Adjunct Faculty, Oceans and Coasts
My current research interests examine (1) the role of biotic processes, and human perturbations, in controlling the flow of energy among trophic levels both within and between marine habitats, with emphasis on submerged vegetated habitats, (2) the use of biodindicators in seagrass ecosystems to detect water quality assessment and ecosystem change.
Much of the emphasis of the first objective is on experimental assessments of grazing intensity in temperate and tropical seagrass habitats, the responses of temperate and tropical seagrasses to this grazing, the population dynamics of the main herbivores (sea urchins, herbivorous fish, green turtles and dugongs) and the role of the seascape in changing the trophic interactions in marine systems. The second objective is mainly focused on the development of indexes for water quality assessment using bioindicators from the molecule to the ecosystem.
The overall significance of this research lies in its attempt to understand the processes that control the distribution and productivity of seagrass dominated habitats. Because of the widespread occurrence of these habitats, the extraordinary productivity and richness of their associated biota and the services they provide, the understanding of the factors controlling their distribution and the effect of human perturbations on those controlling factors is essential to our understanding. Both approaches clearly define good objectives of a better management and conservation.
- Journal Article2016For traditional island communities in the Nicobar archipelago, complete no-go areas are the most effective form of marine managementFor traditional island communities, no-go areas are the most effective form of managementOcean & Coastal Management 133, 53-63 http://dx.doi.org/10.1016/j.ocecoaman.2016.09.003Download
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For traditional island communities in the Nicobar archipelago, complete no-go areas are the most effective form of marine management
The ability of local communities to sustainably manage natural resource harvests in coral reefs ecosystem depends heavily on the strength of traditional institutions. Coastal communities have evolved a suite of restrictive practices to control marine offtake and there is considerable recent evidence of their effec- tiveness in protecting and enhancing resource stocks. However, traditionally imposed restrictions can vary considerably in their complexity and in their functional effectiveness. The indigenous communities of the Nicobar Islands are dependent on marine resources for sustenance, managing them with a range of traditionally imposed restrictions. These include limited entry to certain locations, closed seasons and areas, and restrictions on species, size-classes of fish and fishing methods. We tested the relative effectiveness of protection in areas managed under different traditional control regimes by comparing the abundance and biomass of targeted fish groups in managed and unmanaged areas. Our results indicate that reef sites with the strictest form of restriction e essentially no-go areas e had significantly higher abundance and biomass values of most functional groups of fishes compared with partially protected and control locations. In contrast, targeted food fish stocks did not differ from control locations in partially protected sites managed with even complex forms of traditional management. Ensuring that traditional harvest rules are complied is critical to the success of any management system, and our re- sults suggest that they can be most strictly enforced in traditional no-go areas. Our work highlights the importance of critically evaluating the factors influencing traditional management systems to strengthen their ability to protect these reefs from unsustainable overharvest.
- Journal Article2016"Choice" and destiny: The substrate composition and mechanical stability of settlement structures can mediate coral recruit fate in post-bleached reefsCoral Reefs. 35: 211-222
Increasingly frequent and intense ocean warming events seriously test the buffer and recovery capacities of tropical coral reefs. Post-disturbance, available settlement structures on a reef (often dead coral skeletons) vary considerably in their mechanical stability and substrate composition, critically influencing coral recruit settlement choice and fate. In the wake of a coral mass mortality in the Lakshadweep archipelago, we examine (1) the relative availability of recruit settlement structures (from stable to unstable: reef platform, dead massive coral, consolidated rubble, dead corymbose coral, dead tabular coral, and unconsolidated rubble) in 12 recovering reefs across three atolls in the archipelago, (2) the substrate composition [crustose coralline algae (CCA), mixed turf, macroalgae] of these structural forms, and (3) whether the choice and fate of young coral are mediated by the substrate and stability of different structural forms. For this, we measured the abundance and distribution of recruit (<1cm), juvenile (1–5 cm), and young adult (5–10) corals of 24 common coral genera. Four years after the mass mortality, reefs differed considerably in composition of settlement structures. The structures themselves varied significantly in substrate cover with dead tables largely covered in CCA [60 ± 6.05 % (SE)] and dead corymbose coral dominated by mixed turf (61.83 ± 3.8 %). The youngest visible recruits (<1 cm) clearly preferred CCA-rich structures such as dead massives and tables. However, older size classes were rarely found on unstable structures (strongly ‘‘avoiding’’ tables, Ivlev’s electivity index, E = -0.5). Our results indicate that while substrate cover might mediate coral choice, the mechanical stability of settlement structures is critical in determining post-settlement coral survival. The composition and availability of settlement structures on a reef may serve as a characteristic signature of its recovery potential, aiding in assessments of reef resilience.
