Rapidly spreading seagrass invades the Caribbean …...Florida/Caribbean Inventory and Monitoring...
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546 www.frontiersinecology.org © The Ecological Society of America Write Back hypothesis. In our first hypothesis, exemplified by the metaphor of the “low-hanging fruit”, the lion’s share of our capacity to explain and predict is made possible by long-established theories. The “explanation of resid- ual variation” described by Patten and Hartnett could have been substi- tuted with our use of the term “mar- ginal explanatory power”. We did not, however, speculate on the advent of a “paradigm shift” in ecology or the advent of a new crop of fruit. We do not identify as philosophers or historians of science, but we do feel the portrayal by Patten and Hartnett of “paradigm shift” in con- trast to “normal science”, sensu Kuhn, is not entirely adequate, even if this distinction may be highly sub- jective. We would suspect that para- digm shifts are accompanied by leaps in R 2 in the specific context that the advancement applies. While the dis- covery of relativity could undoubt- edly be labeled a “paradigm shift”, it is not because this theory offered a step improvement on Newton’s the- ories. Rather, Einstein’s theory pro- vided explanatory and predictive power (R 2 ’ 1) in a context where Newton’s theory failed (R 2 ’ 0) – the prediction and explanation of the movement of extremely large objects or movement at extreme speeds – while also providing expla- nation and prediction in all contexts where Newtonian physics had not been falsified. The effect of “para- digm shifts” on explanatory power or complexity is a suitable question for future metaknowledge studies. We likely have not presented an exhaustive list of the possible mech- anisms for the observed trends in R 2 and number of P values in ecology. These trends may be best explained by hypotheses that make reference to “normal science” and “paradigm shifts” as suggested by Patten and Hartnett, beyond what is included in the “low-hanging fruit” hypothesis. We would suggest that further meta- knowledge studies are required to discern between proposed hypothe- ses and to accurately describe the state of our discipline. Etienne Low-Décarie *† , Corey Chivers, and Monica Granados Department of Biology, McGill University, Montreal, Canada; † Current address: School of Biological Sciences, University of Essex, Colchester, UK * ([email protected]) doi:10.1890/14.WB.015 Rapidly spreading seagrass invades the Caribbean with unknown ecological consequences The non-native seagrass Halophila stip- ulacea has spread rapidly throughout the Caribbean Sea (Willette et al. 2014); without additional research, the ecological ramifications of this invasion are difficult to predict. Biodiversity, connectivity of marine ecosystems, and recovery of degraded coral reefs could all be affected. The invasive seagrass, native to the Red Sea and Indian Ocean, has taken over sand bottoms and intermixed with or replaced native seagrasses, including Thalassia testudinum, Syringodium fili- forme, and Halodule wrightii (Figure 1). H stipulacea is an established inva- sive species in the Mediterranean Sea, probably introduced after the opening of the Suez Canal. Com- petition between H stipulacea and native Mediterranean seagrasses is minimal to absent due to habitat pref- erences; H stipulacea grows in deeper, bare sand habitats and over sub- merged dead mats of native seagrass (Sghaier et al. 2011). The only other known invasive seagrass species, Zostera japonica, has displaced a native seagrass at some locations off the coast of the Pacific Northwest (Jun Bando 2006). Experimental introduction of Z japonica to bare mud flats increased the density and num- ber of animal species observed therein (Posey 1988). Sediment disturbance, such as the excavation of underwater substrate by storms, provides an advantage to both of these faster- growing invasives over their native counterparts (Jun Bando 2006; Willette and Ambrose 2012). In the Caribbean, H stipulacea could stabilize previously unvege- tated sand bottoms, thereby reducing erosion of nearby coastal shorelines during storm events, which are expected to become more frequent and stronger under a changing cli- mate. Improved understanding of the potential effects of this invasive sea- grass in the Caribbean requires more Figure 1. The invasive seagrass Halophila stipulacea (bright green, short elliptic/oblong blades 3–8 cm long, with distinct mid-veins) growing intermixed with Thalassia testudinum, Halodule wrightii, and Syringodium filiforme near St John, in the US Virgin Islands. CS Rogers
Transcript of Rapidly spreading seagrass invades the Caribbean …...Florida/Caribbean Inventory and Monitoring...
