Alternations in the foraging behaviour of a primary consumer drive patch transition dynamics in a temperate rocky reef ecosystem

Keystone interdependence: Sea otter responses to a prey surplus following the collapse of a rocky intertidal predator

The sea star Pisaster ochraceus and sea otters (Enhydra lutris) are two predators capable of shaping rocky intertidal and kelp forest community structure and functioning. In 2013, a sea star wasting event decimated populations of Pisaster along the west coast of North America. The collapse of this species in the rocky intertidal revealed an unexpected relationship between two keystone predators. In this study, we show how the loss of Pisaster along the Monterey Peninsula, CA, USA led to an increase in mussel (Mytilus californianus) size and expansion into lower tidal zones. Before the sea star wasting event, the local sea otter population fluctuated around a near equilibrium. However, in the absence of Pisaster, sea otters increased their dietary intake on mussels, which contributed in part to a local population-level rise. These results demonstrate how the loss of a keystone predator in one ecosystem may impart population-level changes to another.

Long-term exposure to prometryn damages the visual system and changes color preference of female zebrafish (Danio rerio)

Color vision, initiated from the cone photoreceptors, is essential for fish to obtain environmental information. Although the visual impairment of triazine herbicide prometryn has been reported, data on the effect of herbicide such as prometryn on natural color sensitivity of fish is scarce. Here, zebrafish were exposed to prometryn (0, 1, 10, and 100 μg/L) from 2 h post-fertilization to 160 days post-fertilization, to explore the effect and underlying mechanism of prometryn on color perception. The results indicated that 10 and 100 μg/L prometryn shortened the height of red-green cone cells, and down-regulated expression of genes involved in light transduction pathways (arr3a, pde6h) and visual cycle (lrata, rpe65a); meanwhile, 1 μg/L prometryn increased all-trans-retinoic acid levels in zebrafish eyes, and up-regulated the expression of genes involved in retinoid metabolism (rdh10b, aldh1a2, cyp26a1), finally leading to weakened red and green color perception of female zebrafish. This study first clarified how herbicide such as prometryn affected color vision of a freshwater fish after a long-term exposure from both morphological and functional disruption, and its hazard on color vision mediated-ecologically relevant tasks should not be ignored.

When species don't move together: Non-concurrent range shifts in Eastern Pacific kelp forest communities

Species range shifts due to changing ocean conditions are occurring around the world. As species move, they build new interaction networks as they shift from or into new ecological communities. Typically, species ranges are modeled individually, but biotic interactions have been shown to be important to creating more realistic modeling outputs for species. To understand the importance of consumer interactions in Eastern Pacific kelp forest species distributions, we used a Maxent framework to model a key foundation species, giant kelp (Macrocystis pyrifera), and a dominant herbivore, purple sea urchins (Strongylocentrotus purpuratus). With neither species having previously been modeled in the Eastern Pacific, we found evidence for M. pyrifera expansion in the northern section of its range, with no projected contraction at the southern range edge. Despite its known co-occurrence with M. pyrifera, models of S. purpuratus showed a non-concurrent southern range contraction and a co-occurring northern range expansion. While the co-occurring shifts may lead to increased spatial competition for suitable substrate, this non-concurrent contraction could result in community wide impacts such as herbivore release, tropicalization, or ecosystem restructuring.

Consequences of kelp forest ecosystem shifts and predictors of persistence through multiple stressors

Ecological communities can be stable over multiple generations, or rapidly shift into structurally and functionally different configurations. In kelp forest ecosystems, overgrazing by sea urchins can abruptly shift forests into alternative states that are void of macroalgae and primarily dominated by actively grazing sea urchins. Beginning in 2014, a sea urchin outbreak along the central coast of California resulted in a patchy mosaic of remnant forests interspersed with sea urchin barrens. In this study, we used a 14-year subtidal monitoring dataset of invertebrates, algae, and fishes to explore changes in community structure associated with the loss of forests. We found that the spatial mosaic of barrens and forests resulted in a region-wide shift in community structure. However, the magnitude of kelp forest loss and taxonomic-level consequences were spatially heterogeneous. Taxonomic diversity declined across the region, but there were no declines in richness for any group, suggesting compositional redistribution. Baseline ecological and environmental conditions, and sea urchin behaviour, explained the persistence of forests through multiple stressors. These results indicate that spatial heterogeneity in preexisting ecological and environmental conditions can explain patterns of community change.

