Person:

Hay, Mark E.

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https://hdl.handle.net/1853/71334

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School of Biological Sciences

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Now showing 1 - 10 of 60

Impact of Herbivore Identity on Algal Succession and Coral Growth on a Caribbean Reef

(Georgia Institute of Technology, 2010-01-29) Burkepile, Deron E. ; Hay, Mark E.

Herbivory is an important top-down force on coral reefs that regulates macroalgal abundance, mediates competitive interactions between macroalgae and corals, and provides resilience following disturbances such as hurricanes and coral bleaching. However, reductions in herbivore diversity and abundance via disease or over-fishing may harm corals directly and may indirectly increase coral susceptibility to other disturbances. Methodology and Principal Findings In two experiments over two years, we enclosed equivalent densities and masses of either single-species or mixed-species of herbivorous fishes in replicate, 4 m2 cages at a depth of 17 m on a reef in the Florida Keys, USA to evaluate the effects of herbivore identity and species richness on colonization and development of macroalgal communities and the cascading effects of algae on coral growth. In Year 1, we used the redband parrotfish (Sparisoma aurofrenatum) and the ocean surgeonfish (Acanthurus bahianus); in Year 2, we used the redband parrotfish and the princess parrotfish (Scarus taeniopterus). On new substrates, rapid grazing by ocean surgeonfish and princess parrotfish kept communities in an early successional stage dominated by short, filamentous algae and crustose coralline algae that did not suppress coral growth. In contrast, feeding by redband parrotfish allowed an accumulation of tall filaments and later successional macroalgae that suppressed coral growth. These patterns contrast with patterns from established communities not undergoing primary succession; on established substrates redband parrotfish significantly reduced upright macroalgal cover while ocean surgeonfish and princess parrotfish allowed significant increases in late successional macroalgae. Significance This study further highlights the importance of biodiversity in affecting ecosystem function in that different species of herbivorous fishes had very different impacts on reef communities depending on the developmental stage of the community. The species-specific effects of herbivorous fishes suggest that a species-rich herbivore fauna can be critical in providing the resilience that reefs need for recovery from common disturbances such as coral bleaching and storm damage.
Integrative graduate education and research traineeship: signals in the sea

(Georgia Institute of Technology, 2008-08-31) Hay, Mark E. ; Sobecky, Patricia A. ; Webster, Donald R.
Propagule pressure of an invasive crab overwhelms native biotic resistance.

(Georgia Institute of Technology, 2007-07-24) Hollebone, Amanda L. ; Hay, Mark E.

Over the last decade, the porcelain crab Petrolisthes armatus invaded oyster reefs of Georgia, USA, at mean densities of up to 11 000 adults m–2. Interactions affecting the invasion are undocumented. We tested the effects of native species richness and composition on invasibility by constructing isolated reef communities with 0, 2, or 4 of the most common native species, by seeding adult P. armatus into a subset of the 4 native species communities and by constructing communities with and without native, predatory mud crabs. At 4 wk, recruitment of P. armatus juveniles to oyster shells lacking native species was 2.75 times greater than to the 2 native species treatment and 3.75 times greater than to the 4 native species treatment. The biotic resistance produced by 2 species of native filter feeders may have occurred due to competition with, or predation on, the settling juveniles of the filter feeding invasive crab. Adding adult porcelain crabs to communities with 4 native species enhanced recruitment by a significant 3-fold, and countered the effects of native biotic resistance. Differences in recruitment at Week 4 were lost by Weeks 8 and 12, when densities of recent recruits reached ~17 000 to 34 000 crabs m–2 across all treatments. Thus, native species richness slows initial invasion, but early colonists stimulate settlement by later ones and produce tremendous propagule pressure that overwhelms the effects of biotic resistance.
Population dynamics of the non-native crab Petrolisthes armatus invading the South Atlantic Bight at densities of thousands m⁻²

(Georgia Institute of Technology, 2007-04-27) Hay, Mark E. ; Hollebone, Amanda L.

The green porcelain crab Petrolisthes armatus recently invaded oyster reefs of the South Atlantic Bight. In 2 estuaries of coastal Georgia, USA, crab densities reached peak densities of 4000 to 11 000 crabs m–2 in some periods and locations. Densities generally were higher in the low versus the high intertidal and in the lower versus upper regions of the estuaries. In warmer months, 20 to 90% of adult females were gravid, recruits were dense, and population levels were high. In colder months, densities dropped by 64 to >99%. Male:female ratios were near 1:1 across times and locations. Maximum mean densities of P. armatus in Georgia were 37 times the highest densities recorded in the presumptive native range. Crabs in the new range reproduced at a smaller size, and the percentage of gravid females was similar between the old and new range. Thus, population fecundity in Georgia exceeds that of the native range by more than 1 order of magnitude. Densities of native mud crabs in the genera Panopeus and Eurypanopeus were unrelated to, or positively correlated with, densities of the exotic crabs; correlations were never significantly negative. The impact of Petrolisthes armatus on native communities is unclear, but could be considerable if this filter-feeding crab impacts oysters, which are the foundation species of inshore reefs.
Herbivore vs. nutrient control of marine primary producers: context-dependent effects

(Georgia Institute of Technology, 2006-12) Burkepile, Deron E. ; Hay, Mark E.

