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BlueChip

The Sound School Inter-District Marine Education Program Newsletter
Habitat Information for Fishers and Fishery Area Manager
Understanding Science through History
Did Eelgrass Help the Rise of Blue Crabs 1998-2012?

Timothy C. Visel, Member – DEEP EPA LISS Habitat Restoration Workgroup*
The Sound School, New Haven, CT

Why We Need An Accurate Habitat History for Eelgrass:

It May Become the Best Climate Change Indicator for Crab Species

Report in Progress – Capstone Project Proposal October 2013 Revised to March 2014
Does Eelgrass Help the Spread of Green Crabs?

IMEP #13 February, 2014

Introduction
* Views/Opinions are those of Tim Visel and do not represent consensus of the Long Island Sound Study or the LISS Habitat Restoration Workgroup.
This paper was started in May 2012 but was modified for high school Capstone questions just recently. It does not reflect dozens of reports now coming in regarding eelgrass and green crab habitat profiles. Although green crab blade attack had long been reported in the shellfish literature regarding predation of bay scallops, studies from northern waters are again pointing to a strong eelgrass green crab habitat relationship. Several papers from the North Sea, Denmark, (where green crab is a harvested as an edible species) agree with western Atlantic and Eastern Pacific research just coming online. Eelgrass may represent an important habitat type for both green and blue crabs in New England.

This paper is being made available soon as a joint newsletter, to both IMEP and Search for Megalops email lists. The information includes history (IMEP) and blue crab habitats (Megalops) and I want to acknowledge and thank CT Fish Talk™ (http://www.ctfishtalk.com/) for continuing to post both under Saltwater Report threads and the Blue Crab Info-Forum™ (http://www.bluecrab.info/forum/index.php) for posting Megalops reports under Northeast Crabbing. Crabbing resources and for the IMEP fisheries history newsletter under Eeling, Shellfish and Oystering thread. The Blue Crab Blog spot http://bluecrabblog.blogspot.com also continues to post all Megalops Blue Crab newsletters. I have obtained many positive comments from all three sites; thank you for this continued cooperation and support. Tim Visel
Eelgrass As a “Habitat Type”
During the past thirty years, questions have been raised about the habitat value and consequences of eelgrass loss and if it is worthy of resource protection public policy discussions. Without an accurate and long term habitat history in our state, I cannot fully answer those questions. However, what I do know and mentioned in a presentation to the NOAA Shellfish Aquaculture Seminar on March 14, 2012, is that it has a very different habitat history than is generally presented to public officials, fishers and especially bay scallopers. It may, however signal a massive habitat reversal and post 1974 may have preceded a huge increase in blue crabs and a collapse of the lobster fishery. Recent studies in Canada have focused upon habitat suitability for the green crab Carcinus maenas and found a direct eelgrass habitat association. We may find a much stronger relationship to crab species than to bivalve species including even the bay scallop. Reports from the North Sea, especially the coastline of Denmark, refer to a very positive habitat relationship between green crabs and eelgrass, both native species. This habitat association goes back several centuries. This habitat relationship has raised new questions regarding disposal of each as wrapping to an edible food and transit to our shores.

A Possible Eelgrass Habitat History
Eelgrass (Zostera marina) is an opportunistic colonizer of disturbed marine soils. It shares many of the characteristics of a suspected Mongolian strain of Phragmites introduced into Connecticut when Interstate Route 95 was constructed (soil erosion control). It spreads by way of rhizome root shoots and flowering/fruit body seeds. Its presence signals a habitat reversal of unprecedented scale, and it follows colder, more energy-prone periods. After the energy-filled and much colder 1870s, eelgrass meadows became dense and widespread, sometimes spreading out to depths of 90 feet (between 1890-1915 Nichols 1920). Many hard clam, bays scallop and oyster beds were completely overrun with eelgrass killing the shellfish below. This previous clean or clear alkaline habitat also was vital to several fish species such as winter flounder. The eelgrass grew so dense at times that it collapsed these habitats that were needed for bay scallops and other shellfish such as the razor clam (Ensis spp.) Eelgrass can gather organic matter effectively sealing marine soils from oxygen dependent benthic species. When bay bottoms are clean and slightly alkaline, bay scallops may prefer to set upon a coralline red algae, estuarine shells or even pebbles. In fact, the bay scallop veligers that seek out eelgrass may in fact be trying to set above acidic waters and keep off of sulfur rich (Sapropel) bottoms.
[Sulfur rich anoxic zones lethal to bay scallops. Bay scallopers on Cape Cod were some of the first to recognize “dead lines” --areas in which bay scallops would not set, sometimes observed on lost eel pots lines and mooring areas of chain or lines were nearly devoid of life or formed a “dead line.” Direct evidence of this decline was observed on the Centerville River when looking for an old natural oyster bed (it was present only buried by leaf matter); we hit a Christmas tree discarded the year before. It was loaded with bay scallops until about 1 foot about the bottom which was all black and no scallops had set. The bottom was black and smelled of sulfur. This had also been noticed to impact mussels grown on nearby mooring lines to “drop off”. It is now suspected that such “deadlines” were caused by sulfide toxicity. (George Sousa, Shellfish Officer, Town of Falmouth 1981) That is why high temperature and low pH conditions are so damaging to bay scallop habitats. Eelgrass meadows in high heat are acidic: they naturally trap organic matter isolating sediment respiration processes. The organic matter trapped adds to further oxygen removal from bays and coves especially during warm storm free periods as described by the previous 1880-1920 period.

