Species around the world are shifting their ranges in response to climate change. To make robust predictions about climate‐related colonizations and extinctions, it is vital to understand the dynamics of range edges. This study is among the first to examine annual dynamics of cold and warm range edges, as most global change studies average observational data over space or over time. We analyzed annual range edge dynamics of marine fishes—both at the individual species level and pooled into cold‐ and warm‐edge assemblages—in a multi‐decade time‐series of trawl surveys conducted on the Northeast US Shelf during a period of rapid warming. We tested whether cold edges show stronger evidence of climate tracking than warm edges (due to non‐climate processes or time lags at the warm edge; the biogeography hypothesis or extinction debt hypothesis), or whether they tracked temperature change equally (due to the influence of habitat suitability; the ecophysiology hypothesis). In addition to exploring correlations with regional temperature change, we calculated species‐ and assemblage‐specific sea bottom and sea surface temperature isotherms and used them to predict range edge position. Cold edges shifted further and tracked sea surface and bottom temperature isotherms to a greater degree than warm edges. Mixed‐effects models revealed that for a one‐degree latitude shift in isotherm position, cold edges shifted 0.47 degrees of latitude, and warm edges shifted only 0.28 degrees. Our results suggest that cold range edges are tracking climate change better than warm range edges, invalidating the ecophysiology hypothesis. We also found that even among highly mobile marine ectotherms in a global warming hotspot, few species are fully keeping pace with climate.

Economic incentives to harvest a species usually diminish as its abundance declines, because harvest costs increase. This prevents harvesting to extinction. A known exception can occur if consumer demand causes a declining species' harvest price to rise faster than costs. This threat may affect rare and valuable species, such as large land mammals, sturgeons, and bluefin tunas. We analyze a similar but underappreciated threat, which arises when the geographic area (range) occupied by a species contracts as its abundance declines. Range contractions maintain the local densities of declining populations, which facilitates harvesting to extinction by preventing abundance declines from causing harvest costs to rise. Factors causing such range contractions include schooling, herding, or flocking behaviors-which, ironically, can be predator-avoidance adaptations; patchy environments; habitat loss; and climate change. We use a simple model to identify combinations of range contractions and price increases capable of causing extinction from profitable overharvesting, and we compare these to an empirical review. We find that some aquatic species that school or forage in patchy environments experience sufficiently severe range contractions as they decline to allow profitable harvesting to extinction even with little or no price increase; and some high-value declining aquatic species experience severe price increases. For terrestrial species, the data needed to evaluate our theory are scarce, but available evidence suggests that extinction-enabling range contractions may be common among declining mammals and birds. Thus, factors causing range contraction as abundance declines may pose unexpectedly large extinction risks to harvested species.

The siting of protected areas to achieve management and conservation objectives draws heavily on biogeographic concepts of the spatial distribution and connectivity of species. However, the marine protected area (MPA) literature rarely acknowledges how biogeographic theories underpin MPA and MPA network design. We review which theories from biogeography have been incorporated into marine spatial planning and which relevant concepts have yet to be translated to inform the next generation of design principles. This biogeographic perspective will only become more relevant as climate change amplifies these spatial and temporal dynamics, and as species begin to shift in and out of existing MPAs. The scale of climate velocities predicted for the 21st century dwarfs all but the largest MPAs currently in place, raising the possibility that in coming decades many MPAs will no longer contain the species or assemblages they were established to protect. We present a number of design elements that could improve the success of MPAs and MPA networks in light of biogeographic processes and climate change. Biogeographically informed MPA networks of the future may resemble the habitat corridors currently being considered for many terrestrial regions.

Human-caused global climate change now affects, directly or indirectly, all biomes and levels of biological organization (Scheffers et al., 2016). One of the most profound effects has been changes in the spatial distributions of species that align with shifting climates-up mountains, deeper in the oceans, and generally toward the poles (Parmesan & Yohe, 2003; Pecl et al., 2017).A strong correlation between regional climate change and shifting species ranges has been documented in many taxa (Chen et al., 2011;Pinsky et al., 2013). However, individualistic responses and "ecological surprises" are also common (La Sorte & Jetz, 2012;Poloczanska et al., 2011;Zhu et al., 2012), underscoring the need to consider the interplay of climatic constraints and non-climate processes in determining the edges of species ranges (Sexton et al., 2009; Urban et al., 2016).

Caribbean coastal ecosystems have undergone severe degradation both historically and recently, primarily caused by the synergistic effects of overfishing, eutrophication, sedimentation, disease, and other factors associated with humans. Baseline conditions from pristine Caribbean reefs and seagrass beds are required to understand and quantify degradation. Only the fossil record can provide pre-human baselines. We present preliminary results from a recently discovered mid-Holocene (7.2-5.7 ka) fossil fringing reef and seagrass system in Bocas del Toro, Panama. Molluscan assemblages from the fossil reef and seagrass habitats were compared to death assemblages in corresponding modern habitats. The proportion of suspension-feeding molluscs more than doubled from fossil to the present day in the reef habitat, and the proportion of herbivores declined by a third, reflecting declines in coral cover and architecture, and increased eutrophy. Conversely, in seagrass beds, the proportion of different mollusc guilds was remarkably similar between fossil and modern day, suggesting that unlike reefs, seagrass beds are functionally similar today compared to a "pristine" baseline, although key community members were different. Our study reveals novel evidence that the health of molluscan communities on Caribbean reefs may have declined to the extent observed in corals and fish, and that the decline follows a trajectory predicted by known ecosystem degradation. Molluscs represent a biodiverse and functionally crucial component of reefs and must be considered in ecosystem-scale research on reef conservation. Revealing the structure of baseline communities using the fossil record represents one important step toward this aim.