546
www.frontiersinecology.org © The Ecological Society of America
Write Back
hypothesis. In our first hypothesis,exemplified by the metaphor of the“low-hanging fruit”, the lion’s shareof our capacity to explain and predictis made possible by long-establishedtheories. The “explanation of resid-ual variation” described by Pattenand Hartnett could have been substi-tuted with our use of the term “mar-ginal explanatory power”. We did not,however, speculate on the advent of a“paradigm shift” in ecology or theadvent of a new crop of fruit.
We do not identify as philosophersor historians of science, but we dofeel the portrayal by Patten andHartnett of “paradigm shift” in con-trast to “normal science”, sensuKuhn, is not entirely adequate, evenif this distinction may be highly sub-jective. We would suspect that para-digm shifts are accompanied by leapsin R2 in the specific context that theadvancement applies. While the dis-covery of relativity could undoubt-edly be labeled a “paradigm shift”, itis not because this theory offered astep improvement on Newton’s the-ories. Rather, Einstein’s theory pro-vided explanatory and predictivepower (R2 ’ 1) in a context whereNewton’s theory failed (R2 ’ 0) –the prediction and explanation ofthe movement of extremely largeobjects or movement at extremespeeds – while also providing expla-nation and prediction in all contextswhere Newtonian physics had notbeen falsified. The effect of “para-digm shifts” on explanatory power orcomplexity is a suitable question forfuture metaknowledge studies.
We likely have not presented anexhaustive list of the possible mech-anisms for the observed trends in R2
and number of P values in ecology.These trends may be best explainedby hypotheses that make reference to“normal science” and “paradigmshifts” as suggested by Patten andHartnett, beyond what is included inthe “low-hanging fruit” hypothesis.We would suggest that further meta-knowledge studies are required todiscern between proposed hypothe-ses and to accurately describe thestate of our discipline.
Etienne Low-Décarie*†, CoreyChivers, and Monica GranadosDepartment of Biology, McGillUniversity, Montreal, Canada;†Current address: School of BiologicalSciences, University of Essex,Colchester, UK*([email protected])
doi:10.1890/14.WB.015
Rapidly spreading seagrassinvades the Caribbean withunknown ecologicalconsequences The non-native seagrass Halophila stip-ulacea has spread rapidly throughoutthe Caribbean Sea (Willette et al.2014); without additional research,the ecological ramifications of thisinvasion are difficult to predict.Biodiversity, connectivity of marineecosystems, and recovery of degradedcoral reefs could all be affected. Theinvasive seagrass, native to the RedSea and Indian Ocean, has taken oversand bottoms and intermixed with orreplaced native seagrasses, includingThalassia testudinum, Syringodium fili-forme, and Halodule wrightii (Figure 1).
H stipulacea is an established inva-sive species in the Mediterranean
Sea, probably introduced after theopening of the Suez Canal. Com-petition between H stipulacea andnative Mediterranean seagrasses isminimal to absent due to habitat pref-erences; H stipulacea grows in deeper,bare sand habitats and over sub-merged dead mats of native seagrass(Sghaier et al. 2011). The only otherknown invasive seagrass species,Zostera japonica, has displaced anative seagrass at some locations offthe coast of the Pacific Northwest(Jun Bando 2006). Experimentalintroduction of Z japonica to bare mudflats increased the density and num-ber of animal species observed therein(Posey 1988). Sediment disturbance,such as the excavation of underwatersubstrate by storms, provides anadvantage to both of these faster-growing invasives over their nativecounterparts (Jun Bando 2006;Willette and Ambrose 2012).
In the Caribbean, H stipulaceacould stabilize previously unvege-tated sand bottoms, thereby reducingerosion of nearby coastal shorelinesduring storm events, which areexpected to become more frequentand stronger under a changing cli-mate. Improved understanding of thepotential effects of this invasive sea-grass in the Caribbean requires more
Figure 1. The invasive seagrass Halophila stipulacea (bright green, short elliptic/oblongblades 3–8 cm long, with distinct mid-veins) growing intermixed with Thalassia testudinum,Halodule wrightii, and Syringodium filiforme near St John, in the US Virgin Islands.