The Great Heat – The Rise of Eelgrass and Blue Crabs After 1898 – A Previous Case History

By 1900, dense eelgrass meadows also affected navigation interests in rivers and bays so special propellers were developed to cut through this very thick vegetation. Combined with high heat, sulfide levels under eelgrass meadows soared and acidic conditions often caused its roots to dissolve, releasing the plant that now drifts in search of more suitable marine soils. This process appears to be part of the natural reproductive cycle of the plant. It forms a dense monoculture and as all monocultures, it is then very susceptible to diseases. When eelgrass died in the 1930s from the wasting disease that appeared in Connecticut; the disease also appeared in many other countries at the same time following similar dense monocultures. Therefore, the disease outbreaks appear to be natural cycles and worldwide. Eelgrass therefore may be the best indicator of habitat decline for bay scallops, not improvement. That is why the habitat models for bay scallops setting relating to eelgrass remain for the most part unfinished or inconclusive.

When eelgrass appeared again in New England and the Northeast in the 1960s, following the hurricanes of the 1930s, 1940s and 1950s, shell fishermen and regulatory agencies made a determined effort to arrest its spread. This effort included “Cabot Cutters” that were chain sweeps and the development of underwater mowing machines (Massachusetts and New York), herbicides (Massachusetts, Maine and Canada), and explosives (Niantic Bay, Connecticut in 1974). Fisherman and biologists remembered the habitat damage from the early 20th century. In fact, Massachusetts issued several marine bulletins in the 1950s and 1960s that described the negative impacts of eelgrass. These viewpoints and references are never or rarely mentioned today. [The most recent attempts for eelgrass protection and conservation appear to be largely an effort to support previous anti-bottom disturbance policies. This effort has a direct impact upon coastal structures and dredging in near-shore areas perceived to have had at one time or may have in the future eelgrass populations. With the selection of eelgrass as an important indicator species, dredging and building coastal erosion control structures are now subject to review. The truth of the matter is that eelgrass benefits from such coastal energy even dredging it loosens the soil and extends the “habitat clock” for eelgrass. It behaves as most terrestrial grasses periodic energy inputs extends, (thinning) not ends its “habitat clock” similar to terrestrial lawn care.]

In the late 1960s, as shellfish habitat “damage” increased more extreme efforts were used to eradicate eelgrass and they included granulated salt esters of 2 4, D and 2 4 5, T, more commonly known as Agent Orange. It was described by a retired Cape Cod shell fishermen and bay quahogers as their “last stand against eelgrass.” This was reported but not confirmed to have been done in Pleasant Bay on Cape Cod in Massachusetts. However, Canadian officials did utilize 2 4 5, T to eradicate eelgrass from oyster beds and published papers about it in the 1960s. That effort was unsuccessful though because of the reproductive capacity of eelgrass and oyster habitats eventually succeeded to eelgrass meadows killing the oysters.
Another concern is the possibility that this eelgrass strain is in fact invasive to our shores. Our eelgrass indeed could be a strain that is from the Thames River Estuary in Great Britain. In the 1600s, green crabs (Carcinus maenas) were the desired food choice of the English Channel coastal fishers. In fact today, green crab is still considered a delicacy in some parts of England, and many green crab recipes can be found on the internet. When leaving England’s shores, it was customary to wrap live crabs (and shellfish in general) in seaweed for the trip across the Atlantic, and this is still a wide-spread industry practice. [It is still an industry practice. See Long Island Sound Study Report EPA Assistance Award Final Report (1) Submission Date of Final Report LISS, #LI-97149601 January 30, 2009; Project Description: Multi-Component Evaluation to Minimize the Spread of Aquatic Invasive Seaweeds, harmful Algal Bloom Microalgae, and Invertebrates via the Live Bait Vector in Long Island Sound.] When these ships arrived on our shores, the seaweed was most likely discarded overboard. It is highly probable that the flowering/fruit body seeds of the eelgrass and small green crabs survived and were in this seaweed. We know that the green crabs are invasive to our shores as of 1805 (Visel, 2012, “A Habitat History for Eelgrass in New England”) but I believe isolated small populations existed for centuries before spreading north from the Chesapeake Bay into New England and the northeast. It is not that surprising that many worldwide Colonial settlements of England now contains non-native resident populations of green crabs. The presence of green crabs and eelgrass may have a direct habitat link as recorded in the history of eelgrass spreading north followed shortly afterwards by green crabs spreading north as well (Victor Loosanoff BCF 1950s) written communication, the Madison Shellfish Committee(Gordon King, Chairman, from V.L. Loosanoff, Laboratory Director, US Fish & Wildlife Service, Milford, Connecticut, Feb 5, 1953). This habitat link is now being studied in Canada as mentioned by crabbers as preferred habitat in Niantic Bay (Megalops Report #14, August 14, 2011).

