Living on the edge: tolerance to environmental stressors and reproductive dynamics of the gastropod Crepidula fornicata across the intertidal-subtidal boundary.
Abstract: Species' ranges are generally studied on a latitudinal scale, and
species are often limited by their tolerance and responsiveness to physical stressors. Many
organisms, though, live in the transitional area between terrestrial and marine
environments, the intertidal zone. Most of the species that occupy the intertidal zone are
of marine descent and many can also be found deep into th... read moree subtidal zone where they live
their entire lives covered by seawater. Thus, the intertidal zone represents a range
boundary for many marine organisms, beyond which they cannot survive. For these organisms,
the intertidal range edge is characterized by a suite of stressors associated with aerial
exposure that may limit their upper distribution and can ultimately cause them negative
physiological impacts; such stressors include desiccation, high aerial temperature, and
reduced feeding time, and they are absent only meters away, in the subtidal zone. Comparing
particular aspects (e.g. phenotypic traits, fecundity) of adjacent intertidal and subtidal
organisms of a single species can provide insight into which factors control the upper
distribution of that species in the intertidal zone, the ability of organisms to adapt to
stressful intertidal conditions, and the healthiness of the populations that reside there.
I investigated some basic biological aspects (thermal tolerance, desiccation tolerance,
feeding physiology) of the sessile suspension-feeding gastropod, Crepidula
fornicata at Bissel Cove in Narragansett Bay, Rhode Island, USA in order to
better understand the factors that limit the upper distribution of this species and also
the effects of intertidal stressors on the reproductive capacity of these organisms. I
found that high summer temperatures are probably the most important factor limiting the
upper distribution of this species, but desiccation stress can be particularly troublesome
for very small individuals; reduced available feeding time is probably not a major limiting
factor. Intertidal and subtidal C. fornicata at Bissel Cove had
similar upper thermal tolerances, desiccation tolerances, and feeding rates. However, they
differed both in their behavior when exposed to the air and in their gill morphology: when
emersed, intertidal individuals spent less time with their tissues exposed to the air than
did subtidal conspecifics, and intertidal individuals also had relatively larger gills. The
stresses associated with intertidal life had no immediate effects on their ability to
successfully reproduce. In fact, the breeding season was slightly longer for intertidal
individuals of C. fornicata and their fecundities higher when
compared to those of subtidal conspecifics. Taken together my results suggest that
C. fornicata has had a long association with the intertidal
zone, and though desiccation and high temperatures are likely keeping them from living high
up in the intertidal, the individuals that recruit to the mid/low intertidal are not
particularly stressed there as adults. Their high tolerance to environmental stressors and
their adaptability may be partially responsible for their extreme success as an invasive
species. As global temperatures rise, this species will likely be relegated to the subtidal
zone only, but will probably continue to colonize new locations.
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Biology.
Advisor: Jan Pechenik.
Committee: David Cochrane, Colin Orians, J Reed, Sara Lewis, and Brian Helmuth.
Keyword: Biology.read less