Kelp forest loss and emergence of turf algae reshapes energy flow to predators in a rapidly warming ecosystem.

Climate change is decimating habitat-forming species in ecosystems around the world. Yet, the impacts of habitat loss on the energetics of the wider food web remain uncertain for many iconic ecosystems, including cold-water kelp forests. Here, we assessed how the loss of kelp forests and the subsequent proliferation of low-lying turf algae in the Gulf of Maine have altered the trophic niches of, and energy acquired by, predatory reef fishes.

Turf algae redefine the chemical landscape of temperate reefs, limiting kelp forest recovery.

In temperate regions experiencing rapid ocean warming, kelp forests are being replaced by chemically rich turf algae. However, the extent to which these turf algae alter the surrounding chemical environment or affect the rebound potential of kelp forests (through chemically mediated interactions) remains unknown. Here, we used underwater visual surveys, comprehensive chemical profiling, and laboratory experiments to reveal that turf algae release bioactive compounds into the water that fundamentally alter the reef "chemical landscape" and directly suppress kelp recruitment.

Laboratory-Reared Lobster Larvae Yield Inaccurate Estimates of Thermal Tolerance.

Physiological response to temperature stress defines the distribution of many marine invertebrates, and their thermal limits provide a foundation for understanding marine invertebrate response to climate change. In bottom dwelling species with free swimming planktonic larvae, such as the American lobster (Homarus americanus), thermal tolerance of early life stages influences vertical distribution in the water, settlement patterns on the bottom, and ultimately the species' range. We used measures of scope for activity, size, survivorship, and molecular techniques to demonstrate that wild-caught lobster larvae were more tolerant of temperature stress than laboratory-reared larvae (reared at 18°C and fed brine shrimp).

Rearing condition influences gene expression in postlarval American lobster (Homarus americanus).

The American lobster (Homarus americanus) is an economically important species in the western Atlantic and its climate-driven range shift northward along the east coast of the United States is well documented. The thermal tolerance of lab-reared postlarvae of this species has been extensively investigated to better understand settlement and recruitment dynamics. However, there have been few studies focused on wild-caught postlarvae, and even fewer that have analyzed lab-rearing conditions in context of diet.

Ocean warming undermines the recovery resilience of New England kelp forests following a fishery-induced trophic cascade.

Ecological theory predicts that kelp forests structured by trophic cascades should experience recovery and persistence of their foundation species when herbivores become rare. Yet, climate change may be altering the outcomes of top-down forcing in kelp forests, especially those located in regions that have rapidly warmed in recent decades, such as the Gulf of Maine. Here, using data collected annually from 30+ sites spanning >350 km of coastline, we explored the dynamics of Maine's kelp forests in the ~20 years after a fishery-induced elimination of sea urchin herbivores.

Species richness and identity both determine the biomass of global reef fish communities.

Changing biodiversity alters ecosystem functioning in nature, but the degree to which this relationship depends on the taxonomic identities rather than the number of species remains untested at broad scales. Here, we partition the effects of declining species richness and changing community composition on fish community biomass across >3000 coral and rocky reef sites globally. We find that high biodiversity is 5.

Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem.

Predator loss and climate change are hallmarks of the Anthropocene yet their interactive effects are largely unknown. Here, we show that massive calcareous reefs, built slowly by the alga over centuries to millennia, are now declining because of the emerging interplay between these two processes. Such reefs, the structural base of Aleutian kelp forests, are rapidly eroding because of overgrazing by herbivores.

Tropical fish diversity enhances coral reef functioning across multiple scales.

There is now a general consensus that biodiversity positively affects ecosystem functioning. This consensus, however, stems largely from small-scale experiments, raising the question of whether diversity effects operate at multiple spatial scales and flow on to affect ecosystem structure in nature. Here, we quantified rates of fish herbivory on algal turf communities across multiple coral reefs spanning >1000 km of coastline in the Dominican Republic.

Attenuating effects of ecosystem management on coral reefs.

Managing diverse ecosystems is challenging because structuring drivers are often processes having diffuse impacts that attenuate from the people who were "managed" to the expected ecosystem-wide outcome. Coral reef fishes targeted for management only indirectly link to the ecosystem's foundation (reef corals). Three successively weakening interaction tiers separate management of fishing from coral abundance.

Cascading predator effects in a Fijian coral reef ecosystem.

Coral reefs are among Earth's best-studied ecosystems, yet the degree to which large predators influence the ecology of coral reefs remains an open and contentious question. Recent studies indicate the consumptive effects of large reef predators are too diffuse to elicit trophic cascades. Here, we provide evidence that such predators can produce non-consumptive (fear) effects that flow through herbivores to shape the distribution of seaweed on a coral reef.

Marine and terrestrial herbivores display convergent chemical ecology despite 400 million years of independent evolution.

Chemical cues regulate key ecological interactions in marine and terrestrial ecosystems. They are particularly important in terrestrial plant-herbivore interactions, where they mediate both herbivore foraging and plant defense. Although well described for terrestrial interactions, the identity and ecological importance of herbivore foraging cues in marine ecosystems remain unknown.

Competition induces allelopathy but suppresses growth and anti-herbivore defence in a chemically rich seaweed.

Many seaweeds and terrestrial plants induce chemical defences in response to herbivory, but whether they induce chemical defences against competitors (allelopathy) remains poorly understood. We evaluated whether two tropical seaweeds induce allelopathy in response to competition with a reef-building coral. We also assessed the effects of competition on seaweed growth and seaweed chemical defence against herbivores.

Effects of herbivory, nutrients, and reef protection on algal proliferation and coral growth on a tropical reef.

Maintaining coral reef resilience against increasing anthropogenic disturbance is critical for effective reef management. Resilience is partially determined by how processes, such as herbivory and nutrient supply, affect coral recovery versus macroalgal proliferation following disturbances. However, the relative effects of herbivory versus nutrient enrichment on algal proliferation remain debated.

Macroalgal terpenes function as allelopathic agents against reef corals.

During recent decades, many tropical reefs have transitioned from coral to macroalgal dominance. These community shifts increase the frequency of algal-coral interactions and may suppress coral recovery following both anthropogenic and natural disturbance. However, the extent to which macroalgae damage corals directly, the mechanisms involved, and the species specificity of algal-coral interactions remain uncertain.

Seaweed allelopathy degrades the resilience and function of coral reefs.

Coral reefs are in dramatic global decline due to a host of local- and global-scale anthropogenic disturbances that suppress corals and enhance seaweeds. This decline is exacerbated, and recovery made less likely, due to over-fishing of herbivores that normally limit seaweed effects on corals. Seaweeds were known to suppress coral reproduction and recruitment, but in a recent study, we demonstrated that numerous seaweeds also directly poison corals via lipid-soluble allelochemicals transferred during contact.

Coral reefs in crisis: reversing the biotic death spiral.

Coral reefs are disappearing due to global warming, overfishing, ocean acidification, pollution, and interactions of these and other stresses. Ecologically informed management of fishes that facilitate corals by suppressing seaweeds may be our best bet for bringing reefs back from the brink of extinction.

Chemically rich seaweeds poison corals when not controlled by herbivores.

Coral reefs are in dramatic global decline, with seaweeds commonly replacing corals. It is unclear, however, whether seaweeds harm corals directly or colonize opportunistically following their decline and then suppress coral recruitment. In the Caribbean and tropical Pacific, we show that, when protected from herbivores, approximately 40 to 70% of common seaweeds cause bleaching and death of coral tissue when in direct contact.