One species that appears over and over again in historic fish reports is associated with eelgrass, is eels (American eel Anquilla rostrata). They have special skin glands that excrete protective mucus that allows the eel to survive in sulfide-rich, low pH, acidic eelgrass meadows during winter thus, the very old commonly associated habitat type we call eelgrass. They also have special skin cells that absorb oxygen bypassing gills in low oxygen environments during warm weather. In times of high heat eelgrass meadows harm species that in colder more energy prevalent periods it helps. It (eelgrass) has a very complicated habitat “history.” A habitat connection is evident over time between blue crabs – eelgrass and eels (see Megalops report #10, September 2013). An increase in eelgrass populations indicates a potential for improving blue crab habitat.

I know that much discussion in the environmental community has centered on the bay scallop and eelgrass habitat association, but biological and historic reports show a closer association to coralline red macro algae species worldwide. There are numerous reports today from other countries citing this red algal connection and unique chemicals (rhodoliths) found in coralline species (Maerl) that serve as scallop spawning and setting stimulants. My habitat history research to date indicates eelgrass does not contain these chemicals.

The habitat services that eelgrass provides needs a complete and objective review; it may be that in terms of shellfish it is a much better indicator of temperature and energy change than a provider of suitable shellfish habitat. Eelgrass may emerge as a new indicator of cyclic marine habitat succession events that follow energy and temperature changes. It is often “first in” after storms, following bivalve shellfish sets within two to three years. The storm impact recultivates and rinses marine soils of sulfides and organic acids, providing for increased habitat quality for eelgrass, thus often leaving a habitat history in coastal coves.

The Rise of Blue Crabs After 1998

For the blue crab, eelgrass seems to have a positive habitat relationship in Connecticut, more important perhaps than first suspected. It helps blue crabs in three ways, first as thin new growth eelgrass–the “clean and green” eelgrass which provides excellent cover for Megalops and star life stage blue crabs and in small areas, patches helps form narrow shallow layers of Sapropel, the acidic and sulfur smelling organic compost (organic debris) provides a soft area in which to burrow and winter hibernate (cold water has sufficient oxygen), and thirdly, as a forage base to hunt for food. Blue crabs must hide in the winter time to escape opportunistic predators such as conch and starfish. Dredged channels that contain soft organic deposits appear now to provide key blue crab over wintering habitats (Megalops Report #1, April 17, 2013). Eelgrass patches (not dense meadows) provide opportunity for blue crabs to burrow in and have something to hold on to. When eelgrass returned to New England after the very cold and storm filled 1870s period so did the blue crabs. Three decades later, eelgrass is now also suspected of providing key habitat services to the green crab as well. When eelgrass grew quickly after 1974, blue crab habitat’s improved in Connecticut. But similar to stopping lawn care energy, these habitats gradually eventually succeeded into other habitat types, namely Sapropel flats and extirpated the eelgrass. In high heat and low oxygen conditions, stagnant eelgrass meadows slow flushing, can starve shellfish and quickly cause acidic bottom conditions. In winter, these same areas that have colder oxygen rich water and can provide blue crab habitat. Eelgrass has a very complex “habitat history” and appears to contribute to the nitrogen problem in poorly flushed coves. These negative features were first noticed by shellfish researchers at the turn of the century although rarely mentioned today. At the end of the Sapropel habitat cycle, it (eelgrass meadows) becomes toxic to blue crabs as other species- it is now implicated in a century old sulfide block (chemical barrier) to returning alewife. This is also under review for the 1909 Saprobien System based on rotting or organic matter degrading estuarine habitats.

