Laguna Beach Nearshore Giant Kelp and Bryozoan Encrustation

Keanu Mir-Scaer , Zen Mir-Scaer 

Kelp forests are highly productive marine ecosystems that provide habitat, food, and coastal protection, yet they are increasingly stressed by warming ocean conditions. This paper examines the scattered nearshore kelp beds in Laguna Beach subtidal shallow rock reef substrate between Brooks Street and Thalia Street, referred to as town. The nearshore kelp is approximately 200 meters from shore. This area has been protected since 2012 when it was considered a California Marine Protected Area (MPA) and classified as Laguna Beach State Marine Reserve (LBSMR). We observed a lack of historic nearshore kelp in town during the period from 2015 to 2023. Our observations were confirmed by reviewing images from KelpWatch.org, where data is processed from NASA’s Landsat satellite program (1). We observed an increase in marine life in town from 2022 to 2024, and in spring 2024 we observed a resurgence of native giant kelp (Macrocystis pyrifera). Most of the giant kelp blades quickly succumbed to bryozoan (Membranipora membranacea) encrustation in less than two months, and by month three the kelp beds had been reduced by approximately 70%. Giant kelp fronds naturally senesce when they reach between three to twelve months (2). Although kelp has a natural growth cycle and warmer sea temperatures may expedite senescence, our observational data suggest that bryozoan encrustation may have delayed visible blade deterioration by providing physical structure to disintegrating blades, though this relationship remains correlative rather than causal. Nearshore kelp is once again growing in Laguna Beach, likely due to the biodiversity afforded by MPA protection; however, additional action may be needed to protect kelp in warming waters associated with the climate crisis, and further quantitative research is required to better understand the relationship between kelp and bryozoan.