Habitat selection of coral reef invertebrates mediated by environmental stimuli
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Habitat selection is a critical process for most organisms that are mobile for at least a portion of their lives and can influence survival and lifelong fitness. Selection of optimal habitat is accomplished through the detection and assessment of environmental cues such as waterborne chemicals or structural morphology. Substrate availability on coral reefs is limited, giving rise to high competition between benthic species. Here, I assessed different aspects of sensory-mediated habitat selection of reef invertebrates through a variety of research methods, invertebrate species, and geographic locations to develop an integrated and diverse understanding of the process and implications of habitat selection. ☐ First, habitat selection is not a singular event, but rather, an evolving process throughout development. I investigated the developmental variations in coral larvae preference and associated behaviors in response to general reef cues using three species of Caribbean corals. Larvae of Acropora palmata, Orbicella annularis, and Pseudodiplora strigosa were exposed to general reef or offshore cues each day of their larval duration. A. palmata were tested in both flowing water, using a two-channel choice flume, and in a novel still-water behavioral assay; due to weaker swimming capabilities, the other species were only tested in the still-water assay. A. palmata larvae prefer reef cues compared to offshore cues throughout development, but all three species displayed minute, yet distinct, behaviors that varied based on cue and developmental stage. These behaviors may be indicative of emerging sensitivities to environmental stimuli and should be investigated further. ☐ Sensory-mediated habitat selection is not solely dependent on general reef cues but may also rely on specific cues of the benthic reef environment. A. palmata were tested in the still-water behavioral assay to determine attraction or repulsion to algal and cyanobacterial chemical cues. Regardless of benthic species, coral larvae increased the percent of time spent moving after the cues were presented. Notably, coral larvae significantly increased the proportion of time spent in directed motion or swimming in small circles only when presented with crustose coralline algae (CCA), potentially revealing these minute behaviors as indicators of positive habitat cues. ☐ Habitat selection is not only relevant early in organismal life history, but is also vital for roving, migrating, or homing adults. Sensory-mediated adult habitat selection was investigated in the specialized reef shrimp, Lysmata pederseni, which resides within Caribbean tube sponges, but nocturnally vacates to feed or mate. Using mark and recapture techniques, reef transects, cue isolation experiments, and patch reefs, I discovered that while shrimp use both chemical and morphological cues to assess potential habitats, the optimal sponge habitat is defined more by shape than by chemistry. ☐ Morphological characteristics of specialized habitat are further investigated in my final chapter, where I attempt to relate habitat to fitness of a coral-dwelling Indo-Pacific shrimp, Coralliocaris graminea. Transects reveal non-random associations of shrimp within 7 species of Acropora corals. Shrimp abundance is closely related to coral morphology, especially coral head diameter and branch height. Further, C. graminea individuals were collected from host corals to reveal that many aspects of body and claw size, as well as fecundity, can be positively correlated with coral size. The potential exists for this habitat-specialized shrimp to survive within structurally similar, non-host corals if preferred hosts are stressed or degrading. ☐ In all, this body of work contributes to our understanding of habitat selection, from ontogenesis to adults. Knowledge of both the environmental stimuli that influence habitat selection and the implications of that choice can guide research and management practices. An integrated approach was taken to each of these projects, where multiple methods were incorporated and compared to determine varying behaviors, motivations, and repercussions of correctly interpreting stimuli to select the optimal habitat. However, during the current period of unprecedented environmental change, the optimal habitats are changing and so are the various cues by which organisms can detect and select this habitat. This research has made strides towards not only understanding habitat selection of cryptic, specialized, and/or foundational species, but also predicting how these sensory-mediated behavioral responses might shift as environmental conditions decline.