BIOLOGY and METHODS of CONTROLLING the STARFISH, Asterias Forbesi {DESOR}
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BIOLOGY AND METHODS OF CONTROLLING THE STARFISH, Asterias forbesi {DESOR} By Victor L. Loosanoff Biological Laboratory Bureau of Commercial Fisheries U. S. Fish and Wildlife Service Milford, Connecticut CONTENTS Page Introduction. .. .. ... .. .. .. .. ... .. .. .. ... 1 Distribution and occurrence....................................................... 2 Food and feeding ...................................................................... 3 Methods of controL........................................ ........................... 5 Mechanical methods : Starfish mop...................................................... .................. 5 Oyster dredge... ........................ ............. ..... ... ...................... 5 Suction dredge..................................................................... 5 Underwater plow ..... ............................................................. 6 Chemical methods .................................................................. 6 Quicklime............................. ........................... ................... 7 Salt solution......... ........................................ ......... ............. 8 Organic chemicals....... ..... ... .... .................. ........ ............. ...... 9 Utilization of starfish................................................................ 11 References..... ............................................................... ........ 11 INTRODUCTION Even in the old days, when the purchas ing power of the dollar was much higher, The starfish has long been regarded as the direct damage caused by starfish to one of the most destructive enemies of shell the Connecticut oyster industry was as fish on the Atlantic coast of North America. sum.ed to be $463,000 in 1887; $631,000 in The greatest part of the loss caused by 1888; and $412,000 in 1889. Now, according these pests is borne by the oystermen, to the estimates of. biologists and practical WJ"lO often find their stock depleted or oystermen, the value of oysters destroyed entirely destroyed. Beds populated with by starfish in Long Island Sound alone may young oysters are especially vulnerable. reach several million dollars in some years. UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES Fishery Leaflet 520 Washington 25, D.C. July 1961 (Revised) For example, in 1958 starfish almost en these animals live near the shore in com tirely destroyed one of the h eaviest oyster paratively shallow water. A. vulgaris is sets in the history of shellfish cultivation found from Labrador, Canada, to Cape in Connecticut. The monetary loss that year Hatteras, North Carolina, and from the was considered to be between $10,·000,000 shoreline to a depth of 170 fathoms. This and $15,000,000 and, perhaps, even greater species, however, is most com.m.on in because of the present high price of oysters. water of moderate depth, preferring deeper and cooler water than A. forbesi and, con Starfish also kill large quantities of sequently, is rarely found in shallow places oysters in the States of New York, Rhode where oysters are grown. Only A. forbesi, Island, and Massachusetts . Scallop beds, the species causing the most damage to as in Buzzards Bay, are often invade d and oyster beds, is discussed in this article. their population partially or completely destroyed by starfish. One phase of depreda Surveys ' by the U.S. Fish and Wildlife tion, the extent of which is very difficult to Service have disclosed great concentrations estimate, is the heavy destruction of oyster of starfish in Buzzards Bay, Mass.; Nar spat caused by newly set starfish. In re ragansett Bay, R. I.; in the waters of Long gions where heavy setting of these pests Island Sound; and, at times, in Chesapeake im.m.ediately precedes or coincides with Bay. In all cases the majority of the animals setting of oysters, the latter may be de were found to live in comparatively shallow voured in a short time. water not deeper than 40 feet, their number decreasing with increasing depths. Usually, DISTRIBUTION AND OCCURRENCE large concentrations were found near the shore where natural and cultivated oyster Of the several species of starfish found beds are located. Starfish appeared to be on oyster beds only two are serious preda equally abundant on hard and soft bottoms, tors of commercial mollusks. These are wherever food was available. In Chesapeake Asterias forbesi (Desor), the com.m.on star Bay they were concentrated chiefly in fish (fig. 1), and Asterias vulgaris (Verrill), areas where an abundant supply of the small known as the purple starfish. The range of clam, Mulinia lateralis, was found. distribution of the first species extends from Maine to Florida and to the Gulf of It has been reliably established by semi Mexico. This form, h owever, is most abun annual surveys that the number of starfish dant between Cape Cod and Virginia. It is in Long Island Sound varies tremendously found at all depths ranging from the low in different years. Although there are no water mark to 250 feet, but the majority of definite cycles in its population density, ........