Does experimental seaweed cultivation affect benthic communities and shorebirds? Applications for extensive aquaculture

Abstract

Extensive seaweed aquaculture is a growing industry expected to expand globally due to its relatively low impact and benefits in the form of ecosystem services. However, seaweeds are ecosystem engineers that may alter coastal environments by creating complex habitats on previously bare mudflats. These changes may scale up to top-consumers, particularly migratory shorebirds, species of conservation concern that regulate trophic webs at these habitats. Understanding how habitats are transformed and how this affects different species is critical to direct ecological applications for commercial seaweed management. We experimentally assessed through a Before-After Control-Impact design the potential changes exerted by Gracilaria chilensis farming on bare mudflats on the abundance, biomass, and assemblage structure of benthic macroinvertebrates, and their scaled-up effects on shorebirds' habitat use and prey consumption. As predicted, experimental cultivation of G. chilensis significantly affects different components of biodiversity that scale-up from lower to upper trophic levels. The total biomass of benthic macroinvertebrates increased with seaweed cultivation and remained high for at least 2 months after harvest, boosted by an increase in the median size of polychaetes, particularly Nereids. Tactile-foraging shorebirds tracked these changes at the patch level increasing their abundance and spending more time foraging at seaweed cultivated plots. These results suggest that seaweed farming has the potential to impact shorebird populations by favoring tactile-foraging species which could lead to a competitive disadvantage to species that rely on visual cues. Therefore, the establishment of new seaweed farms in bare mudflats at key sites for shorebirds must be planned warranting habitat heterogeneity (i.e., cultivated and non-cultivated areas) at the landscape level and based on a previous experimental approach to account for local characteristics. Fostering properly designed extensive seaweed farming over other aquaculture industries with greater negative environmental impacts would provide benefits for human well-being and for ecosystem functions.

GPS tracking analyses reveal finely-tuned shorebird space use and movement patterns throughout the non-breeding season in high-latitude austral intertidal areas

“…Contrary to previous evidence in other godwit species [e.g., 31 ], our prediction about home range size and bill length was not supported by the data. This could be explained by the high availability of polychaete worms (the preferred prey items of godwits) on Chiloé [ 26 , 33 ], as well as a general low rate of interspecific competition in high austral latitudes. In this scenario, godwits with different bill lengths may be able to successfully exploit the rich food supply in the same bays by minimizing the number of patches visited and, consequently, having similar home range sizes.…”

“…In godwits, bill length is a good proxy for body size [ 29 ]; indeed, individual differences in bill length may reflect social dominance and foraging skills, with larger individuals being generally dominant over smaller individuals [ 30 ], and thus different movement strategies to exploit resources in a tidally structured environment [e.g., 31 , 32 ]. Outside the breeding season, godwits are tactile foragers that prey mainly on polychaete worms [ 33 ] and, as such, a longer bill allows them to access more prey, especially large worms [ 29 ].…”

Perceived risks and rewards of foraging sites strongly affect density and condition of non‐breeding Hudsonian Godwits

“…The harvesting of red algae Agarophyton chilensis , an important local economic resource, from the intertidal areas is one particularly common form of disturbance (Martínez‐Curci et al . 2022). This practice involves several people labouring together, often with oxen‐ or horse‐drawn carts, to transport collected algae off the intertidal area to dry in supratidal areas (Navedo et al .…”

Flexibility in the face of climate change? A rapid and dramatic shift toward later spring migration in Hudsonian Godwits (Limosa haemastica)

“…The effects of such practices on shorebird communities are complex. In some cases, they may be mutually beneficialareas with algae cultivation promote higher levels of benthic macroinvertebrates and are preferred by tactile-foraging shorebird species like godwits 45 . In other cases, though, the human disturbance associated with the maintenance and harvesting of algae negatively influences godwit foraging efficiency and leads to decreases in body condition and survival in individuals from highly disturbed sites [46][47][48] .…”