Substrate Selection in Caprellid Amphipods of Southern California, with Emphasis on Caprella Californica Stimpson and Caprella Equilibra Say (Amphipoda) !
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Substrate Selection in Caprellid Amphipods of Southern California, with Emphasis on Caprella californica Stimpson and Caprella equilibra Say (Amphipoda) ! DONALD E. KEITH 2 ABSTRACT: The substrate affinities of Southern Californian caprellids were studied with principal interest in two species, Caprella califol'11ica and Caprella equilibra. Experiments designed to test the selectivity for three substrates at Long Beach Marina showed C. calijornic« to "prefer" the bryozoan Bugula neritina over the algae Polysiph onia pacifica and V iva lobata. Caprella equilibr« showed no preference between Bugul« neritina and Polysiphonia pacifica, but selected these substrates over VI va lobata. Selectivity of Caprellu calijornica was attributed to its cryptic adapta- . tion. THE CAPRELLIDEA CON STITUTE a highly spe grahami Wigley and Shave, as a commensal on cialized suborder of amphipoda. Previous pub the starfish Asterias [orbesi (Desor.) . lished works have dealt primarily in systematics The apparent dependence of most caprellids and very little information is available concern on other living organisms for support and pro ing caprellid ecology. tection makes this relationship an obvious place Caprellids are most commonly found clinging to begin an ecological investigation. The primary to some living substratum. Among those most importance of this study is to establish whether frequently cited in the literature are: algae, substrate affinities exist among certain associated sponges, hydroids, and bryozoans. According to species of caprellids and to evaluate factors Mayer ( 1882, pp. 170-171) there are some which could influence selectivity of these ani caprellids which do not live on other organisms. mals. Pseudolirius kroyeri (Halleri), for example, During the summer of 1961 at the Virginia lives exclusively on sand or muddy sand. This Institute of Marine Science, I obtained some species cannot clasp large objects since the hind evidence to support the thesis that substrate legs do not possess a spine fold for the claw. affinities do exist in some species. The data col Another species, Pariambus minatns (Mayer), is lected from the various habitats showed the most known to live, at least for the most part, on common caprellid of the lower York River, dur sand. Mayer does agree, however, that the vast ing the months of June and July, to be Caprella majority of caprellids do prefer a living sub geometric« Say, which was found in abundance strate. Caprella equilibra was reported by Mayer on nearly all of the substrates examined. This from the tunicate Ciona intestinalis (L), where species was particularly dominant on hydroids, he observed it sitting near the incurrent opening bryozoans, and sponges. Paracaprella tenuis where it could utilize the water current and the Mayer was the species next in abundance during outer muddy surface for feeding. Patton ( 1968, these 2 months, being dominant on bryozoa. p. 119-120) described the caprellid , Caprella The third species was Caprella equllibra, which was not present on any substrate examined prior 1 Based on a portion of a dissertation submitted to early August, at which time it replaced C. by the auth or in partial fulfillment of the require geometries as a dominant on sponges. Para ments for the doctoral degree in Biological Sciences caprella tennis seemed to show an affinity for at the University of Southern California. Manuscript the brown bryozoan Victorella pavida Kent. received June 30, 1970. 2 Tex as Christian University, Department of Biol This species also occurred in large numbers on ogy, Fort W orth, Texas 76129. the sponge, H aliclona permollis Bowerbank, as 387 388 PACIFIC SCIENCE, Vol. 25, July 1971 it began to grow over the bryozoan in late July. tected. Samples from Punta Penasco, Mexico, The sample number was insufficient for statis and Santa Catalina Island were also utili zed. tical verification. The results did encourage Caprellid abundance was expr essed in number fur ther investigations into the caprellid-substrate per unit volume for each substrate. relationships. Locomotion should be considered in studies Seasonal Effects at Long Beach Marin a of substrate selection since the ability of an orga Long Beach Marina is situated in Alamitos nism to move from one place to another might Bay; it is a small body of water used primarily influence the results of experiments. The as for recreational purposes by the city of Long sumption is made that an individual is able to Beach. For a further description and history of move from one substrate to another, selecting Alamitos Bay, see Reish and Winter, 1954, pp . the one which is most suitable. 