CS
Rog
ers
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data on herbivory rates, selectivefeeding, and relative nutritional val-ues of the native and introducedspecies. For example, the proximityof seagrasses, mangroves, and coralreefs in the Caribbean supports highlevels of fish biomass and diversity(Nagelkerken et al. 2001), whichcould decline if the invasive seagrassreduces the extent of native sea-grasses, if native seagrasses are pre-ferred by herbivorous fish, or if nativeseagrasses provide superior nutrition.
Recovery of degraded coral reefs(Jackson et al. 2014) could be eitherhindered or promoted indirectly bythe spread of this invasive seagrass,depending on its effects on the abun-dance and diversity of herbivorousfish and sea urchins that, by feedingon algae, open up substrate for coralrecruitment and growth. Preliminarydata from experimental fish trapsplaced in seagrass beds dominatedeither by H stipulacea or by S filiformeshowed the former had larger indi-vidual fish, fewer juvenile fish, andmore fish species (Willette andAmbrose 2012). Notably, few her-bivorous fish were caught in trapswithin either of these seagrass beds.Moreover, a significantly greaterabundance of epibiotic (surface-attached) organisms – particularlymembers of the Crustacea, many of
which serve as important preyspecies for fish – was associated withthe invasive seagrass (Willette andAmbrose 2012). More data areneeded on the role of H stipulaceabeds as nurseries and foraging areasfor parrotfish, green sea turtles, seaurchins, and other herbivores.
Further research is also required todetermine whether positive effects ofthe spread of this seagrass outweighthe negatives and what, if any, man-agement actions should be taken.Given the rapid spread of H stipu-lacea, only weekly monitoring of baysand removal of the invasive wouldkeep it from getting a foothold.Physical removal of the seagrass afterit has become established, however,would likely not be feasible due tologistic and monetary constraints.
H stipulacea now joins a growing listof habitat-altering species, includingthe Indo-Pacific lionfish (Pterois voli-tans), invading the Caribbean.Caroline S Rogers1*, Demian AWillette2, and Jeff Miller3
1US Geological Survey, SoutheastEcological Science Center, CaribbeanField Station, St John, US VirginIslands *([email protected]);2Department of Ecology andEvolutionary Biology, University ofCalifornia–Los Angeles, Los Angeles,CA; 3National Park Service, South
Florida/Caribbean Inventory andMonitoring Program, St John, USVirgin Islands
Jackson JBC, Donovan MK, Cramer KL,and Lam VV (Eds). 2014. Status andtrends of Caribbean coral reefs: 1970–2012. Gland, Switzerland: Global CoralReef Monitoring Network, IUCN.
Jun Bando K. 2006. The role of competi-tion and disturbance in a marine inva-sion. Biol Invasions 8: 755–63.
Nagelkerken I, Kleijnen S, Klop T, et al.2001. Dependence of Caribbean reeffishes on mangroves and seagrass bedsas nursery habitats: a comparison offish faunas between bays with andwithout mangroves/seagrass beds. MarEcol-Prog Ser 214: 225–35.
Posey MH. 1988. Community changesassociated with the spread of an intro-duced seagrass, Zostera japonica.Ecology 69: 974–83.
Sghaier YR, Zakhama-Sraieb R, BenamerI, and Charfi-Cheikhrouha F. 2011.Occurrence of the seagrass Halophilastipulacea (Hydrocharitaceae) in thesouthern Mediterranean Sea. Bot Mar54: 575–82.
Willette DA and Ambrose RF. 2012. Effectsof the invasive seagrass Halophila stipu-lacea on the native seagrass, Syringo-dium filiforme, and associated fish andepibiota communities in the easternCaribbean. Aquat Bot 103: 74–82.
Willette DA, Chalifour J, Debrot AO, et al.2014. Continued expansion of thetrans-Atlantic invasive marineangiosperm Halophila stipulacea in theeastern Caribbean. Aquat Bot 112:98–102.
doi:10.1890/14.WB.016
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