The Role of Biological Disturbance in Temperate Subtidal Encrusting Communities

Abstract

Biological disturbance was investigated in three subtidal encrusting communities in the warm temperate region of northeastern New Zealand. The mode of operation of the major dis· turbance agents was established and their effect on encrusting organisms quantified where possible. The three communities were all dominated by crustose coralline algae, sponges, and ascidians.The urchin Evechinus chloroticus was the most widely influential of the grazers in these encrusting communities. At densities >6-7 urchins/m 2 this species grazed over the entire surface area in any locality, modifying community structure and reducing diversity to form crustose coralline flats (often referred to as barren grounds). At densities below this level urchins usually confined their grazing to patches within the encrusting community. The mean rate of free space release by an individual urchin was different in the three communities; the rate was four times higher where the urchins occurred at high densities on a coralline flat community than in the other two areas. Larger urchins appeared to clear space at a rate 1.5 times higher than that of smaller urchins. A 2-yr exclusion experiment in a community heavily grazed by Evechinus resulted in an increase in cover of ephemeral algae and coralline turf algae, but no basic change in species composition.Large numbers of five species of herbivorous gastropods, Cellana stellifera, Cantharidus purpureus, Trochus viridis, Micrelenchus sanguineus, and Cookia sulcata were positively associated with high densities of Evechinus. Removal of high densities of Cellana resulted in an increase in the cover of ephemeral algae and coralline turf algae in spite of continued Evechinus grazing. At high densities the grazing fish Parika scaber occasionally fed in loose schools that removed large sponges and ascidians and released free space at a rate of =0.2% of the surface per fish per year. This species also grazed selectively on small encrusting organisms in which case free space was not released. Exclusion of high densities of Parika for 2 yr resulted in a major shift in community structure from sponge/ coralline domination to ascidian/sponge domination. Episodic outbreaks of a bacterial/fungal disease occasionally affected populations of long-lived sponges. In the summer of 1975, 18% of the population of Ancorina a lata was destroyed and in 1976, 45% of Polymastia fusca degraded completely. These two episodes were the only extensive outbreaks of this disease in 10 yr of observation.The abundant grazing species investigated are generalist feeders that are capable offeeding on the entire size range of most encrusting species. Hence there is no escape from biological disturbance either in small or large size for encrusting organisms in these areas. The populations of the common grazers frequently fluctuate in numbers in a local area and their effect on the encrusting communities is not constant through time. The selective consequences of these features for long-lived encrusting organisms are discussed. It is sugg...

Variation in sunscreen compounds (mycosporine‐like amino acids) for marine species along a gradient of ultraviolet radiation transmission within doubtful sound, New Zealand

“…Evechinus is known to eat a range of algae including E. radiata and U. lactuca (Andrew 1988) but it is unknown if they consume Rhodymenia or A. lyallii. The diet of E. chloroticus is varied and although it is primarily a herbivore, it undoubtedly predates encrusting sponges and smaller sessile invertebrates such as the blue mussel, Mytilus (Ayling 1981;Witmann & Grange 1998). We did not present concentrations of MAAs for other possible food sources although we have made some preliminary measures of the concentrations of MAAs in the blue mussel, Mytilus galloprovincialis, which are found at the outer sites of Doubtful Sound and appear to have high but variable MAA concentrations (53-5036 nmol mg-1 protein, Lamare & Lesser unpubl.…”

Depth distribution and abundance of benthic organisms and fishes at the subtropical Kermadec Islands

“…The temperature shores of northern New Zealand and its offshore islands are characterised by stands of large brown algae and associated organisms (Choat & Schiel 1982). Many species of carnivorous benthic-feeding fishes are abundant, whereas herbivorous species are less numerous (Russell 1977;Leum & Choat 1980;Ayling 1982;Jones 1984). The most important grazers are regular echinoids, and several species of herbivorous gastropods are common (Ayling 1981;Choat & Schiel 1982).…”

“…Many species of carnivorous benthic-feeding fishes are abundant, whereas herbivorous species are less numerous (Russell 1977;Leum & Choat 1980;Ayling 1982;Jones 1984). The most important grazers are regular echinoids, and several species of herbivorous gastropods are common (Ayling 1981;Choat & Schiel 1982). There is considered to be a strong subtropical influence in the fauna of northern New Zealand (cf., McDowall 1979;Powell 1979;Ayling 1982), and several groups, for example labrid and pomacentrid fish, are more abundant at lower latitudes.…”

Formation and disruption of aggregations of Mytilus edulis in the fouling community of San Francisco Bay, California

“…In this study, plates that The maintenance of diversity by fish predation as were submerged 2 mo apart developed very different described above is similar to the maintenance of diverassemblages of early colonists. Of great significance sity by predation and physical disturbance in the exposed rocky intertidal of the Pacific Northwest M. Koehl, for their support, advice, friendship, and enwhere the mussel Mytilus californianus is the dominant spatial competitor (Dayton 1971, Paine 1974, Paine & Levin 1981, Several other investigations of subtidal systems show that predation of the compehtive dominant by fish can maintain diversity (Sutherland 1974, Day 1977, Russ 1980, Ayling 1981. Predaceous fish may thus often play an important role in the organization of subtidal marine communities.…”