- Dataset2016Long-lived groupers require structurally stable reefs in the face of repeated climate change disturbances.Karkarey R, Kelkar N, Lobo AS, Alcoverro T, Arthur R (2014) Data from: Long-lived groupers require structurally stable reefs in the face of repeated climate change disturbances. Dryad Digital Repository. http://dx.doi.org/10.5061/dryad.d7j02
- Journal Article2015Fish community reassembly after a coral mass mortality: higher trophic groups are subject to increased rates of extinctionEcology Letters 18(5): 451–461Download
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Since Gleason and Clements, our understanding of community dynamics has been influenced by theories emphasising either dispersal or niche assembly as central to community structuring. Determining the relative importance of these processes in structuring real-world communities remains a challenge. We tracked reef fish community reassembly after a catastrophic coral mortality in a relatively unfished archipelago. We revisited the stochastic model underlying MacArthur and Wilson’s Island Biogeography Theory, with a simple extension to account for trophic identity. Colonisation and extinction rates calculated from decadal presence-absence data based on (1) species neutrality, (2) trophic identity and (3) site-specificity were used to model post-disturbance reassembly, and compared with empirical observations. Results indicate that species neutrality holds within trophic guilds, and trophic identity significantly increases overall model performance. Strikingly, extinction rates increased clearly with trophic position, indicating that fish communities may be inherently susceptible to trophic downgrading even without targeted fishing of top predators.
- Journal Article2015Erosion of Traditional Marine Management Systems in the Face of Disturbances in the Nicobar ArchipelagoHuman Ecology, DOI 10.1007/s10745-015-9781-x
- Journal Article2015Seagrass Herbivory Levels Sustain Site-Fidelity in a Remnant Dugong PopulationSeagrass Herbivory Levels Sustain Site- Fidelity in a Remnant Dugong PopulationPLoS ONE 10(10): e0141224. doi:10.1371/journal.pone.0141224Download
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Seagrass Herbivory Levels Sustain Site-Fidelity in a Remnant Dugong Population
Herds of dugong, a largely tropical marine megaherbivore, are known to undertake long-dis- tance movements, sequentially overgrazing seagrass meadows in their path. Given their drastic declines in many regions, it is unclear whether at lower densities, their grazing is less intense, reducing their need to travel between meadows. We studied the effect of the feeding behaviour of a small dugong population in the Andaman and Nicobar archipelago, India to understand how small isolated populations graze seagrasses. In the seven years of our observation, all recorded dugongs travelled either solitarily or in pairs, and their use of seagrasses was limited to 8 meadows, some of which were persistently grazed. These meadows were relatively large, contiguous and dominated by short-lived seagrasses spe- cies. Dugongs consumed approximately 15% of meadow primary production, but there was a large variation (3–40% of total meadow production) in consumption patterns between meadows. The impact of herbivory was relatively high, with shoot densities c. 50% higher inside herbivore exclosures than in areas exposed to repeated grazing. Our results indicate that dugongs in the study area repeatedly graze the same meadows probably because the proportion of primary production consumed reduces shoot density to levels that are still above values that can trigger meadow abandonment. This ability of seagrasses to cope per- haps explains the long-term site fidelity shown by individual dugongs in these meadows. The fact that seagrass meadows in the archipelago are able to support dugong foraging requirements allows us to clearly identify locations where this remnant population persists, and where urgent management efforts can be directed.
- Journal Article2014Seagrasses in the age of sea turtle conservation and shark overfishingFrontiers in Marine Science 1:28. doi: 10.3389/fmars. 2014.00028.Download
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Efforts to conserve globally declining herbivorous green sea turtles have resulted in promising growth of some populations. These trends could significantly impact critical ecosystem services provided by seagrass meadows on which turtles feed. Expanding turtle populations could improve seagrass ecosystem health by removing seagrass biomass and preventing of the formation of sediment anoxia. However, overfishing of large sharks, the primary green turtle predators, could facilitate turtle populations growing beyond historical sizes and trigger detrimental ecosystem impacts mirroring those on land when top predators were extirpated. Experimental data from multiple ocean basins suggest that increasing turtle populations can negatively impact seagrasses, including triggering virtual ecosystem collapse. Impacts of large turtle populations on seagrasses are reduced in the presence of intact shark populations. Healthy populations of sharks and turtles, therefore, are likely vital to restoring or maintaining seagrass ecosystem structure, function, and their value in supporting fisheries and as a carbon sink.
