Chelsea Brown
Program: Master’s Program in Ecology
Date: Monday, April 27, 2026
Time: 10:00 am
Location: Donald P. Shiley BioScience Center (BSCI)
Zoom: https://SDSU.zoom.us/j/82940224925
Committee Members
Dr. Matthew Edwards, Biology
Dr. David Lipson, Biology
Dr. Janet Franklin, Geography
Abstract
Kelp forests and offshore rocky reef habitats in southern California play crucial roles in supporting biodiversity and providing a broad range of ecosystem services. However, the trophic connections between these ecosystems remain poorly understood. This study examined cross-habitat energy flow between kelp forests and adjacent offshore, unforested reefs, testing whether kelp-derived organic matter is exported offshore and indirectly incorporated into fish diets.
Bulk tissue stable isotope analysis (BSIA) was used to characterize carbon (δ¹³C) and nitrogen (δ¹⁵N) signatures of fishes and basal sources. Sampling was conducted within and offshore of the Point Loma Kelp Forest, with fish collected via spear- and hook-and-line fishing, and baseline sources sampled concurrently. Fish from kelp forest and offshore habitats occupied highly overlapping isotopic space (>80%) and exhibited δ¹³C values intermediate between kelp and plankton baselines, consistent with mixed basal support.
Distance-based analyses indicated that offshore fishes were at least as closely associated with kelp-derived carbon as fishes within the kelp forest, despite the absence of benthic macroalgae offshore. Spatial analyses further indicated that kelp-associated carbon signatures persisted in consumer tissues up to 10 miles from shore. Temporal patterns in δ¹³C suggest that dietary inputs were structured, strongly aligning with kelp detrital production and senescence dynamics, and integrated over multi-month timescales. Together, these results indicate that offshore reefs are energetically coupled to kelp forests through detrital pathways, highlighting kelp forests as donor ecosystems whose influence extends beyond forest boundaries.
This underscores the importance of incorporating cross-habitat energy subsidies into ecosystem-based and fisheries management frameworks.