The invasion of the Indo-Pacific lionfish Pterois volitans into the western Atlantic, Caribbean Sea, and Gulf of Mexico is the fastest ever documented for a marine fish. Few studies have addressed the establishment of lionfish populations within a location, and habitats other than reefs have been largely overlooked. The present study reconstructed the invasion around South Caicos, Turks and Caicos Islands (TCI), from multiple sources of data. Densities and size frequencies of lionfish were compared in deep reefs (10 to 30 m) and shallow habitats (seagrass, mangrove, sheltered reef, and exposed reef < 5 m deep) over a 4 yr period (2007 to 2010). By the end of 2010, lionfish had been observed in all 5 habitats. There was a lag of almost 7 mo between the first sightings in shallow habitats (December 2007) and in deep reefs. After 2 to 3 yr, the density of lionfish in deep reefs surpassed those in shallow habitats. In November 2010, mean density was over 10× higher on deep reefs (9.51 lionfish seen observer −1 h −1 ± 5.37 SD) than in seagrass (0.87 ± 0.41; p < 0.05), which was significantly higher than in other shallow habitats (sheltered reef: 0.52 ± 0.47; exposed reef: 0.12 ± 0.13; and mangrove: 0.06 ± 0.10; p < 0.05). Lionfish on deep reefs (TL = 22.7 ± 7.5 cm) had significantly larger total lengths (TL; mean ± SD) than those in seagrass (TL = 15.0 ± 4.3 cm; p < 0.05) or sheltered reefs (TL = 14.6 ± 6.8 cm; p < 0.05). Assuming one population with ontogenetic movement between habitats, density and age estimates suggest that lionfish may have moved to deep reefs from other habitats. The results suggest that lionfish may settle preferentially, but not exclusively, in shallow habitats before moving to deep reefs. Only 2 studies have explicitly compared lionfish between different habitats. Barbour et al. (2010) found that mangroves supported higher densities of smaller-sized individuals than nearby reef areas, which has since been interpreted as displaying the nursery function of mangroves (Barbour et al. 2011). Similarly, Biggs & Olden (2011) reported that lionfish in seagrass were smaller than those found on reefs and suggested that lionfish may use seagrass as nurseries. Although the global concern focuses on lionfish's impact on reefs (Sutherland et al. 2010), evidently the threat also extends to other habitats such as mangroves and seagrass, especially in the context of their nursery function for native species (Nagelkerken 2000, Nagelkerken et al. 2001, Mumby et al. 2004. Therefore, whether ontogenetic changes in habitat use are also displayed by P. volitans warrants further investigation (Barbour et al. 2010).Additionally, whilst the international effort to document the spread of lionfish throughout its invasive range has been considerable (Schofield 2009, 2010, Johnston & Purkis 2011, far less emphasis has been placed on how a population develops within a new location as it becomes colonized. Thus, quantitative assessments of densities and sizes of lionfish across habitats, depths, and time have n...
Kelp forests are among the world's most productive marine ecosystems, and they have the potential to locally ameliorate ocean acidification (OA). In order to understand the contribution of kelp metabolism to local biogeochemistry, we must first quantify the natural variability and the relative contributions of physical and biological drivers to biogeochemical changes in space and time. We deployed an extensive instrument array in Monterey Bay, CA, inside and outside of a kelp forest to assess the degree to which giant kelp (Macrocystis pyrifera) locally ameliorates present-day acidic conditions which we expect to be exacerbated by OA. Temperature, pH, and O 2 variability occurred at semidiurnal, diurnal (tidal and diel), and longer upwelling event periods. Mean conditions were driven by offshore wind forcing and the delivery of upwelled water via nearshore internal bores. While near-surface pH and O 2 were similar inside and outside the kelp forest, surface pH was elevated inside the kelp compared to outside, suggesting that the kelp canopy locally increased surface pH. We observed the greatest acidification stress deeper in the water column where pCO 2 reached levels as high as 1,300 μatm and aragonite undersaturation (Ω Ar < 1) occurred on several occasions. At this site, kelp canopy modification of seawater properties, and thus any ameliorating effect against acidification, is greatest in a narrow band of surface water. The spatial disconnect between stress exposure at depth and reduction of acidification stress at the surface warrants further assessment of utilizing kelp forests as provisioners of local OA mitigation. Plain Language Summary Anthropogenic emissions increase atmospheric carbon dioxide (CO 2), leading to increased dissolved CO 2 in the ocean. Elevated CO 2 concentrations increase the ocean's acidity (ocean acidification), threatening marine ecosystems. When kelp photosynthesizes, CO 2 is removed from seawater (reducing acidity), and oxygen is produced. We do not know if kelp photosynthesis is enough to reduce acidity and protect the local ecosystem from acidification. To understand how kelp impacts its local environment over time, depth, and space, we deployed a novel array of monitoring instruments in Monterey Bay, CA. We observed patterns in temperature, pH (acidity), and oxygen over days to weeks related to the strength of offshore winds and the movement of deep, cold, acidic, low-oxygen water into the shallow kelp environment. Below the surface, pH and oxygen were similar inside and outside of the kelp forest. Interestingly, surface pH was slightly higher (less acidic) inside the kelp relative to outside, suggesting that the kelp canopy reduced acidity. However, we observed the highest acidity in deep water, indicating that the impact of the kelp canopy (reducing surface acidity) does not extend to where we see the greatest acidification. Therefore, the ability for kelp to lessen acidification stress may be greater at the surface.
High-latitude kelp beds may be at risk from increasing sedimentation rates due to glacial melt.
Climate change is causing decreases in pH and dissolved oxygen (DO) in coastal ecosystems. Canopy-forming giant kelp can locally increase DO and pH through photosynthesis, with the most pronounced effect expected in surface waters where the bulk of kelp biomass resides. However, limited observations are available from waters in canopies and measurements at depth show limited potential of giant kelp to ameliorate chemical conditions. We quantified spatiotemporal variability of surface biogeochemistry and assessed the role of biological and physical drivers in pH and DO modification at two locations differing in hydrodynamics inside and outside of two kelp forests in Monterey Bay, California in summer 2019. pH, DO, dissolved inorganic carbon (DIC), and temperature were measured at and near the surface, in conjunction with physical parameters (currents and pressure), nutrients, and metrics of phytoplankton and kelp biological processes. DO and pH were highest, with lower DIC, at the surface inside kelp forests. However, differences inside vs. outside of kelp forests were small (DO 6-8%, pH 0.05 higher in kelp). The kelp forest with lower significant wave height and slower currents had greater modification of surface biogeochemistry as indicated by larger diel variation and slightly higher mean DO and pH, despite lower kelp growth rates. Differences between kelp forests and offshore areas were not driven by nutrients or phytoplankton. Although kelp had clear effects on biogeochemistry, which were modulated by hydrodynamics, the small magnitude and spatial extent of the effect limits the potential of kelp forests to mitigate acidification and hypoxia.
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