Benthic Habitats and the Effects of Fishing

Symposium Abstract: Geologic Development and Longevity of Continental Shelf Mudbelt Habitat during the Holocene in the Monterey Bay National Marine Sanctuary, California

E. E. Grossman, M. E. Field, and S. L. Eittreim

doi: https://doi.org/10.47886/9781888569605.ch41

Recent degradation of benthic habitat and fish stocks is related to both anthropogenic and natural causes. Subsurface geological investigations augment seafloor and habitat mapping to provide constraints on habitat development, longevity, and variability due to natural geophysical processes. A principal geologic feature of the Monterey Bay National Marine Sanctuary is a 421 km² mudbelt that extends across a vast proportion of the continental shelf and reaches a maximum thickness of ~32 m. Basal ¹⁴C ages of ~14 ka indicate the mudbelt is Holocene and ²¹⁰Pb accumulation rates show it is presently accreting at 0.24-0.39 cm/yr. Lithologic variations within cores show that the accumulation of this deposit occurred episodically under significantly different depositional energy. Seismic reflection profiles show that mudbelt development on the underlying fossil terrace was governed by complex interactions between fine sediment input (primarily from three major rivers) and transport (cross-shelf and along-shelf) during the Holocene sea-level transgression. Lateral variability in accumulation would have profound impacts on surrounding habitats as muds and sands were partitioned and deposited where they exist today. The composition and age of sediment within mudbelt cores help to define the nature of seabed sediment through time, its longevity as potential essential fish habitat, and its vulnerability to forces acting on the seafloor. Understanding the evolution and rates of sediment transport and accumulation of this and similar mudbelts that occur within important and threatened groundfish habitat along most modern coasts will provide a context for interpreting modern changes to essential fish habitat.