The Shinnecock Bay Brown Tide

Image from Chris Gobler, Stony Brook University

The south shore of Long Island has a series of interconnected lagoonal estuaries.  Shinnecock Bay is the eastern most basin, and it has the least amount of people living along its shores.  That’s not to say that there aren’t people out here, it just lacks the uber-development of the more western bays.  In recent years, the western portion of Shinnecock Bay has been plagued with brown tides (as has the next bay to the west Quantuck Bay).  There was a recent report on NBC News New York on the subject:

View more videos at: http://www.nbcnewyork.com.

The issue is that the brown tides are affecting the Shinnecock Bay shellfish populations negatively.  Brown tides were originally responsible for the crash in bay scallop populations over 25 years ago in the Peconic Estuary.  Brown tides are a very small phytoplankton that are too small for may shellfish to ingest, and it is also accepted that they produce a sort of toxin that is also harmful to things that eat it, a double-whammy of danger to filter feeders.  The problem is these blooms become very dense, essentially outcompeting all other phytoplankton.  Since the brown tide becomes the only food available to filter feeders, many either succumb to the toxin or starve to death.  This is what happened with scallops in the mid 1980s and 1990s.  Luckily, a brown tide hasn’t been seen in the Peconics since 1995 (knock on wood), which led to the restoration efforts I am currently involved with.

However, the brown tide also creates other problems.  Some filter feeders, such as clams, appear able to “weather the storm,” so to speak.  But brown tides occur at the most inopportune time for hard clams and many other native Long Island invertebrates – spawning season.  Clam and other invertebrate larvae are often in the water column at the same time the brown tides appear, and this is extremely harmful to the larvae.  A few studies have demonstrated that high concentrations of brown tide can inhibit clam larval growth, extending the larval period and preventing metamorphosis.  This has devastating consequences for clam recruitment.  Major stressors that occur on basin scales and can severely impact the larvae are likely to lead to recruitment failure (Bricelj and MacQuarrie 2007).  In addition, because brown tides inhibit feeding of adult clams, this too can impact reproductive output by affecting gamete formation in adults (Newell et al 2009). This is likely whats been happening in the western portion of Shinnecock Bay highlighted by the above news video.

Brown tides also severely darken the water column.  This creates a situation which is harmful to benthic primary producers, such as seagrasses.  The brown tide is responsible for shading out eelgrass in a number of Long Island bays (Dennison et al 1989).  This has created a loss of a vital habitat for numerous commercially and recreationally important species (which I have blogged about numerous times).  This might have been another reason why scallops didn’t recover naturally after the last Peconic brown tide, as eelgrass is often referred to as the preferred scallop habitat.  However, hard clams are also known to survive better in seagrass meadows, where the complex root and rhizome structure protects burrowed clams from predators, mostly crabs (Irlandi 1997).  Clams also appear to grow better in seagrass habitats (Irlandi 1996, Judge et al 1993).

So now we have a potential triple-whammy for hard clams:

1)Brown tides inhibit feeding in adults, which could impact condition and reproductive output.

2)Brown tides affect the growth of larval clams, preventing metamophosis, and potentially leading to recruitment failure.

3)Brown tides shade out seagrass, causing it to disappear, which has potential negative consequences.

So water quality has deteriorated, and brown tides are becoming an annual occurrence.  However, is poor water quality solely to blame? It is also likely that overharvesting of filter feeding shellfish might also play a role in development of brown tide blooms.  High densities of hard clams are capable of preventing brown tide bloom formation – densities above current levels but below historic levels, prior to overharvesting (Cerrato et al 2004).  It is possible, then, that overharvest of clams (estimated bay wide average for Shinnecock Bay ~1 per square meter) has led to low population densities which are incapable of filtering the water column.  This, in addition to water quality issues, allows for the initiation, persistence and recurrence of brown tide blooms, which further prevents hard clam populations from replenishing themselves, a negative feedback loop.

Brown tide in mesocosms with and without clams from Cerrato

This has created some interest in restoring Shinnecock Bay.  Both my advisor and one of my committee members are involved in a project investigating the feasibility of restoration, and naturally, I have been tasked to do a lot of work on this project.  Before restoration can happen, however, we first need to know the reasons WHY certain shellfish aren’t found in high numbers in Shinnecock Bay.  If we are correct in our assumption that recruitment failure due to larval supply is to blame, then we need to investigate recruitment.  We are doing this at a series of sites within the Shinnecock Bay-Quantuck Bay complex, and I blogged about this over on the Southampton Patch.  If we see many settlers in our collectors, which are generally protected from predators, but we don’t see corresponding numbers on the bottom, we can then correct our theory of recruitment failure to some post-settlement mortality.  Once we have this information, we can make better decisions about ways to approach potential restoration projects.  And since scallop restoration is working in the Peconics and hard clam restoration appears to be working in Great South Bay, there is reason for hope.

All user groups – baymen, researchers, environmental advocates, recreational users and vacationers – want Shinnecock to be restored to its previous glory, with lush seagrass meadows, clear waters, and loads of clams, crabs, and fish.  We need to work hard to achieve this goal.  Shellfish restoration will help, but other means are necessary for restoring water quality.  Whether that’s sewering the east end, and building tertiary treatment plants, or somehow increasing ocean flushing to the more isolated portions of the bay remains to be seen.  However, if everyone involved is as invested as they claim, and that will be the ultimate test, restoration is possible.

Judge, M., L. Coen, and K. L. Heck. 1993. Does Mercenaria mercenaria encounter elevated food levels in seagrass beds? Results from a novel technique to collect suspended food resources. Marine Ecology Progress Series 92:141-150

Irlandi, E. (1996). The effects of seagrass patch size and energy regime on growth of a suspension-feeding bivalve Journal of Marine Research, 54 (1), 161-185 DOI: 10.1357/0022240963213439

Irlandi, E. (1997). Seagrass Patch Size and Survivorship of an Infaunal Bivalve Oikos, 78 (3) DOI: 10.2307/3545612

Dennison, WC, Marshall GJ, & Wigand, C (1989). Effect of “brown tide” shading on eelgrass (Zostera marina) distributions in: Novel Phytoplankton Blooms: Causes and Impacts of Recurrent Brown Tides and Other Unusual Blooms, 675-692

Cerrato, R., Caron, D., Lonsdale, D., Rose, J., & Schaffner, R. (2004). Effect of the northern quahog Mercenaria mercenaria on the development of blooms of the brown tide alga Aureococcus anophagefferens Marine Ecology Progress Series, 281, 93-108 DOI: 10.3354/meps281093

Bricelj, V., & MacQuarrie, S. (2007). Effects of brown tide (Aureococcus anophagefferens) on hard clam Mercenaria mercenaria larvae and implications for benthic recruitment Marine Ecology Progress Series, 331, 147-159 DOI: 10.3354/meps331147

Newell, R., Tettelbach, S., Gobler, C., & Kimmel, D. (2009). Relationships between reproduction in suspension-feeding hard clams Mercenaria mercenaria and phytoplankton community structure Marine Ecology Progress Series, 387, 179-196 DOI: 10.3354/meps08083