When the Northeast Atlantic Oscillation (NAO) became negative in the 1950s and 1960s, eelgrass meadows were destroyed by storms, it became colder and blue crabs became scarce; I find a much stronger historical relationship to crabs and eelgrass than shellfish species and eelgrass. [This is frequently referred to as a cold water/warm water shift but it is more complex as it also involves energy pathways driving habitat quality and quantity (Visel, 2010-2011).] In fact, I have discovered by researching the bay scallop fisheries in Narragansett Bay, Rhode Island, dense eelgrass over time destroys bay scallop habitats, not improves them. When eelgrass populations were dense in New England at the turn of the century, blue crab populations soared. Bay scallops became scarce; it has over time a negative not a positive abundance relationship. When it becomes too dense (and again temperature and energy related) it can become deadly from heavy Sapropel buildup to many species (sulfide toxicity). It even seems to help end its habitat clock by its aggressive succession attributes which is a natural feature of its own biology. It has a habitat succession process that needs more historical review, but its link to blue crabs hibernating especially or living near dredged channel edges here appears solid. Removing vast quantities of rotting acidic oak and maple leaves in high heat by dredging would likely benefit both species. A washed and clean estuarine soil is able to hold eelgrass but deep soft sulfur rich bottoms can arrest eelgrass growth – it “dies off.” In fact I have recently made a habitat proposal to dredge Phragmites meadows making them into possible blue crab habitats instead. It might be possible in those areas that have a glacial till base and such sands able to grow eelgrass.

At the end of The Great Heat eelgrass meadows became very dense and in 1931 a worldwide disease outbreak (A problem that plagues all monocultures) wiped it out in many countries. That year the weather pattern suddenly changed – it started to get colder; blue crab production plummeted (see Megalops report #9, 2012). Bay scallops which virtually disappeared during The Great Heat – rebounded after 1931 to the surprise of Niantic Bay fishers having gone so many decades without a scallop set they started their own seeding program (see Adult Education publication – Bay Scallop Genetics and Transplant Programs To Niantic Bay, 1916 to 1935: An Historical Account - Timothy C. Visel, The Sound School Regional Vocational Aquaculture Center - March 2007, Scallop Report For Dr. Sheila Stiles, NOAA Milford Laboratory – Milford CT). After 1912 reports indicate that blue crab populations dropped as catches of Bay Scallops generally improved. In fact, looking at the historical fisheries literature the reversal was across Southern New England, not just in Connecticut.

As blue crab catches dropped, lobster populations recovered and some of the best Connecticut bay scallop catches were made when eelgrass populations were very low almost nonexistent. The climate pattern had now turned colder and storm filled, storms tore up any remaining offshore eelgrass meadows and replaced them with kelp cobblestone forests as lobster populations recovered. When the climate turned against lobsters they died off and blue crabs returned, eelgrass became more abundant eelgrass may in fact be an indicator of habitat reversals and not a distinct a constant habitat type. Eelgrass does not have the spawning and setting chemical attractants that coralline red algae are now recognized worldwide to provide several scallop species. Many years ago Niantic Bay fishers told Nelson Marshall that “red weed” not eelgrass was the true “scallop grass” – the fishers it seems were correct.

