Degree of Master ofScience Florida Atlantic University Boca Raton, Florida December 2012 HABITAT SELECTION AMONG FISHES AND SHRIMP IN THE PELAGIC SARGASSUMCOMMUNITY: THE ROLE OF HABITAT ARCHITECTURE by Chelsea O. Bennice This thesis was prepared under the direction of the candidate's thesis advisor, Dr. W. Randy Brooks, Department of Biological Sciences, and has been approved by the members ofher supervisory committee. It was submitted to the faculty ofthe Charles E. Schmidt College of Science and was accepted in partial fulfillment of the requirements for the degree ofMaster ofScience. Gary W. erry, Ph. Dean, Charles E. Schmidt College of Science ~~z;e_....... 4~J'Z-~)~ Barry T. Ro~n, Ph.D: Date Dean, Graduate College ii ACKNOWLEDGEMENTS First and foremost I want to thank my advisor Dr. Randy Brooks for his guidance and supervision throughout my graduate career, as well as his willingness to take me specimen collecting on his boat, even ifthe seas were looking a little ferocious. I want to thank Dr. Brian Lapointe for his support and guidance as my co-advisor and sampling in the Florida Keys with himself and Captain Carl. Thank you to Dr. Ed Proffitt for serving on my committee and his guidance for the development ofmy experimental design and statistical analyses. Also, I want to thank numerous funders who have allowed me to pursue my research: Guy Harvey Ocean Foundation and administered by Florida Sea Grant, Manasquan River Marlin and Tuna Club Inc., and the Marsh Scholarship for Marine Biology. Graduate students that deserve a thank you for all their hard work in assisting me in the field and lab: Lorin West, Ed Davis, Derek Cox, Bethany Augliere, lana Boerner, Bethany Resnick, and Erica Baugh. A special thanks to Lorin West for making long days in the lab interesting and tolerable, Bethany Augliere for her critiques and edits on my thesis that she has probably read or listened to me talk about more than we both can imagine, and Bethany Resnick for being my personal field assistant. Last but not least, I would like to thank my family for all their love and support. 111 ABSTRACT Author: Chelsea Bennice Title: Habitat Selection Among Fishes and Shrimp in the Pelagic Sargassum Community: The Role ofHabitat Architecture Institution: Florida Atlantic University Thesis Advisor: Dr. W. Randy Brooks Degree: Master of Science Year: 2012 Pelagic Sargassum was used to determine the effects ofhabitat architecture for one species of shrimp (Leander tenuicornis) and two species of fish (Stephanolepis hispidus and Histrio histrio). Inter-thallus spacing (low, medium, and high) and depth (shallow versus deep) were manipulated independently to test whether the spatial components ofhabitat architecture. Two differing habitats (Sargassum versus seagrass species) were tested for the structural component ofhabitat architecture. There were no significant results for inter-thallus spacing experiments for 1. tenuicornis and S. hispidus. H histrio selected habitats with medium inter-thallus spacing in two treatments. Large individual H histrio contributed mostly to the significant effects. All three species selected habitats with a greater depth aspect. Finally, 1. tenuicornis and H histrio selected habitats with greater structural complexity (i.e., Sargassum). These results demonstrate clearly that habitat architecture ofSargassum influences habitat selection by these shrimp and fishes. IV HABITAT SELECTION AMONG FISHES AND SHRIMP IN THE PELAGIC SARGASSUM COMMUNITY: THE ROLE OF HABITAT ARCHITECTURE FIGURES vii INTRODUCTION 1 Habitat Architecture 2 Objectives 4 MATERIALS AND METHODS 6 Collection and maintenance ofspecimens 6 General Experimental Procedures 8 Spatial Components ofHabitat Architecture Procedures 9 Differing inter-thallus spacing experiment.. 10 Differing depth experiment "A" 11 Differing depth experiment "B" 12 Structural component ofHabitat Architecture 13 Sargassum versus seagrasses patches experiment.. 13 RESULTS 14 General Habitat Selection 14 Differing inter-thallus spacing experiment 14 High versus Medium 14 Medium versus Low 15 v High versus Low 15 Differing Depth Experiment 16 "A"-Deep (with completely submerged superior surface) versus Shallow 16 "B"- Deep (with floating superior surface) versus Shallow 16 Structural Component for Habitat Selection Experiments 16 Sargassum versus seagrasses patches 16 General Behavioral Observations in Laboratory Experiments and Field 17 DISCUSSION 18 Differing inter-thallus spacing experiments 18 DifferiI renng dept hexperiments . "A"an d "B" .. 