Season-specific impacts of climate change on canopy-forming seaweed communities

Understory assemblages associated with canopy-forming species such as trees, kelps, and rockweeds should respond strongly to climate stressors due to strong interaction strengths. Climate change can directly and indirectly modify these assemblages, particularly during more stressful seasons and climate scenarios. However, fully understanding the seasonal impacts of different climate conditions on canopy-reliant assemblages is difficult due to a continued emphasis on studying single species responses to a single future climate scenario during a single season. To examine these more complex interactions, we used mesocosm experiments to expose intertidal assemblages associated with the canopy-forming golden rockweed, Silvetia compressa, to elevated temperature and pCO2 conditions reflecting two projected greenhouse emission scenarios [RCP 2.6 (low) & RCP 4.5 (moderate)]. Assemblages were grown in the presence and absence of Silvetia, and in two seasons. Relative to ambient conditions, p..., MATERIALS AND METHODS
Study site: 
We selected sites adjacent to two southern California long-term monitoring sites; Navy South (32.68306 °N, -117.24963 °W; hereafter NASO) and Navy North (32.692312 °N, -117.25297°W; hereafter NANO). These Multi-Agency Rocky Intertidal Network sites (MARINe) contain dense patches of Silvetia, perhaps because of the rarity of some stressors such as trampling (Denis 2003, Tydlaska & Edwards 2022) and runoff (Whitaker et al. 2010). We surveyed the Silvetia assemblages, collected the algae and grazers used in the mesocosm experiment, and conducted the field experiment at NASO. We then added NANO as a secondary collection site. Silvetia at both sites grows on emergent substrata at intertidal elevations between 0-1 m above Mean Lower Low Water (hereafter MLLW). Average water temperatures at these sites are ~18 °C and maximum summer water temperatures reach ~24 °C (SeaTemperatures 2023). 
Mesocosm experiment: To examine the impacts of projected changes in ..., , This readme file was generated on 2023-07-14 by Anthony Truong.
ORCID: 0009-0005-0693-0270
Institution: San Diego State University
Email:

Date of data collection:
Mesocosm summer trial: 2021-08-05 through 2021-09-17
Mesocosm winter trial: 2021-11-09 through 2021-12-20
Field experiment: Established 2021-07, surveyed in 2021-10 and 2021-12.

Geographic location of data collection:
Mesocosm experiment conducted at the San Diego State University Coastal & Marine Laboratory Institute.
Collection for mesocosm experiment conducted at Navy North (32.692312 N, -117.25297W) and Navy South (32.68306 N, -117.24963 W), San Diego, CA.
Field experiment conducted at Navy South (32.68306 N, -117.24963 W), San Diego, CA.

This work was supported by grants received from the Cabrillo National Monument Foundation, the National Parks Service (P20AC00867), and San Diego State University

## Season-specific impacts of climate change on canopy-forming seaweed communities.

File List:

1. mesocosm_paramet...