User:Nlapunzi/Cellana exarata

Introduction: Cellana exarata, common name the black-foot ʻopihi and Hawaiian blackfoot is a species of edible true limpet, a marine gastropod mollusc in the family Nacellidae, one of the families of true limpets.

Distribution & Habitat:

The species is native to the Hawaiian Islands and abundant on the basalt or elionite wave-exposed rocky windward shorelines. The limpet, C.exarata, resides in the high intertidal zone on the shores of the Hawaiian islands. The coastline on each island differs such that the different substrates, basalt and eolianite, affect the shape of the limpets in each location. Additionally, the issues of the intertidal zone, such as wave stress and exposure to heat, have further impacted the shape of the limpet species. The basalt substrate increased the risk of desiccation while the elionite substrate had increased exposure to waves, so each required different adaptations. The unique species of limpet, C. exarta, has adapted to develop a shell with increased height compared to its relatives in the lower tidal zones. This gives the limpet an oblong shape as to increase the ratio of volume to evaporative surface area to endure the thermal stress. With their typical habitat being above their common predators, their increased shell height does not have any negative effects for the limpet.

Reproduction & Growth:

Fertilization occurs externally and sexes are separate within this species of limpets. Without any parental care, the embryos drift in the ocean currents until they settle onto shoreline rocks. C.exarata has a continuous monthly shell growth of 4-5 mm until it reaches sexual maturity. Following that event, its growth decreases to 2-3 mm monthly. Similarly, its weight increases monthly until sexual maturity, then decreases following that. Lastly, Its lifespan is less than one and half years. It takes just one year for the shell lengths of Cellana exarata and Cellana sandwincensis to grow over 40 mm. Before sexual maturity, shell length continues to increase at a rate of 4 to 5 mm every month. After sexual maturity, this slows down to 2-3 mm every month. The absolute body weight of both species increases every month as well, until they reach sexual maturity, when that absolute body weight still increases but at a slower rate. However, C. sandwincesis have a lower height and heavier shell than the shells of the species C. exarata, and it has been hypothesized that this may be due to the fact that they live in a more wave-exposed habitat. Lastly, neither species grows very large due to their lifespan being less than 1.5 years long.

Human Use:

A Hawaiian delicacy and ‘Opihi can be served either raw or cooked. Very important in Hawaiian culture, it is used for celebrations and those special events. Due to overpicking, legislation was passed in 2006 to limit the sale of ‘Opihi and collection is reserved solely for personal use.

Differing Phylogeography:

While Limpets have similar life histories, behavior and habitat affinity also plays a major role in the way that three different species of the endemic Hawaiian Cellana spp. which are sympatric species in a monophyletic group. The three species are Cellana exarata, C. sandwincensis, and C. talcosa. The main reasons for these differences are habitat specificity and biogeography. In terms of habitat, C. exarata and C. sandwincensis both live above the waterline, however, the third species, C. talcosa remains in a subtidal habitat. Additionally, these stark differences between species also relate to the restricted gene flow that comes from geographical partitioning and, somewhat, the restriction of channels that separate the species from each other. All in all, this revelation that species so similar to one another, especially ones that have such similar life histories is detrimental to the understanding of these species and especially for Hawaiian Limpets that are so important to the ecosystem of Hawaii, it is important to recognize the differing phylogeography between these three species.

Ecological and evolutionary factors influencing growth:

Since the Proto-Historic Period, the average limpet size has increased, especially in terms of the mean limpet size in the western shoreline harvests. There are two main reasons why, for one, shelter from trade winds and strong ocean currents in Hawaii have allowed for limpets to grow larger than they were previously able to. Another reason is that there has been less harvesting pressure placed on these limpets allowing them time to grow and evolve.