Networks Of No-take Reserves Research Articles

Effects of reduced water quality on coral reefs in and out of no-take marine reserves.

Near-shore marine environments are increasingly subjected to reduced water quality, and their ability to withstand it is critical to their persistence. The potential role marine reserves may play in mitigating the effects of reduced water quality has received little attention. We investigated the spatial and temporal variability in live coral and macro-algal cover and water quality during moderate and major flooding events of the Fitzroy River within the Keppel Bay region of the Great Barrier Reef Marine Park from 2007 to 2013. We used 7 years of remote sensing data on water quality and data from long-term monitoring of coral reefs to quantify exposure of coral reefs to flood plumes. We used a distance linear model to partition the contribution of abiotic and biotic factors, including zoning, as drivers of the observed changes in coral and macro-algae cover. Moderate flood plumes from 2007 to 2009 did not affect coral cover on reefs in the Keppel Islands, suggesting the reef has intrinsic resistance against short-term exposure to reduced water quality. However, from 2009 to 2013, live coral cover declined by ∼ 50% following several weeks of exposure to turbid, low salinity water from major flood plume events in 2011 and subsequent moderate events in 2012 and 2013. Although the flooding events in 2012 and 2013 were smaller than the flooding events between 2007 to 2009, the ability of the reefs to withstand these moderate floods was lost, as evidenced by a ∼ 20% decline in coral cover between 2011 to 2013. Although zoning (no-take reserve or fished) was identified a significant driver of coral cover, we recorded consistently lower coral cover on reserve reefs than on fished reefs throughout the study period and significantly lower cover in 2011. Our findings suggest that even reefs with an inherent resistance to reduced water quality are not able to withstand repeated disturbance events. The limitations of reserves in mitigating the effects of reduced water quality on near-shore coral reefs underscores the importance of integrated management approaches that combine effective land-based management with networks of no-take reserves.

Spatiotemporal Variation in Oyster Fecundity and Reproductive Output in a Network of No-Take Reserves

Adult fecundity and reproductive potential can be critical determinants of subsequent larval supply and juvenile recruitment, and important determinants of placed-based management, especially when selecting sites for marine reserves where larval export is an expected outcome. We quantified spatiotemporal variation in fecundity and reproductive potential of female oysters (Crassostrea virginica) within a network of no-take oyster broodstock reserves by sampling over 3 y at 3 spatial scales: (1) per capita, (2) per square meter, and (3) per reserve. A total of 2,596 oysters were collected using scuba from six reserves in Pamlico Sound, NC, during 2006 to 2008 and processed in the laboratory for fecundity. Per-capita fecundity ranged from 0–340,500 eggs, and increased exponentially with oyster size, peaking in May of all years. In general, per-capita fecundity was highest at more inland mesohaline reserves, whereas reproductive potential per square meter and reserve reproductive potential were highest at more seaward polyhaline reserves as a result of a combination of relatively high density, and large oyster size and reserve areas. All 3 reproductive metrics increased in general over time. These results suggest that inland broodstock reserves should be prioritized for stock enhancement/seeding—and more seaward reserves for reserve expansion—and highlight the need to consider spatiotemporal variation and the scale at which a key demographic rate (fecundity and reproductive potential) is expressed when assessing the efficacy and conservation/restoration targets of marine reserves.

Estuarine circulation and predicted oyster larval dispersal among a network of reserves

A critical component to understanding connectivity of isolated populations of marine organisms (i.e., metapopulations) is quantifying hydrodynamic paths of dispersal, and variation in the strength of these hydrodynamic connections. We replicated 3-dimensional wind-driven circulation patterns in Pamlico Sound (PS), North Carolina, USA using a numerical hydrodynamic model (ADCIRC, ADvanced CIRCulation) in conjunction with a particle-tracking model (PTM) to predict larval dispersal of the eastern oyster (Crassostrea virginica) and estimate connectivity among a network of ten no-take oyster broodstock reserves in PS to inform restoration efforts. ADCIRC was forced with wind observations, which were predominately southwesterly during May–November 2007 when oyster larvae were dispersing in PS. Acoustic Doppler Current Profilers and surface drifters were used to validate ADCIRC-predicted current velocities and PTM-predicted larval dispersal, respectively. ADCIRC reliably predicted current velocities at different locations in PS, especially currents near-surface (R = 0.6, lags < 2 h). The PTM accurately predicted (R > 0.5) the total and net distance transported by drifters, which ranged from 1 to 63 km and 0.3–42 km, respectively over ≤7 days. Potential oyster larval connectivity was not uniform among broodstock reserves in PS. Of the 100 possible connections, 24 were present. Eight of the 10 reserves provided ≥ one inter-reserve connection, with 4 being the most. Self-recruitment occurred at all but one reserve. Spatial variation in the degree of potential oyster larval connectivity in PS, combined with evidence for spatiotemporal dynamics of oyster populations, provides strong evidence for an oyster metapopulation and possibly source-sink dynamics within the network of no-take reserves.

Connectivity, biodiversity conservation and the design of marine reserve networks for coral reefs

Networks of no-take reserves are important for protecting coral reef biodiversity from climate change and other human impacts. Ensuring that reserve populations are connected to each other and non-reserve populations by larval dispersal allows for recovery from disturbance and is a key aspect of resilience. In general, connectivity between reserves should increase as the distance between them decreases. However, enhancing connectivity may often tradeoff against a network’s ability to representatively sample the system’s natural variability. This “representation” objective is typically measured in terms of species richness or diversity of habitats, but has other important elements (e.g., minimizing the risk that multiple reserves will be impacted by catastrophic events). Such representation objectives tend to be better achieved as reserves become more widely spaced. Thus, optimizing the location, size and spacing of reserves requires both an understanding of larval dispersal and explicit consideration of how well the network represents the broader system; indeed the lack of an integrated theory for optimizing tradeoffs between connectivity and representation objectives has inhibited the incorporation of connectivity into reserve selection algorithms. This article addresses these issues by (1) updating general recommendations for the location, size and spacing of reserves based on emerging data on larval dispersal in corals and reef fishes, and on considerations for maintaining genetic diversity; (2) using a spatial analysis of the Great Barrier Reef Marine Park to examine potential tradeoffs between connectivity and representation of biodiversity and (3) describing a framework for incorporating environmental fluctuations into the conceptualization of the tradeoff between connectivity and representation, and that expresses both in a common, demographically meaningful currency, thus making optimization possible.