20 Structural Component ofHabitat Architecture 21 CONCLUSIONS 24 APPENDIXES 26 REFERENCES 36 VI FIGURES Figure 1. Experimental aquarium set up 26 Figure 2. Differing inter-thallus spacing experiment set up 27 Figure 3. Image ofinter-thallus space experiment.. 28 Figure 4. Differing depth experiment "A" and "B" set ups 29 Figure 5. Structural component experiment set up 30 Figure 6. Habitat selection based on differing inter-thallus spacing 31 Figure 7. Habitat selection based on differing inter-thallus spacing 32 Figure 8. Habitat selection based on differing inter-thallus spacing 33 Figure 9. Differing depth experiments "A" and "B" 34 Figure 10. Structural component experiment.. 35 VB INTRODUCTION The importance ofhabitat architecture and structural complexity is often overlooked in studies ofhabitat selection by animals. Some ofthe more well-known systems (e.g., forests, coral reefs, rocky intertidal, mangrove) demonstrate how habitat complexity influences species diversity and abundance (Grinnell 1917, Gause 1934, Crisp and Barnes 1954, Huffaker 1958, Connell 1961, Emson and Faller-Fritsch 1976, Keough & Downes 1982, Fletcher and Underwood 1987, Walters and Wethey 1996, Beck 1998). Pelagic Sargassum represents a community with excellent potential to study effects ofhabitat architecture on biotic interactions with its associated inhabitants. Floating, macrophytic algal mats (either permanently floating forms or from detached benthic forms) can serve as nursery areas for juvenile fishes, as they provide prey resources and protection from predators (Lenanton et al. 1982, Lenanton and Caputi 1989, Wells and Rooker 2004). Ofthese nursery habitats, pelagic Sargassum has received the least amount ofresearch inquiry. Pelagic Sargassum is commonly labeled "floating reefs" because ofthe plethora oforganisms, such as juvenile fishes, invertebrates, and endemic organisms (e.g., Sargassum fish Histrio histrio) that use the patches for food, shelter, or substrate attachment in the open ocean. The complex Pelagic Sargassum mats are also used for shelter by organisms that have been swept away by strong currents from their previous habitats and would otherwise be left stranded and vulnerable in the open ocean (Lapointe 1986). Habitat Architecture In general, objects floating in the ocean, including Sargassum spp., attract and concentrate fauna (Hunter and Mitchell 1968, Lapointe 1995, Ing6lfsson 1998, Robert and Poore, 2005, Casazza & Ross 2008) by creating habitat substrate and thereby increasing the complexity ofthe pelagic environment (Kingsford 1995, Ingolfsson 1998). Dean and Connell (1987) studied specific mechanisms ofecological succession in such habitats. They concluded that the "ecological time" (i.e., inhabitant diversity increases with time as more algae accumulates) and "algal toxicity" (i.e., inhabitant diversity is low initially because early algal mat species are more toxic than subsequent algae) hypotheses were less likely valid than the "habitat complexity" hypothesis (i.e., based on biomass and surface area characteristics ofalgal thalli) in explaining succession and species diversity in pelagic algal mats. Algal biomass alone can be deceptive, as similar shaped thalli can be rearranged into different densities by natural effects (e.g., currents, wind) in the open ocean. This, in turn, could cause a change in habitat complexity by changing the habitat architecture (i.e., relative spatial arrangement ofalgal thalli). Additionally, surface area characteristics alone might be manipulated naturally (e.g., through grazing or biodegradation) to confound interpretation ofeffects on colonizing inhabitants. Thus, a comprehensive approach would involve looking at a system in which both algal biomass and surface characteristics are studied simultaneously. 2 Hacker and Steneck (1990) and Hacker and Madin (1991) define algal habitat architecture as the number, size, shape and arrangement ofhabitable spaces and structures for organisms. This definition takes a comprehensive approach in that both spatial (i.e., size, shape and arrangement ofspaces between fronds) and structural (i.e., number, length, and the width offronds, branches, and vesicles) components are measured. Hacker and Steneck (1990) examined the influence ofdiffering spatial components by using different benthic species and algal mimic counterparts that ranged from filamentous, foliose and leathery macrophyte morphologies. They found that the more densely branched algal mimic attracted greater numbers ofamphipods. Subsequently, Hacker and Madin (1991) focused specifically on structural components ofthe Sargassum habitat, because the two species ofshrimp used in their experiments (Latreutes fucorum and Hippolyte coerulescens) both