2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
Discussion
Considerable variability in the infaunal invertebrate community was recorded by the coring work.
Patchiness is an established characteristic of benthic invertebrate communities. Most marine
invertebrates are rapid colonizers, with community composition being driven by sediment
characteristics and the frequency and spatial scale of disturbances (Thrush et al. 1996, Levin and
Talley 2002). The variability see in invertebrate abundance and biomass through time and across
stations in 2008 can be attributed to an uneven distribution of food or other resources, subtle substrate
differences, or localized environmental impacts within a community. During the sediment core
collection, considerable variability in sediment type was noted within stations, with some having a
hard clay component, others with clean sand, and others composed of very soft muds. Additionally,
the monitoring program was not conducted at a frequency capable of identifying seasonal patterns or
with enough replication to detect directional trends amidst the high variability within station
elevations.
However, the two sampling events during the second year post-restoration did serve to document that
the creation of the FTB has provided benthic food resources available to birds, fish, and other
invertebrates. The created basin was quickly colonized by polychaetes, amphipods, tanaids, bivalves,
and gastropods. Similar trends were seen at Batiquitos Lagoon following the introduction of marine
influence to the wetland, which was quickly dominated in both density and biomass by molluscs
(gastropods and bivalves), annelids (primarily polychaetes), and arthropods (primarily crustaceans)
(M&A 2009). Benthic monitoring conducted during the comparable second year post-restoration at
Batiquitos Lagoon (1998) found the mean density of all infauna at the –2-foot elevation to be 3,518
indiv./m 2 in January and 3,020 indiv./m 2 in July, and at the +1-foot elevation to be 2,265 indiv./m 2 in
January and 2,321 indiv./m 2 in July (Merkel & Associates 2009). The mean densities found at Bolsa
Chica in 2008 were within the same order of magnitude, with a density at the –2-foot elevation of
6,365 indiv./m 2 in January and 3,540 indiv./m 2 in July, and at the +1-foot elevation a mean density of
2,172 indiv./m 2 in January and 8,562 indiv./m 2 in July. This suggests infaunal density is not falling
short after the second year post-restoration.
The FTB experienced considerable tidal muting during the first two years post-restoration, with its
ability to drain at low tides increasingly hampered over time by the accumulation of the anticipated
sand shoal in the inlet (see Appendix 2-A). This had the effect of increasing the inundation period at a
given elevation, so that by the end of 2008, the +1-foot elevation was exposed much less frequently at
low tides. This inundation shift probably had an effect on the invertebrate community that could not
be detected by the limited sampling program, but likely influenced the distribution of fauna
elevationally. Following maintenance dredging scheduled for 2009, the tidal range will rapidly be
restored and subject the infaunal community to a less gradual shift in tidal elevation. The benthic
community is anticipated to respond quickly, re-establishing at the elevations with the appropriate
inundation conditions for their environmental tolerances. Although the response of the benthic
community to tidal muting is not monitored, it should additionally be kept in mind when considering
the variability between stations and seasons.
The lack of lower level taxonomic data makes it impossible to compare the relative health of the FTB
benthic communities with some popular indices (e.g., Index of Biotic Integrity, Benthic Response
Index) to local reference standards. However, the basic goal of the sampling program was met;
monitoring allowed documentation of the conversion of the basin to a tidally influenced bay capable of
supporting a substantial prey base of infauna for marine fish and birds present in the basin.
Merkel & Associates, Inc. 65