Detritus from common seagrasses and other marine angiosperms may often be a less important basis for estuarine food webs than previously believed. In NW Gulf of Mexico seagrass meadows, epiphytic algae have high productivities, palatability, and a more important trophic role than common large plants have. Interdisciplinary field experiments show (1) intensive night-time ingestion of epiphytes by various invertebrate "detritivores", (2) very high productivity of epiphytic algae on seagrasses, and (3) assimilation of epiphytes rather than seagrasses, as measured by δC comparisons. These combined data show that many naturally concentrated and potentially competing invertebrates in Gulf of Mexico seagrass meadows feed largely on the algal overgrowth on seagrass blades, even when such algae appear to be sparse. Primary productivity of these epiphytic algae can equal that of the seagrasses, per blade or per unit biomass. Animal δC values tracked epiphytic values rather than seagrass values when comparisons were made over six sites. These measurements reinforce the view that epiphytic algae can be the primary basis of the food web in seagrass meadows.

Sea-grass meadows appear to be a primary habitat for young red drums Sciaenops ocellatus in south-Texas estuaries. The abundance of small red drums (6-27 mm standard length) in different meadows averaged 0.10-0.80/m e. Density estimates of young red drums showed no significant or nearly significant differences between the two types of sampling gear (benthie sled or 1.0-m e cage) or among sampling sites, which differed in plant height, blade density, or water depth. Small red drums were not found on large (>5 m across) nonvegetated sites; however, the ecotone between sea grass and nonvegetated bottom had significantly more red drums than did homogeneously vegetated sites. Heterogeneous sea-grass meadows, therefore, may support more young red drums than homogeneous ones. The red drum Sciaenops ocellatus is one of the most important sport and commercial fishes on the Gulf of Mexico coast (Bass and Avault 1975). Several studies have addressed the life history of large (> 100 mm)juveniles and adults (Pearson 1929; Miles 1951; Simmons and Breuer 1962; Boothby and Avault 1971), but very little is known of their early life history. Red drums apparently spawn near the passes connecting the Gulf of Mexico with estuaries (Simmons and Breuer 1962) and the eggs or larvae move into the bays with tidal currents (Mansueti 1960; King 1971). Simmons and Breuer (1962) reported that "very young" red drums have a preference for isolated grassy clumps or slightly muddy bottoms. Miles (1950) found that red

Epiphytic algae growing attached to shoalgrass (Halodule wrightii) blades accounted for nearly half of the aboveground live biomass and primary productivity of two seagrass

Plate limpets, Acmaea (Notoacmea) scutum, are common in central California on mid—intertidal vertical faces, where they ignore erect algae and consume primarily two encrusting algae, Petrocelis middendorffii (=P. franciscana) and Hildenbrandia occidentalis. This mid—intertidal system offers a manageable diversity of species, slow—moving consumers, and a two—dimensional, stationary food resource. Such an assemblage of organisms enables detailed studies on food selection within localized sets of available foods, and provides an example of how an animal utilizes a particular, mixed assortment of foods as it forages. Previous theories of diet selection predict that an animal will maintain a fixed hierarchy of preferences; less preferred foods would be consistently passed over if a preferred food is encountered frequently. However, individual Acmaea scutum preferentially consume mixtures of foods, even when each of these foods is readily available. Adjacent individuals tend to select the same mixture of foods while sharing the same foraging area, without intraspecific partitioning of food species. A family of simple graphic models illustrates hypothetical tendencies to select a particular (proportioned) mixture of foods, and predicts how food preferences would differ where relative abundances of the foods differ. Avoiding either too much or too little of a given type of food, relative to other foods, yields a mixed diet. Unlike foraging patterns leading to increased diversity of coexisting foods, maintaining a mixed diet involves seeking out separate components of the diet, particularly when a component is locally rare. Hypothetically, this would drive rare foods toward local extinction, decreasing diversity of available foods within each foraging area. The models of food selection were tested in the natural environment using adult limpets on a series of isolated rocks where percentage cover (probability of random encounter) of each food differed. Feeding of labeled individuals on these rocks was observed repeatedly during successive high tides. Acmaea scutum is seen to fit the mixed diet model with about 60% of its algal diet consisting of Petrocelis and 40% Hildenbrandia; this is true over a wide range of availabilities of these two foods. Maintaining this mixed diet appears to avoid excessive tooth wear associated with eating tough Hildenbrandia, though this food is palatable in limited quantities. Hypothetical consequences on the food resources due to diet mixing were tested by manipulating population densities of limpets on a series of boulders, and determining overall effects of foraging on various sets of algal abundances. However, even unusually high experimental densities of limpets failed to decrease algal abundances detectably. Algal declines on both experimental and control boulders are attributed to physical factors. Simple underwater listing techniques reveal feeding activities of individual adult molluscs. Contrary to visual observations, local molluscs almost always bite part way into the macroscopic al...

Aggregations of the sea anemone Metridium senile in Monterey Harbor sometimes contained only one clone (genetically identical individuals) but often contained two or more intermingled clones. The frequent occurrence of mixed clonal aggregations was perplexing, because M. senile uses fighting ("catch") tentacles in intraspecific agonistic interactions. A photographic survey of 19 quadrats showed that mixed clonal aggregations of anemones persisted throughout the 3.5 year study. Locomotion by the anemones, low frequency of nonclonemate contact, low population density, and infrequent occurrence of fighting tentacles were eliminated as possible explanations for the persistence of mixed clonal aggregations. Laboratory studies revealed differences among clones in the frequencies of fighting tentacle inflation and of injury to nonclonemates. We believe that low expression of these aggressive traits might permit intermingling of clones. However, high expression of aggressive traits was not found consistently in clones which were not intermingled, and therefore may not cause the segregation of such clones. Apparently, the most important factor contributing to the intermingling of clones was habituation of anemones to nonclonemate contact. The decrease in fighting tentacle inflation observed during two, six-day laboratory experiments was not due to fatigue, because contact with unfamiliar nonclonemates renewed aggression. We believe that habituation to nonclonemate contact occurs in situ, and that loss of habituation must occur occasionally to account for the occurrence of fighting tentacles.