Award: OCE-1458845

Connectivity across ecosystems provides raw material that fuels many biotic communities and food webs. A better understanding of exchanges between ecosystems, and how their variability affects diversity and ecosystem function is needed to predict ecological responses to environmental change. However, evaluations of cross-ecosystem fluxes, their variation in time and space, and resulting ecological responses of recipient communities are few, particularly for marine ecosystems. Nearshore forests of giant kelp, Macrocystis spp., and sandy beaches provide an outstanding example of cross-ecosystem connectivity. Giant kelp is a highly productive foundation species that strongly shapes the kelp forest ecosystem. The majority of kelp forest primary production is exported to other marine ecosystems, providing energy, nutrients, and habitat that profoundly affect recipient ecosystems. Disturbance, like waves, and turnover removes kelp from the forest, setting it adrift in ocean currents. On sandy beaches, where in situ primary production is low, this subsidy, known as kelp wrack, supports productive intertidal food webs. Kelp wrack deposition to beaches varies greatly but can exceed 1000 kg per meter of shoreline annually, making it one of the largest cross ecosystem subsidies known. Once kelp wrack is cast on beaches, it is consumed by a diversity of small intertidal invertebrates, such as amphipods, isopods, and insects. They, in turn, are important prey for predators, including invertebrates and vertebrates, such as shorebirds and fishes, as well as terrestrial reptiles, birds and mammals. We sought to quantify connectivity between a donor ecosystem, kelp forests, and a recipient ecosystem, sandy beaches, to evaluate how variation in kelp wrack input affects beach ecosystems and develop a quantitative understanding of the transport of drift kelp from kelp forests to sandy beaches. We gauged the strength of cross-ecosystem linkages between kelp forest and sandy beaches by quantifying kelp wrack biomass and species diversity of macroinvertebrates and shorebirds on beaches over time. We assessed effects of variation in wrack subsidies on beach ecosystem function by measuring consumption and secondary production of wrack consumers in field and laboratory experiments. To track fate of drift kelp from the kelp forest to the beach we tagged thousands of kelp plants living in three kelp forests arrayed along 25 km of the Santa Barbara, CA coast. We used individually numbered wooden drift cards printed with information for the public to use to report the locations of beached tagged kelp plants (Fig 1) and distributed flyers to community groups, hotels and parks and set up a web portal and social media for reporting tags. We also conducted monthly surveys of the distribution of beached kelp plants along the 25 km study coastline We monitored direct tracks of drift kelp plants in currents by releasing three ?kelp drifters? consisting of a kelp plant attached to a Microstar satellite buoy at each reef every month. Results of surveys of beaches and field and laboratory experiments on kelp consumption found close links between spatial and temporal inputs of kelp and responses of recipient beach communities and ecosystem functioning. Biodiversity, species composition, abundance of wrack consumers and higher trophic levels and ecosystem function were strongly affected by variation in kelp wrack inputs. Estimates of kelp wrack consumption at our study beaches provided new insights on the high variability among beaches and over time associated with variation in consumer identity, abundance and size structure as well as beach conditions and wrack availability. The importance of key species of intertidal consumers in driving variability in kelp consumption rates was a key result that suggests species identity may be more important than biodiversity for this ecosystem function. Most tagged kelp plants reported traveled <5km before beaching, however, tags were reported on beaches 100's of km away, particularly in winter. Tag returns suggested kelp plant loss and fate varied strongly among the three reefs. Microstar drifter tracks also indicated the fate of drifting kelp plants varied temporally and among reefs. Track length varied from hours to a few days and ~30% of the plants beached. Drifters also moved toward the open ocean where they could be picked up by the California current. Monthly surveys along 25 km of coast yielded strong spatial and temporal patterns in the distribution of beached kelp plants with totals varying >3 orders of magnitude among months, ranging from 39 plants to a peak of 17,266 plants, underlining the high variability in cross ecosystem connectivity between kelp forests and beaches caused by kelp forest condition and productivity and the condition and receptivity of beaches. Our project results suggest changes in connectivity between kelp forest and beach ecosystems associated with the effects of climate change, warming seas and sea level rise, as well as human interventions, will profoundly affect coastal biodiversity and food webs. Quantifying cross ecosystem connectivity can enhance our ability to predict consequences of climate change on coastal ecosystems and their functioning. Last Modified: 12/23/2021 Submitted by: Jenifer E Dugan