106--107. Caprellids move over their substrate with ease. To determine seasonal effects on the total They are also capable of swimming in an ante caprellid populati on and their abundance on riorly directed manner by quick, jerky move various substrates, samples were taken from ments involving sudden ventral flexing and November 1965 through October 1967 from straightening of the body. the sides of the floats which support the wooden When placed in an aquarium, the caprellids boat docks. The floats are constructed of rein often appear to have no direction to their swim forced molded fiberglass plastic (Reish, 1964, ming ; they sometimes swim to the top of the p. 126) . A total of 144 samples was taken at water where they become trapped by the surface this station from April 1966 to October 1967. tension. In their natural habitat, however, ca Twen ty-five samples were taken durin g each prellids swim with a sense of direction. When sampling period and preserved separately in 10 the bryozoan Bugula neritina (L) was detached percent formalin. The caprellids were removed, from the dock float at Long Beach Marina so counted, and stored in 70 percent alcohol. It that it began to sink, the caprellids swam up was found that the most effi cient means of re ward from the Bttgttla to the other bryozoan moving the caprellids was to shake the preserved colonies attached to the floats. sample in a half-gallon jar filled about one-third Observations of caprellids kept in the lab with water, and then quickly removing the sub oratory show that they move from substrate to strate and pouring the water through a screen substrate, stopping for varying length s of time. with a pore size of .0070 mm. This process was Th eir ability to swim and to move readily over repeated until caprellids could no longer be ob the substrate eliminated locomotion as a problem tained in this manner. The substrate was exam in substrate selection experiments. ined under a dissecting microscope and any Feeding studies by Keith (1969) showed that remaining caprellids removed. Caprellid abun caprellids in captivity feed principally on detri dance was expressed as number per cubic centi tus and diatoms which are associated with the meter of substrate. During each samplin g period substrates. Food was removed from the sub the water temperature and relative substrate strates prior to each experiment to eliminate it abundance were noted. as a possible factor influencing selection. Substrate Selection METHODS AND MAT ERIAL S LABORATORY STU DIES : Caprellids were col lected along with their substrates at Long Beach Occurrences and Substrates Marina from July 5 to September 8, 1967 to Samples were collected along the Southern determine if substrate affinities could be detected. California coast duri ng Ap ril 1966 from Dana There were three principal substrates on which Point to San Simeon, and all of the information caprellids could be found in abundance at this available from the literature on caprellid occur location : the bryozoan Bngnl« neritina and the rences was tabulated in anticipation that certain algae Polysiphonia pacifica H ollenberg and Viva caprellid-substrate relationships might be de- lobata (Kiitzing) .Samples of these substrates Substrate Selection in Caprellid Amphipods-KEITH 389 were collected and placed in large plastic bags the influence of one species on the substrate along with a generous supply of seawater and selection of the other. transported to the laboratory in Styrofoam Approximately equal volumes of each of the containers. The caprellids and their respective three substrates, from which all of the caprellids substrates were kept in separate aquar ia. The and food had been removed, were placed in the environmental temperature was determined each experimental tanks so that they made contact time specimens were collected so that the tem with one another. Twelve specimens were ob perature of the experimental tanks could be tained from Bngula neritina and four were adjusted to that of the environment. placed on each of the three substrates and ob Th e experimental tanks consisted of four 3 served over a 48-hour period. Seven observa gallon plastic Aqu aflair aquaria partially sub tions, which consisted of counting the number merged in a 60-X -7-inch insulated Plexiglas of caprellids on each substrate, were made dur tank designed to hold four of the small aquaria ing this period at approximately equal intervals end to end. The large vessel was filled with during the daytime. These numbers were then distilled water and acted as a water bath to averaged to give a figure representing one trial. maintain the experimental tanks at the desired Averaging the number of independent counts temperature. help ed to reduce the error due to periodic wan Th e water bath was cooled by circulating dering of individuals. Th e substrates were care distilled water from a beverage cooler through full y separated prior to counting to prevent the one-half-inch plastic tubing by means of a model caprellids from moving from one to the other 2U March submersible water pump (Bakus, dur ing the count. Af ter counting, the substrates 1965, pp. 230-231) . The tubing made two were again placed in contact. Ten trials were loops in the bottom of the water bath and completed during one experiment and a t-test occupied almost its entire length .