-: -- - - - - ---- Figure l..--Common starfish. Asterias forbes;, moving on b:lnolIl, 2 there are periods when starfish are ex Laboratory observations also showed that tremely numerous and. also. periods when movements of starfish are irregular and they are' comparatively scarce. For ex quite slow, usually not exceeding a few ample. pronounced increases in the starfish inches per minute. In the winter, when population were observed during the years the temperature of the water is near the of 1934-35. 1939. 1948-50 and. especially. freezing point, locomotion is slowed con in the fall of 1957. The starfish set of siderably or ceases entirely. However, 1957. although not unusually heavy. sur severe storms or hurricanes, which cause vived well. increasing the number of star strong movements of water near the bottom, fish in Long Island Sound about tenfold. may carry masses of starfish from one area Since then. because of the preponderance to another over considerable distances in of starfish and the difficulty of combatting a short time. them. many sections of Long Island Sound that were formerly very productive as FOOD AND FEEDING oyster grounds have been completely aban doned. The heavy damage to the shellfish in dustry from starfish predation has caused It is important to recognize thaOt in 1957 great interest in the method employed by a comparatively good setting of starfish starfish to open shells of bivalve mollusks. occurred although the population of adult In general. all the suggestions offered in starfish. at that time. was one of the the past may be reduced to two probable lowest recorded since systematic surveys alternatives. One of these is a "toxin" of their occurrence and distribution were theory. It proposes that starfish release a begun in the middle 1930's. This and similar chemical substance which produces relaxa observations clearly demonstrated that in tion of the adductor muscles of the bivalves. the case of starfish there is no direct The second. the so-called "mechanical" correlation between the numbers of parents theory, maintains that starfish are able to and the intensity of setting. pull ope n the valves of molluscan shells by means of their tube feet. At presen t . Starfish cannot exist in water containing the second or "mechanical" theory is ac l ess than 1.8 percent of salt. However, they cepted by most biologists. There is evi are capable of withstanding. without serious dence that the opening of the valves is a injury. sharp reductions in salinity provided rapid process involving overwhelming, dis that the low salinity periods are of short continuous f orc es . In experiments with duration. Prolonged exposures eventually mollusks i t was found that the tube feet r esult in death of the starfish. Because of did pull the valves open. and forc es of over the inability of these animals to adjust 3,000 grams were recorded. themselves to water of low salinity they do not penetrate far into harbors and bays In addition to bivalves. such as clams, where the water is too brackish. oysters, and mussels. the food of sta rfish also consists of sea snails. small cru s ta Surveys on the occurrence and distribu ceans, worms, and various dead marine tion of starfish conducted semi-annually in animals. However, the small s i ze of the Long Island Sound during the last 22 years starfish mouth, which in adult a nimals is f ail to support the opinion prevalent among only about one-fourth of an inch in d i ameter, oystermen that seasonal migration. occurs does not permit taking in large pi eces of regularly from shallow to deep water. and food. To compensate for thi s handicap, vice versa. Results of these surveys in nature provided starfish with a very unique dicate that the distribution of these animals method of feeding. After the shells of the in relation to depth is fairly constant and attached mollusk are open, the s t a rfish that in many instances large groups of extrudes its stomach, insert s it bet we en starfish found in inshore areas remain the shells, and digests the soft meat of its there for a period of several years. Studies prey in situ. As soon as the mollusk is of movements of starfish. stained blue with eaten, the stomach of the starfish i s with the harmless dye. Nile Blue Sulphate. and drawn. It has been found that a single, then released at a definite point in Long medium-sized starfish may