Insights from the 2-year-long human confinement experiment in Grand Cayman reveal the resilience of coral reef fish communities

In March 2020, the world went into lockdown to curb the spread of the novel coronavirus (SARS-CoV-2), with immediate impacts on wildlife across ecosystems. The strict 2-year long lockdown in Grand Cayman provided an unprecedented opportunity to assess how the 'human confinement experiment' influenced the community composition of reef fish. Using a suite of multivariate statistics, our findings revealed a stark increase in reef fish biomass during the 2 years of lockdown, especially among herbivores, including parrotfish, with drastic increases in juvenile parrotfishes identified. Additionally, when comparing baseline data of the community from 2018 to the 2 years during lockdown, over a three-fold significant increase in mean reef fish biomass was observed, with a clear shift in community composition. Our findings provide unique insights into the resilience of reef fish communities when local anthropogenic stressors are removed for an unprecedented length of time. Given the functional role of herbivores including parrotfish, our results suggest that reductions in human water-based activities have positive implications for coral reef ecosystems and should be considered in future management strategies.

Examining the reproductive success of bull kelp (Nereocystis luetkeana, Phaeophyceae, Laminariales) in climate change conditions

Climate change is affecting marine ecosystems in many ways, including raising temperatures and leading to ocean acidification. From 2014 to 2016, an extensive marine heat wave extended along the west coast of North America and had devastating effects on numerous species, including bull kelp (Nereocystis luetkeana). Bull kelp is an important foundation species in coastal ecosystems and can be affected by marine heat waves and ocean acidification; however, the impacts have not been investigated on sensitive early life stages. To determine the effects of changing temperatures and carbonate levels on Northern California's bull kelp populations, we collected sporophylls from mature bull kelp individuals in Point Arena, CA. At the Bodega Marine Laboratory, we released spores from field-collected bull kelp, and cultured microscopic gametophytes in a common garden experiment with a fully factorial design crossing modern conditions (11.63 ± 0.54°C and pH 7.93 ± 0.26) with observed extreme climate conditions (15.56 ± 0.83°C and 7.64 ± 0.32 pH). Our results indicated that both increased temperature and decreased pH influenced growth and egg production of bull kelp microscopic stages. Increased temperature resulted in decreased gametophyte survival and offspring production. In contrast, decreased pH had less of an effect but resulted in increased gametophyte survival and offspring production. Additionally, increased temperature significantly impacted reproductive timing by causing female gametophytes to produce offspring earlier than under ambient temperature conditions. Our findings can inform better predictions of the impacts of climate change on coastal ecosystems and provide key insights into environmental dynamics regulating the bull kelp lifecycle.

Impact of the extinct megaherbivore Steller's sea cow (Hydrodamalis gigas) on kelp forest resilience

Giant kelp forests off the west coast of North America are maintained primarily by sea otter (Enhydra lutris) and sunflower sea star (Pycnopodia helianthoides) predation of sea urchins. Human hunting of sea otters in historical times, together with a marine heat wave and sea star wasting disease epidemic in the past decade, devastated these predators, leading to widespread occurrences of urchin barrens. Since the late Neogene, species of the megaherbivorous sirenian Hydrodamalis ranged throughout North Pacific giant kelp forests. The last species, H. gigas, was driven to extinction by human hunting in the mid-eighteen century. H. gigas was an obligate kelp canopy browser, and its body size implies that it would have had a significant impact on the system. Here, we hypothesize that sea cow browsing may have enhanced forest resilience. We tested this hypothesis with a mathematical model, comparing historical and modern community responses to marine heat waves and sea star wasting disease. Results indicate that forest communities were highly resistant to marine heat waves, yet susceptible to sea star wasting disease, and to disease in combination with warming. Resistance was greatest among systems with both sea cows and sea otters present. The model additionally predicts that historical communities may have exhibited delayed transitions after perturbation and faster recovery times. Sea cow browsing may therefore have enhanced resilience against modern perturbations. We propose that operationalizing these findings by mimicking sea cow herbivory could enhance kelp forest resilience.