Pervasive overharvesting of consumers and anthropogenic nutrient loading are changing the strengths of top-down and bottom-up forces in ecosystems worldwide. Thus, identifying the relative and synergistic roles of these forces and how they differ across habitats, ecosystems, or primary-producer types is increasingly important for understanding how communities are structured. We used factorial meta-analysis of 54 field experiments that orthogonally manipulated herbivore pressure and nutrient loading to quantify consumer and nutrient effects on primary producers in benthic marine habitats. Across all experiments and producer types, herbivory and nutrient enrichment both significantly affected primary-producer abundance. They also interacted to create greater nutrient enrichment effects in the absence of herbivores, suggesting that loss of herbivores produces more dramatic effects of nutrient loading. Herbivores consistently had stronger effects than did nutrient enrichment for both tropical macroalgae and seagrasses. The strong effects of herbivory but limited effects of nutrient enrichment on tropical macroalgae suggest that suppression of herbivore populations has played a larger role than eutrophication in driving the phase shift from coral- to macroalgal-dominated reefs in many areas, especially the Caribbean. For temperate macroalgae and benthic microalgae, the effects of top-down and bottom-up forces varied as a function of the inherent productivity of the ecosystem. For these algal groups, nutrient enrichment appeared to have stronger effects in high- vs. low-productivity systems, while herbivores exerted a stronger top-down effect in low-productivity systems. Effects of herbivores vs. nutrients also varied among algal functional groups (crustose algae, upright macroalgae, and filamentous algae), within a functional group between temperate and tropical systems, and according to the metric used to measure producer abundance. These analyses suggest that human alteration of food webs and nutrient availability have significant effects on primary producers but that the effects vary among latitudes and primary producers, and with the inherent productivity of ecosystems.
Reefer Madness: Drugs and Coral Reefs

(Georgia Institute of Technology, 2006-11-11) Ludovice, Peter J. ; Hunt, William D. ; Hay, Mark E.

Dr. Mark Hay of the Georgia Tech School of Biology will discuss the ecology of coral reefs and their connection to pharmaceuticals from the sea
Chemically mediated competition between microbes and animals: microbes as consumers in food webs

(Georgia Institute of Technology, 2006-11) Burkepile, Deron E. ; Parker, John D. ; Woodson, Clifton Brock ; Mills, Heath Jordan ; Kubanek, Julia ; Sobecky, Patricia A. ; Hay, Mark E.

Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.
Integrating prey defensive traits: contrasts of marine worms from temperate and tropical habitats

(Georgia Institute of Technology, 2006-05) Kicklighter, Cynthia Ellen ; Hay, Mark E.

Marine worms are speciose and numerically prominent members of marine communities where they play critical roles in trophic interactions and in affecting biogeochemical cycles. Despite the ecological importance of this group, little is known about their palatability to, and defenses against, consumers. In addition, most studies of prey defenses in marine organisms have focused on overt, sessile species: few studies have investigated more mobile and behaviorally complex species that could potentially be integrating predator deterrents with refuge use and other escape behaviors. To increase our understanding of consequences of defensive traits among mobile marine prey, we surveyed the palatability of 81 species of worms from the Caribbean and warm-temperate western Atlantic. Thirty-seven percent of the species were unpalatable. Worms with differentially exposed body portions commonly defended exposed feeding appendages with chemical or structural deterrents, while palatable and undefended bodies remained sheltered within structural refuges. Unpalatable worms tended to be brightly colored and sedentary, exposed to epibenthic predators, and to occupy hard substrates. Palatable worms tended to be drab, to live in structural refuges from consumers, to be mobile, and to inhabit unconsolidated sediments. Overall, taxonomy (Sabellidae and Terebellidae) and color were the traits most strongly associated with unpalatability. Unpalatable species appeared less constrained by predation and freer to forage for long periods on higher quality surface sediments or on other invertebrates at the sediment surface (thus, potentially influencing the distribution and abundance of other species). In contrast, palatable species appeared more constrained by predation risk. They fed on lower quality subsurface sediments and foraged at times or locations where consumers were less active. These ecological patterns may be generalized to other soft-bodied prey, such as caterpillars, which show similar trends regarding palatability and lifestyle.
Fishes learn aversions to a nudibranch’s chemical defense

(Georgia Institute of Technology, 2006-01-24) Long, Jeremy D. ; Hay, Mark E.

The nudibranch Doriopsilla pharpa was rejected as food when tethered in the field and when offered to 2 species of co-occurring crabs (the lesser blue crab Callinectes similus and the mud crab Panopeus herbstii) and 2 species of co-occurring fishes (the mummichog Fundulus heteroclitus and the striped blenny Chasmodes bosquianus) in the laboratory. When the fishes were offered squid-based artificial food containing nudibranch extracts (i.e. defended food), both species initially consumed this food, but rapidly developed aversions in subsequent feedings. Although both fishes rapidly learned to reject the food, they learned using different cues. The striped blenny Chasmodes bosquianus regurgitated following the initial feeding and then avoided all food made of squid regardless of whether or not it contained the extract. In contrast, the mummichog Fundulus heteroclitus did not regurgitate, and learned to avoid only food containing the extract; it still consumed squid-based food without the extract. Thus, the mummichog detected the deterrent chemical and avoided only defended food while the striped blenny was a less effective feeder, avoiding both defended and undefended food that tasted like squid. Bioassay-guided separation using the mummichog demonstrated that the sesquiterpene polygodial was responsible for the deterrent effects of the nudibranch extract. This metabolite also resulted in the striped blenny avoiding either squid- or tuna-based food treated with this metabolite.
An invasive crab in the South Atlantic Bight: friend or foe?

(Georgia Institute of Technology, 2005-08-31) Hay, Mark E.