Population Dynamics of Two Gorgonian Corals

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Abstract
The gorgonian corals Muricea calofirnica and Muricea fruticosa, co—occur at shallow depths along the western coasts of the Americas. Their northern geographic limit is Point Conception in California; the southern limits are unknown but may be Peru. In California, the depth range of both species is 1—30 m. Their abundances range up to 7.90 and 2.35 colonies/m2, respectively. Both species spawn once each year at a time which corresponds to annual peak temperature, which corresponds to annual peak temperature, which in California occurs later in the year for deeper segments of the population. Depth—staggered spawning has the effect of extending its duration from 2 to about 6 mo. During the larval stages of both species, mortality rates are low and nearly constant. Field records that detachment and abrasion rather than predation are the major sources of mortality for sessile stages. Several lines of evidence suggest that recruitment is generally spaced limited. In habitats where space is fully occupied, space limitation may regulate recruitment. In such habitats recruitment and mortality of populations of Muricea are nearly constant (i.e. in steady state), and their actual rates of natural increase are close to zero. In contrast, intrinsic rates of natural increase (rmax) are very high: 0.92 for M. californica and 1.45 for M. fruitcosa. These enormous rates of potential increase are offset by high rates of larval mortality in the plankton. Although M. californica is significantly more longevous than M. fruticosa, both species share similar patterns of life history. Competition for settlement and living space rarely occurs between the two species rather, it often takes place with other plants and invertebrates. These interactions may be sufficiently unpredictable for either species of Muricea to develop a competitive advantage over the other and hence may explain their coexistence. Thus, in the absence of significant direct competition between the two species, their similarities in life history may simply represent similar adaptations to the same set of environmental variables. Both species exhibit life history correlates of both K—selection (iteroparity, delayed reproduction, and relative great longevity) and r—selection (high (rmax). Life history at tributes of a single species may be located at different points along the r—K continuum. In fact, their colonial habit allows for combination of good characteristics of both patterns of selection and may be explain the evolutionary success of this type of life history, phenomena.

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