Oregon Institute of Marine Biology REU Program (2019)

Take a look at my research BLOG HERE from my 2019 OIMB research experience.

Strongylocentrotus pupuratus spawning. Image captured by Shae Wilkinson — *Strongylocentrotus pupuratus* spawning. Image captured by Shae Wilkinson

Introduction

Most marine animals are restricted to a relatively narrow range of depth in the sea. For example, many intertidal animals are found only in tidepools, and many animals living in the shallow subtidal zones are not found in the intertidal. The causes of zonation have inspired some of the classic studies of marine ecology, including (1) Connell’s work on the vertical limits of barnacles and (2) Payne’s experiments on the role of starfish in controlling the distribution of mussels. In the deep sea, many species are limited by physiological tolerances to pressure or temperature ( Sven Thatje, Bob Carney, embryos and larvae research by Young and Tyler).

In the present study, I will compare the pressure and temperature tolerances of the embryos and larvae of two species of sea urchins in the genus Strongylocentrotus. Strongylocentrotus purpuratus is limited to the intertidal and shallow subtidal zone, where it feeds on drift algae. Strongylocentrotus fragilis lives on the continental slope between 200 and 1000m, where it feeds on sediment and probably on algal detritus sinking from the surface. My research will investigate whether the early stages of these two species have different tolerances to the physical factors of pressure and temperature. If they do, then it is possible that the initial distributions of these species might be set during the early life-history stages. If the embryos and larvae of both species have similar tolerances, then the distributional limits are most likely determined by post-settlement factors such as mortality of juveniles.

Previous research on pressure and temperature barriers has provided evidence that temperature tolerances relate to deep sea fauna origins (4). Are either species limited to their depth? If so, what are the possibilities for migration patterns for their larvae? 2.

Exploring multiple tolerances of early embryo and later larval stages of marine invertebrates can lend useful data for future scientists, and can give insight to the individual's behavior in the open ocean, due to the fact that there is very little experimentation with deep sea larval tolerances (2). We may also find the lower limits of this studies larvae which has never been documented before (3).

Methods

Strongylocentrotus purpuratus, an intertidal species will be compared to for a deep sea urchin species S. fragilis. S. fragilis will be spawned through thermal shock, and S. purpuratus will be spawned by shaking or by injection of KCl. The development of S. fragilis has been studied, but the details of development have not previously been published. .

Four separate cultures of S. fragilis larvae will be held in the coldwater room tanks at 7°C, M.edulis and S. purpuratus kept in the Tyler aquarium at 15°c. Water circulation should be maintained by a motorized stir rack, with ⅔ water changes on alternating days. For the first experiment, a temperature gradient apparatus will be used in a fashion similar to Tyler and Dixon, (5) with larvae exposed to temperatures from 5°c to 19°c. Mortality rate will then be recorded after 24 hours of exposure. Experiment shall be repeated with both Strongylocentrotus species in addition to a potential fertilization of the muscle M. edulis.

Pressure experiments will be taking place for all species mentioned above, using pressure vessels at 100-200 atms of pressure at a consistent temperature to isolate pressure resilience (4). The combination of pressure/ temperature experiments can yield ample data for the tolerances of early embryo to later larval stages in our variety of deep sea and shallow water species, where a comparison shall be derived.

Anticipated results

The expectation is for S. fragilis larvae to be less tolerant of warmer waters due to its narrow temperature ranges in the deep sea. S.purpuratus should tolerate warmer and colder waters alike, as it frequently travels from shallow to intertidal waters.

Broader impacts

Apart from creating a developmental timeline of S. fragilis for future observations, the data on deep and intertidal larvae can serve for modeling phylogenetic constraints of deep water and shallow water species (2). We can expect to provide data which can be repeated in further studies resulting in decreased larvae mortality rates. We may also correlate temperature/pressure data to the vertical distribution of deep sea larvae (1).