Ecological spillover from a marine protected area replenishes an over‐exploited population across an island chain

Abstract

Quantifying successful ecological spillover from marine protected areas (MPAs) is challenging yet crucial for conservation planning. The queen conch (Lobatus gigas) supports an iconic Bahamian fishery, but populations are declining. Here we provide evidence for MPAs as a solution: showing that a well-enforced MPA supplies ecological spillover through larval supply. Dive surveys throughout the Exuma Cays, including a centrally-located MPA, provided information on abundance, size, and age. Data showed higher-adult abundance within the MPA and positive associations between enforcement and conch size and age. A biophysical model estimated that MPA larvae settled in unprotected areas, and that MPA larval sources included unprotected sites with densities too low for reproduction. The MPA is currently sustaining nearby populations, yet its future is in jeopardy without upstream larval sources. Our results and consultations with stakeholders regarding management of the Bahamian conch fishery support creating a network of MPAs that exchange larvae for a sustainable future.

The potential of marginal coastal nursery habitats for the conservation of a culturally important Caribbean marine species

“…While completely protecting large, high‐quality areas would be efficient to conserve queen conch populations (and more broadly a range of marine species), it is rarely an economically viable option as those areas also concentrate much of the economical human activities (Halpern et al, ). In some cases, rather than protecting a single large area, it has been advocated that a network of smaller protected areas targeting key habitats (or part of the life cycle, such as nursery grounds) and relying on spillover effects would be as efficient for conserving a species (Gaines et al, ; Kough et al, ). While it is not known exactly how far queen conchs disperse along the Yucatan coast, a significant relationship between genetic and geographical distances exist for this species, suggesting that dispersal mostly occurs locally (Truelove et al, ).…”

“…While it is not known exactly how far queen conchs disperse along the Yucatan coast, a significant relationship between genetic and geographical distances exist for this species, suggesting that dispersal mostly occurs locally (Truelove et al, ). Therefore, a network of well‐enforced reserves locally connected by adult and larval spillover is likely to be a valuable alternative to larger reserves (Gaines et al, ; Kough et al, ). This management approach was for example recommended for improving the sustainability of the Bahamian queen conch fisheries (Kough et al, ).…”

“…If the level of protection is maintained or expanded (i.e., by preventing the removal of juveniles, subadults and adults that have yet to breed) this network, while encompassing large area of marginal habitats, might efficiently contribute to the conservation of this species in the region through adult and larval spillover. However, further work on the quantification of population exchange will be required to fully assess the efficiency of those marine protected areas (see for example, Kough et al, ), or if additional protected marine habitats would be required along the coast. Further, this network of marine protected areas would likely also contribute to the conservation of a range of other commercially or culturally important species, for example fish populations (Gaines et al, ), hence contributing to the larger‐scale management of sustainable resources to support the local population.…”

“…Therefore, a network of well-enforced reserves locally connected by adult and larval spillover is likely to be a valuable alternative to larger reserves (Gaines et al, 2010;Kough et al, 2019). This management approach was for example recommended for improving the sustainability of the Bahamian queen conch fisheries (Kough et al, 2019). There is currently a network of marine protected areas (including our study site Xel-Há, see Figure 1) receives important amounts of groundwater (Lagomasino et al, 2015) and has several core zones designed to reduce the pressure on the main marine resources (Mazzotti et al, 2005).…”

“…Specifically, while groundwater-affected areas can be suitable for the growth of juveniles, with a foraging behaviour adapted to the marginal conditions (Dujon et al, 2019;Stieglitz & Dujon, 2017), it is to date not documented if adult individuals emigrate from those marginal habitat to marine areas more suitable for breeding aggregations a prerequisite to adult and larval spillover in the core habitats (Kough et al, 2019;Stoner & Ray-Culp, 2000). This information is of key importance as ecological spillover from strongly enforced marine protected areas has been shown, in certain cases, to be efficient in repopulating habitat depleted by fisheries (Grüss, Kaplan, Guénette, Roberts, & Botsford, 2011;Kough et al, 2019). Here, we investigate whether queen conchs inhabiting groundwater-fed marginal habitats exhibit an ontogenetic niche shift similar to what is observed in the core habitat, and if these populations are connected to offshore core habitats.…”