- Journal Article2014Long-lived benthic predators require structurally stable reefs in the face of repeated climate-change disturbancesCoral Reefs. 33: 289-302
Benthic recovery from climate-related disturbances does not always warrant a commensurate functional recovery for reef-associated fish communities. Here, we examine the distribution of benthic groupers (family Serranidae) in coral reef communities from the Lakshadweep archipelago (Arabian Sea) in response to structural complexity and long-term habitat stability. These coral reefs that have been subject to two major El Nin ̃o Southern Oscillation-related coral bleaching events in the last decades (1998 and 2010). First, we employ a long-term (12-yr) benthic- monitoring dataset to track habitat structural stability at twelve reef sites in the archipelago. Structural stability of reefs was strongly driven by exposure to monsoon storms and depth, which made deeper and more sheltered reefs on the eastern aspect more stable than the more exposed (western) and shallower reefs. We surveyed groupers (species richness, abundance, biomass) in 60 sites across the entire archipelago, representing both exposures and depths. Sites were selected along a gradient of structural complexity from very low to high. Grouper biomass appeared to vary with habitat stability with significant differences between depth and exposure; sheltered deep reefs had a higher grouper biomass than either sheltered shallow or exposed (deep and shallow) reefs. Species richness and abundance showed similar (though not significant) trends. More interestingly, average grouper biomass increased exponentially with structural complexity, but only at the sheltered deep (high stability) sites, despite the availability of recovered structure at exposed deep and shallow sites (lower-stability sites). This trend was especially pronounced for long-lived groupers (life span [10 yrs). These results suggest that long-lived groupers may prefer temporally stable reefs, independent of the local availability of habitat structure. In reefs subject to repeated disturbances, the presence of structurally stable reefs may be critical as refuges for functionally important, long-lived species like groupers.
- Journal Article2013Complex ecological pathways underlie perceptions of conflict between green turtles and fishers in the Lakshadweep Islands.Biological Conservation 167: 25-34
Managing human–wildlife conflict is often complicated by apparent mismatches between community perceptions and measures of directly incurred losses. Fishers in Agatti Island (Lakshadweep, India) associate recent increases in green turtle (Chelonia mydas) populations with declining fish catches, resulting in targeted killing of turtles. We compared fisher perceptions in Agatti with a very similar atoll, Kadmat, with much lower turtle densities. Nearly 90% of Agatti fishers interviewed blamed turtles for declining catch compared with 20% in Kadmat and proposed two mechanisms for this decline: direct interference (e.g., turtles damaged gear) which we define as first order conflict, and indirect mechanisms (second order conflict): turtles overgrazed seagrasses, thereby reducing fish catch. We evaluated the magnitude of gear loss with interviews and tested proposed indirect mechanisms with a turtle density gradient, before–after comparisons (taking advantage of an increase in turtles in Kadmat and concurrent decrease in Agatti) and a natural herbivore exclosure. These complementary approaches supported fisher-pro- posed second-order mechanisms: at high densities, turtles heavily grazed seagrasses, significantly reduced canopy heights, lowered fish recruit abundance, food fish biomass and catch. Estimates of losses incurred in Agatti show that first-order conflict cost fishers USD 0.6 fisher-1 year1, while second-order pathways accounted for USD 887 fisher-1 year-1. Our results show that local perceptions are fueled by often-complex mechanisms that, though not always straightforward to measure, are very important in generating conflict. Reconciling the human–wildlife interface requires an adequate accounting of direct and indirect mechanisms to more completely reflect true losses communities bear for living with wildlife.
- Journal Article2013Green turtle herbivory dominates the fate of seagrass primary production in the Lakshadweep islands (Indian Ocean)Marine Ecology Progress Series. 485:235-243
Historical global declines of megaherbivores from marine ecosystems have hitherto contributed to an understanding of seagrass meadow production dominated by detrital path- ways — a paradigm increasingly being questioned by recent re-evaluations of the importance of herbivory. Recoveries in green turtle populations at some locations provide an ideal opportunity to examine effects of high megaherbivore densities on the fate of seagrass production. We conducted direct field measurements of aboveground herbivory and shoot elongation rates in 9 seagrass meadows across 3 atolls in the Lakshadweep Archipelago (India) representing a gradient of green turtle densities. Across all meadows, green turtles consumed an average of 60% of the total leaf growth. As expected, herbivory rates were positively related to turtle density and ranged from being almost absent in meadows with few turtles, to potentially overgrazed meadows (ca. 170% of leaf growth) where turtles were abundant. Turtle herbivory also substantially reduced shoot elongation rates. Simulated grazing through clipping experiments confirmed this trend: growth rates rapidly declined to almost half in clipped plots relative to control plots. At green turtle den- sities similar to historical estimates, herbivory not only dominated the fate of seagrass primary pro- duction but also drastically reduced production rates in grazed meadows. Intensive turtle grazing and associated movement could also modify rates of detrital cycling, leaf export and local carbon burial, with important consequences for the entire seascape.