Blog: Why You Should Oppose the Proposed Army Corps 50-year Shoreline Protection Program. Part 2.

In an effort to demonstrate my argument regarding the failure of previous analyses for the proposed borrow sites to base descriptions, decisions, and estimates of recovery durations on the “trees” in the infauna rather than the “weeds”, my wife and I spent about an hour examining the surface of sand that was deposited at Moonlight Beach in Encinitas during the recent winter beach nourishment program.  My purposes were to: 1) collect and identify the clam and snail shells that were included in the sand that was dredged from the borrow site; and 2) compare this list of mollusc species with the mollusc species listed as most commonly collected among infaunal invertebrates species occurring offshore from Oceanside to Imperial Beach (Table 3.4-3 in the Final EIS for the San Diego Regional Beach Sand Project; KEA, 2000.  The San Diego regional beach sand project final environmental impact report/environmental assessment.  Prepared for San Diego Association of Governments and U. S. Dep't. of the Navy, SWDIV NAVFAC Engineering Command.  June 2000.).  That list, depicting the species that are common in grab or core samples from sandy nearshore habitats between Oceanside and Imperial Beach, was a primary data source used in assessing impacts and required recovery time for proposed dredging activities in the borrow sites.  The objective of this quick survey was to gage how accurately the approach taken in previous beach replenishment programs measures potential long-term impacts and recovery times. We wanted to see how closely the clams and snails dominating the shell material in the dredged material reflected the data used to conclude “No Significant Impacts’ and “No Ecological Value”.

The mollusc species represented by shells in the dredged sand at Moonlight Beach are listed in the attached table.  In all, nineteen species of clams and six snail that typically reside in nearshore sand habitats similar to the borrow sites were collected and identified based on a variety of shell characteristics.  All of the shells collected represent large, long-lived species, i.e., they are analogous to “trees” in terrestrial ecosystems.  The sizes of the shell fragments shown in the attached photograph provide a basis for estimating the sizes of the various species.  It is notable that most of the shells have been broken during their passage though the dredge and pipeline while being transported to the beach. 

A large part of the shell breakage is due to the large quantity of small and large pebbles that we observed in the dredged material.  Comparison of quantity of “gravel” in this sediment with the particle size analyses conducted for the borrow sites in the EIS/EIR indicates that the sediments in the borrow sites were inadequately sampled.  Gravel and coarse sand were not reported in the upper 2-feet of sediment sampled at both SO-5 or SO-6 in Table 4.4-5 but it is quite conspicuous in the sand at the Moonlight Beach receiver site.  Obviously, sampling the upper 2 feet of sand is inadequate when the dredging plan calls for 20-feet dredge cuts.  Any gravel in the material pumped onto the receiver sites subtracts from the effectiveness of the nourishment effort and, moreover, adds to the amount of coarse material that the program is supposed to deal with and subtracts from the effectiveness of the nourishment effort.

Only nine molluscs are listed in Table 3.4-3  and only one species listed in is similar to those found in the dredged sand at Moonlight Beach.  Thus, it is clear that the species used in previous studies to measure long-term impacts and recovery durations have been completely inappropriate and inadequate.  Many of the species for which shells were collected and abundant in the dredged material live over 10 years and only recruit to the ecosystem infrequently.  Some, like Pismo clams, the most numerous shell collected in this study, live up to 50 years.  For these species, even if conditions are suitable, recovery of a stable, balanced age structure will require several decades.  In contrast, most of the species listed in Table 3.4-3 live only about 1-2 years.

What this comparisons clearly shows is that the species collected in previous surveys and used to assess the ecological value and recovery periods for the potential borrow sites is inappropriate and inadequate.  It is clear from this brief survey of the dredged material deposited on Moonlight Beach that large numbers of long-live species (analogous to “trees”) were “harvested” by the dredging process but were not surveyed by the types of surveys that have been conducted previously to assess the ecological impacts of the dredging and beach nourishment programs.  In particular, several species of large clams (e.g., Pismo, surfclams,  and butterclams) were common in the shell debris.  This is an unfortunate idiosyncrasy of the type of sampling that was adopted by agencies and consultants in the early 1970s, when implementation of the National Environmental Protection Act resulted in a great demand for sampling these habitats to evaluate potential contaminant issues around offshore discharges around the nation.  These ecosystems in soft sediments are the only ones I’m aware of where we make our decisions and projections for recovery based on the “weeds” rather than the “trees”.  It is a very flawed approach to evaluating impacts and managing ecosystems.

BIVALVES

Pectinidae

Lucinidae

Cardiidae

Here excavata –
Pit lucine

Trachycardium quadragenarum – spiny pricklecockle

Lucinisca nuttalli – Nuttall lucine

Veneridae

Mactridae

Amiantis callosa –
White venus

Tellinidae

Mactromeris ?catilliformis – Dish surfclam

Chione californiensis – California venus

Leporimetis obesa – California fat-tellin

?Simomactra sp. – surfclam

Chione undatella – Frilled venus

Macoma nasuta – Bent-nose macoma

Tresus sp. – Gaper

Leukoma staminea – Pacific littleneck

Macoma ?secta – White-sand macoma

Saxidomus nuttalli – California butterclam

Tellina ?idae – Ida tellin

Semelidae

Tivela stultorum – Pismo clam

Tellina bodegensis – Bodega tellin

Semele decisa – Clipped semele

SNAILS

Polinices lewisii – Lewis’s moon-shell

Neverita reclusiana – Recluz’s moon-shell

Nassarius fossatus –
Great Western nassa

Bursa californica California frog-shell

?Ophiodermella sp. -
turrid snail

Megasurcula carpenteriana – Carpenter’s turrid

As would be expected when dredge depth exceeds 3 feet, shell condition indicated that the largest proportion of the “harvested” clams and snails had not  been freshly killed.  Nevertheless, their presence in the sediments indicates they occur locally.  Moreover, the presence of periostracum on the exterior surface and the shiny interior surfaces on many of the shells indicated that an appreciable proportion had been killed by the recent dredging project. 

A final point: it is important to recognize that this collection of  shells represents only a hint of the magnitude of the injury that the “trees” in the infaunal assemblages in the borrow sites experienced as a consequence of the beach nourishment project.  The largest proportion of the “trees” in this ecosystem, probably ≈90%, do not have shells that would survive dredging and transport through the pipelines to the beach.  They would arrive on the beach as unrecognizable minced meat.  Thus, no evidence of that loss would be observed by examining the beach.