Sanctuary Integrated Monitoring Network
Monitoring Project

Shipwrecks on sanctuary shores: disturbance and recovery along a rocky intertidal exposure gradient

Principal Investigator(s)

  • Laurie McConnico
    Moss Landing Marine Laboratories, California State University
  • Mike Foster
    Moss Landing Marine Laboratories, California State University
  • Andrew DeVogelaere
    Monterey Bay National Marine Sanctuary
  • Ron Walder
    Moss Landing Marine Laboratories, California State University
Start Date: April 01, 1996
End Date: December 31, 2002

Recovery rates and processes were assessed along a rocky intertidal exposure gradient impacted by a shipwreck in Monterey Bay, California. This anthropogenic disturbance was used to determine if recovery rates varied inversely with tidal height due to reduced abiotic stress. Disturbed and control (undisturbed) plots were established in a mid/high intertidal red algal (dominated by Endocladia muricata and Mastocarpus papillatus), mid intertidal mussel (Mytilus californianus), and low intertidal surfgrass (Phyllospadix torreyi) assemblage.

Percent cover of sessile organisms in 0.25 x 0.25-m plots in each of the assemblages was assessed between 1996-1998 and 2001-2002.

Summary to Date

Results indicated recovery was variable over the exposure gradient. Ephemeral seaweeds initially colonized all disturbed plots, but were replaced by later successional species within 2-12 months.

Recovery rates did not vary inversely with tidal height as expected. Instead, relative recovery was greatest in the high intertidal red algal assemblage, followed by the surfgrass and Mytilus assemblages.

The patterns of recovery suggest that assemblages characterized by a few dominant species that recruit rapidly and grow quickly will recover faster than those dominated by organisms with variable, episodic recruitment, or those that have limited success with sexual reproduction relative to vegetative propagation. This study highlights the importance of speciesí life history to recovery after disturbance, and the inability of current ecological models to accurately predict successional pathways and community development on rocky intertidal shores.

Monitoring Trends

  • High intertidal red algal assemblages recovered most rapidly (less than 3years). This recovery is attributed to early re-colonization of Mastocarpus papillatus and Endocladia muricata.
  • Low intertidal surfgrass assemblages have not recovered 6 years after the initial disturbance, but appear to be recovering more rapidly than mid intertidal Mytilus assemblages. Presumably seed production, and seedling mortality contributed to the delayed recruitment of Phyllospadix and reduced recovery within this assemblage at Pt. Pinos as well as slow re-colonization of invertebrates.
  • Mytilus assemblages have been the slowest to recover (more than 6years) and have yet to reach abundances similar to those observed in natural stands. Most recruitment has been from plots edges and suggests that re-colonization up until now has not been from new recruitment, but was instead from individuals creeping in from surrounding areas.
  • Recovery does not vary inversely along an intertidal exposure gradient. Instead, recovery appears to be related to varying complexity in species life histories that characterize each assemblage.

Study Parameters

  • Disturbance
  • Abundance
  • Dispersal & Recruitment

Study Methods

Permanent plots were established at the site in May 1996 to examine recovery in each of these assemblages. Five 0.25 x 0.25 m plots physically disturbed by the shipwreck (granite surfaces cleaved/scoured to expose 100% bare rock) were established in the surfgrass assemblage, 5 in the mussel assemblage and 3 in the red algal assemblage. All plots were located on flat, relatively horizontal surfaces to limit variability and standardize sampling. Each disturbed plot was paired with the nearest undisturbed plot (control) at a similar tidal height and slope. Since these plots were also affected by fuel and oil, an additional set of control plots were randomly established outside of the wreck site, but in the same assemblages to control for the effects of possible chemical disturbance. Initial sampling of control plots outside the wreck site revealed no significant differences between them and the controls within the wreck site. Sampling of these plots was terminated after 2-24 months and the data are not reported here. Thus, the control plots within the wreck site functioned as the predisturbance condition and were compared to disturbed plots for recovery assessment.

Percent cover of macroalgae and sessile invertebrates was assessed in May and August 1996 and then at 6-month intervals between May 1996-December 1998 and May 2001-May 2002 using a point quadrat frame modeled after Foster et al. (1991). A metal rod was lowered through 30 random holes in a 0.25 x 0.25 cm clear plastic plate raised and centered above the sampling area and all sessile organisms contacted at each point were recorded. When algae were layered beneath a point, successive layers were recorded by moving upper layers aside. Multiple contacts of the same species were not recorded. When layering occurred total percent cover exceeded 100%.

Figures and Images

Grounded ship, the F/V Trinity being rolled to shore in the salvage operation.

F/V Trinity on the rocks, just north of Pt Pinos.

Healthy mussel bed. An undisturbed, healthy 25 x 25 cm control plot.

In a mussel bed, after six years of recovering from the vessel grounding.

A 25 x 25 cm area of healthy seagrass, Phyllospadix.

A seagrass area after six years of recovery from the vessel grounding.