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Smulders FOH, Bakker ES, O'Shea OR, Campbell JE, Rhoades OK, Christianen MJA. Green turtles shape the seascape through grazing patch formation around habitat features: Experimental evidence. Ecology 2023; 104:e3902. [PMID: 36310424 PMCID: PMC10078154 DOI: 10.1002/ecy.3902] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Revised: 08/10/2022] [Accepted: 09/07/2022] [Indexed: 02/03/2023]
Abstract
Understanding how megaherbivores incorporate habitat features into their foraging behavior is key toward understanding how herbivores shape the surrounding landscape. While the role of habitat structure has been studied within the context of predator-prey dynamics and grazing behavior in terrestrial systems, there is a limited understanding of how structure influences megaherbivore grazing in marine ecosystems. To investigate the response of megaherbivores (green turtles) to habitat features, we experimentally introduced structure at two spatial scales in a shallow seagrass meadow in The Bahamas. Turtle density increased 50-fold (to 311 turtles ha-1 ) in response to the structures, and turtles were mainly grazing and resting (low vigilance behavior). This resulted in a grazing patch exceeding the size of the experimental setup (242 m2 ), with reduced seagrass shoot density and aboveground biomass. After structure removal, turtle density decreased and vigilance increased (more browsing and shorter surfacing times), while seagrass within the patch partly recovered. Even at a small scale (9 m2 ), artificial structures altered turtle grazing behavior, resulting in grazing patches in 60% of the plots. Our results demonstrate that marine megaherbivores select habitat features as foraging sites, likely to be a predator refuge, resulting in heterogeneity in seagrass bed structure at the landscape scale.
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Affiliation(s)
- F O H Smulders
- Aquatic Ecology and Water Quality Management Group, Wageningen University & Research, Wageningen, The Netherlands
| | - E S Bakker
- Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.,Wildlife Ecology and Conservation Group, Wageningen University, Wageningen, The Netherlands
| | - O R O'Shea
- The Centre for Ocean Research and Education (CORE), Gregory Town, The Bahamas
| | - J E Campbell
- Department of Biological Sciences, Institute of Environment, Florida International University, Miami, Florida, USA
| | - O K Rhoades
- Department of Biological Sciences, Institute of Environment, Florida International University, Miami, Florida, USA
| | - M J A Christianen
- Aquatic Ecology and Water Quality Management Group, Wageningen University & Research, Wageningen, The Netherlands
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Siegfried TR, Reimer J, Roberto E, Noren C, Vidal A, Dixon K, DuBois M, Piacenza SE. Size-Mediated Sea Turtle Behavioral Responses at Artificial Habitats in the Northern Gulf of Mexico. Animals (Basel) 2022; 13:ani13010114. [PMID: 36611724 PMCID: PMC9817786 DOI: 10.3390/ani13010114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 12/24/2022] [Accepted: 12/26/2022] [Indexed: 12/29/2022] Open
Abstract
Our understanding of size-specific sea turtle behavior has lagged due to methodological limitations. However, stereo-video cameras (SVC) are an in-water approach that can link body-size and allow for relatively undisturbed behavioral observations. In this study, we conducted SVC dive surveys at local artificial reefs, piers, and jetties in the northern Gulf of Mexico (nGOM) from May 2019 to August 2021. Using SVCs, we measured sea turtle straight carapace length, documented behaviors, and quantified wariness by assessing minimum approach distance (MAD). In green sea turtles (Chelonia mydas), the observed MAD ranged from 0.72 to 5.99 m (mean 2.10 m ± 1.10 standard deviation (SD), n = 73). For loggerhead sea turtles (Caretta caretta), the MAD ranged between 0.93 and 3.80 m (mean 2.12 m ± 0.99 SD, n = 16). Kemp's ridley sea turtles (Lepidochelys kempii) were similar to loggerheads, and MAD ranged from 0.78 to 3.63 m (mean 2.35 m ± 0.99 SD, n = 8). We then evaluated what biological factors could impact the MAD observed by species, but we excluded Kemp's ridleys as the sample size was small. Using a linear mixed model and model selection based on AICc, the top ranked model for both green and loggerhead sea turtles included SCL as the most important factor influencing MAD. MAD did not vary with habitat type for either species. Our results showed that larger individuals, regardless of species, have a greater wariness response, becoming startled at greater distances than smaller individuals. The findings of our study support the use of SVC as an accessible, non-invasive tool to conduct ecologically relevant in-water surveys of sea turtles to link behavioral observations to body size.
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Affiliation(s)
| | - Jackson Reimer
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
| | - Emma Roberto
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
| | - Christopher Noren
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
- Darling Marine Center, University of Maine, Walpole, ME 04573, USA
| | - Alex Vidal
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
- United States Fish and Wildlife Service, Maryland Fish and Wildlife Conservation Office, Annapolis, MD 21401, USA
| | - Kristi Dixon
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
| | - Morgan DuBois
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
| | - Susan E. Piacenza
- Department of Biology, University of West Florida, Pensacola, FL 32514, USA
- Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, Corvallis, OR 97331, USA
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