Acidic marine soil conditions in high heat has also been a concern of shellfish biologists for over a century Shellfish researchers were some of the first to raise this low pH alarm. Some of the work of Anthony Calabrese in the Milford National Marine Fisheries NOAA Lab in the early 1970s illustrates this concern. [How Some Pollutants Affect Embryos and Larvae of American Oyster and Hard-Shell Clam by Anthony Calabrese, US Department of Commerce, National Oceanic and Atmospheric Administration; National Marine Fisheries Service. Nov.-Dec. 1972, Volume 34, numbers 11-12.]
“The tidal estuarine waters that form the principal habitat of most commercial mollusks are one of the most complex environments in nature. Yet of the various interacting biological, physical and chemical factors affecting commercial mollusks, pH has received less attention than any other major factor. While the pH of the open ocean usually ranges from 7.5 to 8.5, the pH in tide pools, bays and estuaries may decrease to 7.0 or lower due to dilution, hydrogen sulfide production, and pollution. Since clam and oyster larvae must, at times, encounter a wide range of pH in their natural habitat, it is possible that success or failure of recruitment of these mollusks in some areas may be determined by variations in pH. With this in mind, a study was initiated to determine the effect of pH on embryos and larvae of clams and oysters (4). Both clam and oyster larvae showed about normal survival throughout the pH range from 6.25 to 8.75. Oyster larvae, however were somewhat more tolerant of low pH levels than clam larvae. At pH 6.0, for example, 21.5% of the oyster larvae survived, but none of the clam larvae. At pH 9.0, some larvae lived for a few days and showed some growth, although eventually more than 50% died; at 9.25 and higher, there was no survival of either species. The pH range for normal growth of clam larvae was 6.75 to 8.75. The pH range for normal growth was, therefore, slightly narrower than that for normal survival. The rate of growth of clam larvae was most rapid at pH 7.5 to 8.0, while oyster larvae grew most rapidly at pH 8.25 to 8.5. Although oyster embryos and larvae survive at lower pH levels than clam embryos and larvae, the optimum pH for growth of oyster larvae is somewhat higher than the optimum for clam larvae. The rate of growth decreased rapidly below 6.75 and above pH 8.75 for both clams and oysters. It can be concluded that the pH of the tidal estuarine waters that form the principal habitat of the hard shell clam and American oyster must not fall below pH 7.0 for clams or pH 6.75 for oysters, even though the larvae of both species can survive at lower pH levels. Moreover, neither species could reproduce successfully in waters where the pH remained appreciably above 9.0. Laboratory experiments have shown that high concentrations of silt can lower the pH of sea water to 6.5 or below the lower limit for normal embryonic development of clams and oysters. It is apparent, therefore, that heavy siltation, or any pollution that can change the pH of tidal estuarine waters, could cause failure of recruitment of these clams and oysters.”
In high heat the pH of eelgrass meadow is low – due to the sulfur reducing bacteria. When water temperatures drop oxygen becomes available to sediment and pH may move toward 7 or slightly alkaline. During winter it offers blue crabs an overwintering habitat, during summer oxygen drops and eelgrass habitat services turns negative. But for crab species, they can move in and out of eelgrass meadows daily and seasonally. In winter with more oxygen Sapropel eelgrass is a great cover for the winter in the summer in heat it becomes the source of deadly sulfide events and when blue crabs detect sulfide; they often walk out of the water as they did in Niantic Bay a few years ago.

Summary – An Incomplete Habitat History for Eelgrass
In cold water and high energy habitats, eelgrass “clean and green” has significant ecological services however, in high heat and low energy or restricted flushing it often becomes deadly the “brown and slimy” eelgrass. The study of the relationship for high heat, high organic loadings and the tendency for dense eelgrass meadows to lower sediment ph is long overdue. Sediment pH is also looked at for assisting blue crab Megalops survival; an acid bottom interferes with crabs to create shell material just as shellfish sets. Sediment pH may also hold a vital clue to blue crab Megalops survival and why it is often first found amid bivalve shell called shell hash by fishers (buffers low pH conditions). The green crab habitat relationship also appears to be solid; some of the Cape Cod shell fishers that linked eelgrass to green crabs were apparently correct. In reviewing studies of the Danish coast, they show similar grazing and foraging attributes. I t was green crabbers themselves that reinforced that link here (edible food size crabs) that the largest green crabs feed over eelgrass beds at night.

At the turn of the century key researchers mentioned the negativ
e aspect of eelgrass meadows to shellfish populations, those references are rarely mentioned today. Rather eelgrass has been promoted as helping estuarine fish and shellfish species when a long term review often finds evidence that it is not all that it is or been proclaimed to be. It is an opportunistic grass, and like terrestrial grasses needs energy to survive.
The change in blue crab populations may have an eelgrass habitat link and we need to know much more about that relationship before we can finish the chapter on eelgrass and its habitat services here in Southern New England…my view.

Always welcome suggestions and comments please email me at tim.visel@new-haven.k12.ct.us

Anyone interested in a short review of the Climate Pattern (NAO) North Atlantic Oscillation that directly affects habitat and therefore Connecticut’s shell and fin fisheries see The Search for Megalops-The rise of Blue Crabs Special Report #1, January 2014, available from Sue Weber at susan.weber@new-haven.k12.ct.us or can be obtained or accessed on the Adult Education and Outreach directory by accessing the Sound School website: www.soundschool.com/publications%201.html.

For information about The Sound School website, publications, and / or alumni contacts, please contact Taylor Samuels at taylor.samuels@new-haven.k12.ct.us

The Sound School is a Regional High School Agriculture Science and Technology Center enrolling students from 23 participating Connecticut communities.

Program reports are available upon request. For more information about New Haven Environmental Monitoring Initiative for IMEP reports, please contact Susan Weber, The Sound School Adult Education and Outreach Program Coordinator, at susan.weber@new-haven.k12.ct.us.